Why must a solid roller cam have lash?

dfree383 wrote:Like Lem has said lash can be used as atuning tool and a way to see what canim a motor likes, looser lash = slightly smaller lobe, tighter lash = slishtle larger lobe. Good rule of thumb is no less than .006-.008 or no more than .035-.040. For most cams when your expermenting

Boy! Did somebody get drunk on magaritas last night? Because they sure as heck, can't spell "sheeit", this morning!

Uncle Charlie

Hay CharleeWere knot skloars weergeerheds

c.evans wrote:

dfree383 wrote:Like Lem has said lash can be used as atuning tool and a way to see what canim a motor likes, looser lash = slightly smaller lobe, tighter lash = slishtle larger lobe. Good rule of thumb is no less than .006-.008 or no more than .035-.040. For most cams when your expermenting

Boy! Did somebody get drunk on magaritas last night? Because they sure as heck, can't spell "sheeit", this morning!

Uncle Charlie

Bla!!! This coming from the "OG" that's running late the breakfast!!!

"Bla!!! This coming from the "OG" that's running late the breakfast!!!"
Charlie can't be late for breakfast....he's on duty for breakfast 20 hrs a day .

The simple fact is that it is in the design of the "take-up" ramp and lobe flank characteristics on that particular cam lobe profile; (most common race lobe ramps are at .017" but there are many at different heights, both more and less. Lash is normally to be SOMEWHERE on that constant "take-up" ramp). They can be designed with VERY little ramp height however...

A wider/longer design lash ramp on a cam lobe profile can impart a SLIGHTLY greater contact velocity upon the lifter with a flat tappet; (acceleration is already higher than a roller cam lobe). And, SLIGHTLY more acceleration can be achieved with a roller lobe; (contact acceleration is limited more than with a flat tappet). Hollow ground flanks with a roller lobe can only gain back so much as lobe to roller angularity becomes a problem.

Unfortunately, getting a "happy" dynamic valve train and making horsepower differ in what they need.

Very good topic, and answers... I have found through T&T, that my 521 likes a bit tighter lash... I set my lash cold then check it hot, and like Jon said, with my aluminum heads it grows right around .004... My combo likes it at .012 cold and it ends up around .016 hot...







Doug...

Messing with the lash can sometimes be a great fine tuning tool. It allows you to make the cam a little bigger or a little smaller on intake, exhaust or both.

How much it changes when the engine warms up really depends on the engine and what type of heads it has or the block material. I believe that the engines that Jon Kaase builds end up with negative lash when the engine is cold just because the great big aluminum block and heads grow so much as they come up to operating temperature. It would seem that this would make the engine impossible to start cold but I would say that because the engine is so large and the compression ratio is quite high that it's not a problem.