E: Engine Exhaust valve not right

greg brillus

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I've never seen a stock Vincent with broken springs, so I'd be worried there is more than just the springs that need attention, being an air cooled engine and all.
 

evcomet

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Well, it is a new day!
It is difficult to express the frustration with my current challenge. I also greatly appreciate the suggestions offered here.
Taking apart a perfectly beautiful Comet to find a fault that I do not understand was not what I intended to do today.
I will post more when I know more.

Jerry
 

Bill Thomas

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With all these funny names, I had to look it up to see if it was our friend with the HOT Comet !.
I have said it before, With how old these Bikes are, We must be ready to do some work on them.
I feel sorry for people who pay a lot of money for a rebuilt Bike, Thinking they will have no trouble.
You will feel ten feet tall when you have fixed it. Cheers Bill.
 

davidd

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You can remove the spring, in situ. Something similar has been done on the side of the road. It is not easy and you might miss something doing it this way. Additionally, it took two other riders to help get it done.

That being said, you will likely need to replace the inlet spring. The springs do not last very long, but they are run very long...almost forever. I bought a bike once that had some power issues and I could move the springs by hand. The head came off and I replaced the springs.

It sounds like the same thing. If you did not break a spring, or it broke as it shut down, I suspect all is well. I also had a Vincent drop the valve guide and the ex stayed open just enough to do roughly the same thing. This tends to happen right as you are shutting down when the engine is hot.

The first time is always the worst, but racers tend to take the UFM and forks off in one piece, quite often and can do it quite fast. It is more difficult with a wiring harness. It is nice if you can do an overhead lift of some type just to steady the UFM and forks.

So, by the side of the road you put the piston at bottom dead center, or close. Cut one end off a bungee cord and slip the cord itself through the spark plug hole. The other end with the clip on it will stay outside the engine. turn the engine to get the piston toward TDC and the cord will close the valve. At this point you can do what you wish with the spring. In this case, the circlip on the valve flew off and it was reinstalled while others pried the spring and retainer down.

Best of luck,

David
 

evcomet

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I am just now ready to separate the engine from the UFM and Fork assy. (wire harness and cables are a pain)

Just needed to take a break and be certain I haven't missed anything.

What I do know is that no springs are broken. It appears that the upper guide seized on the valve stem.

A tap with a plastic mallet and everything went back into place.

Not sure why this happened, but complete removal and inspection of the head is required.

Jerry
 

bmetcalf

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I have one of these at the back of my UFM to make disconnecting easier:

https://www.amazon.com/Hopkins-11147955-Pole-Line-Set/dp/B004BE60Y6


1531420244527.png
 

evcomet

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Found that upper guide ET40 had galled to the valve.
Not sure if it was too tight a fit or lack of lubrication.

The alloy stuck to the valve stem was easily removed
Can I hone the hole in the ET40 and put it back together?

No other damage found. Piston and valve never made contact.

What do you suggest?

I prefer not to do this again.

Jerry

Exhaust valve and parts.jpg
Exhaust Valve.jpg
Comet ....Front.jpg
Comet ... rear 2:3's.jpg
 

evcomet

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Another observation....

I am not sure that I understand how any oil gets to the upper guide to provide lubrication.

Jerry
 

greg brillus

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Jerry it is a mixture of mist and splash as the oil passes down from the rocker feed bolts on the oil return pipes across the top of the head. I wonder how tight the cylinder hold down nuts were, when they are done up too tight this can distort the head and cause misalignment of the upper and lower guides, which may explain the top guide seizure. You should be able to refit the upper guide temporarily refit the valve and "Feel" some slight play sideways of the valve head in several directions. If the valve is very snug with no play, then the guides might need reaming slightly. Being air cooled they tend to need some running clearance as the engine temp climbs more so than a modern liquid cooled engine. You might be able to polish the valve stem, lubricate and assemble, and all will be fine. The cylinder head hold down nuts should be torqued to 30 to 32 Ft Lb's in an even opposite manner. Use either some oil, grease, or anti seize on the threads, and be careful to align the pushrod tubes as you lower the head back onto the barrel. Cheers and good luck..............Greg.
 

davidd

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I always give the upper valve guide more clearance just for this reason. You can do all the work on the lower valve guide, but there is no guarantee that it will put the stem exactly in the center of the top guide. I suspect there was a substantial misalignment to get the top guide to gall. As Greg said, check the lower guide for fit. Check to see that the button on the valve is not to worn. It probably is not too worn, but you can certainly see where it has been working. Get some extra circlips if you do not have a supply.

You can polish the stem. I keep new valves in the shop so I am not tempted to use old ones. I don't know what the free height of the stock springs should be. I have been using Gold Star springs instead.
Renwick v RD 01.jpg

The new spring is on the right. The Vincent spring is considerably longer and owners rarely replace them.

Good luck.

David
 
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