valve lash for chromoly push rods

Hello,

Just wondering what figure everyone is using for valve
lash on their engines that use chromoly push rods. I
wonder becuase the stock figures are .006 for intake and
exhaust however the stock setup uses aluminum rods
which expand with the engine. As everyone knows chromoly
rods don't expand as much so what's a good # for the adjustment?
I've read some sources that recommend .003, any thoughts on this?

J-P

VW performance guys set the chrome-moly PR's to .000" lash but this can be dangerous (burned valves, etc.) and you need to check them OFTEN. I use .0015" to .002" with chrome-molys and that seems to work well and reduce valve train noise considerably.

The engine expands more than chrome-moly PR's so at operating temperature you might have .010" additional clearance over and above your cold setting clearance; this reduces effective camshaft duration measured at .050", can reduce valve lift by about .011", and is noisy.

Aircooled.net has some HD aluminum PR's that seem to be working well in performance engines with dual valve springs; these expand at about the same rate as the engine and settings of .004" for intake and .006" for exhaust would work well with them.

I adjusted the PR's to .003 and the engine seems more peppy than before @.006. I've read a couple of posts in the shop talk forums about this subject also. Those posts recommend .003. I'm just trying to see if anyone else is adjusting their valves a little tighter also to make up for the expansion diff. Anyway, sounds like .003 could be safe. The valves also seem a little less noisy.

J-P

One other question.............

what do you recomend for total timing....32 deg. ?

J-P

Jean-Paul, a lot depends on your compression ratio the fuel's octane rating. Try 30 degrees total BTDC, then try 32. The engine will give you feedback as to which it likes better. If you get pinging back off 2 degrees.