> I'M TRYING TO BUILD A TR3 RACE MOTOR HEAD FROM 3 DONOR HEADS OF UNKNOWN
> ORIGIN. THE PROBLEM I'M HAVING IS THAT THE EXHAUST VALVES I WANT TO
> USE DON'T FIT
> INTO THE GUIDES IN THE HEAD I WANT TO USE. THE DIA. IS TOO LARGE. THE EXHAUST
> VALVES STEMS HAVE A SMALLER DIA AT THE TOP TRANSITIONING TO A LARGER DIA.
> TOWARDS THE HEAD OF THE VALVE. I'M ASSUMING THE CHEAPEST FIX IS NEW
> GUIDES.
Those thick valve stems are heavier, thus more prone to float. If it were me,
I'd look for some thin stem valves. When Triumph converted to 5/16" stems, they
were able to eliminate one of the exhaust valve springs.
> THE QUESTION IS WHAT GUIDES DO I NEED? THANKS, KEN M
The switch to 5/16" stems happened in mid-TR4, CT21471E according to the Moss
catalog.
Which guide you need depends on which head you're trying to use. The later
heads were drilled smaller for the exhaust guides. To put a 5/16" guide into an
early head requires a thicker walled "conversion" guide. Sorry I don't recall
the od offhand, but compare the exhaust guide od to the intake guide od. If the
exhaust is larger, it's an early head.
In any case, the answer to your question is that the thicker stems were used on
TR2 through early TR4, so you need a guide for those cars. Moss P/N 830-010
(cast iron) or 830-025 (bronze).
If you have a later head, and want to use early exhaust valves in it, you'll
need to bore the guide holes in the head larger to use the early guides. I
don't know, but I suspect that boring out the later guides for the early valves
would be a mistake. The thinned guide walls might not be strong enough, and apt
to break.
Randall
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