I decided it was time to replace all the original leaking gaskets, clean up the heads etc. in our 74 L48. After replacing the heads, but before adjusting the valves, I ran a compression test that showed approximately 140Lb compression in all cylinders. I then adjusted the valves as per GM. (TDC compression stroke, distributer pointing to #1 cylinder.) At that point, I showed 140 Lb compression on cylinder #1 and zero, nothing, nada, not a single ounce of compression on any other cylinder. Obviously, for some reason, once adjusted, the valves are not closing fully. (Per GM, I took one full turn after feeling drag on the push-rods.)

I have no idea what is the cause or the solution but wondered if it may be a hydraulic lifter problem as the engine is not running to pump oil?

Any and all suggestions will be greatly appreciated.

 

you will have to turn the mill over several times once you adjust some of the lifters to move the plunger in the lifter or you are adjusted too tight ...on each cylinder, adjust the intake valve first when the exhaust valve STARTS to OPEN then on the same cylinder adjust the exhaust valve when the intake STARTS to CLOSE, then rotate the mill to the next cylinder....

i hope you did not adjust all the valves with the #1 at tdc..if you did this do NOT turn the mill over!!.....loosen the rocker arms and adjust as i have suggested....good luck

valve order...EIIEEIIE

 

Pull the spark plugs out and turn the engine over a few revolutions with a breaker bar. If the valves still are not closing fully, you have bottomed the lifter plungers out in the lifter bodies and then turned the valves down 1 turn from there. You need to back the adjusters off and do it again, starting the 1-turn (most prefer 1/2 turn) adjustment when the pushrod is right at "0" lash.

Lars

 

Thanks, I'll give it another try in the morning.

 

Did you adjust all the valves with the distributor pointing to the number one cylinder?

 

No per GM, I adjusted 1/2 the exhaust valves and 1/2 the intakes at TDC cylinder No. One and 1/2 of each while at TDC cylinder No. Six.

 

Guessing valve lash set too tight so they aren't closing and or out of order on intake versus exhaust when adjusting. I just went through replacing all valve springs and got the car to where it would start and run, then used the valve cover with a window cut in it to adjust them while running. Might be old school but it worked like a champ.

 

you must have screwed something up...do them one cylinder at a time with the plugs removed

 

I copied this method for you to see. It worked for me to get it running at least.

To set cold do the following.

Rotate the engine until the mark on the timing tab by the damper lines up with the ZERO position in the number one firing order. You will want to pull the #1 spark plug (driver side front) with your finger in it while turning. When it pushes out air hard as the line comes to ZERO - you are there.

In this position - you can adjust

Exhaust - 1, 3, 4, 8
Intake - 1, 2, 5, 7

You will want to run the nut on the rocker down while spinning the push rod in your fingers. When you can't easily spin it - are at zero lash. From there go one full turn.

Now, rotate the engine one full revloltion

Exhaust 2, 5, 6, 7
Intake 3, 4, 6, 8

 

The valves were initially adjusted this morning exactly as outlined in tonak's post above except that I used 1/2 turn as Lars suggested. That didn't work, so what I have been doing is backing off the 1/2 turn to zero lash. At that point (and so far I have backed off only the left bank) I have approximately 140 lbs compression in each cylinder on that bank.

What I am thinking about doing next is to add 1/8 turn on the intake valve and test. If I still have my 140 lbs, then add another 1/8 turn and test again. This should tell me if it is the intake valve on that cylinder. I can the repeat the process on the exhaust valve until I have as much adjustment as I can get while still maintaining compression.

How this will pan out once the lifters are pumped back up, I have no idea. If my reasoning is off or I'm missing something please let me know.

Thanks again.

 

Based on my experience, one full turn will be too far. Go a half and come back later if you get valve clatter.

 

are you SURE you have hydraulic lifters??

 

I am the first and only owner, they are hydraulics.

 

if that is the case..call a mechanic because there is something you are just not doing right and hopefully you have not bent any valves..jmo..good luck

 

do you have the intake installed? if not remove the lifters and soak them in oil overnight so they are not totally dry, then try again making sure when you set for zero lash you stop immediately after removing the free play, you may be going too far when setting zero lash

 

It sounds to me like you may not be getting to zero lash properly in the first place.

The lifters have a small spring inside. When there is not oil pressure it's very easy to over tighten the push rod down into the spring and go past zero lash. When you adjust the lifters to zero lash you should just be lightly contacting the lifter spring. In other words just taking the free play out of the system. That's zero lash. You can feel it on the push rod or you can feel it by placing your finger on the top of the lifter. You just want to take the slack or "Lash" out.

When you tighten the bolt one turn as GM suggests you compress the spring down to the middle of it travel inside the lifter, 50% of the way down. If you tighten a half turn, you are placing the spring 25% of the way down its travel. 3/4 turn is 33% of the travel. etc. They will all work once you get oil pressure in the system. Anywhere between 1/2 turn to 1 full turn will get you to a usable place. It's not terribly critical with hydraulic lifters as long as you start with zero lash and compress the spring some.

Oil pressure, when the engine is running, holds the position correctly inside the lifter and acts as a cushion. If you don't start with the correct zero lash, however you can easily overcome the spring and hold the valve open. You do not want this to happen because you can bend a valve stem by allowing it to hit a piston.

It's easy to set them using the GM system of setting half the valves rotating the engine and setting the other half. As long as you can feel zero lash.

If you decide to do it with the engine running it's easier to feel zero lash because the oil pressure is holding the spring in the lifter at the top of it' s travel. You can feel and hear zero lash in that case. It's just very messy and it takes longer.

 

When you start a car after cold setting the valves I would wager the first thing people check is whether or not they have clatter, and a multitude of other things too I guess. I personally found that if the car will start and run, "'fine tuning" the lash with the engine running is the cat's meow. Not original to me, but an old valve cover with a window cut in it for access to the lifters works great. Advanced Auto has a brand new pair of sbc covers for 35$, junkyard here was 1 for 10$. It's easy and not too messy at all. I have friends that say just a sheet of cardboard can be used, but I guarantee my engine would have been out of oil if I tried it that way.

Also proper setting of the poly lock is critical too.

 

At this point I have gone to zero lash plus 1/8 turn and have full/normal 140 lb compression. Anything more than that and the valves do not close fully. Once I get the car restarted (something that is a bit down the road as I need to come up with funds to replace the entire exhaust system) I will do the fine tuning.

Once again, I want to thank everyone for their help. I've had several stress related heart attacks in the past and had begun to wonder if playing with the old girl was such a good idea.

 

Which 1/2? Seriously, there's a specific approach required if you use the "companion cylinder method":

#1 at TDC compression
Adjust exhaust valve: 1, 3, 4, 8
Adjust intake valve: 1, 2, 5, 7

#6 at TDC compression
Adjust exhaust valve: 2, 5, 6, 7
Adjust intake valve: 3, 4, 6, 8

There's no reason to ever adjust SBC valve lash with the engine running.

 

Except that it works and there is no doubt at all as to how the valve train sounds when done