When the smaller stem exhaust valve, PN# 136567, was fitted from CT21471E,
there was a conversion
valve guide with the big OD and small ID, PN# 136575, used until the
cylinder head bore for the exhaust guide was later reduced. I even have
several NOS
factory sets of them in the basement.
Hardy
Subject: RE: [TR] Valve job
> I do not have the equipment to measure accurately, but I'm puzzled by
> the descriptions in the relevant catalogs of 3/8 to 5/16 conversion
> guides, if that is what happened previously.
TR2-early TR4 (CT21470E according to Moss) originally had exhaust valves with
3/8" diameter stems. Both the inside and outside diameter of the exhaust
guide
was larger than the 5/16" intake, although as I recall, the outside
difference
wasn't as much as the inside difference.
After that point (approximately), the exhaust valves had 5/16" stems and the
intake and exhaust guides were the same. Although the head casting didn't
(necessarily) change, the holes drilled in it for the exhaust guides got
smaller.
The smaller stem valves flow better, and weigh less (so less prone to
float), so
fitting them to the early head is a popular upgrade. The "conversion" guides
have the right od for the early heads, and the right id for the 5/16" valves.
Not certain, but ISTR someone telling me the factory even offered these.
I can't quite imagine someone not noticing the huge clearance; but I also
can't
explain the oversize guide any other way. The mistake might have been at the
factory, though.
Randall
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