E: Engine Nip up Comet

[oexing]

Are you sure with muriatic acid ? I´d think caustic sodium attacks aluminium better ?

Vic

 

[greg brillus]

The head was over torqued to stop the head/liner joint leak...........and unsuccessfully at that. You need to address that issue or the problem will remain.

 

[Cyborg]

Are you sure with muriatic acid ? I´d think caustic sodium attacks aluminium better ?

Vic

I have used muriatic and it worked quite well. One of the few things in my life that I’m reasonably sure about. There obviously are other things that will work, but it is easy to come by here. It was my brother, who recommended it to me. At the time he was working in a Honda dealership. One of the fellows that worked there as a gopher rode a CR250 2 stroke. He was completely deaf and basically judged RPM by feel. Not sure what the total sum weight of all the piston material my brother removed from his cylinders, but it was significant.

 

[Cyborg]

Yes I really think this was the problem. Cylinder is quite a snug fit in the cases. The head had been pulled down VERY tight. I have since checked and the torque setting is only 32ft Ibs. I am going to clean everything up, check out the head, valve guides etc. If all is OK I will replace what is needed and put back together.

Well after this mornings coffee. I see that passenger0-0 mentioned the studs previously. Great minds think alike and/or my reading comprehension sucks?

 

[vibrac]

I work on 3 thou round the head outer surface when sitting on the liner top I keep meaning to make up a turning jig as I find the grinding method very messy

 

[greg brillus]

Yes you want to be able to run a 3 thou feeler gauge around the outer joint with no binding. I use a large surface plate of 12 mm glass sheet with sheets of 40 grit paper glued together to cover most of the glass. Just need to hang the outer lower exhaust port off the side of the glass........takes some effort and you work up a sweat after several goes. If it needs more I have a special jig that the head mounts to in the mill and you can rotate the head like a gimbal. You can pretty much machine any part of the head using this, which is great.

 

[bmetcalf]

Steve Hamel has a gimbal jig like that, but I last saw it ~10 years ago, so I don’t remember much about it.

 

[vibrac]

Yes you want to be able to run a 3 thou feeler gauge around the outer joint with no binding. I use a large surface plate of 12 mm glass sheet with sheets of 40 grit paper glued together to cover most of the glass. Just need to hang the outer lower exhaust port off the side of the glass........takes some effort and you work up a sweat after several goes. If it needs more I have a special jig that the head mounts to in the mill and you can rotate the head like a gimbal. You can pretty much machine any part of the head using this, which is great.

Yes that protruding exhaust port just makes a unlikable job really nasty it restricts an even approach Grrrr..

 

[robin]

Your piston is a GPM. SCRAP. GPM pistons are round. The fore/aft dimension should be at least 10 thou bigger the port/starboard dimension. GPM's are noted for seizures.
Robin.

 

[Bill Thomas]

I think Clev Trev told us sometime ago, It's in my little book. Cheers Bill.