[TR] pcv valve tr3 t4

[Randall]

> I think it may be moss part #397-680.

That doesn't appear to be a valid Moss number, Frank.  Perhaps you mean
379-680?  My catalog describes that as an "adapter".
http://mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29123#67

> What else does the big assembly do (moss 360-630) that this 
> little valve does not?

The big valve is a kind of pressure regulator; it limits how much of the
manifold vacuum can be applied to the crankcase.  It's also a flow
regulator, so limits how much air can be admitted to the manifold.  In
addition to being a check valve.

Note that for true "ventilation", you also need a fresh air intake for the
crankcase.  This should supply filtered air, and be fairly large diameter
(IMO the Triumph vented caps aren't large enough).  I'd say at least 3/4"
id, 1" would be better.  This is because the labyrinth rear seal is very
sensitive to positive pressure inside the crankcase, and at full throttle
(where blowby is greatest), there is no manifold vacuum to pull fumes
through the PCV valve.  For best emissions reduction, the fresh air intake
should also be arranged such that any fumes that do escape from it are
directed into the carb intake to still be burned.

Randall