Rings/Piston

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Marley
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Joined: Wed Jan 25, 2017 12:02 pm
Location: NORTH YORKSHIRE UK

Rings/Piston

Post by Marley »

Hi,
recently i bought G3L motor partly rebuilt seller said , bottom end rebuilt, rebore, and Norton piston fitted, not sure of quality, so stripped to find top ring large bit missing, so are the 350 Norton bits interchangeable with Matchless/AJS particularly the piston rings, or should i simply get a Matchless 350 replacement,
. Don't know what year the piston is from, does it matter.
SPRIDDLER
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Location: WEST SUSSEX UK

Re: Rings/Piston

Post by SPRIDDLER »

If you don't know which Norton piston you have then you can only measure the rings (and the ring recesses in the piston) to find out if AMC rings will suit.
Perhaps you can send the Norton rings to a supplier to be matched for a new set.

If the Norton piston height/width/gudgeon pin diameter dims are different from an AMC piston and the cylinder was rebored to match the Norton piston then 'No' you can't fit an AMC piston without a further rebore and/or little end bush.

The 'partly rebuilt' claim gives me an uneasy feeling and why fit a Norton piston when the correct ones are available?
Does the cylinder bore look as though it has just recently been rebored?
As a matter of interest, what is th'engine number which is stamped on the crankcase?

BTW - You've put your post in the G80/Model 18 (500cc) section, not the G3/Model 16 (350cc).

A later thought...
Where is the 'missing large piece of piston ring'?
Last edited by SPRIDDLER on Tue Jun 27, 2017 9:24 am, edited 2 times in total.
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dave16mct
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Location: LANCASHIRE UK

Re: Rings/Piston

Post by dave16mct »

They aren't an exact match. The G3L is 69mm and the norton model 50 is about 71mm.
So could be used in a G3L barrell bored to suit. I can't see the point when the G3L pistons are available??
Cheers Dave.
JimFitz
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Joined: Thu Feb 27, 2014 9:27 am
Location: Kent, England

Re: Rings/Piston

Post by JimFitz »

Further to Sprid's reply - if the weight of the Norton piston is different to the AMC one, the crank may have been re-balanced to suit. If so, fitting a new AMC piston will shake your fillings out - may be cheaper to fit new ring(s) if you can.

Jim
Too old to Rock and Roll but too young to die.

1952 G80 rigid, 1960 G12 DL / Watsonian Monza, 1954 G80S.
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