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#1
09-09-2023, 11:42 PM
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#2
09-09-2023, 10:32 PM
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Your math isn’t wrong. The instruction are often wrong, and the keys are not all that accurate. You have not said that you degreed the cam in after using the different key. If you did and it worked as planned, your good. Pay no attention to me.
Last edited by Jay S; 09-09-2023 at 10:43 PM. |
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#3
09-10-2023, 12:09 AM
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Then we turned the nut 3/4 turn more while rotating the push rods until there is a slight resistance before the 3/4 turn. I believe we are advanced a little more than I intentionally intended, I was shooting for 109 total Cam advance, but I have read that 108 is also in the ball park for race ready concerns. I won't be taking this vehicle to the track to test whether it works at 60' times vs 1/4-mile times. What I want is a well-tuned Engine that is as performance orientated as it was built in 1967. By the way this Motor is well documented with 2/22/68 date?, written on the Passenger side front Block. This 428 ci HO went to a machinist to be further modified with the "886" Cam and Tri-power Carbs. in 1968 and I possibly think someone Blueprinted this motor and balanced it for racing, just as my father did to his race vehicles. Now with the "041" Cam I am trying my best to make it performance orientated to the best of my ability. Oddly, the machine had to break down with odd noises for me to find out that the pistons are reversed and one isn't. I still believe that even though we won't know the reason until this Engine is fully disassembled, the why of it all, that the builder knew exactly what he was doing.JMO Last edited by TRADERMIKE 2012; 09-10-2023 at 12:48 AM. |
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#4
09-09-2023, 08:26 AM
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.078" quench is HORRIBLE in one of these engines, even worse using factory iron heads with their flat chamber floors/machined combustion chambers.
Good thing you have a RAIV cam in it, or it would pound the rod bearings out of it in a week due to detonation. The RAIV cam saves the day here as it bleeds off a LOT of cylinder pressure and pushed peak VE high in the RPM range. Put a 10 degree smaller cam @ .050" in this build on a 110LSA and it wouldn't last a month......IMHO.... +2 on moving the heads away from the pistons to increase valve to piston clearance. These engines have a BUTT-LOAD of that right to start with with factory "low lift" cams in them. The only Pontiac engine I ever had close for piston to valve clearance was a 455 with forged TRW Super Duty pistons in it (2 small valve reliefs). With a 276/284 @ .050" cam with .750" lift it still had just under .040" piston to valve bumping it thru without a head gasket in place. The heads were CNC ported early round port E-heads at 330cfm with 72 cc chambers (milled to .068cc). So basically, without writing a book here on building these engines and checking critical areas during the process, piston to valve with the cam you are using shouldn't even be on the list of things to worry about........FWIW........
__________________
If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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#5
09-09-2023, 10:29 AM
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Butler’s composite gaskets crush to around .042”. to .044” thick.
Blue felpro crush to about .045”, most cheaper head gaskets crush to .045” also. I assume the cam is still using the comp 9 way timing set using full advance 4th key yet, as reported earlier. Could be just a miscommunication on my end. I will reiterate it though, the 4th key should be 8* advanced, each key changes the advance 2*. Using the extreme 4th key ends up at roughly 105.5* if it started at 113.5*. Like Cliff said, quench is marginal to bad, if the cam is advanced to far, you”ll wish you never touched the cam timing. If your convinced all is good though, carry on. There is plenty of valve to piston clearance with the SPC-8 cam and 1.5 rockers. No reason to bother checking that. Should be good unless the install is really messed up. |
| The Following User Says Thank You to Jay S For This Useful Post: | ||
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#6
09-09-2023, 12:46 PM
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https://www.summitracing.com/parts/f...6/make/pontiac |
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#7
09-09-2023, 01:08 PM
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#8
09-09-2023, 01:37 PM
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#9
09-09-2023, 10:05 PM
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You go 113.5 - 8 degrees at the Crank = 105.5 advanced at the Crank. Measuring the way, you are, I beg to differ, here is why, 113.5 = 8 + 1.5 degrees (built into the Cam) = 9.5 113.5 - 9.5 = 104 advanced at the Crank. Mike is measuring via the Cam degrees: 4 advanced degrees + 1.5 (built into the Cam) = 5.5 113.5 - 5.5 = 108, A little more advanced than my 109 target, but I have read people advancing their race timing to between 108-109. If I am wrong or I have advanced this Engine too far, please correct me now, before it is too late. P.S You said: " Butler’s composite gaskets crush to around .042”. to .044” thick. Thus, we add Piston TDC to Deck clearance @ .023" +.042” crush = .065 Quench, in my case approx.? Still a safe place to be for now? By the way the Piston to cyl. walls are smooth to begin with and the Piston clearance is between .005" - .010", in addition the Cam Bearings looked so good that we used them when we installed the new "041" Cam. For this very reason we deduced that the Crank Bearings would have held up as well. The lower part of this Engine has been dependable so far, never a noise anomaly until the Trans. disinegration. I firmly believe that accident caused the majority of the issues today, especially the Thrust impact through the Trans. thrusting toward the Crank and lastly arriving at the Harmonic Balancer. The Head is a time related issue and stands alone, this is my view, and I am sticking to it. Nothing happens from nothing here it all happened at once, too bad I am still repairing this Engine from the accident I had, running over a root beneath an asphalt driveway. Last edited by TRADERMIKE 2012; 09-09-2023 at 10:29 PM. |
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#10
10-31-2023, 12:54 AM
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Since the Heads are installed, one can calculate the crushed gaskets that I bought from Butler Brothers with the metal ring inserts to find the new quench by using the newly found compression ratio stats that I have provided? A typical Head job takes off .010 " shaved to flatten the Heads, approx. Also, the 428 ci Pontiac motor is 10.75:1 CR, out of the box, so what is my CR today? Can these new facts I have provided be why This motor is hotter than it should be? I will say it again, I am in a new territory and need some help, this engine has become a new project with the Head changes and advanced Cam timing, especially if the timing Cam numbers are doubled compared to what I have been thinking, getting confused here. I am thinking that the CR has risen with this build and the Fuel could be too low in octane with these new changes I have made to this Engine? Last edited by TRADERMIKE 2012; 10-31-2023 at 01:00 AM. |
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#11
09-09-2023, 08:48 PM
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You said: "The RAIV cam saves the day here, as it bleeds off a LOT of cylinder pressure and pushes peak VE high in the RPM range. Put a 10-degree smaller cam @ .050" in this build on a 110LSA and it wouldn't last a month"......IMHO.... Mikes reply: How close are those specs., that you mention above, to my original # 886 Cam. The Tri-Power one, that ran like a raped ape, when the Cam lobes were worn down and I was bending push rods, because the Rocker arm bolt mounted on the Rocker stud was cracked, that I found out, while testing and tuning at 130 mph, simultaneously, ruining the new Cooper tires, that I later discovered, where rated for 80 mph. Note, I don't know whether or not the worn lobes, not giving the correct lift, that the used Cam was intended to have, works in your favor or not, considering your statement, both ways? |
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#12
09-09-2023, 12:47 PM
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One thing I've tested that most folks haven't is moving cams around then street testing, followed by track testing.
Another "myth" about advancing cams is "making more low end torque". You may see of "feel" a shift in power but may not make as much power anywhere as before the move. When I advanced the cam in my first 455 from 109ICL to 107ICL it KILLED it at the track at every point on the run including 60' time. I also moved it to 111ICL, and on up to 113ICL. It was a TURD at 107 and again at 113, if you went by the track times, but superficially "felt" pretty peppy at 107ICL and made a little tiny bit more vacuum at idle.. Remarkably the car ran almost the same at 109 and 111ICL, just fuzz-nut quicker in 60' at 109 than 111. In any case I would NEVER just advance a cam just to improve low end power, street manners or compensating for chain stretch, or following random advice on the NET from someone who probably Googled up their information instead of actually trying it out.......and, IF your chain is going to stretch out that much, buy a better timing set......FWIW.........
__________________
If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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#13
09-09-2023, 11:25 PM
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#14
09-09-2023, 01:07 PM
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To many pages and I have a bad memory. What CR does he have and what thickness head gasket was that figured with. As the head gasket get thinner for better quench it will also be increasing his CR.
Stan
__________________
Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
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#15
09-09-2023, 01:19 PM
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Doesn’t sound like it matters anyhow, heads are back on. |
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#17
09-09-2023, 01:27 PM
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One could pull the engine and fix it in less time than it takes to read this entire thread.... Normally I'm all for "trying to learn" but a lot of words have been typed trying to justify mistakes that just need to be corrected or lived with. You can discuss this as long as you want but nothing will change the outcome unless something is "actually done" or its decided to live with the situation at hand.... It's that simple.
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| The Following User Says Thank You to PAUL K For This Useful Post: | ||
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#18
09-11-2023, 04:51 AM
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Here is the way to degree a cam:
How to Degree A Cam The following is the method of degreeing a cam that Lunati Cams recommends. The first step in degreeing a Cam is to obtain a few items that should be a part of every serious engine builder’s tool chest. These items are: A large Degree Wheel, such as LUNATI CAMS P/N 80000 A Dial Indicator & Magnetic Base Stand, such as LUNATI CAMS P/N 80012 A Steel Deck Strap Kit, such as LUNATI CAMS P/N 80013 All of the above is available as LUNATI CAMS DEGREE WHEEL KIT, P/N 80001 Some suitable pointer (made from coat hanger wire, paper clip, etc.) rigidly attached to the block Step 1 1. The first step is to install your new camshaft and line up the stock timing marks. 2 To begin the actual degreeing procedure, the degree wheel should be attached to the front of the crankshaft. A pointer of some type such as a piece of wire should be secured to the front of the engine. The engine should be capable of turning in either direction. Use a crank socket or other suitable tool to rotate the engine. At this point you will leave the wheel somewhat loose. Step 2 Step 3 3 Rotate the crankshaft until the number one piston is at approximately Top Dead Center and align the pointer with TDC on the degree wheel. Tighten the wheel. 4 The next step is to find the true Top Dead Center (TDC). The most accurate method is to secure a flat strap (1-1/2 x 1) that will bridge the bore (with the heads removed). A Steel Deck Strap Kit is included in the Lunati Degree Wheel Kit, or is available separately (P/N 80013). (If the heads are on the engine, another method of finding TDC is necessary. This method uses an old, discarded spark plug. Remove the porcelain and use a tap, 3/8" 24NF, to cut threads through the plug. Insert a Bolt so that it will protrude through the plug approximately one inch. Remove the rocker arms and push-rods so the valves will not be bent. Step 4 Step 5 5 Rotate the engine clockwise until the piston contacts the stop. At this point you should mark the degree wheel. 6 Next, rotate the engine counterclockwise until the piston contacts the stop again. Make another mark on the degree wheel. If the degree wheel is properly located, the marks will be an equal number of degrees on both sides of TDC. If not, the degree wheel will have to be relocated. For example, if you come up with 34 degrees on one side and 30 degrees on the other side, the wheel will have to be rotated 2 degrees to compensate for the misalignment. After the wheel has been relocated, the piston should hit the stop the same number of degrees on either side of TDC. After TDC has been found, remove the piston stop to allow complete engine rotation. Step 6 Step 7 7 Install the lifter in the number one intake lifter bore. Use a mechanical lifter for flat tappet grinds and a roller tappet if the cam is a roller grind. The indicator must be positioned securely above the lifter. The stem from the dial indicator should be aligned with the lifter as close as possible. Misalignment will cause an improper reading. Rotate the engine at least two revolutions. Make sure the dial indicator is working freely and the lifter is not sticking or binding in the bore, and that you have adequate indicator travel. Rotate the engine clockwise until the lifter is on the heel, or base circle of the cam lobe (minimum lift). Zero the dial indicator. 8 Rotate the engine in clockwise direction until a 0.050" reading is reached. Step 8 Step 9 9 Rotate the engine in clockwise direction until a 0.050" reading is reached. View the degree wheel at this time. This point is 0.050" of lift on the opening side of the intake lobe before top dead center. 10 Compare the reading on the degree wheel with the "IN OPENS" specification on the cam card. If it does not match, your cam is either retarded or advanced. For example, if the degree wheel reading at 0.050" comes up 10 degrees before top dead center (BTDC), and your P/N 00010 cam card lists the 0.050" intake opening at 8 degrees, your cam is 2 degrees advanced. If the degree wheel reads less than 8 degrees, your cam is retarded. If either is the case, proceed to step 11. If it matches, your cam is installed as designed. Step 10 Step 11 11 So, what do you do if your 0.050" opening lift point doesn’t match the cam card (or you want to set your cam timing to something other than the cam card specifications)? There are several methods to adjust the valve timing: Degree bushings can be used on the cam sprocket to offset the cam locating pin. 3- or 9- keyway timing chain sets have additional keyways cut into them to index the crank sprocket. After you have adjusted your cam using one of the previous methods, go back to step 10. The Racer's Company. Since the 1960s, Lunati has manufactured engine components of the highest quality using cutting-edge technology. Every single product we sell undergoes extensive testing and analysis to ensure the end result is a superior product that can withstand demanding race conditions. |
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#19
09-11-2023, 07:33 AM
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Here are a few links that I used to degree my Cam:
https://youtu.be/cAlw9RpTZ4I https://youtu.be/wzKtaDke22k https://youtu.be/57gfBu8uc6k https://youtu.be/Prj0GUZ7nes https://youtu.be/n_9rUXYxAY0 Camshaft Math Camshaft Math to Design Competitive Performance Engines JANUARY 24, 2015 BY MUSCLE CAR DIY Camshafts are a subject that all car guys love to talk about, and those who listen tend to roll their eyes at the staggering number of terms and numbers. There’s lift and duration, overlap and lobe centers, lobe separation angles and so on, and all of them have numbers attached. Most enthusiasts have a basic understanding of the cam, lifter, pushrod, rocker arm, and valve relationship, but keeping all the numbers straight is often intimidating. This chapter looks at the basic calculations relating to camshafts and valvetrain components and how you can use them to equip and tune your particular combination for top performance. This Tech Tip is From the Full Book, PERFORMANCE AUTOMOTIVE ENGINE MATH. For a comprehensive guide on this entire subject, you can visit this link: LEARN MORE ABOUT THIS BOOK HERE SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://musclecardiy.com/performance...mance-engines/ 1 a) A. Exhaust Valve Opens – Power Stroke B. Intake Valve Opens – Exhaust Stroke C. Exhaust Valve Closes – Intake Stroke D. Intake Valve Closes – Compression Stroke b) The basic cam lobe shape is an eccentric with the lifter riding on the base circle. As the cam rotates, the lifter moves up the flank of the lobe and over the top to open the valve. (Courtesy Comp Cams) Lobe Centers Imagine a line passing from the center of the cam directly through the highest point on the cam lobe. This is the geometric centerline of that particular lobe. To avoid confusion when comparing cams, remember that the lobe center angle is measured between the centerlines of the intake and corresponding exhaust lobes, while lobe centerline is the angle measured between the center of the lobe and TDC. The lobe center angle is fixed and cannot be changed after the cam is ground. The lobe centerline can be altered by advancing or retarding the cam. When you do this, you are effectively moving the intake lobe centerline closer to or farther from TDC. 2 This illustration tells you everything you need to know about camshaft operation. In addition to lift duration and overlap, it also indicates the intake and exhaust centerlines, lobe separation angle, and the location of timing events relative to the four cycles. Note that 0.050-inch tappet lift equals 0.050 times the rocker ratio to indicate valve lift at the checking point. (Courtesy Comp Cams) In terms of engine performance, the lobe center angle is significant. A larger angle yields less valve overlap (the period when both valves are open at the same time). This permits the cylinder to begin building pressure sooner and that boosts low-speed torque. Decreasing the angle creates greater overlap and moves the torque curve higher in the RPM range, effectively narrowing the engine’s powerband. For most street applications always select a cam that builds as much torque as possible. Generally, you want valve events that produce a wider lobe center angle, decreasing valve overlap. One of the advantages of the new high-velocity street roller profiles is that you maintain good idle quality by using wider 112- to 115-degree lobe centerlines, but you also have a high-RPM boost with more aggressive lobe profiles (increasing effective duration). The result is a broad torque curve ideal for street use. Muscle Car B Supercharged or turbocharged applications should avoid cams with excessive overlap because the pressurized intake system already provides effective cylinder filling and forced exhaust scavenging. In these applications, long overlap can be detrimental because some of the intake charge can be blown right through the engine without being burned. For the average street and strip enthusiast, all of these factors are taken care of by the cam manufacturer. Their vast experience lets them provide you with a Cam that they know will work for your application. Understanding Cam Specs For the purpose of this discussion, I will speak in terms of opening and closing valve events. Intake opening (IO) and exhaust opening (EO) represent the intake and exhaust opening points in crankshaft degrees. Intake closing (IC) and exhaust closing (EC) are the intake and exhaust closing events. Cam cards publish these points based on the manufacturer’s chosen reference points: typically, 0.006 inch for advertised duration and 0.050 inch for a universal checking reference based on an agreed amount of lobe lift where reasonable flow is initiated. The following formula is used to calculate intake and exhaust duration. It applies to any lift as long as your cam card specifies opening and closing figures for a particular lift value. 3 The camshaft timing card included with your cam provides the essential specifications for installing your cam correctly. It includes lobe lift, net valve lift, timing points at the advertised duration, duration at 0.050-inch lift, lobe separation angle, and the installed intake centerline. Some cards also include overlap and valve-spring specs. Most manufacturers now publish all their standard cam cards online for your convenience. Duration at Specified Lift = opening point + 180 degrees + closing point For example, a COMP Cams XE274H-10 hydraulic cam lists the following opening and closing points for a checking lift of 0.006 inch: IO = 31-degrees BTDC IC = 63-degrees ABDC EO = 77-degrees BBDC EC = 29-degrees ATDC Hence, Intake Duration = 31 + 180 + 63 = 274 degrees at 0.006-inch lift Exhaust Duration = 77 + 180 + 29 = 286 degrees at 0.006-inch lift From this you can calculate the intake and exhaust centerlines. To find the intake lobe centerline, divide the intake duration by two and subtract the indicated intake opening point as shown in our example with the Comp Cam, XE274 example. Intake Centerline = (duration ÷ 2) – IO Intake Centerline = (274 ÷ 2) – 31 = 106 degrees Sometimes you find a very mild or stock cam where the IO occurs after TDC (ATDC). In this case just add the IO figure to one half of the duration. On the exhaust side the formula is similar, but instead of subtracting the intake opening point, subtract the exhaust closing point. Exhaust Centerline = (calculated duration ÷ 2) – EC Exhaust Centerline = (286 ÷ 2) – 29 = 114 degrees Once you know this it’s easy to calculate the lobe separation angle (LSA) which is the difference between the two centerlines. Simply add the calculated centerlines together and divide them by 2. Lobe Separation Angle = (intake centerline + exhaust centerline) ÷ 2 LSA = (106 degrees + 114 degrees) ÷ 2 = 110 degrees If a cam is ground “straight up,” both centerlines are the same and the LSA is one half of their sum. More commonly you find that cam companies grind their street cams 4 degrees advanced to help boost low-speed torque on longer-duration cams. You can see this in the Comp XE274 example where the intake centerline is 106 degrees, but the LSA is 110 or 4 degrees advanced. Note that 110 degrees is exactly halfway between 106 and 114 degrees. This practice moves the IC event 4 degrees ahead, which tends to diminish top end power in favor of more low-speed grunt for street engines. One other point to note is the use of parenthesis around some timing points. This notation indicates that the cam actually closes the valve after TDC instead of before, even though the card indicates BTDC. You only find this on short-duration cams, but it is important to note if you’re making calculations with a small cam. Calculating Valve Lift The net valve lift is a function of camshaft lobe lift and rocker arm ratio. Lobe lift (sometimes called cam rise) is the height of the eccentric portion of the cam lobe above the base circle. The rocker arm transfers the motion of the valve lifter riding on the cam lobe to the valve and increases the lobe lift by the amount of the rocker ratio, which is typically 1.5 to 1.7:1. It provides a convenient means of increasing valve lift without a space or packaging penalty. This is very evident in a pushrod engine where the valvetrain is compact and easily packaged compared to the complication and excessive size required for single and double overhead cam arrangements. 4 The Cam Analyzer from Performance Trends uses hand measured cam profiles or computerized file formats such as Cam Doctor and Cam Pro Plus to provide detailed camshaft lobe evaluation for use in performance simulations. 5 Cam Analyzer uses its motorized unit to rotate the cam so the profiler can read the lobe. 6 Cam Analyzer generates its own cam card for your reference files. 7 Degreeing the cam requires accurately locating TDC with a degree wheel and pointer, and a dial indicator set up to read lifter travel as you rotate the engine. Net valve lift differs according to the type of lifter. To accommodate thermal expansion, clearance is built into the system in the form of clearance ramps and valve lash for mechanical (solid) lifter cams. The valve lash clearance must be subtracted from the total valve lift to obtain the net valve lift for this type of cam. Mechanical Lifter Cam Net Lift = (lobe lift x rocker ratio) – valve lash Example: For a Lobe Lift of 0.300 inch and a 1.5:1 rocker ratio with a 0.022-inch valve lash: Net Lift = (0.300 x 1.5) – 0.022 = 0.428 inch A hydraulic camshaft automatically adjusts for thermal expansion via lifter preload against an internal hydraulic plunger. No clearance is necessary and these lifters are typically adjusted with a specified amount of preload or a preferred degree of turn from zero lash; usually one-quarter to one-half turn down. In this case the net valve lift is based on the lobe lift and the rocker ratio alone. Net Lift = lobe lift x rocker ratio Net Lift = 0.300 x 1.5 = 0.450 inch Mechanical (solid) cams are typically smaller than their hydraulic counterparts due to loss of lift attributable to valve lash. But mechanical cams, unlike hydraulic cams, can be tuned somewhat by altering valve lash. Tightening the lash adds lift and starts the valve event sooner, effectively mimicking a larger cam. To accommodate various tuning changes, this is often limited to either the intake valves or the exhaust valves and sometimes only on the end cylinders to accommodate variations in runner length. A racer might tighten the lash on the exhaust side to increase the exhaust event if he feels that the engine is exhaust limited. Or he might tighten the lash on the outer four corner cylinders to compensate for the longer intake runners on those cylinders. That’s equivalent to running a bigger Cam on those cylinders. You may recall from Chapter 8 that sometimes you can affect dual torque peaks and a broader torque curve by running different-size (c/s area) primary pipes on alternating cylinders in the firing order. This is a fine-tuning measure, but in some cases, you can combine this with valve lash adjustments on selected cylinders to further tune the torque output at different speeds. In theory this is predictable, but in practice it often requires dyno verification to quantify gains. Valve lash changes should be limited to a maximum of 0.004 inch, and consideration should be given to the known valve-to-piston clearance before going too far on the exhaust side. These tuning measures can net small gains, but the correct combination can effectively broaden a torque curve with surprisingly good results. This may be just enough to give you some added leverage on the competition without having to make major engine modifications. Finding TDC Locating TDC accurately is absolutely essential to proper camshaft installation. Exact TDC is the timing basis for all camshaft timing events. The method for locating it varies according to the engine’s state of assembly. Whatever that is, a temporary piston stop is used to stop the piston at some arbitrary distance before and after TDC. 8 A cam checking kit like this one from Comp Cams provides all the necessary measuring tools to successfully degree your high-performance camshaft. For fully assembled engines that are not already equipped with an accurately set TDC indicator, a threaded piston stop can be installed in the spark plug hole of the number-1 cylinder. Note that on most V-8 engines, the number-1 cylinder is almost always the farthest one forward in the V configuration. Paired rod and piston assemblies on each crank throw dictate that one is always offset farther forward than its counterpart. Study the front of the block to see which of the front cylinders is farther forward. That will be number-1. If the degree process is being performed during engine assembly, it is best to do it with only the number-1 piston and rod assembly installed on the crankshaft. Rotating the engine to degree the cam is much easier this way. In this case, a flat bar piston stop is bolted to the block deck surface above the number one piston. This type of piston stop has a center bolt that can be adjusted to stop the piston at any desired point below TDC. Begin by installing the degree wheel on the crank snout, or the balancer if it is already installed. Before installing the piston stop, rotate the engine until the piston top visually appears to be at TDC. You should be able to see this through the spark plug hole on an assembled engine. It doesn’t have to be exact—just close. Install a temporary wire pointer and adjust it so the tip is close to the graduated marks on the degree wheel. Adjust the degree wheel so the pointer indicates TDC (0 degrees) and snug it lightly. Rotate the engine counterclockwise approximately one-half turn and install the piston stop. Tighten it securely so it won’t move when the piston contacts it. Slowly rotate the engine clockwise until the piston contacts the piston stop. in degrees before top dead center (BTDC). Record that number and then rotate the engine in the opposite direction (counterclockwise) until it completes a revolution and contacts the piston again. Record the reading on the degree wheel and note that it indicates degrees after top dead center (ATDC). If your calibrated eyeball is very accurate, the recorded numbers indicate the same number of degrees on either side of TDC and the pointer reads zero with the piston stop removed and the piston brought to the top. In practice, most of us aren’t that accurate, so we have to locate TDC based on a common reference point on either side of TDC. That’s the piston stop. The reason you can’t accurately locate TDC visually is because the piston experiences a brief period of dwell (stationary) at the top of its stroke as the rod angle transitions from one side to the other. The piston is stopped at this point and you have to split the dwell point exactly to find true TDC. Since the piston stop does not move, it represents a fixed reference point before and after TDC. True TDC is found by splitting the difference between the degree wheel readings. For example, let’s say your recorded numbers are 34-degrees BTDC and 30-degrees ATDC. The exact number will depend on the depth of your piston stop in the cylinder bore, but it is all relative. TDC is halfway between the recorded readings. Loosen the degree wheel and rotate the degree wheel only until the pointer reads 32-degrees. Lock down the degree wheel and make sure not to touch or move the pointer from this point forward. Check your work by rotating the engine back and forth to the piston stop in both directions. The pointer reading should be the same in both directions (32 degrees in our example). If it is not the same, repeat the steps until the pointer indicates the exact same number of degrees before and after TDC. Once it does, remove the piston stop and degree the cam with confidence that you are locating your timing events based on exact TDC. Degreeing the Cam There are two methods for degreeing a camshaft. One compares the opening and closing points of the intake valve to see if they match the manufacturer’s specs on the cam card. The other method locates the intake lobe centerline relative to TDC. Both methods are successful, but the intake centerline method does not verify the intake opening and closing points according to the cam card. Both methods are described below, but the intake opening and closing method is recommended for initial setup. Then you can check your work with the intake centerline method. In either case you need an accurate means of reading lifter travel. 9 Most degree wheels are precise if you are careful about locating the position of the pointer. You can degree accurately with all of them, but many tuners prefer the larger-diameter professional degree wheel. 10 The professional degree wheel offers larger spacing between degree increments for more precise positioning and it can be used to turn the engine by hand if only the number-1 piston is installed. I prefer the cam checking tool available from Jegs, Summit, and many other suppliers, but successful results can be obtained using a solid lifter or a modified hydraulic lifter with the internal plunger reversed to give the dial indicator plunger a flat surface to bear against. You can also locate the plunger against the edge of the lifter. Make sure that the contact is stable and that the direction of the indicator travel is parallel to lifter travel. Then adjust the dial indicator to ensure that it has enough available range to read total intake lifter travel for the number-1 cylinder. Intake Opening Method Install the cam with the timing marks correctly aligned for your engine. Set up your dial indicator and check lifter, or the cam checking tool in the number-1 intake lifter hole as described above. Zero the dial indicator and rotate the engine in the normal direction of rotation for several revolutions to verify that the dial indicator reads full lifter travel and returns to zero each time. You can take this opportunity to verify that lifter travel matches the indicated lobe lift on the cam card. If the lifter does not return to zero on the base circle, determine the cause and correct before continuing. 11 Good degree wheels are marked to indicate a range where valve events normally occur. If you’re measuring an event that occurs outside that range, it is probably incorrect and you should recheck your work. 12 A cam checking tool reads lifter motion directly without the need for dial indicator spindle extensions. It can only be used with the cylinder heads off the engine, but it is the most accurate method. 13 You can read net valve lift and duration with the valvetrain installed by checking it at the retainer. This method incorporates the rocker ratio and any clearance lash to yield an accurate indication of true valve motion. Once you’re satisfied, begin with the lifter on the base circle and slowly rotate the engine clockwise until the indicator shows 0.050-inch lifter travel. Note the reading on the degree wheel. It should match the intake opening point (IO) indicated on the cam card for 0.050-inch lift. Continue rotating the engine through full lifter travel and down the other side of the lobe until you reach 0.050- inch lift before the intake closing point. Since you know the lobe lift and the recommended closing point from the cam card, you should be able to anticipate the closing point as you rotate the engine. If you miss it, simply back up about 60 degrees to compensate for timing chain slack and approach the 0.050-inch closing point again. Compare it to the cam card and then continue rotating to verify that the lifter returns to zero again. Your readings should show the intake opening and closing points and the total lifter travel or lobe lift. If the intake opening event doesn’t match the cam card, you will have to advance or retard the cam to bring it into spec. For example, if your cam is supposed to open the intake valve at 36-degrees BTDC and close at 70-degrees ATDC (at 0.050-inch lift), but your measurements show that it is opening 34-degrees BTDC and closing 72-degrees ATDC, the cam is retarded. The valve event is occurring later than the recommended spec. If it were to open at 38-degrees BTDC and close at 68-degrees ATDC it would be 2-degrees advanced because the valve event is occurring 2 degrees earlier than specified. Muscle Car B In either case it is easy to correct using offset cam bushings or a crank gear with multiple keyways. Both allow you to adjust the position of the cam and then recheck it for compliance with the cam card specs. Note that they can also be used to reposition the cam if you deliberately choose to advance the cam to promote low-end torque or retard the cam for a little more top end power. If your degree results are plus or minus 1 degree of your published specs, consider leaving the engine as assembled because it is entirely possible that the small degree wheel you are probably using is not that accurate. Larger-diameter degree wheels space the degree marks farther apart and, therefore, have a greater chance of improved accuracy. You can check the accuracy of your wheel by placing it on a large sheet of paper and marking the four 90-degree positions of the wheel. Then move the wheel to various positions and check to see that each 90-degree mark is an equal number of degrees from 90. You may well find that your wheel is not completely accurate. This is why fussing over less than 2 degrees (unless for example, the cam is retarded 2 degrees and you want 2 degrees advanced) may not be worth the effort. Intake Centerline Method The intake centerline method finds the location of the intake lobe centerline relative to TDC. The recommended intake centerline is indicated on the cam card and when correct, it should yield the specified intake opening and closing points when you degree the cam. Finding the centerline is easy. Rotate the engine clockwise until you find the maximum lobe lift, then zero the indicator. Now rotate backward about 0.100 to 0.150-inch to compensate for timing chain slack. Then rotate clockwise until you reach 0.050 inch. This is 0.050 inch before max lift. Note the reading on the degree wheel. Then continue over the nose of the cam until you reach 0.050 inch again. This is the 0.050 inch after max lift. Note the degree wheel reading again. Now add the two readings together and divide by 2 to find the center line. It should match the cam card. For example, if your numbers are 80 and 132: (80 + 132) ÷ 2 = 106-degree centerline The cam card indicates the correct installed intake centerline. If it calls for 106 degrees and you come up with 108 degrees, the cam is early and you have to retard it 2 degrees to bring it into spec. If you get 104 degrees the cam is retarded and you have to advance it 2 degrees to correct it. If you have degreed the cam with the intake centerline method, go back and check to see if the intake opening and closing points match those indicated on the cam card. If incorrect, determine the direction of error and reposition the cam accordingly. Calculating Valve Overlap Overlap is the number of degrees where both valves are off their seats at the same time. It is a combination of the intake opening event and the exhaust closing event. Adding these two points together yields valve overlap. Valve Overlap = IO + EC For example, a cam with an intake opening point of 29-degrees BTDC and an exhaust closing point of 23-degrees ATDC has a valve overlap of 52 degrees. 29 degrees + 23 degrees = 52 degrees overlap Written by John Baechtel and Posted with Permission of Car Tech Books , |
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