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E: Engine Exhaust valve not right

evcomet

Well Known and Active Website User
VOC Member
Took an extended ride on the Comet today. All seemed to behave as one would expect.
I put the bike on the center stand put my gear away and got my Multimeter out to check battery charging.

Comet was off for 10 to15 minutes. When I attempted to kick the bike over, it behaved as if the compression release was being engaged.

I kicked a few more times without success. Got a cold drink, 15 minutes later the bike started immediately. But being a "the sky is falling" kind of guy, I
decide to put the bike on the lift and take a closer look.
I found the exhaust valve spring loose. I can grab the spring with my fingers and lift spring and valve 3/8".

Looking at the parts book, I am guessing that the valve guide has come adrift of its proper position.


Questions...

1) Is the easiest way to remove the head to remove the UFM?
2) Do you replace with an oversized guide?

Any advice would be appreciated.

Jerry
 

timetraveller

Well Known and Active Website User
VOC Member
Not realistically. The design of the Vincent is so clever that removing the front end is trivial apart from the fuel tank, which is a pain in the posterior. You need to support the engine/gearbox very well and then just get stuck into it.
 

vibrac

Well Known and Active Website User
VOC Member
I just had to do my comet head as a quick and dirty task two points:

!uckily I put extra length in my wireing to the headlamp I take out the front wheel (might as well check it) and the front end sits on a mat upright at the front on rear of mudguard and fork end the ufm does not unbalance it (at least mine was stable)
Be ready with a funnel and tin when taking off the rear oil supply at the back unless you know the stop valve works
 

greg brillus

Well Known and Active Website User
VOC Member
The real issue is that if the exhaust ones have broken then the inlet ones could let go at some point. The springs could be changed without head removal but it would be quite difficult. If the springs are failing then removal and inspection of the head/barrel and piston would be very wise. They are not difficult to carry this work out on, but there are a few important things that need to be brought to your attention to return it to reliable service. Keep us posted on what you decide, but there is plenty of help on this forum.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Greg,

Can the springs be removed without removing the head?

Jerry
I have done it on a car, You will have to make a few tools, Get the piston to TDC, Make a rod to go into the spark plug hole to hold the valve up.
But if you can feel a lot of side play in the guide, The head will have to come off anyway.
You could take the Exhaust pipe off and see if you can see anything wrong with the lower guide.
The upper guide you could change once the spring is off.
I have known an engine work with just the top guide !!.
Good Luck. Bill.
 

timetraveller

Well Known and Active Website User
VOC Member
Sometimes with a problem it pays to walk away and sleep on it. You write that you can 'lift' the valve spring 3/8". Thinking about that and it seems to me that Greg was probably quickest to the problem. Even if the top guide had collapsed then the spring would still be supported at its lower end on the cylinder head casting. If the valve had stretched or the valve seat pulled through then the valve spring cover would be marked seriously. I've had a bike with the lower valve guide having disappeared totally and yet I did not hear or see any change until I took the bike apart for another reason. If you can lift the spring can you rotate it? If so then you might be able to see that both springs have turned into odd bits of steel. Either spring on its own exerts enough pressure to stop you moving things easily by hand. Good luck with it and let us know what you find.
 

Bob

Active Website User
VOC Member
You coud try the 'rope trick' to hold the valves in place. Remove the sparl plug and put a few feet of soft nylon rope into the cylinder. Turn the engine and the rope will compress against the valves. I chaned the valve seals on my V8 pickup this way and it saved a shed load of work!
 

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