[Steve C.]

I had a lifter fail in a BBC and broke the block. It was a comp cams roller and the recomended lash was .028 and .030 so that is what I ran..I thought that was too loose but figured the cam company knows more than me ..well now I am paranoid .My new engine has a Crane grind and the cam card said .026 and .028..but to be safe I set them at .017. My question is...will this hurt anything? I used to think that the recomended lash was just whatever made the best power on the dyno...but since reading this board the last few months,I gather from the posts here,that the lobes on the cam are designed for a certain lash....that it isn't just a tuning thing.So, what effect(other than making the engine think it has more cam) will running a considerable amount less lash than recomended have?

Answer......

It depends on how the clearence ramp was designed. It'll either have no effect on valvetrain stability, or it'll help. It won't hurt anything but performance.

It's not the tightness of the lash, it's the velocity of the cam at that point that dictates how hard the lifter hits the cam. You can have a cam designed for a looser lash that has less velocity at the lash point then a cam designed for a tight lash.

Source: http://speedtalk.com/forum/viewtopic.php?t=8265



( Does this relate to the typical .006" lash used on the Hybrid set up with the solid roller lifters ? And a fwiw, my comments here regarding valve spring pressure are for the most part regarding the solid roller set up not using hydraulic roller lifters. Nor do I have a issuew with the Crane spring as long as it measures correct and used in conjunction with adequate pressure for the intended use )


.

[Dave Bisschop]

Originally Posted by Steve C.

It's not the tightness of the lash, it's the velocity of the cam at that point that dictates how hard the lifter hits the cam. You can have a cam designed for a looser lash that has less velocity at the lash point then a cam designed for a tight lash.

Source: http://speedtalk.com/forum/viewtopic.php?t=8265

.

I'm not convinced that statement is 100% correct, I know from experience with our race car, that when the springs were getting to the end of their life (borderline valve float going through the traps) if we tightened the lash up a few thou from the .028/.030" recommended by the cam manufacturer it would help at least finish the race weekend, which leads me to believe that less lash reduces lifter bounce.

When it comes to requiring more spring pressure on the hybrid set-up vs. running a hyd. roller lifter with all things the same and no more rpm is being sought with the solid roller lifters there's no reason why more spring pressure is required (lots of smart people at Comp Cams and other cam companies, but there seems to be a lot less smart people answering tech questions a lot of the time and you can call and talk to 10 different people and get 10 different answers). I did a back to back, same day dyno test with a 246/252 .400" lobe lift hyd. roller cam in a 468ci engine swapping from hyd. to solid roller lifters and there was no indication of valve float turning the engine up to 6200-6300rpm, using the 99893 springs set up around 1.800". The solids showed 6-8 more hp over the hyd. above the torque peak. Maybe if we backed the lash way off there might be something there, but until I actually see some solid back to back data to prove that the solid lifters need more spring pressure I'm just not buying it.

Valve, retainer and spring weight all have to be taken into consideration when figuring out how much spring pressure is required for an application along with how aggressive the cam lobe is and how much rpm the engine needs to turn to optimize the combo.