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spudulike

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I am currently porting a MS361, I knew the top end was aftermarket but on pulling it apart, noticed the top piston ring had a locating pin that ran straight down the middle of the exhaust port. The arrow on the top was pointing toward the exhaust port but had NEVER seen unsupported ring ends in a port cavity before.

 

If manufacturers have to do this, they usually put a support pillar down the middle of the port so knew something was wrong. The piston ring had a bit of bevelling on its ring ends so it was having a hard life springing in and out of the port.

 

I decided to pop it back together with one ring and the pin facing backward toward the inlet. I checked the ring end wasn't visible in the inlet port at BTDC and it wasn't. A few sharp pulls and good compression was reached so decided to lightly hone the bore to allow the ring a chance of bedding in again and quickly. The base gasket can be dropped on this kit but I don't think it could on the standard kit.

 

Dropping the lower ring allows greater flexibility on widening the ports and also produces less piston friction/drag so faster revs:thumbup:

 

I also noticed one of the transfers was poorly shaped and had lost around 1/3rd of its opening just through poor casting so it should go well once completed.

597671d3ec88a_AMPiston.jpg.3cdb36f446b68cb85dd7a0326005303d.jpg

transfers.jpg.da4ee323d3448c9f44a7e81c0dc020ae.jpg

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  • 2 weeks later...

People are always asking how good aftermarket parts are. I had a MS660 in a few months back, the crank and piston were buggered. After discussion with the owner that the crank was around £250 we decided to go aftermarket.

 

It came back in a few days ago and was seized solid. A quick inspection showed the top end was good so pulled it and found the crank had split in two. I am currently splitting the cases and going to try another and see how it goes. Never seen this type of carnage before!

Crankshaft.jpg.049b67b34bfb61d4b46eef2460f52192.jpg

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People are always asking how good aftermarket parts are. I had a MS660 in a few months back, the crank and piston were buggered. After discussion with the owner that the crank was around £250 we decided to go aftermarket.

 

 

 

It came back in a few days ago and was seized solid. A quick inspection showed the top end was good so pulled it and found the crank had split in two. I am currently splitting the cases and going to try another and see how it goes. Never seen this type of carnage before!

 

 

 

Nice job I don't trust any chinky bits after a couple of pot and piston failures very soon after rebuild

 

 

Sent from my iPhone using Tapatalk

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Nice job I don't trust any chinky bits after a couple of pot and piston failures very soon after rebuild

 

 

Sent from my iPhone using Tapatalk

 

It is devil and deep blue see job with the OEM part being an eye watering £250 and the aftermarket ones at £40. The OEM part makes repair non economical so there you go. Another Chinky one going in and will hopefully last longer. The customer would have made his money back on the previous repair and I did point out the dangers of aftermarket kit....it is all I can do!

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