The Knowledge - Velocette Owners Club

good oil return flow to the tank. Compression feels fine. I had oiled the barrel and piston/rings using
Silkolene 40. I'm using the same oil in the tank. I understand what's been said about rings not bedding
in but I'm sure the amount of smoke it's producing is more than would be caused by this alone. If it were
a 2-stroke the amount of smoke would indicate a problem. About 24 hours after being used and making
smoke I drained the crankcase and got around 100cc of oil. Thinking about drain down from inside the
engine over 24 hours I don't think this is excessive. This and the good return flow is inclining me away
from wet sumping as being the cause. This pointed me more at the top end and the suggestion of
blocked oil drain from the rocker box. I removed the oil drain pipe (head to pushrod tube) and this was
clear. I was half hoping for a gush of oil from the rocker box but there was only a drip. Poked into the
drain holes with a cable tie and I'm certain they are clear. So where now? I won't be able to do any
more until next weekend so please keep thinking. What about the fact that it seems to get worse the
longer it ticks over and is more pronounced on the overrun? My current plan is to go for another run in
the probably vain hope it sorts itself out, then, if it doesn't, start by removing rocker box then head then
barrel and checking as I go. I have a nagging feeling that the cause might be really simple and might
just be very embarrassing - in a way I hope it is!
#3060 When you take the head off - and it's looking like you are going in that direction - unseated rings
will give you a fairly even deposit of soot on the outside margin of the piston crown. You'll have oil on
the stem and tulip of the intake valve if that guide is at fault and lots of soot in the exhaust port if that
guide and valve are letting oil by. I've tried knurled guides a few times and sometimes it worked,
sometimes it didn't. I'd suggest valve guide seals with knurled guides, but that may not be an option
here. Hope you don't have to dig this deep.
#3062 I have had a think about this, and it might be a guide going up and down with the valve. I have
seen it happen before. velocette idea of putting guides in without a landing is not a good idea in my
book. hope you sort it out. cheers.
#3061 My experience is that a lot of oil getting by the rings will keep the top of the piston clean at it's
circumference with the carbon growing like a weed just 1/4" away from the bore
#3063 The oil surely comes from the head. The smoke development will get worse during a long tick
over period because the head gets hotter and hotter and this might increase the gap between guide
and head. When checking for loose valve guides, make sure to do it when the head is hot because it
might be that they are a tight fit when cold. If the guides are really loose, you probably have to bore out
the guide holes because of the action of the rocker they will not be round anymore but somehow
elliptic. Then you need to buy/make oversize valve guides and re-cut your seats afterwards.
sorry mate, hope this is not the case.
#3064 I had an appalling amount of smoke from my MkI a while ago. It was expensive to buy all that R!
The cause was a cracked oil ring which had fallen into four pieces. New ring = no more smoke; no rebore
etc.
#3116 Sorted the smoking out and, as I feared, it was something I'd done and am duly embarrassed
about. So here it is, just to complete the story and prevent anyone else doing the same. The ideas
about oil covering the guides as a cause pointed me in the right direction. I took off the rocker cover
and poured oil into the recesses on the top of the head to see how much needed to be in there to cover
the guides. The drain rate was slower than I'd expected but the exhaust side was significantly slower
than the inlet. When I had fitted the rocker cover I had used what I thought was a very small amount of
silicone sealant on the gasket. The fixing screw just in front of the pushrod tube had taken some
silicone down in front of it and squeezed this into the exhaust side rocker drain drilling, partially blocking
it. I hadn't realized that the two rocker drain drillings are just broken into by the fixing screw holes. The
drain was reduced to maybe two thirds of its full diameter. Anyway, cleaned it all out, refitted the rocker
cover with no sealant, started it up and it still smoked but by no means as badly. Went for a ride, maybe
10 miles, no sign of smoking afterwards so think that what there was just burning off from inside the
exhaust. There we are then, Ian with red face but relieved.
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