damaged VH barrel

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robin rose
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damaged VH barrel

Postby robin rose » Sun Jul 10, 2011 8:24 am

The barrel for my basket case 51 VH had a bad time over the last 40 years and part from broken fins (now repaired) there was impact damage to the spigot/head interface. The damage has been ground out but now the head is just about touching the
top of the barrel. I am therefore thinking the best solution may be to make a round copper gasket to sit on the spigot and lift the head away, although the later iron engines seem to have a gasket sitting outside of the protruding spigot. Any ideas out there?

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brenton.roy
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Postby brenton.roy » Sun Jul 10, 2011 9:19 am

Hi Robin, the later copper gaskets do work fine on your engine. The seal can be better than the spigot.
I'd be having visions of a copper O ring trying to find it's way out of the exhaust valve!
I'm not sure exactly how much metal you have removed, but have you checked the valve to piston clearance? You can buy proprietary stuff, but kids plasticine works well enough to check this.
If you are worried about the closeness of the top ring to the lip of the barrel, and if the spigot seal is working, you could put a copper, or aluminium gasket under the barrel (like a compression plate).
I hope this helps, Brenton
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.

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Postby pete.collings » Sun Jul 10, 2011 10:17 am

I had solved a similar problem with a VHA head that had been lapped in too many times, and was not mating with the spigot of my nice new alloy barrel. After a little while running, it would whistle to me!

I found that a head gasket for a Velocette was just the right size to sit on top of the spiggot, and seal the head/spiggot joint.
The gasket was laminated, and by carefully delaminating, there were two 10thou rings, just the right thickness needed.
I also used one of the Ariel copper gaskets to help seal the other joint, but ensured it was less thick than the head/barrel flange gap, to avoid any distortion of the alloy head when tightened.

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adrie.degraaff
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Re: damaged VH barrel

Postby adrie.degraaff » Sun Jul 10, 2011 3:44 pm

You have mentioned the best way already, a copper gasked around the ridge is the savest, becouse if it's on the ridge there is a chance you will crack the head.
This is wy 50% of the 4 valve heads are cracked.

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Re: damaged VH barrel

Postby david.anderson » Sun Jul 10, 2011 11:50 pm

Robin
If the head is getting close to touching at the outer mating surface you can use the principle of a double ground joint. Use course valve grinding paste on the outer surface and fine valve grinding paste on the spigot and lap the head in by rotating it until there is an even polish all around. Using this principle a little more metal is removed from the outer surface. When tension is applied to the head bolts the head will seal on the spigot and under tension may just touch on the outer. You should not have to worry about valve clearances as I have a VH engine that has had 0.125” removed from the base of the barrel which was apparently a standard way of increasing compression ratio. It raises a 7.5 piston to just over 9 to 1. I checked valve clearances with plasticine and found there is still plenty.
If you want to use a head gasket it should be fitted over the spigot. It is easy to cut one from sheet copper. The copper should be annealed before use by heating it to a red and dunking in water. Re anneal with each reuse. I used to have a VH engine that ran happily at 10.5 to 1 on a 50/50 petrol benzol mix. The bike ran well until BP stopped selling benzol at the pump. I then had to reduce the compression to stop pinking. I did this by fitting a 0.080” plate under the barrel and a 0.20 copper head gasket to the spigot. The bike did a further 20,000 miles like this until the bore was worn out.
regards
David


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