Question about valve lash

[lippy]

My engine is an all aluminum FE with a solid roller cam. I set my valve lash to 0.025" hot per Brent's recommendation, and this corresponds to cold lash of 0.014" cold.

I understand why you wouldn't want lash too tight (hanging the valves open), but why wouldn't you want to set lash as close to zero as possible under the minimum clearance condition? In other words, for my build, if I were to set lash at, say 0.003" cold (allowing for a few thousandths extra), it would give me roughly 0.014" hot.

Wouldn't this give more power and less wear?

[redmt]

for one thing it changes your valve timing.

[CHANMADD]

I agree and tend to set them tight 0.010 to maximize the cam and to prevent wear from hammering..not to mention the noise .

[blykins]

It's because all solid lifter cam lobes have lash ramps built into them. This is a slow acceleration portion of the lobe, meant to slowly ease into things.

You can close up the lash a little amount (as I did initially, as your cam card actually says .028"/.030"), as that does change the cam's personality, like John stated above. However, you can't get too carried away with it as you can change the dynamic (read 'violence') that your cam lobe and lifters usually see. Solid cams are different than hydraulics by the fact that you spend a little amount of duration taking up that lash before parts actually make contact and you start opening valves. When you tighten up the lash, you essentially make the cam think it's bigger than what it is. Conversely, if you loosen lash, the "effective duration" of the cam is decreased.

Lash depends on the cam lobe's individual design, and it's calculated by multiplying the lash ramp that's built into the lobe, by your rocker arm ratio. You have a Bullet camshaft, and some of their lobes use a good amount of lash. Others, like some Comp Cams lobes that I have here, work on .016/.018" hot lash. It's just a function of the design that the particular lobe has in it.

The cam designer puts a spec on the card where he wants you to be, and you can vary a few thou in either direction, but that spec is put on there for a guideline.

[stangman]

If you want to adjust valves cold wouldnt you adjust higher . Lets say hot is 25 wouldnt you adjust to 28 and when heat expands it would be 25

[blykins]

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

[stangman]

wow just goes to show ya that your never to old to learn that means I have been making my camshaft smaller since I am a kid. thanks for explaining

[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]

It seems odd, but it's true. I've had a lot of these engines on the dyno and it seems like they all follow the same trend:

Cast iron block with cast iron heads, lash usually doesn't change, or it grows by a thou or two.

Cast iron block with aluminum heads, lash usually grows about .006".

All-aluminum stuff, lash usually grows .010-.011".

[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/

[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.

[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.

[Rick Parker]

On another note regarding Aluminum components. The aluminum absorbs the bulk of the heat from combustion and until things warm up there isn't a lot of power.

[RICK LAKE]

Solids are a pain period. When racing 1/4 mile we adjusted a hemi after every run. Some days the motor liked a tight lash and other days we ran .004" looser than spec. Iron heads and block. Dyno time will show you which way to go. Down side is running loose and the hammering problem even when running a 15-40 race oil. If you have a great oiling system, running a little loose will give more power and let the lifter last a little longer. I have not used a clinging oil in a solid lifter motor. This sound like a good idea. Might also keep the hammering down too. I do know running tight will extend the lifter life but cut a little power. Rick L.

[mdross1]

All my years running solids always ran them tight (cold) even more so with air cooled engines. Always about longevity what little if any power loss was never an issue. No sweeter sound than solid tappet engine for this ole boy.