350cc cylinder fins and possible engine rebuild

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
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BrianDowning
Posts: 63
Joined: Sat Aug 27, 2022 3:51 pm
Location: Norfolk UK

350cc cylinder fins and possible engine rebuild

Post by BrianDowning »

My bike has several broken cooling fins on the cylinder. At least thee fins on both sides are damaged. I'd like to have the fins as they were originally, but it might not be worth the expense as the cylinder isn't cracked. I'm guessing I would need a total replacement or pay a metal shop to build up the fins. Any idea of either cost?

The engine sends out a lot of oil smoke when starting after a month off. Suggestions as to the cause? The oil burns off after a few minutes so I'm guessing there may be worn piston rings and/or valve guides. While I'm taking the gearbox out to find the source of two oil leaks, I'm looking at the lump and debating whether or not to rebuild the whole thing myself before spring.

Just curious what a garage would charge to rebuild the engine if it were out of the bike?

Brian
vigo
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Posts: 114
Joined: Sat May 18, 2019 5:50 pm
Location: Cheshire UK

Re: 350cc cylinder fins and possible engine rebuild

Post by vigo »

Engine: bought my non runner 3 years ago and in my case "nipping up " cylinder head bolt 5 was not enough and oil was feeding across the gasket into the cylinder. After giving the job to someone who knew better, no more probs.
Gearbox: I had this apart and replaced main bearing and seal, layshaft and bush, seals to kick start and selector. Evidence of historical corrosion but, I was unable to cure the infamous leak down main stand.
I think this stems from the sleeve gear (SG)area and if the mainshaft Bush within SG is sloppy this could help to cause leaks. I think it's a limitation excercise because the metal to metal design in this area could have been better.
SPRIDDLER
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Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: 350cc cylinder fins and possible engine rebuild

Post by SPRIDDLER »

BrianDowning wrote: Thu Dec 29, 2022 4:37 pm My bike has several broken cooling fins on the cylinder.
One of the guys in my/your section has just repaired a couple on his bike by welding on bits cut from a scrap cylinder and you can't see any evidence whatsoever of the repair.

(Para deleted after posting as it was only relevant for H/W engines.).
I'm looking at the lump and debating whether or not to rebuild the whole thing myself before spring.
Are there any other issues with the engine?
Just curious what a garage would charge to rebuild the engine if it were out of the bike?
Rob Swift and Ian Farrington, both pretty local, advertise in the Jampot mag classifieds and could give you a guide, subject to what needs replacing or how 'fussy' you want to be with replacing parts.
Last edited by SPRIDDLER on Thu Dec 29, 2022 9:17 pm, edited 1 time in total.
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Andy51
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Posts: 742
Joined: Thu Mar 31, 2005 1:00 am
Location: BERKS UK

Re: 350cc cylinder fins and possible engine rebuild

Post by Andy51 »

I had broken fins rebuilt by local classic bike dealer who used old cylinder, make unknown, as fin donor. You cannot see the join! Regarding sleeve gear bush(es), they are easy and cheap enough to replace, but you will need to bore them to size after fitting, in the lathe, you are looking for 2 thou clearance
Last edited by Andy51 on Fri Dec 30, 2022 10:57 am, edited 1 time in total.
BrianDowning
Posts: 63
Joined: Sat Aug 27, 2022 3:51 pm
Location: Norfolk UK

Re: 350cc cylinder fins and possible engine rebuild

Post by BrianDowning »

Thank you all for the responses.

In addition to the broken fins there's a large cloud of oil smoke on start-up, which is why I'm thinking of a rebuild.
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