Hi all,
Mates scooter it's a stage 4 indian 200 motor running a franspeed3 and 30mil delly
which must be a common enough combination i would think, the ports haven't been
touched and the piston is in around 700 miles ,it dropped the bottom ring down the
exhaust port, so before he rebuilds top end what should we look at for cause and
fix, it was a 2 ring asso piston , thanx Lammer205.
Asso piston rings?
Lads ,
He had around 750 miles on new piston ,ran in ok, don't think the
ports had been cleaned up, something that was mentioned was the possibilty of a ring cracking due to over heating any thoughts on this?
Thanx Lammer205
He had around 750 miles on new piston ,ran in ok, don't think the
ports had been cleaned up, something that was mentioned was the possibilty of a ring cracking due to over heating any thoughts on this?
Thanx Lammer205
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Donnie
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could have done, most likely overheating issue would be on the exhaust port I'd have thought?
Was the post matched with the exhaust, and was the gasket intact and tight?
Was the post matched with the exhaust, and was the gasket intact and tight?
Donnie.
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Adam_Winstone
- registered user
- Posts: 1693
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- Main scooter: Lambretta GP
- Contact:
Asso (or Mahle copy) rings break pretty easily if you seize the top end, as a good pal of mine could confirm... a couple of times over 
The last set of rings being on the A34 on our way to Avignon because of his ignition timing being too advanced. Once corrected the replacement piston didn't miss a beat for the rest of the rally, including 650km in one day! It would have been very easy to mistake this seizure + subsequent ring failure for ring failure alone. He had also done best part of 1000 miles of slower road use on the piston that nipped up and broke the rings, so running in was not the issue.
That said, he also had issues with his previous engine, which broke rings on a number of pistons and rebores, which was traced to a soft iron liner + alloy jacket kit (as per SR kit) that would wear the exhaust port edges until the exhaust port became too square, then catch and snap rings. The chrome edged hard rings actually made the wear of the soft liner even more rapid than standard rings would have. This combo of hard rings and soft bore is one to avoid!
Regardless of the comments/reasons above (mine that is!), any wide or badly shaped exhaust port, or one with poor chamfer, will do rings too.
Adam
The last set of rings being on the A34 on our way to Avignon because of his ignition timing being too advanced. Once corrected the replacement piston didn't miss a beat for the rest of the rally, including 650km in one day! It would have been very easy to mistake this seizure + subsequent ring failure for ring failure alone. He had also done best part of 1000 miles of slower road use on the piston that nipped up and broke the rings, so running in was not the issue.That said, he also had issues with his previous engine, which broke rings on a number of pistons and rebores, which was traced to a soft iron liner + alloy jacket kit (as per SR kit) that would wear the exhaust port edges until the exhaust port became too square, then catch and snap rings. The chrome edged hard rings actually made the wear of the soft liner even more rapid than standard rings would have. This combo of hard rings and soft bore is one to avoid!
Regardless of the comments/reasons above (mine that is!), any wide or badly shaped exhaust port, or one with poor chamfer, will do rings too.
Adam