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comet with unmarked timing gear

alscomet

Well Known and Active Website User
VOC Member
If anyone remembers my previous thread from a week ago I just want to post an update,can i have some comments please if i have done anything wrong.
I took my comet to the Bawtry meeting and it seemed to be running worse than before,hard to start and fuel coming out of the carb when running and overheating badly,got there and back(just)spoke to a guy called Rod Hornsby
who i think has pinpointed the problem.When i got back i stripped off the timing side,put my Dial gauge on and here are the readings.Inlet opening 70deg BTDC
inlet closed 40Deg ABDC Exhaust opens 98deg BBDC ex closes 3deg ATDC.
I think the cam shaft is moving on the cam wheel ever so slightly every time i use the bike. I have spot welded the cam to the wheel on the outside and reset the valve clearances to 41degBTDC inlet opens,69degADBC inlet closes and the exhaust has followed suit.the lift on the inlet cam is .28" and the exhaust cam lift
is .3" there are no marks on the cam so i am not sure what it is. the bike runs and starts ok but i havent tried it on the road yet. do i need a new camshaft complete or does it sound like a problem fix. alan
 

Ken Tidswell

Well Known and Active Website User
VOC Member
Camshaft welding

This is the standard method for reclaiming this problem. All the people who reclaim cams and refit to the camwheel, solve the lack of interference by welding. Otherwise you need a camwheel with an undersize hole to regain the interference fit.Expensive
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Comet with slipped timing.

Welding is OK because the shaft and wheel are a good fit - if not good enough to grip. A friend from Shetland got back his irreplaceable Levis cam shaft ground minus 0.002 instead of plus 0.002. So he assembled shaft and wheel with bearing fit Loctite, and the assembly was still running four years later.

You can time the motor by ensuring that lift is equal on both valves at or near TDC. Someone has just checked a set of Robinson cams (set on inlet opening 47 deg BTDC) and, yep, equal lift. I now know of four different performance cams (Norton, Honda, Rudge and Vincent) of which this is true. (I'm not claiming this as a triumph of personal research, I've been told it by others, and four camshafts later, believe it.)
 

nkt267

Well Known and Active Website User
VOC Member
Are you measuring the lift at the top of the tappet adjuster or at the end of the valve stem?Valve lift in the books is usually measured at the valve stem. Gary Robinson once told me that he had a Rapide arrive at his place to have the cams done and I'm sure he said the bike still ran well with only 1/8" lift.Have a look at http://www.thevincent.com/vincent engine.html site there is some info about cams and lift there.
 
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alscomet

Well Known and Active Website User
VOC Member
unmarket timing gear

I have measured the lift on top of the adjuster,i took it out for 50 miles the other day and it ran like a dream other than a leak from the dynamo oil seal,
took the cover off again and changed the seal for a broader seal 8mm instead of
a 6mm seal ,it had slightly twisted over. seal size is 22 Id 35 OD x 8mm thick
£1.00 each. alan
 

nkt267

Well Known and Active Website User
VOC Member
I had to strip the timing side out of my Comet this week to find that I had forgotten:eek: to put a seal in the valve lifter mechanism.I have Mk2 cams in mine and the lift is about what you found measuring on the adjuster tops.So I would think that your cams can't be too bad.
Also found that to get the lifter plunger out I had to remove the gearbox.:mad:
 

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