The Knowledge - Velocette Owners Club

turned down at one end for a length of about one inch to the inside diameter of the guide less about 10
thou of inch for a light easy sliding fit. I placed the head in the kitchen oven at 150 degrees for half an
hour ( make sure it is absolutely clean with no oily traces - wash with Gunk or similar and rinse with lots
of fresh water or your significant other will never forgive you). Take immediately to the bench and have
a pal hold the head steady and you'll find a few sharp blows on the drifts with a good size hammer will
take the guides out easily (don't pussy foot around at this stage as the head will be rapidly cooling). To
fit guides follow same procedure but also place guides in freezer first for an hour and I also rubbed a
smear of light oil on them. As to how far to have the guides protruding into the rocker cover area, I have
had conflicting advice as to what is advised in the workshop manual. However both heads had the old
valve guides protruding about three eights of an inch into this area and I set the new ones to the same
height as there seemed to be plenty protruding into the combustion chamber for support at this setting.
#4703 There has been some good advice posted concerning guide replacement, but I did want to
address your question of doing it yourself. The procedure itself is not terribly difficult. To me the issue is
that when the guide is badly worn, then the valve and seat mating surfaces will be in need of work as
well. The old workbooks recommended lapping the valve with a light grinding paste after guide
replacement, which might be ok if the guide was not badly worn...., but. With modern(ish) tools, this is
best accomplished by recutting the seat and valve using the new valve guide, using tools not usually
available in a home shop. The issue is getting a good mating surface to form both a good seal and also
allow transfer of heat away from the valve head to the valve seat. So while the guide replacement is
something you could do, recutting the seat and grinding the valve face to correct angles is not. That is
the reason I think most Veloists have the valve, seat and guide repaired by a machine shop.
#4693 I have changed valve guides in my 54 MAC with no problems. I have a shouldered punch which
knocked them out with no trouble. Valve seats I haven't recut before as I don't have the tools. If you
need new seats then you might as well have the whole job done in one go.
#4694 Replacing a valve guide is easy-peasy! You will need a suitable drift and also a gauge to know
when the new guide is in far enough. Heat the head - to 'spitting' heat i.e. when a ball of water will
bounce around on the head and no hotter. With the head on a solid location - I use a wooden board on
concrete floor - drift the guide down into the port (not the other way round as there will be some carbon
etc that will not be removed.) The new guide goes into the freezer for a while. The drift to fit the
replacement needs to go over the outside of the guide and preferably have a spigot inside to locate
nicely. Heat the head and again fit the guide from above- i.e. from the valve spring side. Tap it in to the
correct point 0.343" above the lower face. After this the valve seat needs to be re-cut using the new
guide as a reference. It's not too difficult and was a task that just about every owner would have done
up to a few years ago. Read the workshop manual first. And get a decent sized lump hammer - makes
the 'drifting' in & out so much easier!
#4720 Valve guide removal should always be done from the combustion chamber side. Ed G. has an
assortment of Venom cylinder heads that have been broken by attempting to drive a guide out
downward. The top of the guide is often deformed during installation and may not go through the bore
easily. I prefer to tap the top and install an old bolt; then after heating the head a long punch can be
used to push the guide out. This avoids damaging the guide bore in the head. Installation is helped if
you have the correct stepped drift, this is easily turned from a piece of brass. Drive the new guide in
from the top. The head must be hot (275 - 300 F.), the guide cold. MAC guides and VM/VR intakes can
be turned from Harley ones, they are readily available in many ODs, in .001" steps. I've used bronze
Ampco 45 guides for '84 - '99 Evo twins with success. They only need to be shortened a bit. Having the
correct OD can be important, a mate's Clubman once had its exhaust guide exit via the fishtail - in
pieces and in public.
#4704 The 'accepted' way to do the job these days is to have the seat re-cut. This can be done at
home. Use the right tooling & its easy. However, before we were all educated, the way it was done is to
fit the new guide & grind the valve in as normal. If the valve & seat make good contact you need go no
further. As the Velo guides are a simple and normally accurate concentric turning there is a very good
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