After talking with the shop instructor at school the other day about some engine performance, he told me that a simple and cheap method of gaining more duration out of the 12v pulling engines he used to build was to tighten the clearances on the valves. Have any of you done this on your CR? I did some searching and found that with the 10 and 20 tolerances some folks have effectively gone to 7 and 17 (respectively) with no problems. I'm quite comfortable with my own work and really would like see how this might benefit me. I'm in no way trying to jeapordize my engine but would like a little more airflow just to see what would happen.

Please share your thoughts about this.

 

I have read about this a few time but have never seen anyone post up the results or any good answers. Hopfully we can get something here!

 

I did some more searching after I posted this an found that some have set lash all the way down to .006 on intake and .015 on exhaust....but, no answers as to how the engine ran afterwards.

 

If you go too tight, you run the risk of burning the valves because they don't have enough time to transfer heat to the head. Theoretically it'll give you a marginal increase in lift, but in reality the lift gained is so slight the risk of damage is greater than the potential reward.

 

Effective valve lift usually starts at .050". By tightening up the tolerances you can gain a little bit of valve lift. Because the valve reaches that magic .050" of lift sooner in the cycle, you gain 1-2* of duration.

So, you would gain 0.03" of lift, and 1.5* of duration. Not enough to matter.

The down side is that if things get hot, you'll lose all your clearances, and the valves will not close all the way. Especially the exhaust valves, as they usually get hotter during hard use.

Unless you're racing and need every last 0.1hp, leave it alone.

 

That's some good info .boB So, is it not even worth it to tighten up the clearance a couple thousandths on both in. and ex?