If the smoke is bluish it is indeed oil, that in my opinion has reached the sump.
Not something that should keep sleep out of your eyes, AFAIK - every M BSA is doing it. This smoking should stop after a few seconds or minutes, though.

If the smoke is black it is probably an incorrect calibration of the fuel combustion.

When I overhauled my M20, I bought new the 2 non-return valves. One sits inside the oil pump and the other sits in the timing case: there in the case you have to put the ball inside, knock on it one strong blow (not too violent, yes?) With a brass rod and only then insert the spring and close it.
This helps the ball to take its seat correctly on its place.

email (option): michasteinmann@gmail.com

If the oil pump is working properly, it should not wet sump at all whilst the engine is running. The scavenge side of the pump moves more oil than the feed side. Wet sumping usually occurs when the bike is left standing for any length of time. Ron

email (option): ronpier@talk21.com

In countries where it does not get hot in the summer, wet sumping is not as big of a problem. Where I live on a 100 degree day it can be over 120 degrees in the garage where my bikes sit. Even with a new Hepolite cast iron oil pump and the ball check valve working correctly, it can empty most of the oil from the tank in to the motor in a couple weeks.

In the winter at freezing temps, it does not sump at all.

I put a shut off valve on the oil feed line and a label on the speedometer to remind me to turn the valve on!

Thank you Ron,

Yes, this is my concern exactly. Something is a off here, the scavenge side should move all the oil that is feed to the sump if the pump is working correctly.

Best regards,

Simon

(Michael and Bruce: While I appreciate you taking the time to answer, if you read my post thoroughly you will find a description of my problem and see that it is not that the bike wet sumps while sitting but rather while running at idle.)

Simon,

You say that new rings were fitted. They can take some miles before they seat and the oil burning stops. Especially if using old style rings as BSA used back then. With modern three piece oil control rings the problem is not as bad but can still burn oil for a few miles depending upon the cylinder condition and how quickly they wear in.

My M21 burns no oil when running but if it has sat for weeks in the summer and started, it makes enough smoke to make it look like my house is on fire. After 30 seconds the smoke stops.

How long did the bike sit before the new rings were fitted and the bike started? Also, did you have this problem before the new rings?

OK,

Only Ron understood my question not other people who have answered, I obviously was not clear enough when describing the problem. I'll have another go:

1. The bike ONLY wet sumps when running at idle for 10 minutes

2. The bike does NOT wet sump while parked.

3. The bike did not smoke when I started it, it came after 10 minutes of idleing.

4. The problem is not in anyway related to the piston rings.

5. It is the oilpump that is not returning as much oil as it is filling the engine with, AT IDLE.

6. The problem goes away when revving the engine.

7. I interpret this as a sign of the oil pump beginning to lose its oumph.


MY QUESTION: Do you agree with me regarding number 7 and does anyone have a similar experience with an oil pump?

My next question is of course what can I do to fix it? Apart from buying a new pump. I'm thinking perhaps milling some parts of the oil pump housing down in order to make the gears a tighter fit? Was such a long time since I put it together I only have vague memories of how it looked... :wink:


Best regards,

Simon

Hello Simon,

I don't know if this will help, but it's based on my experiences with 1930s bikes.

I am assuming you ran the bike at idle while on its rear stand.

If so, then it may be possible for the oil to 'pool' in a pocket somewhere in the bottom of the crankcase - the engine is not perfectly level when the bike is on its stand, and this can happen. If so, you will get excess oil that the oil scavenger pump cannot reach, and it will cause the engine to smoke. I puzzled over this with a Matchless that would do the same thing when idling on its side stand, and it nearly drove me to sell it on. Once I put the bike level I had no such troubles.

I'd suggest trying the ten minute idle with the bike held level on its tires, and see if that makes a difference. It won't cost you anything, and it might help.

Best wishes, and Good Luck!

Allan

email (option): allanmatchless@yahoo.com

Thank you Allen, that is very useful information!

The bike was in fact not quite leveled, it was on a side stand and also slightly uphill.

I will look into this further before doing anything else such as removing the oil pump for service.

It does seem odd to me that the “pump ratio” on the in vs the out side of the pump changes with revs.

Best regards,

Simon

['It does seem odd to me that the “pump ratio” on the in vs the out side of the pump changes with revs...']..

I'm not quite sure what you mean there Simon...The feed gears have a smaller pumping capacity relative to the return gears as the system is a 'dry sump' system...This ensures the crankcase is scavenged (dry) when the engine is running and is the reason on initial start up that a constant flow will soon turn into an intermittent one once any residual oil is cleared from the crank case....

The capacity of both sides of the pump increases or decreases in proportion to rising and/or falling engine revs but not independently of each other...Ian

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

I think Allans theory is the best fit for that...Ian

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

If you think the scavenge pump is the problem.

Idle the bike until it starts smoking out the exhaust. Shut the engine off and remove the drain plug and see how much oil actually comes out.

Do the same test with increased RPM's until it does not smoke and drain it again. The oil quantities should be identical.

Hello Simon,

Did you ever resolve the problem?

Best wishes,

Allan

email (option): allanmatchless@yahoo.com

this happened to me on a unit Triumph. had me stumped. after a rebore, new pistons and rings, new valves and guides it still kept wet sumping while I was riding. Eventually I pulled the oil pump and found a tiny piece of hard crap that was caught in the scavange side ball bearing. A five minute fix which took me several months and quite a lot of money.

email (option): cas.vanderwoude@gmail.com