Hello folks

I am the recent and very pleased owner of a 1947 M20 that has sat idle for 40 years. I am looking forward to and somewhat daunted at the prospect of renovating this lovely bike. Apparently, it was running up to the point it was stowed all those years ago but had 'some issue' with the oil pressure valves. My plan is to initially just get it going to see how it is before I embark on a renovation exercise on the bits that need the work.

Cosmetically it is not bad at all with superficial rust so that will be easy to sort. My main initial interest is getting the engine going. It looks promising so far. I've got a spark after cleaning points so magneto probably ok and loads of compression. However, petrol tank is very rusty inside and carburettor has not yet cleaned. However, I'm going to pause the excitement to start it as I'm concerned about the history of these oil pressure valves. I don't want to start it to find no oil flows and end up with a big engine job I didn't need.

I have noted the oil tank is essentially empty, which supports the history and the notes you can see in the maintenance manual (pages 3 and 5) that if either of the valves become blocked/faulty, oil can leak back to the sump and empty the tank. I took off the plug on the side of the engine that covers pressure 'relief valve A' in the maintenance manual (page 3). I was expecting a spring and a reluctant ball but was surprised to find neither as far as I can tell. However, I'm not sure what to expect in looking into that orifice? The spring is clearly missing but I can’t tell if the ball is missing, or it is there and stuck in the oil gallery? I took several pictures, but it looks like I cannot load them to this site so can’t share them to see what you think.

So after all that verbiage I have 2 questions.

1. What should I see on removal of spring and ball (assuming both missing) on looking into the orifice with ‘pressure relief valve A’ on p3 of maintenance. manual.
2. Is it safe to run the bike with this valve missing and all the oil in the sump.

email (option): nlhclarke@gmail.com

with the plug removed you can turn the engine over (spark plug out) and oil pressure should eject the spring and ball if they are present.

Drain the sump before attempting to start the engine. Even if you can start it, against the drag of a full sump, it will be messy.

A bit pedantic perhaps but it's an anti drain valve...Ian

email (option): ian@wright52.plus.com

I should say it's an anti drain valve that is operated by oil pressure which is why it's described as a pressure valve...It's not a pressure relief valve..The ball lifts of it's seat at about 7 psi if everything is operating as intended to enable oil feed to the big end etc....Ian

email (option): ian@wright52.plus.com

Many thanks for the replies chaps

Its shame I cant send the photo as I swear it appears there is no ball and certainly no spring! Id say it looks just like the hemispherical cavity that a ball might sit in and also has what looks like witness/wear rings as to where a ball might have chattered in position over the years.

In centre of this cavity looks like a small hole; only a few mm across which might be the start/end of the oilway. I suppose the acid test would be to put the oil back in the tank and if it is an open orifice/oilway with no ball, the oil would just drain out? Do you think that would work?

Also, would you think it a danger to start the engine with such a valve not in place? I don't know where the oil moves in this engine but it seems close to big end/main bearings. Would it risk these parts to run it.

Finally, this valve /spring not so easy to come by. Do you have any suggestions of a good source?

cheers

Neil

email (option): nlhclarke@gmail.com

It is here available:

https://degroot-bsa.nl/nl/product/timing-cover-veertje-en-kogeltje/

email (option): wdmotorcycles@gmail.com

Not an easy hole to photograph.
The Ball should be easy to find, it's just a 1/4" 0.250" ball bearing
Dranganfly say they have the spring 66-1684, but expensive. My supplier is out of stock. So it would be another thousand off order for me.

email (option): pes.sales@btconnect.com

You can get the ball and spring from C & D Autos at a reasonable cost..I bought one only last week....The engine will run without it but if your oil pump is worn, which many are now, the engine will rapidly 'wet sump' if left standing...Ian

email (option): ian@wright52.plus.com

I have been thinking of installing a manual valve on the oil feed line. At least it will not wetsump while running. The risk is you forget to turn the valve to on position before starting the motor and driving off.
I use to fly airplanes and they had boots or covers on important items. They always had red flags. As a pilot you have a check list. The same can be said for an old BSA.

email (option): Cbfatboyhaws@gmail.con

Hello Mark

I'm not normally completely rubbish on the IT front, but how the heck did you upload a picture? Id like to that but after much faffing about i cant seem to find the method?

Cheers
Neil

email (option): nlhclarke@gmail.com

Hello Bastiaan

thanks for the link, I have ordered a couple just in case. Hopefully the Brexit mess doesn't complicate the shipment.

cheers Neil

email (option): nlhclarke@gmail.com

Finally for tonight, many thanks for all the useful comment !
cheers
Neil

email (option): nlhclarke@gmail.com

email (option): wdmotorcycles@gmail.com

Hello All Again

hopefully this maybe the defining post to ask if this looks normal?

I think i have been looking at the wrong orifice mi'lord. I was looking at this in pic below which is different in appearance to that posted by Mark



This is the hole uncovered by the screw underneath the hex nut in pic below but I believe I should be undoing the hex nut itself as in the pic below. Its been a long week :face_with_rolling_eyes:



Incidentally, I dropped the oil tonight; barely 2 pints in the sump but whoops I haven't drained the tank yet so more to come?

Thanks to Bastiaan for the phot upload instructions.

Cheers Neil

email (option): nlhclarke@gmail.com

That screw is the blanking plug for the long deleted oil tell tale. Yes it's the hex plug above that has the ball and spring. Ron

email (option): ronpier@talk21.com

Also, the M20 engine is a 'dry sump' engine so under normal circumstances there should only be a minimal amount of oil in the sump (crank case), with most retained in the oil tank...
The 2 pints you drained from the engine is what has slowly leaked from the oil tank, through the oil pump and past the anti drain valve to the sump while the bike has been standing unused...
That's what people are referring to when they say an engine has 'wet sumped'....Ian

email (option): ian@wright52.plus.com