hydraulic roller lifter preload?

[ericjon262]

howdy folks, I'm working on a turbo build for a GM 3.5l V6 (LX9 3500, non VVT pushrod) the engine uses a hydraulic roller cam, and a non adjustable valvetrain, so to set lifter preload, I have to measure the pushrod length at zero lash, and then add the preload to that length. the problem, is that I can't seem to find a spec for the preload, and the specs I have seen for other engines ranges anywhere from .030" all the way to .1"! again, the valvetrain is NOT adjustable, the rocker is torqued to the head, and that's it, so the preload has to be set with pushrod length.

the lifters are specific to this engine, they are similar to other GM hydraulic roller lifters, but they are much shorter. the plunger travel inside the lifter is about .14"

is there any real science involved here? most of the specs I have seen appear to be an arbitrary number, with the exception of the .1" value, which was based on reducing the amount of oil in the lifter and therefore preventing the lifter from collapsing if aerated oil was supplied.

Thanks-

Eric

[Elroy]

Almost every GM lifter I have measured has had around .200 travel. Factory preload is usually in the middle of that range. I would shoot for .080 to .100 myself. They will operate fine on most things anywhere within the range of travel but tend to be quieter set a little deeper....I wouldn't overthink it.

[ericjon262]

Almost every GM lifter I have measured has had around .200 travel. Factory preload is usually in the middle of that range. I would shoot for .080 to .100 myself. They will operate fine on most things anywhere within the range of travel but tend to be quieter set a little deeper....I wouldn't overthink it.

I just want to make sure it's right. it's fairly obvious the consequences of not enough preload, the only problem I see with too much(way too much) is the springs inside the lifter potentially getting into coil bind, which could have a less than desirable outcome.

[ericjon262]

I've now measured the travel of multiple lifters for this engine, and I'm getting a pretty consistent .15" of travel, if 0.08-0.1 is the recommendation for a lifter with .2" travel, using the same percentages works out to .060"-.075" preload for my lifters, does anyone see a flaw in that logic?

[Elroy]

I've now measured the travel of multiple lifters for this engine, and I'm getting a pretty consistent .15" of travel, if 0.08-0.1 is the recommendation for a lifter with .2" travel, using the same percentages works out to .060"-.075" preload for my lifters, does anyone see a flaw in that logic?

I would shoot for middle of travel myself. I agree with having the internal spring super compressed. It can be hard on things. The lifters in the 60° GM v6 engines are short overall now that I think of it. That .150 travel measurement makes sense.

[travis]

Of the top of my head, I seem to remember that the non-adjustable hydraulic valvetrain in sb fords calls for .040”-.060” of preload.

[ericjon262]

Of the top of my head, I seem to remember that the non-adjustable hydraulic valvetrain in sb fords calls for .040”-.060” of preload.

I had really been trying to find the reason for the spec, so that I could make an educated decision on how long to make the pushrods, not just a guess based on other engines.

[cjperformance]

For a stock/mild build .030" either side of mid travel would work no iffs or buts.
When you talk turbo are you adding boost/extra boost more rpm, bigger cam than stock etc?
Keep in mind if you valve float it due to boost or rpm and allow a hydro lifter to pump up , have you got enough piston to valve clearance to allow for this scenario or are you going to end up with instant scrap metal!
Hydro lifters dont need much preload to operate perfectly reliably and quietly. Id be checking P/V clearance before making any judgment on what preload is best. Make sure valve springs are up to task then preload it to suit. If its modified you are best/safest to err on the side of minimal preload.

[ericjon262]

For a stock/mild build .030" either side of mid travel would work no iffs or buts.
When you talk turbo are you adding boost/extra boost more rpm, bigger cam than stock etc?

all of the above.

Keep in mind if you valve float it due to boost or rpm and allow a hydro lifter to pump up , have you got enough piston to valve clearance to allow for this scenario or are you going to end up with instant scrap metal!
Hydro lifters dont need much preload to operate perfectly reliably and quietly. Id be checking P/V clearance before making any judgment on what preload is best. Make sure valve springs are up to task then preload it to suit. If its modified you are best/safest to err on the side of minimal preload.

I did just clearance the pistons to bring P-V up a bit, I ended up going with .075" of preload, my springs have about 310# open force, on a relatively small valve and lifter, I think it should be pretty good.