Lifter Preload

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Dec 23, 2019 | 11:58 AM

Joshboody

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Burning Brakes

Joined: Apr 2004

Posts: 786

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From: Tucson, AZ

Lifter Preload

Interested in thoughts on my preload after some research.

Base circle cam, dia 1.51 (0.04 diff from stock)
7.40 aftermarket pushrods

I get 2 turns from 0 lash, meaning apprx 0.15" of preload... too much I'd think!
- factoring 0.05 thread pitch and lever arm from bolt to pushrod

BUT considering smaller base circle I should be less preload than stock... UNLESS stock rockers are NOT torqued to 22 ftlbs and just turns from 0 lash.
- If stock pushrods are 7.385 and 0.02 base circle radius diff I should be perfect.

What yall say?

Dec 23, 2019 | 12:17 PM

Joshboody

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Burning Brakes

Joined: Apr 2004

Posts: 786

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From: Tucson, AZ

Seems I may have checked preload incorrectly... should be 0 lash, then turns to "snug" and extra turns to torque do not effect preload... makes sense, Thanks Brad

Dec 23, 2019 | 02:08 PM

bwill03z

Melting Slicks

Joined: Nov 2011

Posts: 3,164

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From: Virginia

You are going to get answers all over the place as to how much preload to run, but pretty much everyone agrees the way you accurately check preload is to measure with an adjustable pushrod while on the base circle of the cam. What lifters are u running? Heads? I have a Texas speed cam with stock heads and ls7 lifters. With 7.4 pushrods I was around .090 preload and I was advised by Texas speed that was too much preload. My car is noisy as hell so I’m going to take their advise and see if a little less preload with help.

Dec 23, 2019 | 02:38 PM

vettenuts

Team Owner

Joined: Mar 1999

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From: At the beach in little Rhody

I get a preload by calculation with 2 turns from zero lash (subtracting 1/3 turn for rocker bottom to 22 lb-ft of torque) of 0.130".

Dec 23, 2019 | 05:08 PM

Joshboody

Thread Starter

Burning Brakes

Joined: Apr 2004

Posts: 786

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From: Tucson, AZ

Thanks guys. It has to be ok... stock heads, lifters with 7.4 rods on smaller base circle. The online info is all over the place on this... even comp cams says turns to 22 ft lbs, but this can't be right since rocker will seat before torqued. Anyway, I'm calling it good and will worry about something else.

Dec 23, 2019 | 05:44 PM

bwill03z

Melting Slicks

Joined: Nov 2011

Posts: 3,164

Likes: 258

From: Virginia

Quote:

Originally Posted by Joshboody

With stock heads and stock lifters I would imagine you’re good with a 7.4. These LS7 lifters I used need a shorter pushrod because the cup sits a bit higher, I think about .050 according to the interweb.

Dec 24, 2019 | 07:47 AM

vettenuts

Team Owner

Joined: Mar 1999

Posts: 22,025

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From: At the beach in little Rhody

Quote:

Originally Posted by Joshboody

I did measurements three ways. With a dial indicator, calculations and an adjustable pushrod. I got all three to match. The key to calculations is I found it took 1/3 turn to go from zero lash to a final torque value of 22 lb-ft. When calculating, you also have to use parallel triangles to get the pushrod movement ratio based on bolt movement, i.e., use 2.7/1.7 as a multiplier. I think your current setup is a little deep on preload and I would install one pushrod and measure preload directly with a dial indicator. This is the only accurate measurement.

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