what effect would to much lifter preload have
02-25-2006, 08:33 AM
#1
what effect would to much lifter preload have I have searched but not found the answer to this. I have .110 preload on stock style crane lifters with the 7.4 pushrods I have now (as measured with an adjustable pushrod) I was thinking about buying a set of 7.350 pushrods . If i took the .020 shim thats currently under the stands (I have jessel shaft mount rockers) that should get me down to .080 preload. I just wonder what are the effects of to much preload? would the high amount of preload pressure balance some of the spring pressure at the closing of the valve allowing it to bounce? I have comp 921 springs
02-25-2006, 08:50 AM
#2
According to Cranes website http://www.cranecams.com/?show=faq&id=3 ,
I don't know if that article is talking about LS1 lifters or not, but I'd bet you are getting close or already there to maxing them out. One of the worst things I can see happening is holding the valves open. Also wearing out the lifters quicker I'm sure. If you remove the .020 shims, that will make the preload worse because you will be lowering the rockers which in turn pushes down on the pushrods which in turn pushes down the lifter cups. If the valve stem swipe looks good with the shims leave them on and just buy the shorter pushrods.
If the opposite occurs and the pushrod descends too far (more than .060”), then you have excessive lifter preload. In theory, a hydraulic lifter can pump up whatever preload you put into it, therefore with excessive preload, as the engine RPM and oil pressure increases, the hydraulic mechanism will pump-up the pushrod seat. This will cause the valve to be open longer and lift higher. This will decrease the cylinder pressure, lowering the performance of the engine. If the preload is excessive it may cause “backfiring” from the engine.
02-25-2006, 03:06 PM
#3
Interesting question as I have done a lot of searching/reading on this. I have about 0.120" of preload per the Crane recommended setup on their lifters. I have been told and read elsewhere too much preload can contribute to "lifter float" or holding the valve open.
Are you running into a problem of some type?
Are you running into a problem of some type?
02-27-2006, 09:39 AM
#6
Originally Posted by vettenuts
Are you running into a problem of some type?
02-27-2006, 09:55 AM
#7
TECH Senior Member
rather than removing the rocker stand shims which are there to probably center your wipe and correct your geometry, and .020>.025 is what you want to reduce preload by, I would suggest Comp 7.375 instead of 7.350.
