Question about valve lash

[Cobra #3170]

Originally Posted by blykins

Valve lash grows with heat. It seems counter-intuitive, but that's the way it works...

Mine is almost 0 when cold .018 hot

[blykins]

Originally Posted by Cobra #3170

Mine is almost 0 when cold .018 hot

Yep. What's unnerving is an all-aluminum engine with a tight lash cam. When the engine is cold, the valves actually hang open a hair until the engine gets heat in it.

[gsharapa]

I have an all aluminum 496 with Comp Cam Solid Roller and T&D shaft mounted rockers and I set mine at .012 cold which ends up .025 hot. My Comp Cam card says .025 hot and numerous times I've checked them cold and it's right on .012. Keith Craft who built the motor told me .012 to .014 cold would be in the ball game! I recently purchased the LSM Racing Valve Lash Torque Adjustment tool and actually checked and adjusted a few of mine yesterday. This tool is so cool and it allows you to hold the set screw and tork the nut at 20 ft lbs.

http://www.summitracing.com/parts/ls...00-3/overview/

[lippy]

Originally Posted by gsharapa

I recently purchased the LSM Racing Valve Lash Torque Adjustment tool and actually checked and adjusted a few of mine yesterday. This tool is so cool and it allows you to hold the set screw and tork the nut at 20 ft lbs.

http://www.summitracing.com/parts/ls...00-3/overview/

I thought about that, but I ordered this instead: [ame]http://www.amazon.com/gp/product/B000I1UOAM/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1[/ame]The folks on the Garagejournal forums seem to love this type and brand of wrench. For valve lash, I adjust the hex and snug the retaining bolt pretty firmly with a box wrench. Then I torque it down to 20 ft-lbs with the PI torque wrench, and recheck the lash to make sure it hasn't tightened. If I snug it enough by hand, the final torquing step doesn't change the lash setting. I like this wrench because it's very accurate, and I also can use it for the rocker shaft hex nuts, as well as intake manifold bolts, etc.

[olddog]

It's not just valve lash.

With an aluminum block, the piston is much closer to the head, when cold. You loose compression ratio as the engine heats up.

The Cady North Star engine had issues with carbon building up. Then on a cold morning the piston tapped on the head, making quite the knocking sound.

Thermal expansion of different materials is a real thing that must be designed around.

OBTW the bearing clearances are changing too.