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E: Engine Potential problems

David Wardingley

Website User
VOC Member
Hi all,
I’m new to Vincent ownership just recently obtaining a fully restored 1951 comet. It hasn’t been used at all for two years and my questions relate to a couple of issues really. 1 is what appears to be clutch slip on starting, ie the kickstart will sometimes not crank over the engine put skid to the bottom of the stroke, if I use the valve lifter to get it over compression then mostly it appears to be ok! And number2 concerns the valve lifter being enormously stiff when trying to use it unlike my Velo which is as light as a feather. Because of these two issues it can be tricky to start from cold although once warm it starts very easily usually on the first or second prod.
Any suggestions gratefully received.
Regards DAVID
 

Bill Thomas

Well Known and Active Website User
VOC Member
Greetings David, Not sure if you have been riding the Bike yet ?,
After a time not run, Our bikes sometimes wet sump, On my Comet the oil in the sump drains through into the primary chain case and gets onto the clutch plates, Making the clutch slip ?.
Or your trouble could be the Kick start ratchet slipping ?.
The cable for the valve lifter has to have a nice gentle turns from the lever down ?, It may be jammed where it goes under the petrol tank, Best not to have tight turns.
Good Luck. Bill.
 

Glenliman

Well Known and Active Website User
VOC Member
With the Valve lifter you could check the operation where the cable attaches to the lifter.
There are different cable abutments out there( the tube portion). I learned this when I swapped the cable & abutment from one Rapide to the other. The setup that works perfectly on my OZ Rapide does not work properly on the other Rapide.
In effect you end up trying to pull the end off the cable as the lengths are all wrong and the cable is working against itself. So it's very stiff at the handle end but doesn't fully lift the valves.
Put it back on the other bike and all is well.
Sorry I can't explain the function better, but if you observe that connection and operation at the engine end, it will quickly become clear as to whether things there are correct or not.
In my case the borrowed tube was too short. The lifter mechanism came to the top end of the tube before the valves were lifted or the hand lever was fully drawn up.
Any force used from this point on was just working to break the cable.
Even before the swap, the valve lifter mechanism on that bike had never been right. The binding problem had been occurring to a lesser degree. That's why the cable end came off. Then the swap just made things worse.
The solution was to make up a new cable and tube of correct length for that bike. Now it's an easy two finger lift, same as the Oz Rapide.
One other way to deal with this problem would be to adjust the position of the valve lifter internal parts. You have to remove timing cover and the steady plate to get at these parts on the Rapide.
That's a lot of work, much easier to make a new tube or cable if needed.
If you are making a new cable I recommend the Teflon lined Venhills Featherlight. This type of cable has reduced friction and needs no maintenance, ( lube) ever.
They will make them to order for you, or you can purchase universal kits and make up your own. I've done a bit of both here.
For the most important cables, the front brake, I had them made up to my drawing.
For everything else, the universal kits are great.

Glen
 
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davidd

Well Known and Active Website User
VOC Member
I would check the easy things and narrow down the range of problems. Check the oil level in the primary case. The decompression cable can suffer from all the issues that any cable has, lack of oil, poor routing, etc. The clutch cable and the decompression cable are the same cable. It is worth checking them both and running them with the most direct route and making sure they work properly.

The decompression under the best circumstances cannot be deployed alone without the possibility of stretching the cable or breaking it. You are trying to lift two 100 lb springs. You have to turn the engine over with the kick start while gradually pulling up on the decompression lever. This way the camshaft will lift the valves and all you have to do is hold them open when they have been lifted.

As a rule, all Vincent kick start levers are indexed to operate way too high. It makes you do all the work in the first quarter of the movement. I think it is best to do all the kicking in the last quarter of movement, which is from about half way down to all the way down (with foot near hitting the pavement). You should never start the bike on the rear stand as it will bend the stand easily. Indexing the KS lower will help with the balance and will allow you to kick with the strongest part of the leg stroke. It will also prevent hitting the KS stop inside the gearbox cover and breaking the cover.

I think if you check these few issues the other problems may go away or be minimized. Any remaining problems will be more obvious.

David
 

David Wardingley

Website User
VOC Member
Thanks all for the replies,
I have been looking at the cable routing as you suggest and mindful of the fact that the bends in the cable should be as gentle as possible. My cable comes out of the timing chest via a tube? Then bends upward on a very tight bend before it meets the battery case, up under the tank and to the lever. To get a more gradual bend it seems sensible to take the cable actually under the battery box and do a gradual u bend somewhere near the rear mudguard and then the normal route up along the underside of the tank etc. My next question is how does one get the cable off the timing chest end? It appears as if my cable could do with being 17” longer!!!!! Although I need it off to send to Venhill as a pattern .
Regards David
 

Gary Gittleson

Well Known and Active Website User
VOC Member
I wouldn't dispute any of the previous comments. They're all valid. But I have an additional thought. As David D says, you need to use the kickstart along with the lifter to allow the cam to lift the valve and the lifter to just hold it. In order for that to work, you will need to first fix the clutch slip problem. Otherwise you won't be able to turn the engine to begin the procedure. Naturally, you should also address the lifter cable issues.
Gary
 

Bill Thomas

Well Known and Active Website User
VOC Member
Make a bit of slack in the cable, Vin's should have a lot of slack anyway, Or you get oil leaks.
Between the cable and the tube, There is a shallow top hat, It should lift an 1/8" away from the tube and remove via slot in top hat.
Pull the tube away from engine,
Then the cable end nipple slides sideways out.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Don't tell me you don't have a Comet Bruce ?, The 8 th wonder of the world,
If you didn't talk to your Bike before, You do with a Comet, Trying to get up the hills !.
Zoom in just above gearbox filler, Only I leave the tube off and no cable, Stupid things !.
Just put it in 1st gear, Roll back on compression, Back into neutral, Give it a kick.

Sorry I have been at the Wifes Wine !!.
 

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David Wardingley

Website User
VOC Member
Hi again,
An interesting thread it’s turned out to be! Tommorrow I will indeed attempt to remove the cable and order a new much longer one. Once I have the cable out and ordered it from Venhill the I will swap my attention to the other side of the machine and take off the clutch cover, I expect that it will be covered in oil and the plates will need cleaning, with what? White spirit perhaps or would you have any other magic solutions!
Regards DAVID
 

Nulli Secundus

Well Known and Active Website User
VOC Member
VOC Forum Moderator
An aerosol of brake and clutch cleaner might get a lot of the oil off, if that is the problem. Available in Halfords etc. Read the warnings on the can.

I do not have a Comet, but going by what others have said the clutch and decompressor cables are the same. They are on the twins. If so you could swap them just as a check.

Good luck.
 

Bill Thomas

Well Known and Active Website User
VOC Member
If it has wet sumped, First you drain it off the engine, There is a drain bolt on the left hand side of the bike,
You get to it via a hole in the prop stand plate,
After running the engine, Check your oil tank and fill till the oil just touches the plate about 4" down the hole.
I like to check the engine oil is returning to the tank, Every time I go out.
After that just take out the oil level bolt in the chaincase and let it find it's level.
If you have been running the bike for long it might not be that problem.
Take the filler cap off the chaincase and look down, if you can see the bottom run of the chain,
It's not too bad.
I don't bother to strip the clutch out after a winter layoff, Just ride it round the block a few times.
 
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highbury731

Well Known and Active Website User
VOC Member
As a rule, all Vincent kick start levers are indexed to operate way too high. It makes you do all the work in the first quarter of the movement. I think it is best to do all the kicking in the last quarter of movement, which is from about half way down to all the way down (with foot near hitting the pavement).
David
What adjustment are you suggesting?
Paul
 

Bill Thomas

Well Known and Active Website User
VOC Member
The thing with a Comet, Is the clutch is built for oil, Not like the Twin,
But with David's Bike we know nothing about it.
We don't know if it has a clutch problem, Or it's over oiled ?.
 

vibrac

Well Known and Active Website User
VOC Member
Has your comet got two plug holes? If it hasn't then you just missed the easy way out for problem two
As to the first problem the Burman clutch often responds to a little love and modern friction plates do wonders. Funnily enough your problems exactly mirror mine last year with my vello KSS the cure was to throw away all those little corks and get the friction surfaces fully covered by friction material from saftek now I don't even use the velo valve lifter.
My comet has a Honda clutch I rarely use the valve lifter
 

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