M20 engine seized when cooling

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Re: M20 engine seized when cooling

Postby Rob Harknett » Fri Mar 31, 2017 11:34 pm

Yes , I've trailered home a mates bike, with molten shellac mag. That was a 30's SV BSA. My rusty bearings had to be replaced. Ken de Groom did it. Did about a mile and the engine blew up. New piston fitted was in 1,000 bits.

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Re: M20 engine seized when cooling

Postby Groily » Sat Apr 01, 2017 5:37 am

Not so long ago I broke the kickstart quadrant on a very expensive motorcycle made in Stevenage - the mag had seized absolutely solid on a hot day, having run well 'til a tea stop. I innocently gave it a good prod expecting the mighty rumble to resume . . . but the noise was a bit different - and very expensive! So quite possible.

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Re: M20 engine seized when cooling

Postby EgLarsen » Sat Apr 01, 2017 5:00 pm

Hello
Thats giving a little hope. I will try removing the magnetogear one of the first evenings.
:-)

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Re: M20 engine seized when cooling

Postby REW » Sat Apr 01, 2017 7:10 pm

You say you tightened a few nuts and bolts after the run - could this have caused the crankcase halves to tighten on the crank or indeed something else to become slightly misaligned?
Ron

1951 Matchless G3L, thumping round the Durham Dales

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Re: M20 engine seized when cooling

Postby 1608 » Sat Apr 01, 2017 7:37 pm

Well spotted Ron, always consider what was last done to the bike.

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Re: M20 engine seized when cooling

Postby EgLarsen » Sun Apr 02, 2017 4:54 pm

Now things are getting better. I sneaked away from the family birthday a few minutes. And loosened some of the crankcase and mounting nuts I tigthened during the winters attempt to keep the oil inside the machine...now the engine can be turned by hand. I will work a little more with that and hopefully get the M20 on the road in the eastertime.
Thanks to all for helpfull advices
Anders Eg Larsen

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Re: M20 engine seized when cooling

Postby JohnHewes » Sun Apr 02, 2017 10:43 pm

Years ago I rebuilt a G9 and after doing the bottom end bearings the crank tightened up when I did the crankcase bolts up tight. It turned out to be the centre bearing which needed scraping a bit. I think I remember a procedure being mentioned where you assemble the centre web with the bolts nipped up slightly, assemble the two halves and give the crank some turns to align the centre web, then take off one half of the crankcase and tighten fully the web bolts.
My engine ran fine for lots of miles subsequently.
Good luck with yours.

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Re: M20 engine seized when cooling

Postby EgLarsen » Wed May 10, 2017 6:25 pm

Yes.. At last I found the gremlin.

Following the advices on loosening every tigthened bolts and nuts, the gremlin showed itself, when I was retigthening everuthing nut by nut.

The cover to the oil-distributor on the left-hand side seized and stopped the engine when beeing tigthened.
It got an extra thick washer, and now I stroll along at 80km/h (sure I will go faster, but I´m still adjusting the clutchsprings ;) )

:D Anders

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