Piston advice

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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asterysk_usa
Posts: 135
Joined: Tue Oct 22, 2019 3:42 pm
Location: florida

Piston advice

Post by asterysk_usa »

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I have started disassembling my 18S (1955) engine. The piston has scratches and some erosion. Was wondering if I should replace or reuse.


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1954 AJS 18S Cyprus export (frame decode says 1954 but many components match a 1955).
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clive
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Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: Piston advice

Post by clive »

The damage to the piston looks like it is from an overheating seizure. Are the rings free to move easily in the piston. If it was overheating the ring slots often get closed up trapping the rings. They look ok in your photo but i would check for clearance. Could be old damage if you do reuse i would clean it up with fine wet and dry paper first and perhaps a very light hone of the bore to make sure that is clean.
clive
if it ain't broke don't fix
asterysk_usa
Posts: 135
Joined: Tue Oct 22, 2019 3:42 pm
Location: florida

Re: Piston advice

Post by asterysk_usa »

Image

This is what the liner looks like


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1954 AJS 18S Cyprus export (frame decode says 1954 but many components match a 1955).
asterysk_usa
Posts: 135
Joined: Tue Oct 22, 2019 3:42 pm
Location: florida

Re: Piston advice

Post by asterysk_usa »

Image

I think this is the main contact point on piston skirt


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1954 AJS 18S Cyprus export (frame decode says 1954 but many components match a 1955).
asterysk_usa
Posts: 135
Joined: Tue Oct 22, 2019 3:42 pm
Location: florida

Re: Piston advice

Post by asterysk_usa »

clive wrote:The damage to the piston looks like it is from an overheating seizure. Are the rings free to move easily in the piston. If it was overheating the ring slots often get closed up trapping the rings. They look ok in your photo but i would check for clearance. Could be old damage if you do reuse i would clean it up with fine wet and dry paper first and perhaps a very light hone of the bore to make sure that is clean.
The rings do move easily. The piston looks like an original hepolite.

I have a year or so before I need it again, open to suggestions on what would be the best thing to do to refurbish it , key thing is that when it goes back into the bike it must run well, I'm likely to be in a very remote location and getting spares or anything done will be a nightmare !
1954 AJS 18S Cyprus export (frame decode says 1954 but many components match a 1955).
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