A spot of bother with the M18S

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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A spot of bother with the M18S

Postby Pharisee » Fri Apr 21, 2017 3:57 pm

I don't know whether it's ironic, coincidental or the God of old motorcycles having a laugh at my expense. Yesterday, I was dismantling the rocker box of the G3/LS basket case I'm working on and to be honest, I was struggling. The nuts holding the valve rocker arms onto the shafts were putting up a fight that they almost won. It was only after breaking a chrome-vanadium spanner and resorting to an air impact wrench that I actually managed to get the thing apart.
This lunchtime I took the M18S out for what I'd intended to be a leisurely ride to a local hostelry for a bacon sandwich and a pint of Tring Brewery's finest. As I came off the A505 dual carriageway at Hitchin, I thought "That doesn't sound good.". The engine was clattering away like a good 'un. I turned around and came home... slowly. Straight round to the workshop and off with the seat, tank and tappet inspection cover.
Yep... the nut holding the inlet pushrod rocker arm had come loose and worked its way off the shaft. The rocker arm was still on the spines but waggling about all over the place. The nut was down on the cylinder head under the rocker shaft. I retrieved it with a magnet on a stick!

Has anyone else had that happen to them?


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Re: A spot of bother with the M18S

Postby Rob Harknett » Fri Apr 21, 2017 5:11 pm

Those nuts tend to loosen on my little1936 250 AJS. I just re- peened them in 3 places with a centre punch. Yes they were already peened, by a PO or when made ??

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Re: A spot of bother with the M18S

Postby Mick D » Sat Apr 22, 2017 7:14 am


Could have been a lot worse - have never had it happen to me, hope that's not the kiss of death I say touching wood.

'Belt and braces' on re-assembly - Loctite and punch the threads ;)

Regards Mick

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