Oil - again

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Joker_Bones
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Re: Oil - again

Post by Joker_Bones »

I have a 55 G9 in my shed, it's not mine, it belongs to a friend who abandoned it there about five or more years ago.
At the time I got it running and rode it fairly regularly.
It was prone to occasional fits of billowing white smoke and generally leaked oil from anywhere and everywhere, but it went okay.
Out of curiosity, I stripped the top of the motor, the bores were glazed, some scoring, had rings of corrosion pitting and the ring gaps were over. While it was apart I honed the bores and put new rings in... It made little if any difference to the smoking or leaking.
I decided to have a look at the breathing... I was puzzled to find that the flap valve on the crank axle was not present and further puzzled to find the axle was solid.
Some reading suggested earlier engines had a solid axle and, IRIC, a timed breather arrangement, this engine didn't have any such arrangement.
My conclusion was an earlier solid axle/crank had been fitted and the engine had no breathing at all.
I fitted a breather with a non return valve to one of the rocker covers. It did nothing for the occasional smoking fits but I think it helped a little with the oil leaks and it still went okay.
shaunstaples
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Re: Oil - again

Post by shaunstaples »

Not managed to find any reference to a breather yet, Had a 1950 maintenance manual for xmas and found a spares list online that I've printed out but cant find anything.
I've got to sort oil leaks on chaincase and one of rocker covers, so was thinking maybe it vents into chaincase via this flap valve ( not seen a pic of it yet though )
Was going to see if I can find a couple of rocker covers, so i don't have to drill my original ones. Also not a bad place at the top to get rid of moisture.
SPRIDDLER
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Re: Oil - again

Post by SPRIDDLER »

shaunstaples wrote: Sat Dec 31, 2022 6:07 pm
I've got to sort oil leaks on chaincase
Club spares can supply an improved seal for the chaincase.

https://www.amoc-parts.com//store/comer ... duct=23441

(IKBA about twins so can't help with the rocker leak but in my ignorance I'd say that installing an additional breather may dealing with the symptoms rather than the cause).
'There is a tide in the affairs of men
Which taken at the flood............'
shaunstaples
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Re: Oil - again

Post by shaunstaples »

Thanks Spriddler, I've got one on my list for chaincase and need to look at centre nut as that always seems to be leaking too.

Gaskets look old and crushed, and its leaking from corner near one of studs, I've checked them and they feel tight, but not sure it's clamping on the gasket at that corner (like the nut has bottomed on the stud?).

Just need to see what kind of breather it has, if at all? Would be busy trying to get it oil tight(er) if it was positive pressure?
shaunstaples
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Re: Oil - again

Post by shaunstaples »

Happy New Year

Just wondered if this is the flap valve rereferred to above? (Mine is a 1952 model 20)

016676 DIAPHRAGM C/CASE RELIEF VALVE TWINS 1952-56 ONLY

Thanks Shaun
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clive
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Re: Oil - again

Post by clive »

shaunstaples wrote: Sun Jan 01, 2023 10:40 pm Happy New Year

Just wondered if this is the flap valve rereferred to above? (Mine is a 1952 model 20)

016676 DIAPHRAGM C/CASE RELIEF VALVE TWINS 1952-56 ONLY

Thanks Shaun

49 to 51 the crankcase pressure relief was bolted onto the crankcase behind the primary chaincase.

https://www.amoc-parts.com//store/comer ... duct=24131
52 to 56 it was within the bolt on the end of the crankshaft that holds the engine sprocket on. The diaphragm is only a part of this assembly.

https://www.amoc-parts.com//store/comer ... duct=21220
clive
if it ain't broke don't fix
shaunstaples
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Re: Oil - again

Post by shaunstaples »

Thanks Clive,
So it breathes through the crankshaft, does the diaphragm fit inside that and act like a one way valve? Looks a small hole for each 250cc piston displacement?
Also is the chaincase vented to make room for crankcase to breath?

When I ran it, I could see oil escaping through rocker cover whilst I revved it up, just gave me the impression breather blocked. So asked Santa to get me a manual for Xmas ( I even gave the link to the wife) 1950 Model 20 Maintenance Manual with no mention of a breather!

Had a day in garage today and found manifold gasket blown(was spitting back through carb when I ran it), studs in manifold for carb stripped and front left-hand rocker cover that was leaking has a dodgy bolt that's been shortened and doing nothing so might get to ride it round the block soon, to see if it needs anything else.
Carb is tight against frame, no wonder they are stripped, 5/16 bsf straight into alloy. Need to fit some sort of air filter!

Hunt for a 12v battery tomorrow to fit in rubber box, and some 1/2 copper tube for oil feed pipe that's loose in banjo and nearly rubbed through from kickstart.
Cheers Shaun
Trefor
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Re: Oil - again

Post by Trefor »

I've been following this thread as I attempted to cure a crankcase-dynamo leak on my G9 ('Crankcase relief shape G9' thread). It occurred to me that pressure build up in the motor could be due to oil build up in the crankcase through dry 'sumping'. The bike had been standing for about 10 days and well over a litre of oil drained out of the sump. I haven't seen inside the engine (I hope I won't for some time) but I'm guessing the crank and its breather hole could be submerged in oil. The previous owner had fitted a tap in the oil line which I removed, in case I forgot to turn it on. I now thinking I should reinstall it.
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Taid
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Re: Oil - again

Post by Taid »

Fit a tap with a built in switch to disable the ignition .. various types available on the net ..
___

Now sold ... 1956 AJS 16MS Bitsa .. HSU 414 .. rebuilt/re-registered 1987
Trefor
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Re: Oil - again

Post by Trefor »

Thanks for the suggestion Taid, unfortunately a '53 model with a magneto. It will have to be a piece of day glo string on the twist grip.
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