Thread: SBC 350 Valve Lash, Push rod length, prime hydraulic lifters in overhaul

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Hi all,

Happy to join, thanks for having me!

To kick things off, I have a question that some of you will probably have no trouble answering. A little background first:

I'm rebuilding my brother's 350 TBI for his G20 Van. We tore the block down completely, bored it, new pistons, rings, bearings, cam, lifters etc. The block was decked and the heads too. Here is where my question lies:

Because of the decking of the block and the heads, I know that I need to adjust my pushrod length, so that the rocker arms will push down straight onto the valves. I did the marker test on the valve stems to see where the rocker arms hit the valves. It was a little off, as expected. So, I bought the Comp Cams push rod length tool to find the right length.

The thing is, when I install the tool (and also with the regular pushrods), after I found zero lash, I turn the rocker arm nuts another 180 degrees as per manual. When I then turn the engine to see where the marks of the rocker arms on the valves will be, I notice that the pistons of the hydraulic lifters are pushed inwards when the cam lobe comes up to open the valve. In normal operation however, the oil pressure should prevent the lifter piston to be pushed completely to my knowledge. So, the reading on the valve stems I get now, would not be an accurate reading to my reasoning, as in normal operation, the hydraulic lifters would be pressurised, causing their pistons not to be pushed all the way in, which will have an effect on the rocker arm geometry.

My question is; how do I make sure that I gain an accurate reading to determine the right pushrod length?

I thought about priming the oil pump in order to pump up the hydraulic lifters, which might be closer to normal operations. However, opinions on whether to pump up the lifters for setting valve lash is much debated.

I would really appreciate your thoughts on the matter! Many thanks in advance!

Regards, Joost

As you already stated, this can be a hotly debated topic. And the hydraulic lifter will still collapse some when full of oil, it uses that compression to get oil up to the rocker. If your test results show your even close to the pattern your after, go with it. Your static "test" may or may not be reality with dynamic operation anyway.

And it is good to see you here, thanks for the question! When you've a chance maybe share a pic of the project.

Are you using CHECKER springs?
https://www.summitracing.com/parts/cca-4758-2

Originally Posted by 36 sedan

Are you using CHECKER springs?
https://www.summitracing.com/parts/cca-4758-2

My first thought too, 36 sedan!

and another hasn't been back to see any answers

Hi all, thanks for having a look at my thread!

@ rspears and 36sedan: I have looked on youtube to find how to use the checker springs you mention, but I couldn't find any. I am not aware on how these work and how it can help me to deterrmine the right pushrod size. Could you please explain?

@ 34_40: I know that when the valvetrain geometry is off, if will wear out the valve guides more quickly, resulting in extra oil consumption, which I like to avoid. If there is no way to accurately measure the needed pushrod size, would there be a good practice on how to do it?

Checker springs are just what it sounds like, a lighter spring so you can test the motion and get the pattern.

And if you can determine IF the geometry is off, how would you propose to "fix it"? If this is really a "stock" build, you aren't using really high load springs, maybe they are single springs also? It's good that you checked it and if the pattern is in the middle even better, but once you get the pattern where you want it using the adjustable length pushrod, do you have the tooling to measure it (the pushrod)? And I do not mean a tape measure.

Again, this can be a hotly debated topic. I would highly doubt your rocker geometry is that far off to wear out the guides. Again, jmho - it's good that you checked it and if it's close to what you want, it's all good!

Thanks again 34_40! I've been reading about the checker springs. I suppose it would work as long as the springs in the lifers can overcome the checker spring tension, which I doubt to be honest. That said, I've never tried them.

I am rebuilding the engine stock, we're enthusiasts of American cars, stock performance is fine. I have a Comp Camps push rod checker tool, so measuring the correct size I can do, I'm just wondering on how to perform an accurate measurement when the lifters are throwing it off.

The springs are the double ones, stock ones. Are you saying that I should not try to measure it? It sounds logical to me that the valve guides will wear out more easily when I get it off. I can't imagine there is no accurate way to measure it... How do you do it?

Some checker pushrods have markings on them that tell you the correct length.

Using checker pushrods with the actual valve springs in place is a sure fire way to bend the checker rods (they are not designed for that much tension). Usually the hydraulic lifter plunger moving down is not a problem as this is usually not more than 50 thousands and movement in the plunger occurs during normal operation.

The checker springs have very little tension (can be installed by hand) and allows the plunger to move up and down while cranking by hand, they are designed to simulate the oil pressure applied movement of the lifter(as well as checking valve clearance and other things), thus giving you a more accurate picture of the valve train geometry as it would be in normal operation.

Welcome to CHR Joost!

I'm with 34_40 on this one - I think you'll be fine to use the stock push rods, adjust 1/2 turn from zero lash, button her up and drive it like you stole it. I'll use checker springs and a push rod length checker when installing new cam with a different profile or when going from flat tappet to roller but on a standard rebuild with a block and head deck it's typically not necessary.

Have fun,
Glenn

Agree, but good to learn.

I want you to check it. But then realize if the geometry is off there is little you can do to fix it in many cases. Pushrod length cannot fix everything, and it isn't always destructive to run a less than normal wear pattern.

Hi guys, thanks all for your input! I'm leaning towards buying checker valves. It will be a good exercise and I suppose it will give me a closer result. I realise that the difference in push rod size may be too little to cause major damage, but I like to do these things by the book.

Before doing the test, would you recommend soaking the lifters in oil? I've also seen some different opinions on that.

@ 36 sedan: would you have a link to the push rod checker that you mean? I only know the ones where a full turn is usually .05 inch.

I'll make sure to make some photo's next time I'm at my brother's.

I was one of those guys that always soaked the lifters. Just the way I was taught.... And I would only make 2 revolutions of the crankshaft ( 1 revolution of the camshaft) any further revs would have a different effect once any oil has left the lifter. Again, just the way I was taught.

Thanks 34_40! Does that mean you took them out in between measurements to soak them again when needed? I know some people prime the oil pump with an electric drill and part of the ignition instead, how do you guys feel about that?

I have decided to order the checker springs and try that way. I'll update you afterwards.