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Ms660 full rebuild with am cyl kit woes

Painlessjoe

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Hello everyone first thank you for accepting me to this wonderful site that has been a wealth of knowledge and interest. Hopefully I can add something positive to the site and it’s members. Ok so I got a wiped out 660 from friend who runs a tree service to get back in service for him . Bad cyl piston. I completely rebuilt it with oem parts from the ground up with the exception of a.m. cyl kit vac tested before start up ran for 2 min then broke ring piston luckily it was idling.was really looking forward to using this cyl as is has the enhanced port timing . Plating flaked off around exhaust port and bottom of cyl at intake feels like tin foil . Questions or comments? Thanks again
 

Rob Stafari

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Welcome to the site. Are you referring the MMWS Cross cylinder kit? If the plating is flaking already I'd say you have a lemon of a cylinder regardless of make/model and I wouldn't bee so keen to run it myself. Pictures should help us help you though...
 

Painlessjoe

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Trying to figure out how to put pics on here I’m not very good at navigating those kind of things yet and well ... yes it was a cross . By no means bashing though.
 

67L36Driver

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Piston in backwards? That will snag/break a ring.

Locator pins go on intake side.
 

Painlessjoe

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Nope arrow to exhaust, 40:1 vp oil 74 main jet in wj 69 ,new oem seals, bearings base gasket with a little 518 approximately .030 squish all new rubber as well vac pressure test before first start even ran a little fine emery by hand around the port openings . Really tried to be meticulous, maybe I was overthinking it or I just s**k
 

srcarr52

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The exhaust port roof and floor can be pretty flat on those cylinders but it varies a lot. Maybe you got an extremely bad one.
 

Painlessjoe

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Thanks for the input got a new Stihl cyl kit on the way from dealer for 270 never bought a new oem cyl before only good used with never an issue and all of those are working fine . More later.
 
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