Expand or Contract?
Thread Starter
Racer
Joined: May 2008
Posts: 385
Likes: 3
From: Hamilton Mass
Expand or Contract?
Getting ready to set valve lash on my L72 and thought I would double check the cold vs hot allowance factor thinking this would be simple.
I expected the factor may vary a bit with some saying .002 and some recommending .005, BUT what I didn't expect was disagreement in the direction of the factor with some saying you need to add clearance when you set the valves cold because when the engine warms up everything expands and lash will tighten and others saying NO you need to subtract clearance because the lash will increase when the engine warms up?
To me if you have cast iron block and heads and choose to set them cold you should add a couple of thousands or so to the recommended "hot setting" because heat expands thus the lash will tighten up when hot ---------- but now I'm not sure???
I was shocked to see so much disagreement/confusion!
I expected the factor may vary a bit with some saying .002 and some recommending .005, BUT what I didn't expect was disagreement in the direction of the factor with some saying you need to add clearance when you set the valves cold because when the engine warms up everything expands and lash will tighten and others saying NO you need to subtract clearance because the lash will increase when the engine warms up?
To me if you have cast iron block and heads and choose to set them cold you should add a couple of thousands or so to the recommended "hot setting" because heat expands thus the lash will tighten up when hot ---------- but now I'm not sure???
I was shocked to see so much disagreement/confusion!
Race Director
Joined: Aug 1999
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From: WI
Thread Starter
Racer
Joined: May 2008
Posts: 385
Likes: 3
From: Hamilton Mass
I find it amazing that even the major cam manufactures are in complete disagreement on this IE: Crane says add .002 to the lash specification because the gap will shrink at operating temperature and Comp Cams says subtract .002 because the gap will grow !
Hell this is a basic cast iron BB Chevrolet block and heads with an flat tappet solid cam that's been around for almost 50 years and you would think there would be sufficient data available to reasonably pin this down to some degree of accuracy??
Thank you,
Ralph PS: and your right; how hot is hot ??? normal idle temperature or after a few pulls on the dyno !!!
Team Owner
Joined: Sep 2002
Posts: 38,369
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From: California
I am an old school solid lifter guy!
Don't know what lifter you have, but I have used vacuum gauge to get the best. But it gets harder and harder the more cylinders that you add with this technic!
For the sake of the tune, who cares if some oil splashes all over, that is why they sell the foaming engine cleaner. Nothing more fun that using foaming engine cleaner!
For the sake of the tune, who cares if some oil splashes all over, that is why they sell the foaming engine cleaner. Nothing more fun that using foaming engine cleaner!
Last edited by TCracingCA; Apr 7, 2014 at 11:54 PM.
Drifting
Joined: Feb 2006
Posts: 1,840
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From: Towaco NJ
MikeM is correct as usual. As a guy that builds engines for 3 different solid axle drag cars and drives them, I disassemble them more than I would like. First time assembled, (all with alum different heads) I set them .002 tight. Then measure them Hot. Record the difference. Next assemble, use that info and still readjust when hot.
Team Owner
Joined: Aug 2007
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Army
The Add vs Subtract parameters in the Crane document are dependent on the metals involved. Is that the controversy you're referring to ? I adjusted my iron/iron lash hot on my '61 (hot after idling 10 min or so) and checked them cold and the Crane parameters were damn near spot on. I've used their cold settings ever since (7 years now).
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Thread Starter
Racer
Joined: May 2008
Posts: 385
Likes: 3
From: Hamilton Mass
The Add vs Subtract parameters in the Crane document are dependent on the metals involved. Is that the controversy you're referring to ? I adjusted my iron/iron lash hot on my '61 (hot after idling 10 min or so) and checked them cold and the Crane parameters were damn near spot on. I've used their cold settings ever since (7 years now).
It's obviously not going to happen; but, I would love to get Crane and Comp Cam on a conference call !!!!!
Thank you all for your help !