G80 Engine oil leaking INTO chaincase

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Prospector1
Posts: 1
Joined: Sun May 31, 2020 4:52 am
Location: Leicestershire UK

G80 Engine oil leaking INTO chaincase

Post by Prospector1 »

I have a 1953 G80 I am trying to bring back to life. While I've owned a fair number of British bikes this is my first Matchless and I am still getting familiar with all its bits. After much fiddling I got it fired up today but have run into a snag. Engine oil is seeping, more like running, into the chaincase via the the crank. I had the outer cover off the chaincase when I started kicking it over and noticed the oil seep then. I thought maybe it had wet sumped, so I drained the crankcase (yes there was some extra oil in there) and tried again. It fired up surprisingly easily and kept pumping oil into the chaincase. I thought maybe I had a block in the oil return line, but oil is burbling out of the return tube in the oil tank.

At some point in its life someone set the bike up as a dirt bike. It looks like it was rode hard and put away wet way too many times. There are several anomalies I should point out about this thing. Perhaps most important is that it has some funky fiberglass primary chaincase rather than the stock metal one. It does not have a dyno. I think it may have the wrong clutch basket on it as I had to put in a thinner spacer at the back to get the correct number of clutch plates in it. Essentially the thing seems to have been cobbled together. I've purchased or downloaded several manuals, but I have not found a good exploded view of this part of the bike to verify I have all the parts that should be in there.

I feel I maybe the only person on the planet trying to keep oil out of the chaincase of a British bike rather than in it. Any advice would be welcome.
SPRIDDLER
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Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: G80. Engine oil leaking INTO chaincase

Post by SPRIDDLER »

Welcome to the Forums, Robert.
You're certainly not the first person to post this problem. It's fairly common. In fact there was an identical question yesterday ;) : http://www.jampot.com/forum/viewtopic.php?f=18&t=26377

Firstly a couple of questions:
1. Is this the first time in your possession that you have run the engine?
2. Have you had the engine apart?
3. Is oil returning to the tank? It will be a slow flow on first start up until the residue in the case has been cleared. It will then return steadily in pulses with the occasional 'bubble'at tickover or slightly faster.
4. Are the oil flow and return pipes connected to the tank the correct way around?
This is the oil flow system..
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Excess crankcase pressure may be the cause. Perhaps through piston blow-by (worn/stuck rings or worn bore) or by a blocked/stuck crankcase breather which is behind the chaincase at the main bearing boss..
Image

There are several other possibilities e.g. the return gallery inside the crankcase may be blocked preventing scavenging (your answer to Qu. 2. and 3. above will help clarify) or there is an air leak at the oil pump end plate.

Are you aware of the resource linked below which has manuals, cutaway drawings and much more?
Workshop and Owners manuals under 'Books'.
Gearbox drawings and exploded dia's and info under 'Technical' - 'Transmission' - 'Burman'.
http://archives.jampot.dk/

I recommend that you join the club to have full access to this site (maintained by members' subs) and the techy info. In addition you will be able to see pictures posted in replies. (I have uploaded the above pics to a separate host site and then inserted them in my reply so that you can see them but it is a bit laborious and the c/case breather pic is rather small).
Your time as a Guest on the Forums is limited. I'm not sure whether as a Guest you can access the Forums 'Search' facility (the spyglass below) to find similar questions and the solutions.

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Enjoy!

EDIT: :oops: just noticed that you say you do have oil returning to the tank so my Q's 3 & 4 are perhaps irrelevant.
'There is a tide in the affairs of men
Which taken at the flood............'
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