The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Tom23 on 13.03. 2010 13:50

Title: oil coming out of crankcase breather
Post by: Tom23 on 13.03. 2010 13:50
Hi,
I have just got my 1960 A10R going after an engine rebuild. It is throwing a fair amount of oil out of the breather hole in the crankcases. It started doing this really badly when I changed the oil pump before the engine rebuild. In fact this was one of the reasons for the rebuild , apart from the fact everything was worn out.
I had the crank ground and new main roller and plain bearings, a new cam, and big end shells. The bottom end was machined ant put together by a specialist. sludge trap was also done and the cases were hot washed.
I put the rest of the engine back together and now starts and runs lovelly apart from the oil that is liberally dripping down the back of the engine! Its okay at tick-over but starts after a run.
I tried the old oil pump and it it is just the same. Also I replaced the oil pressure release valve with a SRM one, no difference.
Any help would be gratefully recieved!
 *conf*

Title: Re: oil coming out of crankcase breather
Post by: coater87 on 13.03. 2010 18:37
 Hi Tom,

 I think we need a little more information. Its fine at idle, you take the bike for a ride (does oil leak out during the ride?) then, you get back, shut the bike off and it leaks badly?

 Is this exactly how it happens, or did I read the post wrong?

 Lee
Title: Re: oil coming out of crankcase breather
Post by: Tom23 on 13.03. 2010 18:56
Hi Lee
When the bike has been standing and I start it up it seems fine. It only starts dripping oil after a short run, every time I stop it is dripping quite alot. When I stop the bike whats already running down the engine drips off and then stops.
I think it must be related to the engine running faster than idle, so increased oil pressure. I have been taking it really easy as I'm running it in.
Thanks for replying,
Tom
Title: Re: oil coming out of crankcase breather
Post by: Brian on 13.03. 2010 21:29
This is actually quite normal after a rebuild. It depends on how quickly the rings bed in as to how much oil will escape.

It can take up to a 1,000 miles before the engine "beds in" and stops pushing oil out the breather.

If you have a pipe in the breather hole then you can put a tube on that and run it into a small bottle until it settles down, I did this with my 61' A10. If not then you just have to put up with it until it comes good.

They do seem to vary a lot after a rebuild. My 61' was the worst of my A's. It was pushing out about 20ml per 100k's for the first 3 or 4 hundred miles but by 1,000 miles it had reduced to almost nothing.

Yours was pushing oil out the breather before the rebuild, thats normal for a worn out motor and pushing oil out a rebuilt motor is normal for a few hundred miles.

Try and get some miles on the bike and hopefully it will stop.

Title: Re: oil coming out of crankcase breather
Post by: BSA_54A10 on 14.03. 2010 02:51
Ditto on Brian's post.
The other thing to check is that the oil is flowing freely back into the oil tank.
It is not uncommon for a bug to crawl into the tube and die in there creating a partial blockage that gets worse as increased flow pushes it harder up the tube.
It was also common for the return line to be obstructed to increase the oil flow to the head and more than one owner went a bit too far with this so the oil ends up filling the cases
Title: Re: oil coming out of crankcase breather
Post by: Tom23 on 14.03. 2010 07:47
Hi
I have only done about 50 miles so far, so I will try to get some miles in today.
Thanks Tom
Title: Re: oil coming out of crankcase breather
Post by: wilko on 14.03. 2010 23:33
Take your sump plate off and prod the ball in the pickup tube to make sure it's not stuck closed. This is a fairly common problem.Spray some petrol up the tube and wiggle the ball so it's free to fall.
Title: Re: oil coming out of crankcase breather
Post by: A10Boy on 18.03. 2010 20:58
On your rebuild, did you put the correct thickness cork washer on the breather/camshaft interface? if this is loose it will blow oil from the breather.

The cork has to be slightly compressed between the cam wheel and the gadget with the hole which fits over a dowel on the cam wheel. If it isn't, it will be like the Torre canyon
Title: Re: oil coming out of crankcase breather
Post by: anjimehra on 19.03. 2010 05:59
I think A10boy is right. Check the thickness of cork washer behind the breather.There should be no end play in the breather after assembling the inner timing cover
Anji
Title: Re: oil coming out of crankcase breather
Post by: Tom23 on 19.03. 2010 15:29
Hi
Yeah I did replace the cork washer, and I have just been out in the garage retiming it to 5/16 btdc to try get rid of the pinking, and I checked there was no play. I can push the breather in with a pair of pliers about half a mill, which I presume is just compressing the cork. There is no free play.
The oil coming out of the breather does seem to be getting less the more miles I do, although I've only done less than 100 miles and its forecast rain all weekend here in Bristol, so probably no chance to get out this weekend!
Title: Re: oil coming out of crankcase breather
Post by: A10Boy on 19.03. 2010 19:11
Tom

That don't sound right to me. When you fit the inner cover it should slightly compress the cork against the cam wheel, I don't think you should be able to then squeeze it more by pushing it with pliers.

Have you still got the old one to compare with a new one? if you fitted a new one which was the same thickness as the old one in its used condition, then it will be slack.
Title: Re: oil coming out of crankcase breather
Post by: Tom23 on 20.03. 2010 08:06
Hi Andy
Unfortunately I don't have the old one.
There is no free play in it in and out, and I have to push pretty hard with the pliers to get it to go in that half a mill, and on release it comes back.
There is some play if you turn it though.
I don't what's acceptable in this department, so any advice is gratefully accepted.
Thanks
Tom
Title: Re: oil coming out of crankcase breather
Post by: chaterlea25 on 21.03. 2010 00:00
Hi Tom,
Its normal to have some play on the drive peg,
however if you can turn the breather sleeve with your fingers it's TOO LOOSE!!!
If you read the service sheets or the manual it gives directions on how much preload is to be applied to the breather cork to make it "work"
I have never (touch wood) had a problem with oil coming out the breather on rebuilt engines!!
HTH
John O R
Title: Re: oil coming out of crankcase breather
Post by: Tom23 on 21.03. 2010 07:49
Hi John
I better get another cork washer then.
I'll let you the results.
Thanks Tom
Title: Re: oil coming out of crankcase breather
Post by: Tom23 on 07.04. 2010 17:02
I've fitted a britie anti-wetsumping valve (britie.motorcycles@virgin.net) and shimmed out the breather so that the holes line up, and also fitted a larger cork washer. The bike has stopped throwing oil out of the breather now, which is great.
Thanks to everyone who helped.
Lyford classics were also very helpful.
Tom
Title: Re: oil coming out of crankcase breather
Post by: Ted_Flash on 01.06. 2012 15:23
I'm resurrecting this thread as I've just found the cause of my A10 throwing oil out of the crankcase breather in quantities enough to slather all over the back tyre dangerously.  Any comments on the likely root cause or on my proposed fix would be welcome.

The engine doesn't smoke especially badly and a borrowed compression tester showed both cylinders the same and OK.  I checked the breather top hat/cork and all fine.  However when the barrels were taken off, I found I could get a 2 thou feeler gauge into the joint between the two crankcase halves where the breather gallery crosses into the left crankcase-half.  The nut in the crankcase mouth was not 100% tight, though not loose by any means.  I loosened it off completely and the feeler would go right into the joint.  Conclusion - oil is being blown into the joint, thence into the breather gallery and out via chain onto the tyre.

I know I should split the crankcases and do a proper engineering fix with an 'o' ring....however I intend: washing out the joint with thinners, get as much sealant as I can into the joint (using some low viscosity Samsonal sealant), tighten up the crankcase mouth nut very tight (with flat washer and loctite on threads), clean excess sealant off.

Any downsides I've not thought of?


Title: Re: oil coming out of crankcase breather
Post by: BSA_54A10 on 02.06. 2012 01:01
When this "suddenly" starts to happen then there is a 99% chance of the sump return tube being blocked.
Next culprit is the cork washer on the breather going hard or breaking up.
Solutions are in the previous posts
Title: Re: oil coming out of crankcase breather
Post by: DazSeaton on 29.05. 2013 21:59
I eventually found the cause of my severe breather oil leak. When stripping the timing covers off i noticed the inner timing cover gasket had not seated properly and was obstructing the oilway on the inner timing cover to the breather and cork gasket. Thus when the engine got warm the breather would get hot and leak oil. Either that or the previous cork gasket I had recently fitted was a duff one. Just something else to check if your having problems.