[TR] Sticking valves?

[Tony Drews]

This is using new bronze valve guides.  We have the machine shop hone 
them for 0.004" clearance between the valve stem and the guide (the 
valve stem outside diameter is 0.004" less than the valve guide 
inside diameter for its entire length).  I'd have to dig out the 
manual to see what the stock spec is, but I KNOW that (in racing, 
anyway), 0.002" will stick valves - generally the exhaust, but the 
intakes will stick too, and 0.003" is marginal.  It seems a little 
sloppy with 0.004" and we generally have to convince the machine shop 
that we really mean it.  Even with this clearance, if we really 
overheat the motor we'll start to see sticky / bent valves.

If you have pushrods mysteriously popping out from under the rocker 
arms, sticky valves is the primary culprit (as is an adjuster that 
backed WAY out).

There are some things you can do to force more water to the rear of 
the engine (reduce the hole diameter for the water through the head 
gasket in the forward cylinders), but we run this clearance regardless.

My understanding is that iron guides expand less so can use a bit 
less clearance, but I have no personal experience with those.

- Tony Drews

At 01:58 PM 9/19/2009, Alan Myers wrote:
>Hi,
>
>
>
>Tony, maybe you can clarify a little on what you've been doing when 
>setting up your engines... And perhaps I can add a bit 
>about?a?possible?reason?this happens...