Leaking head gasket 850 mk3

I have had a constant oil leak from my head/cylinder joint, so thought i would take the head off to have a look.
I was using a solid copper gasket, suitably annealed, with a very light film of sealant that I cant remember. Maney standard bore alloy barrels and pistons, skimmed RH4 head with big inlet and exhaust valves.
The performance was good, but the constant slight oil leak was annoying and visually unappealing. retensioning head had zero effect
When the head came off, there was a lot of oil, especially on underside of gasket, pooling in long allen heads that hold barrels down etc.
I have a brand new AN composite gasket, as well as a selection of good copper gaskets I could use.
I believe the oil to mainly come from pushrod tunnels, and when I look as the composite gasket with the (aluminium?) eyelet rings around the bore holes, I am concerned that they could make the problem worse by holding the pressure and thereby reducing the performance on the rest of the mating surfaces, despite that they are crushable to some degree.
As I would like to solve the issue of oil, which gasket should I go with?
I used to have the 3rd fin porosity but after 30 years the Comstock breather valve finally cured that.
There was a lot of very hard carbon deposits on the piston crowns, looked like weld slag, mainly in the valve pockets, which I assumed was from oil getting into the combustion chambers.
I know there are many opinions but i need to choose a course!
TA
Johnny

Horses for courses, many owners use both and they both use them with no leaks. Other areas to check, ensure that the studs in the head have not been over tightened and raised the first thread as well as the usual flatness checks. Re-torque the head as normal but check it for a second time after another 50 miles or so.

Another route for the oil could be up the barrel hex socket bolts fastenings. They are normally fitted with special extra thick washers. The breather valve I would think should prevent this but you never know ?

Dave

I would also suggest using the waisted head bolt kit that cNw sell - there wasa long thread on this last year. It really does seem to solve the problem of the head bolts loosing their torque.

We lifted the head on my 850 today. Same thing. Oil finding its way out, mainly around the pushrod holes. Changing the studs over and putting inserts in the head because one had failed. The flame ring gasket was measured and we found that the copper was .006" thinner than the material around it. Based on this, a copper gasket is going to replace it.

Fullauto said:

We lifted the head on my 850 today. Same thing. Oil finding its way out, mainly around the pushrod holes. Changing the studs over and putting inserts in the head because one had failed. The flame ring gasket was measured and we found that the copper was .006" thinner than the material around it. Based on this, a copper gasket is going to replace it.

Click to expand...

Ken,
Just as a point of interest. The flame ring gaskets have changed recently. They have gone from .75 mm to 1.0 mm, according to AN due to failure problems. The good side is that maybe it's a better gasket, downside is you go from .30" to .40". My .75 mm started to leak immediately after I did my 500 mile re-torque (it was 30 degrees F. when I did it, so maybe that was part of the problem), and did not stop even with multiple re- torques. I replaced it with a 1.0 mm and have not had a problems in the last 2,000 miles (knock on wood). I was using CNW's head bolts w/ both gaskets.
Pete

Deets55 said:

Fullauto said:

We lifted the head on my 850 today. Same thing. Oil finding its way out, mainly around the pushrod holes. Changing the studs over and putting inserts in the head because one had failed. The flame ring gasket was measured and we found that the copper was .006" thinner than the material around it. Based on this, a copper gasket is going to replace it.

Click to expand...

Ken,
Just as a point of interest. The flame ring gaskets have changed recently. They have gone from .75 mm to 1.0 mm, according to AN due to failure problems. The good side is that maybe it's a better gasket, downside is you go from .30" to .40". My .75 mm started to leak immediately after I did my 500 mile re-torque (it was 30 degrees F. when I did it, so maybe that was part of the problem), and did not stop even with multiple re- torques. I replaced it with a 1.0 mm and have not had a problems in the last 2,000 miles (knock on wood). I was using CNW's head bolts w/ both gaskets.
Pete

Click to expand...

This has been on the bike for 17 months and 17,000 miles. If the copper ring is .010" smaller than the rest of the gasket, it's going to leak. I don't know if this is the new or old type.

Fullauto said:

Deets55 said:

Fullauto said:

We lifted the head on my 850 today. Same thing. Oil finding its way out, mainly around the pushrod holes. Changing the studs over and putting inserts in the head because one had failed. The flame ring gasket was measured and we found that the copper was .006" thinner than the material around it. Based on this, a copper gasket is going to replace it.

Click to expand...

Ken,
Just as a point of interest. The flame ring gaskets have changed recently. They have gone from .75 mm to 1.0 mm, according to AN due to failure problems. The good side is that maybe it's a better gasket, downside is you go from .30" to .40". My .75 mm started to leak immediately after I did my 500 mile re-torque (it was 30 degrees F. when I did it, so maybe that was part of the problem), and did not stop even with multiple re- torques. I replaced it with a 1.0 mm and have not had a problems in the last 2,000 miles (knock on wood). I was using CNW's head bolts w/ both gaskets.
Pete

Click to expand...

This has been on the bike for 17 months and 17,000 miles. If the copper ring is .010" smaller than the rest of the gasket, it's going to leak. I don't know if this is the new or old type.

Click to expand...

Ken,
It's probably a .75 mm one. It was about this time last year I ordered a gasket kit and a spare head gasket from AN. The kit had a .75 mm and the spare was a 1.0 mm. I just measured my old one and the metal portion was consistently .001"-.002" thinner than the composite portion. So your .010" is definitely a leaker.
As a side note I'm glad you stepped up and are manufacturing new heads. Whether some one needs one or just wants one it's nice that they are available. Especially if someone needs one. Now there are options to buy a new or hopefully a good used part from those who just wanted one.
Pete

Check for & take off high spots with a flat plate and wet or dry sand paper - don't bother getting it absolutely perfect cause it will just warp again. Changing HG thickness won't help unless your bolts/studs are bottoming out. A composite gasket should work but they can compress in places and end up giving you a warped head. Waisted bolts are better but as Deets experienced - they don't always help. The sealer to use on copper is "pliobond" - nothing else works as well (bond the sealer on all 4 surfaces). Add .005" copper wire around the pushrod tunnels. Problem solved.

Waisted bolts are better but as Deets experienced - they don't always help.

Jim,
FWIW. I was leak free until I did a 500 mile re-torque. Using standard head bolts and composite gaskets I always got an oil mist from the pushrod tunnels after a sustained 70+ Mph highway run, especially during the summer months. Now, with the waisted bolts, new gasket and different torque schedule I have been good for 2,000 miles. I think the re-torque caused the gasket to shift because the leak started the next day. Might be my fault for trying to re-torque in 30 degree temps, I should have heated the garage before I did it. I don't think that's a problem where your at . At the moment I am very happy with the waisted bolts/composite gasket. But that can change at any moment, after all it is a Norton.
Pete