[gtobird]

I'd like to measure the cam lobe wear in my 350 without dissasembly. Then, if bad, replace the cam.

First off, I've never tried to measure lobe wear with a cam still in the engine. Is it fair to believe that I could simply remove the valve covers and use a dial indicator placed at the top edge of each valve spring to measure the travel?

Second, this is a 68 GTO clone with all of the original factory type A/C stuff in place and working. Assuming the cam lobe wear proves to have issues, I would remove the intake, valley pan, rockers, push rods, etc. Is there any way to remove the cam without having to take the refrigerant out and remove the condensor? The only way I can think of is to pull the engine, or at least disconnect and lift it high enough to remove the cam.

Thanks
Old Joe

[indymanjoe]

should be room to slide all the a/c stuff off to the side with some bungee cords etc..

[JLMounce]

Is there a reason you believe the cam needs to be replaced, or is this more of a piece of mind type situation?

With a hydraulic cam, I don't think I would necessarily measure from a valve spring. I'd want to measure from the lifter body itself. Something that takes any leak down of the hydraulic lifter out of the equation.

In regards to the AC, you should be able to remove the compressor from the engine accessory drive and move it out of the way without purging it and needing a recharge. You can then change the cam if needed with the engine in the car by removing the radiator. There should be enough room at that point to pull the cam out and stab a new on in it's place.

[i82much]

if you wipe a lobe, your engine will let you know!!

[Dragncar]

Put a vacuum gauge on it. If it bounces all over the place, look further.

[Formulas]

I have never tried it but its possible a dial indicator internal spring wont depress a lifter plunger but you would have to remove the rocker arm and take a reading from top of pushrod

[gtobird]

I appreciate the comments, and I'm going to try to stay on topic. I've got a serious vacuum issue, both low and erratic and I've been going through the steps to diagnose what's wrong without engine disassembly first. At this point, I'm just preparing for the "what if" situation where I find no leaks from a smoke test and compression, leakdown and ignition tests all look good. I also understand what the different vacuum readings indicate, so we'll see how this turns out.

I've seen so many comments about bad cams that I'm supiscious. In fact, I've got another engine that I disassembled last winter and you could see just how bad the lobes were. I didn't build that one.

A couple of more questions though. I measured the length of a Pontiac cam and it's approximately 22 1/2 inches. There is less than that for room between the front of the engine block and condensor (assuming all front engine stuff and radiator are pulled). So, how do you swing the condenser out of the way? The hoses don't look to have all that much play in them, or is the condenser short enough that you can just move it up or down to make room? NOTE: I'm talking the condenser, not the compressor.

With respect to measuring lobe wear. I get the point that lifter leakdown could be a problem and removing the rockers would likely provide less chance of a misread from a lifter that is slightly leaked down. Then again, I would think that if I ran the engine just a little bit before hand to ensure the lifters were all pumped up, it should reduce that risk. If I found one or more valves that had reduced travel, I would have to remove the intake and valley pan anyway to get the cam out, so at that point I could check for bad lifters before yanking the cam. I could also at that point put the dial indicator directly on the cam lobes to verify wear before pulling the cam.

Thanks for the input.

[steve25]

Why don’t you send out an oil sample to get tested?
If all those test outs you have already done prove out no issues, yet the sample test with iron in it then it’s extremely likely that such is coming from the cam and lifters, especially if these parts are original and with over 50K miles on them.

Is the motors timing chain and gears original?

If so then that can make for low vacuum that bounces around, and with that condition it will bounce around more at low rpm / idle.

[chiphead]

Here's the stupid simple cam inspection method: If the pushrods are spinning, the cam isn't wiped. The first thing to fail when a cam wipes, is the lobe/lifter taper that spins the lifters and pushrods. No spin usually means bad cam.

Remove valvecovers. Take a white paint marker and draw a 1" line on each pushrod below the rocker arms. Start engine and set on fast idle.
The paint marks will make it easy to tell if the pushrod is spinning like it should. If all 16 are spinning at some rate, the cam isn't wiped.

You may have other issues like stuck lifter, bad rocker adjustment, bent pushrods, burnt valves, etc. But at least you'll know what shape the cam is in.

[Schurkey]

^^^ Yes.

Carve a set of Treasure Yard valve covers to minimize (not eliminate) oil mess.

[gtobird]

The engine is not original and was rebuilt somewhere around 10K miles ago plus or minus. I haven't taken the timing case off yet. Again, doing "non" take apart engine tests right now. I did check compression and leak down. Both were very good.

I try not to do hunting and pecking to diagnose things. I'll let you all know how the rest of the tests progress. Should everything come back negative, I like the idea of doing the oil test to check for cam wear. Sounds like it would save a lot of time. One of the reasons I'm prepared for the possibility it's a cam is that my vacuum at idle came back around 10HG and the needle was vibrating quickly. Seems like it's an issue with a late exhaust valve, bad spring, etc. Certainly could be anything in the valve train including lifters, timing set, etc.

Like I said, I'm not ready to pounce on anthing yet. I'm also suspicious of the HEI distributor as it had problems at the start of all of this. It just seems that the vacuum reading would be unlikely to be that low and vibrating from a distributor issue, but who knows. Nothing is ruled out just yet.

Thanks again, but still waiting to hear how there would be enough room to move the condenser out of the way if I needed to yank the cam while still in the car. Move it up, down, twist the hoses to it, ?

[b-man]

One of my racing buddies who bracket raced his ‘69 GTO was able to swing his A/C condenser out of the way without taking the hoses loose to do a cam swap so it certainly should be the same for your ‘68.

I didn’t personally witness the process but I’m sure he wasn’t lying about how he did the cam swap.

Hood latch assembly will probably need to be removed too I would think.

[Half-Inch Stud]

Half-as-Easy; just do the Exhaust lobes, or Rockers.Half-as-Hard anyway.

[Sirrotica]

Having done more than a few cam changes in A/C equipped Pontiacs, I can say first hand that you will not have to discharge the freon from the system. There is just enough hose to twist the A/C condenser out of the way to remove the cam. It's a little bit labor intensive, but easily accomplished.

Although each model is a little different, the engineers did leave enough slack in the hoses to tip the drivers side up for clearance.

Depending where the center support bracket is on the core support, you may have to unbolt it to pull the cam out of the block. Each model is a little different, and my memory banks aren't good enough to remember every detalil over the past 55 years of working on hundreds of different Pontiac cars.

I can assure you that it is totally possible to change a cam/lifters/timing chain, and gears in chassis, without pulling the engine.

The info about watching the pushrods spinning is probably the easiest/fastest way to decern if a lifter, or lobe is gone, or going away.

The removal of the valve covers will also let you inspect the pushrods, and rocker arms for breakage, or misadjustment. Your problem could be as simple as a rocker arm fell off of the pushrod, I've seen dozens over the years that only took a good pushrod, and resetting the rocker arm adjustment to get the engine running properly, especially when a chevy guy thinks because Pontiacs have a similar valvetrain to a chevy, that the factory parts are adjustable. They're not because Pontiac didn't use crimped adjustment nuts, Pontiac used a 45 degree seat on the bottom of the nut that seats on a 45 degree shoulder on the rocker arm stud, and is then torqued. If the nut isn't seated against the shoulder of the stud, it will vibrate off, until the rocker arm falls off. It happens frequently when chevy guys try to adjust Pontiac valvetrain, without either poly lock nuts, or crimped nuts, and washers in place of the factory nuts.

Just a few things to look for when you remove the valve covers.

[grivera]

Have you cut open oil filter and checked for metal as a start?

[77 TRASHCAN]

Well........
A visual of the cam is not difficult in a Pontiac. You can't see all of them, exactly clear, but with a mirror, you might have a chance.

I don't know what automotive knowledge you have. I will try to explain what I know...

The lifters in your engine rotate in the lifter bores. The pushrods rotate also, because the lifters make them rotate.
The cam lobes are NOT flat (from back front to back). The back of the lobes are higher than the front, all the way around.
Only a part of the lifter contacts the cam lobe. Only the rear section of the cam lobe should have wear on it. IF, IF the lobe is shiny (like chrome) all the way across, that lobe is toast.
The bottoms of the lifters are made convex, so that the lifters can follow the lobe.

If you remove a lifter and place it on the flat edge or surface, it should rock, and not sit flat, if you are not sure. If the lifters are concave ( a recess), the lobe and lifter are bad.

Another thought, before removing the intake and valley cover, Remove the valve covers, mark all the push rods, run the engine for a minute with the valve covers on (Keeping the oil splashing to a minimum) Take the covers off, see what the marks look like...........

[77 TRASHCAN]

Well........
A visual of the cam is not difficult in a Pontiac. You can't see all of them, exactly clear, but with a mirror, you might have a chance.

I don't know what automotive knowledge you have. I will try to explain what I know...

The lifters in your engine rotate in the lifter bores. The pushrods rotate also, because the lifters make them rotate.
The cam lobes are NOT flat (from back front to back). The back of the lobes are higher than the front, all the way around.
Only a part of the lifter contacts the cam lobe. Only the rear section of the cam lobe should have wear on it. IF, IF the lobe is shiny (like chrome) all the way across, that lobe is toast.
The bottoms of the lifters are made convex, so that the lifters can follow the lobe.

If you remove a lifter and place it on the flat edge or surface, it should rock, and not sit flat, if you are not sure. If the lifters are concave ( a recess), the lobe and lifter are bad.

Another thought, before removing the intake and valley cover, Remove the valve covers, mark all the push rods, run the engine for a minute with the valve covers on (Keeping the oil splashing to a minimum) Take the covers off, see what the marks look like...........

[gtobird]

FYI,

I've built a dozen or so engines over the course of 45+ years with 3 of them being Pontiac engines. Owned half a dozen Pontiacs in those years so I'm not new to this. My goal right now is to do the best diagnosis I can before I rip the intake off. Once I do that, I'm in familiar territory. Just never had this type of vacuum issue and never had to remove a cam while the engine is still in an A/C car. My philosophy has been to build them right the first time and leave them alone. I didn't build this engine and I have practically no run time experience with it so I'm just trying to get everything diagnosed first. It's a 350 built pretty much to HO specs, so I'm only willing to go so far in working on it. I have a 400 that I've been wanting to build so if I can't figure this out with a modest amount of labor, the engine is getting yanked and replaced. I have another 400 that is sitting on an engine stand that I built a while back and ran on my test stand. I considered dropping it in, but it's correct all the way through date code wise for my Firebird, so I'm trying to resist doing that.

OJ

[Half-Inch Stud]

Sooooo, you found a loose rocker arm? A few?