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Thread: GPR partial seize
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01-02-2012, 08:32 AM #1
- Join Date
- Aug 2011
- Posts
- 6
GPR partial seize
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.
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01-02-2012, 11:08 AM #2
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.
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01-02-2012, 12:13 PM #3
- Join Date
- Jun 2008
- Location
- Hillsborough, North Carolina
- Posts
- 141
"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?
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01-02-2012, 09:03 PM #4
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.
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01-02-2012, 09:17 PM #5
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?
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01-04-2012, 12:28 AM #6
- Join Date
- Aug 2011
- Posts
- 6
No, didn't pressure check the engine but it seemed to run and idle ok ie didn't seem to be sucking air.
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