Loose Head.

[Bully fanatic]

Hello everyone. I had a stange thing happen on my Sherpa T the other day. I went to ride the MTCQ club day and I had only just got my Sherpa going after replacing the main bearings, crankshaft seals, rings and other seals. I also resprayed the cases and head and barrel. I had gone for a five minute ride on it to make sure it worked and loaded it up. At the trial I had about a five minute warm up and stopped to get a drink and go through scrutineering. My bike then refused to start. It had a good spark and was getting fuel. I thought oh well and packed it up after trying to make it go for a while. When I got home I had a closer look at it. Even checking the timing in case I had left the backing plate screws loose or something similar. I then thought I will check the head bolts and you guessed it all finger tight. They were tight enough not to make a noise when kicking it over but loose enough to leak. Tightened them all up and first kick away it goes. As you can imagine I said oh poo! What had happened was after painting the head and barrel and all of the nuts, bolts and washers the paint had compressed and left everything loose. I was expecting to tighten everything up after an hour or so but not that quick. Has anyone else had this happen to them or something similar. Graham.

[David Lahey]

Well I haven't had that happen, but then again I've never painted the nuts and washers. Sounds like a logical explanation because heat resistant paint does shrink as it cures

[pop]

Did you actually paint the gasket surfaces as well?

[Bully fanatic]

Hello all. Pop, no I did not paint the gasket surfaces. The base gasket area was masked up and the head on mine doesn`t have a gasket but it was masked up as well. I am a spray painter by trade so I know what I am doing. Graham.

[pop]

I just remembered that back in the last century with bikes with the flat copper gaskets, the only way they would not leak is to spray them with coppercoat or some heatproof paint.
If you watch the factory race team mechanics for cars and bikes they all seem to be allways using a torque wrench, checking constantly for loose nuts and bolts, maybe we the average Joes should be doing the same.

[Bully fanatic]

Hello all. The strange thing is I did use a torque wrench at the correct torque for Bultaco head bolts and nuts. You expect them to loosen of a bit after an hour or so but not ten minutes. It looks like one of those things to put down to experience. Graham.

[Guy53]

Wheter it's a new or an old copper gasket you have to heat it properly before you install it or it will leak.

Guy

[pop]

How true, but its too easy to warp and make the thickness uneven, but what is the correct way of softening a copper gasget?? also and another thing that can happen is that the gasket can be hard or soft in different areas of the gasket.

[FM350]

Heat to cherry red and quench in clean water. Hotplate on a kitchen stove seems to work well, but can be a bit smelly..............

[David Lahey]

As long as copper becomes hot enough to become cherry red, it has been fully annealed and can be cooled in water or just left to cool slowly. Some people like to quench in water but it does not make any difference to how soft the copper becomes, and increases the risk of the material distorting.
Every time a copper head gasket is installed and used, the gasket becomes thinner. After many uses and re-annealings, some can become thin enough to make a noticable difference to the combustion chamber volume so it is a good idea to keep a track of the thickness of head gaskets that might have been re-used a few times.