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M20 / 21 oil burning

I have a 1947 M20 but with an M21 engine fitted which I guess is more important... when I start it up it burns oil like nothing I've ever seen, oil even comes out of the head / downpipe joint and additionally burns on the pipe too, the garage is full of smoke in seconds and it's billowing out of the door in no time. After 5 minutes or so it clears and all is well.
The oil level in the tank is about halfway which makes me think it's not wet sumping? as surely I would have lost more oil, given the fact it burns so much on start up as well.
Any clues from anyone please?

email (option): chrisfurnival@hotmail.com

Re: M20 / 21 oil burning

That is classic wet sumping.

email (option): bsansw1@tpg.com.au

Re: M20 / 21 oil burning

What Trevor said.

Also it doesn’t take much oil in the combustion chamber to cause a whole lotta smoke.
And just a few splashes feels like a lot more when their in the wrong place. At least to me, psychological thing kinda.

/simon

email (option): SimonofSweden

Re: M20 / 21 oil burning

Thanks Trevor and thanks Simon, guess I need a new 1/4" ball bearing in the relief valve as a start point then... see how it goes from there, unless you have any other / better ideas??
Chris

email (option): chrisfurnival@hotmail.com

Re: M20 / 21 oil burning

Hi Chris

Whilst it is a good idea to sort out the pressure release valve, your wet sumping is probably caused by oil in the tank seeping past the gears in the oil pump and into the bottom of the crank cases. Many BSAs with gear driven pumps wet sump.

If you used the bike daily, wet sumping would not be noticeable. However, for most of us, these bikes are not ridden regularly and so our bikes wet sump.

Personally, I would deal with this in one of two ways. Either, run the bike more often or remove the sump plug if you are not going to ride the bike for some time and collect the oil in a drip tray.

The downside of the latter approach is that eventually you will srtip the thread where the sump plug screws in (you could always tap the sump plug and screw in plug within a plug).

Another alternative is to fit an anti-wet sumping valve to the oil feed pipe. Personally, I wouldn't do this as I am a d&ck and would forget to open the valve before riding off.

Regards

Pat

email (option): sacombsashtrees@hotmail.com

Re: M20 / 21 oil burning

Thanks Pat, I'd also be worried about forgetting to put the sump plug back in !!
What do you think of the below item on eBay? Number 392077308709

https://www.ebay.co.uk/itm/BSA-M20-21-C11G-C12-ANTI-WET-SUMPING-VALVE-STAINLESS-MADE-IN-ENGLAND/392077308709?hash=item5b49a0f325%3Ag%3ALN4AAOSw8GhZgb65&_sacat=0&_nkw=sumping&_from=R40&rt=nc&_trksid=p2060353.m570.l1313.TR12.TRC2.A0.H0.Xsumping.TRS0

Allegedly works automatically...

Of course heading out to the garage and firing up once a week could be the best option I guess.
Chris

email (option): chrisfurnival@hotmail.com

Re: M20 / 21 oil burning

Followed the info on posting a photo, well I think I did anyway, hopefully it will work;

BSA02

email (option): chrisfurnival@hotmail.com

Re: M20 / 21 oil burning

I was very pleased to see this thread yesterday. A week ago my bike had identical symptoms to Chrisf's. Suspecting wet sumping I drained the crankcase of a small amount of oil which I didn't think would be enough to cause problems & therefore suspected rings, putting this up on another post. Inspired by this thread I tried again & all seems to be well. So presumably there was enough oil in the cases to cause the problem. I wasn't able to measure the quantity but it was enough to cover the bottom of the 5 litre oil container I use for drainage by 5mm or so.

Re: M20 / 21 oil burning

Hi Chris

I have never fitted any kind of valve to the oil pipe. I have always worried that in some way it might reduce flow to the pump.

Hopefully others have experience of using such a valve.

Regards

Pat

email (option): sacombsashtrees@hotmail.com

Re: M20 / 21 oil burning

I have always liked the magnetic sump plug idea.
Pull it out the sit it on the fuel tank.
Thus right after you have started the bike you will see it vanish off the fuel tank and never be able to find it.
A old club member used a magnetic parts dish on his A65 which he dropped the drain bolt from a Devimead deep finned sump exension.
Parts dish was magnetic so it sat on the tank in the shed regardless of weather the bike was on the center or side stands.

email (option): bsansw1@tpg.com.au

Re: M20 / 21 oil burning

I think I'll give it a try, wish me luck !!

email (option): chrisfurnival@hotmail.com

Re: M20 / 21 oil burning

Just change the oil to Morris monograde 50. Works on my 16h and M21, both of which used to sump with multigrade and don't anymore. Switch to 40 if you use in winter

email (option): jeremy@clogmaker.co.uk

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