1963 G80CS Top End Woes

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
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Re: 1963 G80CS Top End Woes

Postby Mick D » Sun Jun 18, 2017 3:45 pm

Hi

Those weights confirm the bush was something pretty close to pure aluminium - certainly not aluminium bronze.

I have to say, I admire your apparent relaxed attitude to this - I'd be chasing the vendor to see if they were aware of the state at sale.

Regards Mick

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Re: 1963 G80CS Top End Woes

Postby dave16mct » Sun Jun 18, 2017 3:46 pm

Funny this, I'm sure they were alloy originally. The twins were, they ran in the alloy conrod, no bush. I'll have a root in the shed, I might be some time.......
Dave

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Re: 1963 G80CS Top End Woes

Postby jack clegg » Mon Jun 19, 2017 10:12 am

My Interceptor runs the pins direct in alloy rods, but they are made from sterner stuff, Hiduminium RR56. I doubt this bush is of the same quality alloy. The way the internal oil groove was so nicely cut had me fooled, that & the staining made it look like a pukka bush. I bought this bike off a Club Member, as seen as driven, only myself to blame. I don't believe he was responsible for the mechanics & used a third party. Bodgetastic workmanship though. I first checked the rotor was secure. I could easily have left it to run a bit rattley, it appeared to function well, plenty of oomph & sounded good until under load at low revs. No-one but me thought it rattled at all. Amazing how these old motors still function despite.
TTFN Jack
John Marshall

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Re: 1963 G80CS Top End Woes

Postby sjr » Tue Aug 29, 2017 9:11 pm

I doubt too whether it rattled a lot, though I haven't even heard it. I can see the polished pressure marks on the piston, and I understand the point that the piston is wrong for the motor, but pressure marks is all they are - no evidence of seizure, even incipiently.

I suspect the motor ran rather well. However, now you have it down, why not strip the big end out and have the rod checked properly for alignment? It is possible to set a con rod manually with a long mandrel through the small end eye and some good measuring equipment. A firm like T&L could do it for you.

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Re: 1963 G80CS Top End Woes

Postby g80csp11 » Wed Aug 30, 2017 5:33 pm

Matchless G85CS, G80CS Piston & Rings, p/n 028196, BHB, Standard Bore,12.5:1 CR
The piston you have appears to be the G85CS piston that is 12:1 compression ratio
It matches the con rod , and should run OK

your pictures show a piston running happily , with minimal polishing on the lower skirt
All normal
I'd recommend fitting a new con rod bush , and run the engine

If you cant feel a problem with the Big end leave well alone


I have the same piston on my G80CS , the late Geoff Myers was supplying these for years as the standard compression piston ws hard to find

I'm thinking you worry too much !
I bet the previous owner had no idea what was fitted if he didn't rebuild the bike

https://www.google.co.uk/search?q=02819 ... 80&bih=550

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Re: 1963 G80CS Top End Woes

Postby bjorn » Wed Aug 30, 2017 5:48 pm

Hi all,
Just a comment on the little end bush material. An aluminium alloy material was used on the singles, also on the scramblers. From the pictures in this thread, the little end bush is either the original or an old stock replacement. I cannot recall that there were any problems with these bushes related to the material used, rather the opposite, I believe wear characteristics were better than with bronze bushes.

regards
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Re: 1963 G80CS Top End Woes

Postby jack clegg » Thu Aug 31, 2017 10:50 am

Hello replyees. It's all back together now with a new bronze little end, rebored & new P&M piston. Reaming the bronze bush in situ is a pain. Took two goes at it. Still not 100% happy, a little bit rattley I think. Could be tappets some say, but not as bad as my first go at it anyway. May yet try fitting a third bush but bearable while running in.
It's hard to seize a piston which has 10 thou bore clearance. The ally little end was a bodge-up, no matter if original or not. All fitted by some goonie in order to sell on to some poor sod (me) I reckon. TTFN Jack
John Marshall

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