Heat damaged heads - repair or replace?

[bigfella]

Hi fellows of the brains trust,

My \7 project has bumped another submerged object that I hope you help with.

Having just purchased all the required valves, guides, seats, springs etc to recondition the heads I have found that they are a little warped and require machining.

In the head there are two pushrod tubes each one pressed to a shoulder. These tubes have come loose at some time and moved away from the shoulder and will need to be removed completely before the head can be machined.

Does anyone know where I can purchase these tubes? is this a common problem with an easy workaround?

Other than this my project is coming along nicely - slowly but nicely.

cheers, Sam.

[SteveD]

Motobins or Motorworks in the UK. Post would be cheap enough and 3-10 days. If you need them Tuesday, Munich in Perth.

Available in stainless too.

[bigfella]

Thanks Steve, They have the pushrod tubes that fit to the cylinders no prob but the one I need fit into the heads under the rockers.

cheers, Sam.

[ME 109]

Where is the head warped bigfella?

[bigfella]

exhaust and inlet sides of the head sitting flat there will be a gap under the middle.

[ME 109]

exhaust and inlet sides of the head sitting flat there will be a gap under the middle.

Not too unusual. Are the heads off a GS?

At least surface grinding or milling will get those valve covers to seal nicely.

[Ken in Oklahoma]

exhaust and inlet sides of the head sitting flat there will be a gap under the middle.

Hmm, I'm a bit out of my element here, and I'm away from my parts, but I have to wonder . . . . .

IIRC with the head and cylinders off the motorcycle you can see that the top of the cylinder has a machined "ring" that fits into a corresponding recess in the head. There is a similar recess for the push rod holes as well. The head gasket has three corresponding metal rings which get squashed in use, one for the cylinder joint, of course, and two for the push rod tubes. The critical joint, compression wise, is of course the cylinder.

Sooo, one could take the cylinder (with the "male" ledge) and rub it on some sandpaper on a flat piece of glass or flat granite and see just how flat that projection is. You should be able to come to a decent conclusion. The inner recess in the head, of course, doesn't allow this visual inspection. But you could mate the cylinder and head together, in their proper orientation, and with a bit of fine valve grinding compound on the mating surface, twist the two back and forth, say a quarter of a turn at a time, and then see what you have. Hopefully you would be able to come to some conclusion as to which surface(s) are not flat, and by how much.

Depending on what you discover/conclude, you could then "flatten" the lip on top of the cylinder twisting it carefully on sandpaper lying on a flat surface, such as a thick piece of plate glass or a flat piece of marble (perhaps a cut out from a granite counter top). Alternatively you could spread a very thin layer of valve grinding compound on the mating surfaces of the cylinder and head, twist the two back and forth, and come to a conclusion how well the surfaces are mating. Then you might want to go further and see if you can get the two surfaces mating together pretty well. Keep in mind that the head gasket has that metal ring which will compress significantly. So I reckon the surfaces don't have to be "perfectly" flat. They just need to not vary much relative to each other in thickness around the periphery of the joint.

In the process of doing the above you might end up with all surfaces clean, but still not have a good idea where you stand because the surfaces now are clean. For that I would suggest marking the surfaces with a Marks-a-Lot pen and rubbing the two together dry. I would expect any high spots to look scrubbed and any low spots to have the marking left pretty much intact.

Caveat: The above is solely the product of my own "fertile" mind. Take that into account as you judge its worth.


Ken

[Manfred]

On my '87 R80RT the pushrod tubes do not attach to the heads - they attach to the jugs just inside the joint to the heads. The heads come off - the jugs are in place with the pushrod tubes in place. Do other airheads have a different arrangement?

[Duane Ausherman]

NO, you just described most of them. Some older models had the push rod tubes on the top instead of the bottom.

[bigfella]

Hi fellows, I have since found out that the tubes in the heads I referred to are actually called protection tubes in the bmw parts book. I'm going to order some this week if they are still available.

The pushrod tubes fit to the outer section of the jugs as you described, the protection tubes continue that path from the bottom face of the heads through the cooling fins to the rocker arms.

I'll try and post a photo

cheers Sam.