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Allan G
Allan G
West Yorkshire
Posts: 7,309
Joined: May 2013
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Thread Like Summary
Allan G
Total Likes: 1
Original Post (Thread Starter)
by MarcB
I've got a combination of issues that seems to point to an issue getting the head to seal but want to get some opinions on how to proceed.

History: Bike was buttoned up at the end of last summer. Head got new valves and guides by a known good britbike expert. Head gasket was annealed and installed without o-rings. Engine only ran about 100 miles before the season ended. There was a bit of oil weeping up two head studs (left rear, right front). Plug on the left side looked good, right side seemed to have a bit of oil sheen to it.

Over the winter I re-torqued the head and fixed a few other leaks unrelated to the head gasket. Since then, I've done about 1000 miles and the weeping has got a bit worst on the right front stud. Also, the right silencer has a bit of gummy black gunk at the back, indicating a bit of oil in the exhaust.

I pulled the head and this is what it looks like:

Gasket top
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Gasket bottom
[Linked Image from]

Barrel surface
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Combustion chamber
[Linked Image from]

Exhaust port
[Linked Image from]

The bits that concern me are these:
  • Center bolt hole appears cracked at the very top. How concerning is this? The center bolt doesn't slip in and out of its hole in the head so how well it's torquing down is a bit suspect.
  • copper gasket is discolored at the front of the left hole. there is the start of a carbon ridge at the top of the cylinder in that same spot
  • combustion chamber actually has more carbon built up on the left cylinder than the right one. right one is pretty clean
  • while the rear of the exhaust has oily stickiness, the exhaust port is dry (dusty gray rather than gummy black)

I have not pulled valves out but can if getting a better view at the intake tracts is worthwhile.

I don't feel great about reusing this gasket considering the multiple leak points. Are any of the pictures or points above indicative of anything besides the gasket? Any other pictures that would be useful to get posted? Thoughts?
Liked Replies
by NickL
The problem with fitting liners that thick is that the barrel is very thin near the base flange and is very likely
to crack. Effectively the barrels have been bored about +0.200 Those liners are way too thick in my opinion.
You could have a few thou skimmed off the surface to true it up but if the liners are moving then more radical
measures need to be taken like drilling the base flange and putting pins or bolts in. Through bolting should also
be thought about as you've very little metal left on the barrel for strength.
I've had several sets of liners done over the years and never used stepped ones, if they are fitted properly
plain liners in iron barrels are fine. In alley barrels a step is nicer but that's if there is room.

Easier to find another set, they are cheap enough.
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