Valve Adjustment Question

[RHGuyettejr]

Hey everyone,

On my 69 GMC 2500, it seems as though the valves are adjusted wrong, almost seems like they are too tight. The truck has a hard skip to it, doesn't misfire, but runs rough and occasionally pops through the intake. I have to check the timing as well to make sure it is not that, but I was wondering if anybody knows what the specs are for the valve adjustments, and where I could get the appropriate set of feeler gauges to adjust them? The reason I am suspecting the valves is that the motor is a fresh rebuild, and the PO said it ran fine, but he adjusted the valves and only drove it about 1 mile back to his house and never drove it again before I purchased it, and I picked up on this problem when I purchased it. I have a video of it running in my build thread, but Ill include it here for simplicity if that helps. Cant really hear much due to lack of exhaust.

1969 C20 Cold Start - YouTube

[Gonepostal]

Sounds like your timing is off

[TBONE1964]

First thing I would do is check the firing order. It goes clockwise 1-8-4-3-6-5-7-2. make sure the plug wires are in this order.

It sounds like the engine has a dead hole as well as incorrect timing which will be the case if the firing order is wrong. Number 5 and 7 are very easy to cross.

You don't need feeler gauges to set up hydraulic lifter cams. If you can find an old motors manual, it has a very detailed example of how to adjust the valves. I have done it with the engine running but it makes a big mess. You need to rotate the engine until the cam lobe is on the bottom and the valve is shut. Then back off the nut until there is just a slight amount of play in the rocker arm. Then tighten until there is no play and continue about 3/4 of a turn.

Usually, if you have stock rockers and nuts, you should be able to see around 3 - 4 threads of the rocker stud.

[RHGuyettejr]

Originally Posted by TBONE1964

First thing I would do is check the firing order. It goes clockwise 1-8-4-3-6-5-7-2. make sure the plug wires are in this order.

It sounds like the engine has a dead hole as well as incorrect timing which will be the case if the firing order is wrong. Number 5 and 7 are very easy to cross.

You don't need feeler gauges to set up hydraulic lifter cams. If you can find an old motors manual, it has a very detailed example of how to adjust the valves. I have done it with the engine running but it makes a big mess. You need to rotate the engine until the cam lobe is on the bottom and the valve is shut. Then back off the nut until there is just a slight amount of play in the rocker arm. Then tighten until there is no play and continue about 3/4 of a turn.

Usually, if you have stock rockers and nuts, you should be able to see around 3 - 4 threads of the rocker stud.

Ok thanks for the info, I never assumed it could be firing order, I will check that. I can hear the dead spot in it. My dad has adjusted valves while running with a scrap valve cover that he cuts a slot in just to get tools in which helps with the oil, I i will check the shop manual I have and see what turns up.

[ChevyCruizer]

Check easy stuff first, timing, firing order

But...Yep, sounds like it is not running on all 8 cylinders (dead hole - as stated above). Pull all the plugs and look at the condition. One should look very different from the rest. If they are new plugs the different one will prob be very white/new looking. If they are old plugs, who knows you might even have one that has the gap pinched shut (helped neighbor last week and he had one pinched shut). If they are old and fouled might as well replace them, then it is easier to see which cylinder has the problem.

The other way is to have a helper keep the truck running (or at least restarting when it stalls) while you pull 1 plug wire off at a time and listen for a change in rpm or the motor will immediately stall, when you find the dead one it will not change. On the "good" cylinders when you plug it back in and the rpm should pick back up (the dead one wont). only do 1 at a time. I know this method might make some here cringe. Just keep your body away from any moving parts. I recently did this on a newer engine and it pointed me to the dropped cylinder and it ended up being a stuck closed fuel injector, so this works for spark and fuel troubleshooting, should also work for compression (incase that cylinders valve is stuck open). Although with a carb engine you should not have that type of fuel problem.

Maybe run a compression test

I know longwinded...

[RHGuyettejr]

Thanks, Plugs are cheap enough and I can swap them out in 20 minutes or so. I'll start with the firing order, then check the plugs, then the timing and see where I get.

[RHGuyettejr]

Just got home and checked the firing order, it is correct.... I also noticed that the truck has a muffler on the drivers side, but just straight pipe on the passenger side, I know this shouldn't make it run this bad, but does it have anything to do with it? Thinking I should just cut the muffler off the drivers side and just leave straight pipe because it needs exhaust from the manifolds back anyway. Im going to replace the plugs next week over spring break, and then I will go from there. Thanks for the help guys.

[motorcritter]

Check the vacuum when it's running- another easy way to get a handle on what's happening. The simple things are best to check first, as has been noted already. Popping the valve covers will allow inspection for loose/bent pushrods, bent valves (they won't sit as high as the others), cranking it can point out any camshaft problems, too (worn lobes).
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[RHGuyettejr]

Update. The truck is running now on all 8 cylinders. It has been forever, but long story short the exhaust valves were too tight. I adjusted lash per manual and we are good to go, well almost. Still a lot of work to tidy up, but she is technically road worthy, although I am not about to trust questionable brakes and electrical for anything lengthy quite yet. Thanks for the advice.

[TBONE1964]

Glad you got it going. It is a good feeling when the old Chevy runs like it should.