barrel lubrication

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Re: barrel lubrication

Postby bjorn » Mon Oct 23, 2017 12:42 pm

Chris,
I would say the piston is a bit more than "scuffed". It has at some time seized in the barrel. This can be due to too small clearance between piston and barrel, insufficient lubrication, overheating or a combination. Whatever, the result is that the piston material gets so hot, dry and semi-plastic that it tries to fuse with the barrel material. You can also see the ring lands material has been "wiped" onto the piston rings.

regards,
Bjørn

PS:I would not reuse the piston.

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Re: barrel lubrication

Postby clanger9 » Mon Oct 23, 2017 5:44 pm

I'd agree with Bjørn: that piston has been seized and the area between the rings looks damaged beyond repair.
That looks much worse than just tight clearance (which tends to scuff the piston skirt).
Most engines don't need a specific oil feed to the barrel (splash is normally enough), but I'd definitely want to check that the oil ways are all clear before fitting a new piston...
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: barrel lubrication

Postby Chris Berry » Mon Oct 23, 2017 9:42 pm

clanger9 wrote:I'd agree with Bjørn: that piston has been seized and the area between the rings looks damaged beyond repair.
That looks much worse than just tight clearance (which tends to scuff the piston skirt).
Most engines don't need a specific oil feed to the barrel (splash is normally enough), but I'd definitely want to check that the oil ways are all clear before fitting a new piston...

don't worry this piston has been redesignated as an ash tray for smokers and will not be going back on the bike. The oil ways do appear clear so I can move on from that and safely assume the engine did not starve for oil. Piston/bore clearance is the next check. This I will check when the new piston arrives

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