Exhaust Valve and guide clearance

[MarkC]

Hi, Can anyone confirm the correct stem diameter of the exhaust valve for late alloy head model (part No. 441-55) and what the clearance should be in the guide (part No. 491-55). Thanks.

[Simon.Gardiner]

Mark:
As a starter, maybe check the docs in the refs in this thread
viewtopic.php?f=21&t=12496

I'm pretty certain the valve stem diameter is 0.375 (nominally, I don't think I've ever seen any tolerances published). Not sure about clearances, in my experience all the new valve guides I've ever had have felt a bit sloppy, so where I've got a choice I use the least sloppy fitting....

HTH

SG

[MarkC]

That's great, thanks Simon, I did try to search, also searched Draganfly site - I must be doing it wrong.
Anyway thanks again, that's got me going.

[keith.mettam]

Mark,
I notice all the VH etc. exhaust valves are 3/8" stem diameter from 1936 to 1958. As for the valve to guide clearance, the ally head models should have Phosphor Bronze guides and, if the valve is free when assembled in a new guide, I imagine that is ok as a valve shouldn't seize in a Phosphor Bronze guide. I replaced both valves and guides in my 1957 NH using Feked parts. When I fitted the new guides in the head and it had cooled down I found the inlet valve was still a free fit in its guide but the exhaust valve guide required reaming to be able to fit the valve stem. The exhaust valve stem went in so far but became stuck at the point the head had shrunk back against the new guide. Not a bad thing really as the exhaust guides often become loose in ally heads. Reamed it out until valve fitted freely with some lube down the guide. Bike up and running fine. Well pleased as the old guides were knackered !
Simon,
Using the original link I posted and you have quoted here, the 54 valve that chap was referring to is now on Feked page 10 and not page 11 which the exhaust valve link now takes you to. Point being that, as on-line catalogues get updated, links may no longer lead to the expected product. In this case it now leads to the valve details Mark requires about his exhaust valve !

[MarkC]

Thanks Keith, that's very useful and encouraging that that the Feked guide needed a little reaming. I hadn't even thought of Feked although now I do.

[Roger Gwynn]

All valve guides are made to the nominal size, in the case of the VH exhaust this is 3/8. The clearance is on the stem, which if you measure and it has been made correctly will be a few thou under nominal. Most parts are made this way as it is easier to machine a male component to an odd size than it is a female one, which can be made using standard sized reamers. All that needs to be done is to run a fixed reamer through the guide after fitting, they shouldn't shrink as the wall thickness is too great but the ends get belled when a 10lb sledge hammer is used to fit them. All valve sizes are listed in a chart available on the Draganfly web site under the technical info banner, not the sort of stuff available on lesser web sites.