Lifter preload

[DionR]

Building an LA/Magnum hybrid Frankenstein motor with an LA block and MP Magnum R/T heads, Hughes retrofit rollers, OEM 5.9 cam and stock Magnum rockers.

Currently I am measuring my lifter preload at .085" with a Ford pushrod measuring 6.88" long.

I know the recommended preload is .020"-.060", and I would prefer to be on the lower side of that, but I need to get my motor together and would prefer to just bolt these up.

To add to the confusion, in the Service Manual, they list a tappet "dry lash" spec for all smallblocks as .060"-.210", and yes they were all hydraulic tappets. Is this an indication that a lifter preload of .085" is ok? Or is "dry lash" refering to something else?

The motor isn't going to run that high in rpm with the stock cam so I don't think lifter pump up will be an issue, but would like to hear some other thoughts on it. Don't want to excede the limits and hurt my lifters either.

I can order some 6.821" pushrods and get my preload down to .026" or so, and I might do that in the future, but I don't really want to wait for them right now.

Thanks.

 

[Coyote Jack]

Get the proper length pushrod. If not you will run a very real risk of wiping the cam even with oil additives.

Jack

 

[RustyRatRod]

Dry lash simply means bled down lifters so that you can measure how far the plunger protrudes into the lifter body. I wouldn't run any more than .030" preload on a performance camshaft, but that's personal preference. So I take it that you are not running adjustable rockers? You might could get shims and put them under the rocker fulcrums, but I don't know enough about Magnum heads to know if this is acceptable or not. They are cheap, so I would go with an adjustable rocker.

 

[moper]

I havent run Hughes lifters but my impression is just run it. The stock roller won't care. If hughes has an anti-pump-up function, you will need to get shorter pushrods and get the preload to what they tell you to run. But to me, as you have it, it's fine.

 

[DionR]

Talked to Tim at Hughes and he said .085 would be fine. He said roller lifters need more preload, and that they get lots of guys calling back because they aren't running enough preload and get a bunch of noise.

Don't think shimming the rocker stands is a good idea, seems like there is some lateral support there in how the stand is square at the bottom. Unless the shim matched the base of the stand. Not sure what it would do to the geometry, either.

 

[dartcuda1]

dry lash simply means bled down lifters so that you can measure how far the plunger protrudes into the lifter body. I wouldn't run any more than .030" preload on a performance camshaft, but that's personal preference. So i take it that you are not running adjustable rockers? You might could get shims and put them under the rocker fulcrums, but i don't know enough about magnum heads to know if this is acceptable or not. They are cheap, so i would go with an adjustable rocker.

x2