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E: Engine Valve Guide Modification

Bill Thomas

Well Known and Active Website User
VOC Member
Just , Thinking ahead, For if we get switch OFF,
Does the Timetraveller Valve guide mod' work with L/ning Cams ?,
I see the Spares Company now stock it.
Cheers Bill.
 

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timetraveller

Well Known and Active Website User
VOC Member
Yes it does. I designed it to try to serve several different purposes. The first is if the guide has been loose enough for long enough to destroy the thread for the lock ring as well as the fit of the lower guide into the head. One needs to get an over diametered guide made and once that is in place my gadget will hold it down by acting as a spacer between the bottom of the top guide and the flange on the lower guide. You need to make sure that the length is correct. No point having a few thou clearance as that would allow the lower guide to start to move again at some time in the future. If the thread for the lock ring is in good order then that can be refitted and then the bottom of my gadget can be cut off. In this case it acts to prevent the threaded lock ring ever becoming loose. It is quite deliberately designed so that it does not restrict the movement of the fork of the rocker at either the top or bottom of its movement. If the top of the lower guide is sufficient to allow half an inch of lift then my gadget will not limit that. As an aside the first pair of these I made years ago were in steel and worked well on the two bikes they were installed on. This time round they are made of the same aluminium alloy as the light weight JE steering stems, 7075. This was to try to ensure that any expansion or contraction due to heat would match the material of the cylinder head itself and also to assist anyone who has to modify the gadget to make it fit. I cannot guarantee that all cylinder heads have exactly the same dimensions at this position and so by using aluminium I have made it easier for those who only have access to hand tools to make the parts a good fit. I fitted one for myself recently and used a lathe to remove the bottom part which would replace the screwed lock ring if that had been destroyed and a file to ensure that the tang which stops any rotation was a good fit in the cut out in the cylinder head. At the same time I used a Dremel to deepen that semi-circular cut out to allow a better gas flow to a 'D' type breather.
 

ClassicBiker

Well Known and Active Website User
VOC Member
Before they were available from the club, TT uploaded a PDF on this forum with dimensions so I could make one for myself as my Shadow with MK II cams had eaten the guide for lunch and spit out the remnants down the exhaust pipe. The ensuing carnage had also destroyed the lock ring and threads in the head. Being fortunate enough to have both a vertical mill and lathe it was easy enough to make and works quite well. In retrospect I only regret not making and fitting them to the other 3 valves whose lock rings were still good, as a safe guard for the lock rings on those valves coming loose. While I like the idea of the lock rings for retaining the lower valve guides, I don't understand why something like the WW wasn't used in the first place. It is far easier to make than cutting a thread down valve guide tunnel and easier to fit than a lock ring down the same tunnel. Add to that in the absence of Loctite one has to resort to punch locking the ring, which has its own issues when trying to replace lower valve guides. I have already decided when I turn my attention to my Comet's engine, it is getting two, even if the lock rings are good.
Steven
 

LoneStar

Well Known and Active Website User
VOC Member
I made and deployed one of these on my Black Shadow, after the ring threads were destroyed by a loose ring.

But why was that ring thought necessary in the first place? I'm not aware of any other engines where a similar secondary device is used; most designers were content with an interference fit on the guide.
 

oexing

Well Known and Active Website User
VOC Member
One reason for the lockring is the very short bore in head for shrinking the guide. They hoped for longer use when a lockring presses the guide onto the shoulder down inside. So I kept the lockring too - plus little punch lock into the slotted ring. Loctite could get a bit very hot there. I wonder why there were so many loose rings and guides at all, seizures of valve stem in guides ?? It is a tricky job to have both guides perfectly lined up by piloted reaming, no lapping with abrasives for me !! My choice is tin bronce, you call it phosphor bronce maybe, don´t know. This is not known for seizures - eccept you got too small clearances stem-guide. 3 thou for exhaust is allright and required, inlet 1-2 . So lots of seized valve stems here ??

Vic
 

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