GPR partial seize

[mick14]

Hi guys I 've just rebuilt my stock GPR1200 -
hone, new pistons and rings, new crank seals and rebuilt carbs (new 1.5 NS as well - 43 psi pop off).
I put about 4.5 hours on it and it and it started to lose a little power. Also on about 3 ocassions the motor just cut out at wide open throttle but as soon as I hit the starter it would start and run fine. The heat alarm came on twice as well but I checked the engine by putting my hand on it and it was not too hot. I did a comp test and #1 was 115, # 2 105 and # 103. I then pulled the head off and found that 2 of the pistons have grabbed the bores (see pics)
The problem I have now is I don't want to rebuild till know what the cause is, otherwise - same again!!
Any ideas about what might be the problem would be greatly appreciated.

[1200Jet]

Looks like a lack of lubrication to me. Or you may have removed the Nikasil lining when giving it a hone although its a pretty tough lining. Generally speaking these cylinders shouldn't be honed, a clean with scotchbrite is all they should need. If they are damaged as they are now they need to be sent to a specialist and re-coated with the Nikasil lining.

[mrtinker]

"Scotchbrite" ??? Wow, I think I may have screwed myself then.....

I am in process of repairing some slight damage too and thought a light sanding of the lower part of the cylinder would be okay...

Sorry to Hijack your thread but can someone with "Great" experience tell me if I should be okay not getting the cylinder repaired/re-nikasilled?

[1200Jet]

If the damage has scored the lining it has to be re-coated.

The idea of a hone is to add fine scoring to aid in oil retention to increase the lubrication between piston/ring and bore. If your intentions are to remove buildup from scoring of piston/ring to bore contact then its to late and the cylinders will need to be re-coated. If the buildup can be removed and the lining is still intact then it should be okay however 9/10 the lining is damaged.

The honing of a nikasil bore isn't going to harm it, in fact the lining is so hard it probably won't even hone it properly. The reason I use scotchbrite is because they usually only ever need a clean up.

[WATER WOODY]

Post a pic of the top of the pistons. So far it looks like a 4 corner seizure. Was the motor pressure tested after the rebuild?

[mick14]

No, didn't pressure check the engine but it seemed to run and idle ok ie didn't seem to be sucking air.