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Old 09-24-2001, 06:11 PM
WS23 WS23 is offline
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Default Valve Lash Adj & Piston to Valve Clearance

Can anyone explain what effect (if any) of adjusting valve lash using adjustable rockers on a hydraulic lifter cam under the following 2 conditions? Is there any difference, why or why not?

1) When the lifters are bled down.
2) When the lifters have not bled down.

As a related follow on question, does anyone know what effect the above has on the accuracy of measuring piston to valve clearance?

Thanks...............
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Old 09-24-2001, 06:28 PM
Mills Mills is offline
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There is a difference - what - I don't know. All I know is when my friend was having problems adjusting his rockers on his 440, he called Hughes engines up (their Cam/lifters/etc.) They told him he needed to make this adjustment with the lifters bleed down. They actually got him to remove the lifters and manually get rid of all the oil. Told him to make the adjustment upon assemble of engine and not to worry about it.

My guess is since you can not adjust them while engine is running, you can not know for sure that all the lifters are at the same point of bled down. This could cause some valves to be adjusted different then other.

The above makes me think I have NO idea.

Mills
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Old 09-25-2001, 11:16 PM
Karl43 Karl43 is offline
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On solid lifter cams with adjustable lifters, you set the clearance or gap in the valvetrain to allow for the growth of the parts when heated up. Hydraulic lifters usually have a set preload on them which is the opposite of clearance. You have to be able to determine when you start to preload the lifter and then put the proper preload on it. If you have too much clearance, the pushrods will come off of location with the rocker arms and possibly bend the pushrod and/or bend the valve. Been there done that when I overheated a 318 this summer.

The valve guides swelled up and stuck the valves. The pushrods came loose and I bent four of them on the right side exhaust, bent the four exhaust valves (broke the valve head off on one of the cylinders), and broke a lifter when the pushrod was off location. Luckily I caught it in time and was able to repair it.
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Old 09-26-2001, 01:00 PM
WS23 WS23 is offline
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Thanks Mills & Karl for your responses. Bummer on what happened to you Karl, and Mills your last line cracked me up! I feel the same.

I felt I understood the valve lash adjustment concept but I wanted to bounce it off others for their unbiased opinions. What I can't come to grips with is the piston to valve measurement when using hydraulic lifters.

With solid lifters this measurement is clear and accurate. All involved components (lobe, lifter, pushrod, rocker, piston position etc) are fixed at the time of measurement. However because the hydraulic lifters depend on oil to "pump up" to some undetermined amount, and that they "bleed down" to some extent in a static (sitting) condition, I don't see how one can ever accurately measure piston to vale clearance using hydraulic lifters.

I have used both light checker springs & a dial indicator, as well as the clay method. But each time I get a different value because the lifters experience some bleed down due to valve spring pressure exerted on the lifter while rotating the engine. Of course the more they bleed down it gives the appearance of greater piston to valve clearance, because the valve lift is decreased. When I have pre pumped the lifters by submersing in oil & pumping the air out using a push rod, the measurement shows a lesser piston to valve clearance. All that seems to make sense. But does not help to explain which measurement is true.

Subsequent measurements show an increasing amount of piston to valve clearance as the lifter bleeds down. So you can see that I really don't know for sure where I am! I would like to understand this so I don't have these doubts running through my head while making a 1/4 mile passes at 6000 RPM!

BTW, I believe I have in the area of .150 to .175 minimum piston to valve clearance, which is sufficient. Am I being too overly concerned?
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