Valve lash

[afret]

I assume most guys adjust lash using the EOIC method where you adjust the intake lash when the exhaust just begins to open.  I've noticed that if you adjust the lash at this point (when the exhaust lifter is just about on the heel of the lobe) the lash will open up a few thousandths if you keep turning the engine until the exhaust valve is almost fully open.  I assume it is due to valve spring pressure against the cam.  When I talked to Dennis at Reed Cams several years ago, he said to find the point where lash was the greatest and set it there so I've been doing that but I wonder if this extra clearance would be present when the engine is running? 

[jayb]

If I had to guess I would say that it might open up even a little more when running than when the engine was stopped.  Momentum effects maybe? 

I'm curious about why you are concerned.  Do you think the additional lash when the exhaust is open is a durability issue, or something like that?

[afret]

Most likely a non issue for solid flat tappets but for a solid roller, where it seems like the less lash you can run the better for durability, maybe it would make a difference?   

So if you set intake lash at the EO start point at say .016 and it increases to .019 with the valve open, is the lash considered .016 or .019?   

[e philpott]

it would be .019

[jayb]

My guess on this is that the cam companies specify the lash depending on the ramp of the cam lobe.  So I think the right place to check the lash, if you want a really precise figure, is just before the ramp on the lobe starts.  Lash at that point will be what the ramp sees as the lobe turns into the roller lifter.

FWIW, I've run hot lash on rollers up to .022" without any durability problems on the street.  Most of the cams I have specify .016" to .024".  I think you are probably correct that running tighter lash would help with the durability, but I'm not sure that a few thousandths either way would make a big difference, unless you went all the way up to .026"-.028" or so.

[afret]

Thanks.  Yeah, I'm probably just getting too picky.