[doubleClutch]

I recently installed a Magnum 280H cam in my 77 400. We built the top end of the car with Rhoades lifters, new push rods, and 1.65 roller rockers. We finally got the car running, and I drove it home today with the new cam over about 90 miles. I could feel the difference the cam made after the highway drive. The car pulls nice, but it spits out black smoke sometimes when I push it hard from a stop. The car also has a really hard time in reverse. It will die after 2-3 seconds in reverse without any gas applied. It also dies in idle about one in every ten traffic lights. Is the timing off, or do I need to tune the carb?

Also, the cam seems to cause huge amounts of engine movement. Idle vibration is really bad after the car has been driving around for 10-15 minutes. Feels like I am off roading in a jeep, but the car is sitting. My exhaust tips are vibrating about 3-4 inches around, and the engine is moving 5-6 inches left and right. Can I get stronger motor mounts to prevent this?

[66bonne]

Not saying that this will cure your ills but it may help: Are you running a MSD [or other manufacturer] ignition box ?
The principle reason why I put a MSD 6AL box in my Catalina was to help smooth out the idle, it worked.
Good luck, Jim

[wheelspin]

I would start w/ the carb; based on the black smoke, be sure that the choke is fully opening. What carb are you running?

Set the initial timing @ 12-14 degrees (vacuum detached from dist.and plugged) w/ the other 20-24 degrees in the distributor, for 34 total.

And I agree w/ Jim on the benefits of a muti-fire ignition system for improving the idle stability of performance motors.

Les

[shaker455]

Sounds like the carb is in need of attention.

[screamingchief]

I recently installed a Magnum 280H cam in my 77 400. We built the top end of the car with Rhoades lifters, new push rods, and 1.65 roller rockers.

Is this a stock '77 400,including the heads and compression ratio?

If not,what heads are being used,what compression ratio?

Were the current heads pushrod slots clearanced to use the 1.65 ratio rocker arms?

You guys took the time to fully grasp and follow the adjustment procedure for those Rhoads lifters I hope?

What valve springs are being used?

What timing chain set was used?

Was the cam degreed when installed?

I sure hope these heads have screw in studs...

Anyhow,I agree the basic engine tune (timing/fuel curve) sounds like it's "off",and you need to address that,sounds like it's pig rich for the current combo,but that's hard to say from over a keyboard.

So basic diagnostics my friend,check the cranking compression,and the engine vacuum,make sure there are no vacuum leaks,that sorta stuff.

[doubleClutch]

I answer as of the questions many as I can, as I just purchased the car about 3 weeks ago, and the seller has been very unresponsive.
Proform Pontiac HEI Electronic Distributor with MSD wires
Its a stock 77 400 (dated 77, block # 500577,y4 samped on front)
Seller told me its similar to this block http://cgi.ebay.com/ebaymotors/1977-...0Q3aRECOQ3aBIN
I don't know what kind of heads are on the car, but I don't think the rods are rubbing the heads because they would have broken by now.
We used to watson guide to adjust the valves
Used the timing chain set from the jegs cam install kit: 720-4422K
its got screw in studs
It sounds like the timing is at factory settings, and the carb is still set up for the old acm.
Engine movement has been getting slightly worse as the cam is getting broken in. The car pulls harder, but shakes A LOT. I won't drive it until the carb is in check.

Anyone have a link to a good carb tuning guide for the 750 Edelbrock.

Thanks again.

[66bonne]

doubleClutch - I seem to recall that Edelbrock has posted the tuning guides/troubleshooting hints on their website. http://www.edelbrock.com/

[screamingchief]

I don't know what kind of heads are on the car, but I don't think the rods are rubbing the heads because they would have broken by now.

With the comp magnum 280 and 1.65 rockers,I can pretty safely assure you the pushrods are rubbing if the intake pushrod slots were'nt opened up for the 1.65 rockers.

Some heads the exhaust side slots clear fine without mods,while other heads may need both sides done to clear.

Dont count on them breaking if they're rubbing,not right away,they can remain intact and not break if they're only rubbing slightly,but this will also affect the rocker arm geometry and valvetrain function,as well as being a good possibillity for loosing lobes if one is not absolutely certain there is adequate clearance for the pushrods.

We used to watson guide to adjust the valves

Sorry,but that wont work with the Rhoads lifters,the Rhoads lifters have a very specific adjustment method,and it needs to be followed for those lifters to function properly.

Simple solution is to follow the instructions that come with the Rhoads lifters describing the proper adjustment method for those lifters,not a manual which is for OE hardware and does not translate to aftermarket hardware much at all.

My feelings at this point say you may be hanging the valves open due to improper valvetrain adjustment and that is possibly aggravated by mechanical intereference issues from the 1.65 rockers,and those things are causing these driveabillity issues most likely.

What pushrods were used?
Was the rocker geometry checked?

So safe to say at this point that the cam was'nt degreed when installed,we know that the timing chain set is a "cloyes" item,though we have no idea which one (there are like three or four different cloyes T/C sets IIRC) specifically,still no mention of what valve springs are being used with this cam,and it seems unlikely that the pushrod slots were opened up for the 1.65 rockers,the Rhoads lifters were'nt adjusted per their instructions,and we have no idea what the compression ratio is because we have no idea what heads are on this engine,but we know it has a Edelbrock 750 carb,and a proform HEI.

I would advise going back to square one,taking some more time and making sure everything is together right before any further efforts are made,and hope that something did'nt get mortally wounded by this initial attempt at doing this cam install.

And I have'nt even asked what the rest of the drivetrain consists of yet.

Dont kill the messenger,he's only trying to help...

[A.W.Dille]

Screamingchief is absolutely right with what he is telling you. I ran into a similiar situation a little over a year ago where someone didn't check everything out one a 77 T/A that had a 74 400 with with 4X two barrel heads, the ones with the bottleneck studs. Wanted me take a look and see why it had a serious miss in it. All it took was pulling one valve cover to see where someone had tried to make an adjustable valvetrain out of a non-adjustable. polylocks on stock rockers. Result, broken rocker stud. Same deal someone had shoved a large cam into this motor and didn't set everything up according. Recheck everything as I know that the Comp that you installed is a really good cam when properly set up.

[smagnotti]

also if this is the stock 77 carb, even with the rhoads lifters on this size cam you will never get this engine to idle as smooth as it is capable of with out doing some work to the carbs idle circuit.
If you keep on having the belching out black smoke problem you will wash out the rings and be rebuilding the motor in short order even with out the possible lifter and push rod problems.

[doubleClutch]

Hey, thanks again for all the replies. The mechanic working on my car was very familiar with classics and Chevy's, but I don't think he did any of these adjustments correctly because once he got the car starting he decided it was running fine. Anyway, they are 6x heads, and I am not sure what the compression is due to the fact the bottom end is foreign to me. I am guessing 8:1.
How do I know how much damage has been done to the engine? The car still starts, and drives, but it stalls in idle sometimes, and stalls in reverse a lot without a long warm up. I am on a small budget, and have about $1000 to spend to fix these problems, but I need to know if I should spend it on tuning, timing adjusting, readjusting the valve train, or are all of them of equal importance. Here is what I was going to fix in order for the advice in the posts:
Checking if push rod slots were elongated, and elongating them if needed.
Readjusting the valve train
Readjust the timing for the new cam going to try initial timing @ 12-14 degrees (vacuum detached from dist.and plugged) w/ the other 20-24 degrees in the distributor first
Also, someone said something about the carb, will this carb be ok properly tuned?

Sorry again if these questions seem extremely basic, this is my first attempt at building a Pontiac motor.

[SergeF]

I ran 280H before. I had stalling problems with it untill I installed 3000rpm converter. You will not get this cam to idle in gear with the stock converter.

[Will]

you MUST check the valvetrain setup first. There is no hope that the engine will run right and there is the potential for damage if the valvetrain setup isn't right.

I'm going to guess multiple problems here.

First, that is too much cam for stock valvesprings even with stock rockers. With 1.65 rockers I guarantee you are coil binding if the springs weren't changed. This will wipe out your cam & lifters and/or pushrods very quickly, sending metal throughout your engine. Don't drive this car any more 'til you've checked on the valvespring coil bind issue.

Possible that the pushrods are now bent from binding on the heads because the slots weren't elongated. The heads must be removed to elongate the pushrod holes.

Possibly misadjusted lifters.

A stock '77 Q-jet will never work right with that cam without making internal modifications to the idle circuit. If you want to take on the task of learning about Q-jets and how to modify them, get yourself a copy of Cliff Ruggle's Q-jet book. Otherwise, find a Q-jet specialist to set this carb up for you. I'm sure board members can suggest someone good. Or, buy a Holley 750 or 850 mechanical secondaries if you don't care about gas mileage. A Holley won't mount to the stock intake though, so you'll have to change the intake too if you do this.

The 280 magnum is a good sized cam and adding 1.65 rockers effectively makes it bigger. No matter what you do it's not going to have a butter smooth idle, it'll be fairly choppy, but it should be possible to tune the engine to idle without it dieing, though the torque converter will give you problems as mentioned.

Honestly, I'd recommend you make your life a lot easier and get a smaller cam. That low compression 400 will run much stronger with a smaller cam and you won't have to change everything else on the engine and car to match it. The comp XE262 would be a MUCH better match.

[doubleClutch]

I found a reputable shop that would elongate the push rod holes, replace the valve springs, and tune the timing for about the same price as buying a new cam, lifters, and the labor to install and retune the car. They also specialize in Q-jet. I am willing to replace the torque converter also if needed. This car isn't a daily driver, just needs to run to track, and back. Can I upgrade the compression later, or is this a strict requirement to even get the car running safely? I am not going to run the car at the track any time soon, but I need it to drive to be able to move it around to different shops etc.

[GTOGreg]

The symptoms sound like incorrect lifter pre-load

[Don 79 TA]

are you also using a stall convertor and some rear gears too? that cam probably wants like 2200-2400 stall

are you sure you set the timing marks up correctly?
you will have to adjust and play with timing since it's an aftermarket cam

also make sure you have at least 9.5:1 compression with that cam, it can be used with lower, but prefers higher comp

that cam should have some chop/lope to it in a 400, which should vibrate the motor, but what you are describing sounds excessive
was the distributor set correctly?
verified firing order
and is the balancer in good shape?

all these little things can add up
i'd love to hear how that cam sounds with your setup

to check what heads you have, get the code from the center exhaust ports

probably something like 6x

just some ideas on top of what the others have said
never assume, go verify

[Will]

Do yourself a HUGE favor and get a copy of Jim Hand's book "How to Build Max Performance Pontiac V8s." Once you understand how compression and cam timing interact and the basics of the Pontiac V8 engine many of your questions will be answered and you'll be able to build a much better combo in the future.

The compression ratio is determined by the heads on a Pontiac, for the most part. The easiest way to increase the compression on this engine would be to buy some of the late '60s to '70 big valve high compression heads.

You really need more compression to make that cam work well, especially with 1.65 rockers.

Even with a higher compression ratio you will definitely want a good torque converter. For max performance with that cam look for 3000 - 3200 stall. Do NOT buy a cheap B&M converter from the Summit or Jegs catalog. They're cheaply made and not well suited for use behind a torque-monster Pontiac engine. They will slip horribly and stall much higher than their rating. Get a converter from Hughes, Coan, Continental, or Redneck. Those are all quality companies that make good products and can custom build a converter for your needs. A good torque converter is worth it's weight in gold in terms of the performance gains you'll see.

I know you have other questions - I'll encourage you to ask them all here so that others can learn.

[jamaca85]

change the rockers to 1.5s and see if you still have problems.

[Brian Baker]

Egad! You're problems are in the cam/valvetrain. Lord knows where the cam is installed and the rockers are most definately not adjusted correctly. You can't follow an old manual designed to instruct you how to adjust factory OEM rockers when you're using aftermarket parts that require the lash to be adjusted to a precise clearance. My guess is your mechanic just cranked the rocker nuts down to 20 ft/lbs. and this simply will not work with the aftermarket parts you have.

Egging out the pushrod holes will requre removing the heads, unless you want to risk getting shavings in the engine. If this isn't an option, I'd nix the 1.65 rockers and go with 1.5 rockers, and definately make sure you have the correct valve springs installed, and that they're installed at the correct height. The factory springs won't cut it, even with 1.5 rockers, and you've probably already killed them with the 1.65's. Check your pushrods, and replace as needed, because they're likely FUBAR. I won't get into a discussion on the valve guides or seals at this point, since you're on a tight budget. If it's not burning oil, don't worry about them just right now.

I can't add any more than screaminchief hasn't already.

[doubleClutch]

Just wanted to give an update for anyone thinking about the same setup. I found out the rods were hitting the heads, and I switched back to 1.5 roller rockers. Also one of the motor mounts was loose which was what was causing the vibration. We advanced the timing 35 degrees, and the car is now a monster. I have a 2000 stall converter, and the idle is slightly choppy, but it stays running in gear and in reverse.
The car pulls very hard, and easily walked a much lighter Infiniti G35 ~280Rwp from a stop and roll. My only problem was that car was leaking oil on the headers after 5-10 min of driving. We used extra sealant and tightened the valve covers. Do the stock valve covers commonly leak oil? Could the leak come from the valley pan? The car was not leaking oil before, and the mechanic didn't touch the valley pan. Also, I am still wondering if I need to raise the compression? Heads are 6x, 2.5" pipes, and the bottom end is stock. Can anyone give me a net hp guess, and if it would make any more hp with a higher compression.
Here a pic of the leak


Thanks again for all the help.