The Knowledge - Velocette Owners Club

#523 I can't remember where I learnt it from, but the answer to "How much do you heat the crankcases
to remove the oil pump or main bearing races" is an easy one. You can use any reasonable heat
source from plumber's blowlamp through to an oxy-acetylene torch - nowadays I've found that a good
electric hot air gun works well with a little patience. Heat the case until spit sizzles off as soon as it
touches the metal and the pump or race will drop out or in perfectly. I've used this method as a guide
for many years and it's never failed yet. If you don't get the cases up to this temperature you will really
struggle to move either component.
#525 Regarding heating crankcases, I wait for my wife to go out for the day and use the kitchen oven
when rebuilding an engine. The RHP catalogue says, “Do not exceed 120 degrees C or the bearing
hardness will be effected.” I have found elsewhere that the maximum temperature is 160 degrees C. At
this temperature the bearings knock out when brought down sharply on a piece of MDF and the pump
slides out of the bore with a very gentle tap. Ralph Seymour used soap turning brown when rubbed on
an ali head to indicate the right temperature for fitting valve guides.
L #513 Throwing my Venom engine together at the last minute before the rally, I finally got in a
test ride the day before the start and half way to Washington. Got it hot and realized I didn't get the
preload right on the mains and could wiggle the crank when hot. Damn! The bike was noticeably
smooth though, smoother than I'd ever recalled it being. Just rumbled a bit at idle. I had all but given
up on using it for the rally then suddenly came up with a bodge extra ordinaire. With it still hot I pulled
the primary and drilled 3 holes in the case around the periphery of the outer race and tapped it in with
a punch. I was then able to slide a .002 feeler gauge between the race and the case, so it moved in
about that far. I squirted some green loctite in the gap, tapped the holes for 8-32 set screws to butt up
against the race, went to bed and prayed. The bodge worked great but I noticed right away the engine
felt rougher. Paul D'O told me years ago that his tapered main Velos always felt rougher when cold
then smoothed out when the cases heated up. I wonder how much the .004 spec pinch on the crank
affects smoothness. I suspect I may have preloaded my mains even more with the bodge. Also was
told by longtime Velo guy Dee that the tapered mains are very forgiving and I probably could have just
left it alone for the rally.
#518 I have to say it's brilliant clever, but I would have done it with the engine cold if I had the nerve to
do it at all, then you have a better idea of what the preload is relative to the standard. How did you get
a feeler gauge in there? But on the subject of preload on taper roller mains, I think they are indeed
very forgiving. If you read the Bible of Bodges, i.e. the compendium of tech articles, there are stories of
everything from zero to 12 thou preload on the taper rollers. The fellow using 12 thou reckoned his
engine was extremely smooth! Go figure. All I know is that when I set up my VMT mains 13 years or
so ago, I went according to the book with no problems to report so far. And re cush drive taking out the
drive side mainshaft, it's too bad the factory didn't use the KTT style cush drive which sits on a taper
and doesn't pull on the shaft at all. All those years of hammering/pulling away on the shaft can do it no
good. And re torque and oil on the threads; how on earth do they stay together at all, knowing all the
ways in which it's possible to get it wrong. Perhaps ignorance is bliss after all..
#522 I've had both of the problems mentioned here at different times in my Venom's life. The drive side
mainshaft pulled out of the flywheel not long after I'd had the big end replaced by an engineering firm
who I suspect didn't really know what they were doing. This can be rectified permanently by pressing
the shaft back into position, making sure that the breather holes line up and are clear, and fixing the
shaft in position by a spot of weld or by pegging the joint. So far mine has lasted over 20 years and is
still going strong! The broken drive side crankcase was a much more recent problem, occurring only a
couple of years ago. This time I sent the case to Seymour's who machined out the damage and
manufactured a new top hat bearing support in Dural which was then screwed and Loctited into the
case. This is apparently an old method of strengthening the cases used by racers in the past, which is
totally invisible until you remove the engine sprocket or split the cases, and is very neat. One of the
great beauties of this method is that you continue to fit bearings in exactly the same way as before,
since the expansion rate of the repair and the original material are to all intents and purposes identical.
I've done quite a few miles on the machine since and can honestly say that it's never run smoother!
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