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M20 Chaincase Oil Leak - Help! #22258
03/07/07 9:10 pm
03/07/07 9:10 pm
Joined: Mar 2007
Posts: 17
Adelaide South Australia
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Sunsett Offline OP
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Adelaide South Australia
Hi,

My M20 has developed a dribble of oil from underneath the chain case when the motor runs but only when the motor runs.

Has anyone had this trouble before?

Is it simply another gasket?

Thanks.

Andrew
Adelaide
South Australia


1926 4.93Hp Model S26
1940's M20 Bitsa
1954 D3 Bantam Major
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Re: M20 Chaincase Oil Leak - Help! #22259
03/08/07 3:53 am
03/08/07 3:53 am
Joined: Feb 2006
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Qld, Aust and Otago,NZ
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Ginge Offline
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Qld, Aust and Otago,NZ
Hello Adelaide!!!

Oil leaks from pressed steel primaries is no revelation. The link between the motor running and the oil leaking could be;

Vibration

Thinner oil when heated

Expansion of the case when hot.

Ride the bike, keep checking oil, park on the grass in the meantime. Next time you need to check primary chain tension, change the gasket for a new one. No point in taking the bike off the road in my view.

A winter job.


Ginge
Re: M20 Chaincase Oil Leak - Help! #22260
03/08/07 4:02 am
03/08/07 4:02 am
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Adelaide South Australia
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Sunsett Offline OP
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Thanks Ginge,

I have owned this bike for 15 yrs and I am aware that she will never hold oil.

But when I say a dribble it is a constant stream. I changed the oil in the case and it went from the used oil look to the newer oil look and did slow up some but I guess due to the viscosity.

More info I should have posted. There is no oil coming from the engine breather so I discount that. I had work done to the clutch a little while ago and havent ridden her mutch since then.

Is there any engine seals I should worry about? I have had a good look through the maintenance manual and there is little info about this problem except make sure there is oil in the oil bath.....

Cheers again.


1926 4.93Hp Model S26
1940's M20 Bitsa
1954 D3 Bantam Major
Re: M20 Chaincase Oil Leak - Help! #22261
03/08/07 11:33 am
03/08/07 11:33 am
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Sydney Australia
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If you find an engine seal, then start to worry.
The only oil seal in the motor is the one behind the magneto pinion.
My first thought is to check that the breather is actually working.
The one way valves are notorous for sticking when they have not been used for a long while. This would allow the crankcase pressure to vent itself into the primay, forcing the oil out.
On mine the gearbox main is just about gone and that allows lots of gearbox oil into the primary.
Whip the primary cover off and run the bike for a while & look. It could be somthing way off left field like one of the chaincase mounting bolts coming loose or even a leak from behind the foot peg spacer.


Bike Beesa
Trevor
Re: M20 Chaincase Oil Leak - Help! #22262
03/08/07 10:38 pm
03/08/07 10:38 pm
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Qld, Aust and Otago,NZ
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Ginge Offline
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Breather - great thought, and probably the best answer.

A constant stream is a bit of a worry though. A constant dribble stream, or a constatnt pumping stream - does it vary obviously with revs?

mmmmm.

I'd love an M20 - an early military one in bits please.


Ginge
Re: M20 Chaincase Oil Leak - Help! #22263
03/09/07 6:28 am
03/09/07 6:28 am
Joined: Mar 2007
Posts: 17
Adelaide South Australia
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Sunsett Offline OP
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UPDATE!

Sorry to sound stoopid. But the breather does leak about the same amount of oil out of the breather. (It didnt the other day).

But today it does.

Can u explain to me what the purpose of the breather is. Which way is it venting into or out from the motor. (I hear old people laughing). Anyway I took the breather off and from both sides of the breather it will let me blow in the direction of 'out from' the motor. And without having to blow hard. So what sort of pressure is required.

If it is blowing in the right direction how do I clean it, or do I need a new one. I put the air hose down there with minimal pressure so as not to damage anything but it still worked the same.

email: tralee@internode.on.net

Andrew


1926 4.93Hp Model S26
1940's M20 Bitsa
1954 D3 Bantam Major
Re: M20 Chaincase Oil Leak - Help! #22264
03/09/07 10:26 am
03/09/07 10:26 am
Joined: May 2004
Posts: 3,740
Sydney Australia
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There are no oil seals in an M20 motor.
Oil tighnness ( ? ) relies on close fitting parts and either discs to "fling" the oil away or a reverse spiral sut into a shaft to push the oil backwards and yes they do actually work, but not for long.

Now when the piston oges down into the bottom of the clyinder it compresses the gasses in the crankcases which will find any hole to escape, taking a lot of oil with them.
The breather's job is to takes this air from a place where there is not much oil and vent it to atmosphere then when the piston goes down then it closes off to create a low pressure area inside your crankcases when the piston goes up.
This will cause the outside air to rush inside the cases thus preventing oil leaks.
So your pipe should allow air to go out but not in.
Pull it appart and you will find a little disc in there and then the way it works will be apparent.
If there is no little disc in there then you need to replace it.
It is common to all M & B series preunit singles so they are fairly easy to come by


Bike Beesa
Trevor
Re: M20 Chaincase Oil Leak - Help! #22265
03/09/07 12:53 pm
03/09/07 12:53 pm
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Adelaide South Australia
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Sunsett Offline OP
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Thanks Guys,

The breather appears to be working fine, especially when oil is coming out. I emptied the crankcase of oil again and a fair bit came out. I havent run it much, just all the fiddling in the last couple of days.

I wanted to test the ball valve from the oil pump pick up (should have done that the other day).

When re started the oil almost immediately started coming out the breather again.

Then I wanted to check on the oil pressure valve on the timing cover side. Alas no spring, so I am thinking that oil may be going into the crank at rest.....

The other test I am about to attempt is to see whether the oil return is working to see whether the oil pump is working.

Its been a learning curve I will keep you posted.

Thanks again the help has been fabulous.

Andrew


1926 4.93Hp Model S26
1940's M20 Bitsa
1954 D3 Bantam Major
Re: M20 Chaincase Oil Leak - Help! #22266
03/09/07 1:30 pm
03/09/07 1:30 pm
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Adelaide South Australia
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Sunsett Offline OP
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OK the oil pump is working.

So to recap, Have I missed anything????

My problem is, I have oil coming from the breather onto the primary chain at about a decent drip per second. Subsequently dribbles out of the chain case.

I have read about breathers which can be pulled apart. This breather appears to be one piece. I am wondering whether it is original.

All filters and oil have been cleaned and replaced.

The check valve in the oil pick up just below the return oil pump (which is working) is ok.

The check valve accessed through the timing cover is missing a spring but the ball appears to be seated at rest due to the lean of the bike at rest (side peg).

Any further suggestions or places to check. Any reason why the oil is still coming out of the breather???? Could it be worn rings making the pressure inside the crankcase so high it picks up oil???

Cheers


1926 4.93Hp Model S26
1940's M20 Bitsa
1954 D3 Bantam Major
Re: M20 Chaincase Oil Leak - Help! #22267
03/09/07 1:51 pm
03/09/07 1:51 pm
Joined: Oct 2004
Posts: 4,429
Melbourne Australia
Tiger Offline
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I wonder if the missing spring could have anything to do with the problem ?
Maybe BSA only put it in there because someone's brother in law bought a shipload as a job lot ?

Sarcasm is the lowest form of wit but I am three parts pissed and scratching my head over why has the timing cover check valve spring not been replaced ?


1969 TR6R
7.62 x 51 is not a maths puzzle.
Re: M20 Chaincase Oil Leak - Help! #22268
03/10/07 5:06 pm
03/10/07 5:06 pm
Joined: Feb 2007
Posts: 91
Pacifica, California
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Rick yb34 Offline
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Hi, The breather is about 3/4" long with a hex on each end. You can unscrew it, then look at the part with the tube on it. You can see what looks like a disc with a hole in the middle and slot cut across for a big screwdriver. Unscrew this, and you will find a phenolic disc. Clean the parts, and reassemble, making sure the little disc is free in the bore.
You may want to: Do a leak down test (excessive blowby). Make sure your oil return hose isn't kinked. Is it wet sumping? Does the leak slow down after running a little while?
Hope this info. helps.
Regards, Rick

Re: M20 Chaincase Oil Leak - Help! #22269
03/10/07 5:48 pm
03/10/07 5:48 pm
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Pacifica, California
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Rick yb34 Offline
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Another point, Although the check ball and spring are missing in the cover (and shouldn't be). The oil leak is new, and the spring has been missing for some time? I may be wrong, but the return pump is designed to pump more volume than the feed side, so even if the pressure relief spring is missing, the crankcase shouldn't be filling up with oil. Maybe the oil pump gasket leaks and both sides of the pump are leaking? Sorry to complicate the issue, but if the spring has always been missing, then you should have always had this leak.
Regards, Rick

Re: M20 Chaincase Oil Leak - Help! #22270
03/10/07 6:15 pm
03/10/07 6:15 pm
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Adelaide South Australia
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Sunsett Offline OP
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Thanks Rick, I read in the manual that under no circumstances unless urgent to fiddle with the oil pump. But maybe I will have to face it.

I have managed to work out how the breather comes apart and yes it does work but will let a little air back in the other way. I took off the return oil pipe and I can blow through it with ease and I ran the motor and oil came out, so I assume all is ok.

But, I believe it is wet sumping, but how much oil should come out when I undo the sump plug. I just tried it and the motor has only run for minutes while testing and I guess about 300 ml came out. My next test is not to run the motor for 24 hrs and just see how much comes out next time.

But I would appreciate knowing how much oil should stay in the sump, sounds like just enough to get to the return.


1926 4.93Hp Model S26
1940's M20 Bitsa
1954 D3 Bantam Major
Re: M20 Chaincase Oil Leak - Help! #22271
03/10/07 7:37 pm
03/10/07 7:37 pm
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Pacifica, California
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Hi, Check oil volume on the return line to the tank to make sure the pump is scavenging properly first. If it is, the leak SHOULD diminish after running a while. Pull the drain plug right after you shut it down and note how much oil you collect. Should be only a few oz. If it's a lot more, than your issue may be the pump. If you leave the drain plug out overnight and you get a lot more oil, the the check valve leaks. The breather cannot compensate for excessive blowby, and if your rings are shot or stuck, it can't perform it's function.(Venting gasses, and maintaining a neg. crankcase pressure). Hope this helps, Rick

Re: M20 Chaincase Oil Leak - Help! #22272
03/11/07 12:25 am
03/11/07 12:25 am
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Adelaide South Australia
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Sunsett Offline OP
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Thanks Rick,

It has put me on track. I did a search on this thread about wet sumping and learnt a whole lot more.

Do you know the size of the spring that I am missing? Or where to get one. Also is there a kit for the oil pump.


1926 4.93Hp Model S26
1940's M20 Bitsa
1954 D3 Bantam Major
Re: M20 Chaincase Oil Leak - Help! #22273
03/11/07 6:01 am
03/11/07 6:01 am
Joined: Feb 2007
Posts: 91
Pacifica, California
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Rick yb34 Offline
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Pacifica, California
Hi, the spring is a little smaller than a ballpoint pen spring, with less tension. You should be able to get it at most BSA parts suppliers. BSA pt# 66-1684. No, I don't know of any oil pump kit, but I have "reconditioned" them before.
Regards, Rick

Re: M20 Chaincase Oil Leak - Help! #22274
03/11/07 6:56 am
03/11/07 6:56 am
Joined: Aug 2001
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California
Ron - in California R.I.P. Offline
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Woa...! This is basic BSA stuff. Without a properly working check valve, then the engine will wet sump, period..! Also do NOT follow the manual's directions to seat that check ball with a hammer blow.! That is not a good idea. Clean out the passage way, replace the check ball with that spring as it is cheap.


Next on the oil pump, they should never wear out..! BUT, they can come loose..! If the pump comes loose, then you will wet sump big time..!

Now STOP, before you take a wrench to those small oil pump bolts.. the oil pump body can be easily warped.. and over tightening will cause it to bind, then eventually wear out the teeth on the oil pump drive. My best suggestion is to replace the stock bolts with allen heads,that are drilled for safety wire. These bolts only need to be snug, not tight..! Then safety wire them so they can not come loose.

Lastly, do NOT over fill the primary..! It only needs enough oil to lube the chain.. so just the lowest part of the chain barely touching the oil, is all that is needed. Being as there is no engine seal on the crank left side, you may always get a little bit of oil coming out there. Next time you split the cases, you can put in a sealed bearing (remove the inner seal). This helps, but not 100%.

Cheers..!

Ron beerchug

Re: M20 Chaincase Oil Leak - Help! #22275
03/11/07 5:43 pm
03/11/07 5:43 pm
Joined: Jul 2001
Posts: 12,830
Central Virginia
Lannis Online content

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Ron is right about the M20/21 primary. You need to check it every once in a while or it will fill up with oil splashing from the engine through the unsealed bearing.

Every 1000 miles or so, I take out the primary oil level plug (NOT the drain plug, the level plug) and drain about 1/4 pint of oil out of it, till it's down to the right level again. I've never had to add oil to the primary!

If you don't, the oil level will keep going up and your clutch might start to slip, even though it has its own gasket sealing the clutch off from the primary oil.

Lannis


I stopped believing for a little while this morning. Journey is really going to be upset.
Re: M20 Chaincase Oil Leak - Help! #22276
03/11/07 5:47 pm
03/11/07 5:47 pm
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Pacifica, California
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Rick yb34 Offline
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Hi Ron, I had an XB34, that I found was missing the check ball and spring, and It didn't wet sump. Why? Your input would be appreciated. I have a few pumps that are warped from being overtightened, and have succesively repaired some by carefully refacing the ends with fine paper on a piece of glass. As for reseating the checkball, I reseat it using a new ball, which I then throw away. I learned from one mechanic, and haven't had the wealth of info. Ive been learning here.
Regards, Rick

Re: M20 Chaincase Oil Leak - Help! #22277
03/12/07 2:40 am
03/12/07 2:40 am
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Adelaide South Australia
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Sunsett Offline OP
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Thanks guys, I have been trying to remember what she was like to kick start 15 yrs ago when I bought her. I think I might do the rings etc.

Your help has been invaluable. Recently I totally did the top end of a 1960's Marinised Ford Diesel in my boat and I had no problems especially considering I have had no diesel experience. But now I am looking into the engineering of this bike, I am learning a whole new way of doing things.

Will keep you posted, may start a new thread, we have come a long way considering I started with an oil leak in the chain case!!!!


1926 4.93Hp Model S26
1940's M20 Bitsa
1954 D3 Bantam Major
Re: M20 Chaincase Oil Leak - Help! #22278
03/16/07 6:00 am
03/16/07 6:00 am
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Posts: 17
Adelaide South Australia
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Sunsett Offline OP
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Thanks Guys for your input with this thread. I now realise it is bsa mechanics 101 but until the internet I was on my own with limited knowledge. The fact that all I had to do was stick in the fuel and oil and she started first kick every time didnt help.

After 2 yrs off the road, I finally have the old girl back on the road. She runs like she used to only less of an oil slick following me up the road and a little less blue smoke.

I rode her to work and back today about 25 kms all up. I missed those looks from people in the street...........

Now wait for my next stoopid question.


1926 4.93Hp Model S26
1940's M20 Bitsa
1954 D3 Bantam Major
Re: M20 Chaincase Oil Leak - Help! #22279
03/18/07 12:38 am
03/18/07 12:38 am
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Sydney Australia
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Rick,
If the oil pump is in really good condition or you lucked one that was on the closer side of the tollerances then the oil should not be able to get past the the pump.
This is particularly so if you are using heavy ( thick) monograde oil.
A lot of BI have no check valve fitted at all which is why Brie-Tie do a good trade in their in line valve.
After 50+ years both the clearence between the gears and between the gears & side plates gets really big so wet sumping is common.
It appears to me that the oil pumps that BSA used as standard were a bit on the sloppy side to start with so perhaps it was a cost thing the spring & ball being substantially cheaper over 1000's of units than fitting a higher quality pump.
Or perhaps it was a durability issue being that the "sloppy" pump would be more tollerant of bad &/or dirty oil than the close tollerance equivalents.
The B34 being purpose built for racing should have been fitted with a better pump than the standard M 20


Bike Beesa
Trevor
Re: M20 Chaincase Oil Leak - Help! #22280
03/18/07 11:44 am
03/18/07 11:44 am
Joined: Mar 2007
Posts: 17
Adelaide South Australia
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Sunsett Offline OP
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Thanks for that Trevor. Sounds like the BSA motto and the reason we love them.

I felt the oil tank after the rides and the oil was warm so I am encouraged that the oil pump is working.


1926 4.93Hp Model S26
1940's M20 Bitsa
1954 D3 Bantam Major
Re: M20 Chaincase Oil Leak - Help! #22281
03/18/07 12:49 pm
03/18/07 12:49 pm
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Sydney Australia
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With some luck I hope to see you & the offending motorcycle at Goolwa atter this year


Bike Beesa
Trevor
Re: M20 Chaincase Oil Leak - Help! #22282
03/18/07 1:03 pm
03/18/07 1:03 pm
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Posts: 17
Adelaide South Australia
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Sunsett Offline OP
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Well you have me on this one. I go to Goolwa all the time to pursue another interest. But due to shift work etc havent made myself known to a club etc.

Is there something I should know about??? Mind you I always see various motoring clubs tour through there, infact today there was Chryslers of all ages and models there.

I generally look with envy when I see the bikes touring around.

What should I take, the M20 bitsa, S26 or the bantam?


1926 4.93Hp Model S26
1940's M20 Bitsa
1954 D3 Bantam Major
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