Crankpin meets main bearing

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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Thomasm
Posts: 11
Joined: Mon Aug 12, 2013 9:54 am
Location: UK

Crankpin meets main bearing

Post by Thomasm »

Hi folks,
today the 14 csr engine was on the bench. all going well. 30mins in the oven and both bearings drop out. However they reveal a 2 mm deep groove cut through the crank pin nut. ( see picture) I'm assuming and judging by the swarf that this is not engineered by AJS but at some point either the crank moved forward ( drive side) or the main bearing outer shell moved back (perhaps not drifted far enough in). I don't see quite how this would be possible, but more importantly how can I ensure it doesn't happen when I bolt it back together. It must have made a hell of a squeal when it happened.

Any ideas ?

ps - the bearings that came out are in fair condition , to be replaced, but show no sign of the corresponding side of the damage. however looking at the picture it looks as though there is a crack at the 7 o'clock position. Back out to the garage to check.

Thks
mainbearingmeetscrankpin.jpg
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Ozmadman
Posts: 2651
Joined: Wed Dec 14, 2011 1:02 am
Location: ESSEX UK

Re: Crankpin meets main bearing

Post by Ozmadman »

Maybe at some point someone never used an arbor press to press the crank pin in and relied just on tightening the nuts to do the job, which it obviously hasn't, something which the manual warns very strongly against?

Paul
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
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Joined: Sun Oct 02, 2016 7:34 pm
Location: Calne Wiltshire

Re: Crankpin meets main bearing

Post by ade »

I have the same mark on my crankcases, was this resolved?
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