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Matchless G3 engine rebuild

Hello to you all,

I’ve recently taken delivery of my new 1940 Matchless G3WO project. I’ve only ever owned Enfields and a James ML up to now, so the Matchless is all a bit new and a bit of a learning curve.

I’m starting to gather parts for the engine rebuild and getting my head around what to do. Do people generally remove the steel plate under the barrel to increase the compression ratio, or leave it in? I read in a postwar manual that you need to machine a lip off from the base of the cylinder barrel, I’m assuming as I’m re-sleeping my barrel that this is no longer relevant?

I’m in need of an outer chain case and a 1” throttle twist grip if anyone has one to sell or swap.

Regards,

Tom

email (option): tomillward@hotmail.com

Re: Matchless G3 engine rebuild

Tom I thought they only fitted the compression plate to the G3L. Maybe a REME mod? But most guys remove it. I hadn't heard anything about machining the liner either. I didn't think that the barrel was modified in any way to fit the plate, so removing it should go back to standard. Maybe Lex can confirm. Ron

email (option): ronpier@talk21.com

Re: Matchless G3 engine rebuild

Ok, no nothing machined there?? just remove the plate, it's not needed with modern petrol.

Cheers,

Lex

email (option): welbike@welb**e.net

Re: Matchless G3 engine rebuild

Thanks gents,

I was quoting from the 'Motor Cycling' Maintenance Series, for Matchless Motorcycles 1939-55, published in 1958. The section on WD models includes tips to improve performance of the de-tuned WD models, including 'Remove the compression plate, then machine away the ridge in the cylinder barrel at the limit of the piston-ring travel'.

Could it be that they were just looking at a heavily worn barrel when they stripped the ex WD engine?

email (option): tomillward@hotmail.com

Re: Matchless G3 engine rebuild

They were referring to the (possible) wear ridge and/or carbon build up at the top of the barrel...If you drop the barrel by removing the plate the top ring would then 'crash into' any wear ridge or carbon deposits resulting in a broken ring.....Ian

email (option): ian@wright52.plus.com

Re: Matchless G3 engine rebuild

That makes sense, thank you Ian. Not something that will be an issue then if I'm fitting a re-sleeved barrel.

email (option): tomillward@hotmail.com

Re: Matchless G3 engine rebuild

tom I normally don’t fit the plate, the barrel should fit ok, if I can remember I’m sure when the compression plate is fitted there’s two thicker washers that go under the bottom push rod tube seals to take the extra gap, I think if you was to fit the plate on the G3 engine then the rocker cover won’t fit on, its very close to the frame due to the slightly higher barrel,

Barry

email (option): fullerbarry@hotmail.co.uk

Re: Matchless G3 engine rebuild

Well my G3L de-compression plate remains firmly in place and will stay that way. I am a bit surprised that people usually so punctilious in preserving the EXACT original specification should think it acceptable to chuck away this bit of the bike's history! It is plainly in view and would have been there in WW2 so why take it off - do you really need to extract a couple more horsepower? Shame on you!!:innocent:

Re: Matchless G3 engine rebuild

Ferg I bet the "Bar None Club" removed the plate toot sweet and fitted a G3 carb if there was one to be had. :ok_hand: Ron

email (option): ronpier@talk21.com

Re: Matchless G3 engine rebuild

I see your point FerG3, I haven’t worked out yet where I feel the compromise is between originality and usability. The engineer in me can’t resist tuning the engine to get the best out of it, just as many budding motorcyclists would have done with their mounts after the war. But the Historian in me wishes to keep the bike as original as possible. If I understand correctly, the plate was put in to compensate for the war departments poor quality/low octane fuel? Which is not an issue anymore.

It’s a balance, as subtle modifications make the vehicle more usable, and sometime safer to use. My 44 Willys Jeep is a veteran of the Rhine Crossing, having been used by 53rd Light Regt RA to tow a 25 Pdr gun. There’s lots of history there, but I’ve also fitted modern LED lights and indicators. It doesn’t necessarily sit well with the historian in me, but that’s why I o make modifications as subtle as hidden as possible and completely reversible.

The compression plate in the G3 is something I will think more about.

Cheers,

Tom

email (option): tomillward@hotmail.com

Re: Matchless G3 engine rebuild

Tom I don't think the compression plate was ever fitted to a G3 as standard. Ron

email (option): ronpier@talk21.com

Re: Matchless G3 engine rebuild

Happy days then. I take it then G3L engine was a de-tuned version of the G3, hence the smaller carb and lower compression ratio?

email (option): tomillward@hotmail.com

Re: Matchless G3 engine rebuild

Perzacly!! The plate is listed in the G3L spares lists only. I think some of the early WOG3's also had the pre war high lift cams fitted. Ron

email (option): ronpier@talk21.com

Re: Matchless G3 engine rebuild

Agree - my G3WO did not have the plate AND this model was recognised as being much nippier than its successor. Alas, it was also about the same awkward lump to work on!

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