roller rockers

[TonyPanchot]

Greeting all,

Doing a little uprating here, I recently installed Harland Sharp BMC rocker arm, with a ratio 1.5:1 from stock of 1.47:1
I am running a stock cam and have the rocker clearance set at .010 (stock)
with the change in rocker arm ratio should I be at stock or is there a formula I can use there a alternate setting ?


Thanks

 

[TR3driver]

Interesting question, but AFAIK you can keep the same valve lash.

 

[poolboy]

From what I've read it's the cam that determines the lash regardless of the rocker ratio.

 

[hondo402000]

I put a set of GP on mine 1.55 and he said to increase the valve lash to .011 so shouldnt make a difference

Hondo

 

[Hap Waldrop]

From what I've read it's the cam that determines the lash regardless of the rocker ratio.

Yes, I agree with that, the cam dictates the lash, not rocker arm ratio. The biggest change when increasing ratio and using the stock ratio pedestals is the pushrod moves a little closer towards the center of the head, for some engine this can create a clearence issue. Also worth mentioning we found that most of all the aftermarket roller rocker arm suffer from the same thing, too low of shaft height for their design when compared to stock rocker arm, in almost all cases shimming the pedestals offer a nice lift increase, and perfecting the pushord length can also buy you a little more lift. Sean Brown at Flowspeed did a noce article on his website about this, and in recent MG Midget 1275 perforamnce 1380cc engine build I was involved with shimming the the pedestals .125" netted us an additional .030" lift. Roller rocker arms are neat but often times not optimized.