More wet sumping

[Greenfield]

As far as I understand, wet sumping can be present in two ways. One way is when a bike is parked for a while and the contents of the oil tank drain into the sump as was the case in my A50, but another way is when the return of oil to the tank doesn't keep up with supply during running, resulting in smoke and oil coming out of the exhaust. The more the engine revs the worse it gets. The latter is what I think is happening in my B40. There is little change in the tank oil level and I can see a steady flow of oil when idling, and dropping the sump plate allows perhaps an egg cup of oil to run out. So is there a scavenging issue and therefore a need to renew the pump or am I missing something?

[berniej]

It doesn't sound like a scavenging problem if the level is not dropping in the tank, you're only seeing about an eggcup-full in the sump and a decent return flow - although it should bubble once a steady state is achieved.

I think it sounds more like you're getting oil in the combustion chamber for some other reason - worn valve guides, worn rings, blocked breather....

If in doubt, you could try what I did to test for the same issue on my Ariel.

• Make sure there's plenty of oil in the tank
• Drop the sump plate and leave it off
• Place a container under the sump to catch the oil
• Start the engine and observe

You won't be getting any oil to the top end but should be OK for the time it take to see if you still have the problem. As there will be no oil in the sump any oil/smoke must be getting into the combustion chamber some other way. I'd also expect the problem to clear if it was due to a breathing problem as the big hole in the bottom of the engine will certainly fix that!

So, if it clears I'd suggest blocked breather. If not, guides or rings.

Cheers,
Bernie

[Greenfield]

Hi Bernie
I've fitted new valves and guides and piston rings so I'm expecting a little oil burning until the rings bed in. I blocked the oil feed to the rockers and ran for a minute with no change. I'm pretty sure that the oil must be coming up, possibly by the crank splashing in sump oil and rings not coping with the excess oil. But this is not supported by the small amount of oil in the sump once parked. To be honest I'm baffled.

[JulianS]

Do you see oil in the combustion chamber?

Rings can take some time to bed in in an old bore which may be a bit out of round. Rings do sometimes get broken on reassembly.

[Greenfield]

I took the head off after a test run, which splattered the back tyre with oil, thinking that there may be a leak from an oilway through the head gasket. Everything looked good apart from an oily cylinder and the new exhaust valve blackened with burnt oil. Compression is very good and I'm pretty confident that the rings were replaced intact, but there must be excessive amounts of oil entering the combustion chamber. There's oil feeding the rockers and returning to the tank so if there's any blockage here its not great. That's why my thoughts focused on scavenging by the pump. My B40 is a 1963 distributor model with rectangular sump. To remove the pump, can this be done through the sump or does the inner timing case need to come off?

[JulianS]

If the pump was not scavenging properly you would find a build up of oil in the sump and you would probably find oil leaking from the engine joints and being pumped out of the engine breather by the piston on the downward stroke.

[Greenfield]

Thanks Julian. Yes I'm clutching at straws. I can't safely take the bike out with oil spitting onto the back tyre, but getting some miles on the clock should certainly help to bed things in. The bore wasn't perfect but from my experience shouldn't allow so much oil past that it flows down the exhaust. I'm looking at all possibilities before being forced to rebore.

[chaz]

dont suppose the oil on the back wheel is comming from the final drive shaft? the original sleeve had a groove to return the oil and a felt washer to soak up but the two new sleeves might not have grooves depending where sourced.

[Greenfield]

The oil is definitely coming out of the exhaust via the cylinder. There's so much that it can't burn it all. If it is coming from below the piston, the bore is very oval or there's a build up in the sump at higher revs. Hence I went for the scavenging side of the pump.
At the mo the silencer is propped on end in the corner of the garage draining out the oil. When I kick it up again I need to start with as clean a system as pos to give a reasonably fair test.

[Mike Farmer]

 

I trust that I am not seeming to be "smart donkey" here but I didn't notice that you said what colour the smoke is.

What colour is the smoke?. Oil smoke is blue and fuel smoke is black and unburned fuel can leave a runny black deposit.

Apologies if you have already been down this line of thought.

Mike

[Greenfield]

Thanks Mike
It'll a nice smelly grey/blue colour. The cars following me are very keen to overtake. Definitely too much oil in the wrong place. The scraper ring is clearly struggling. The gap looked perfect when fitted.
When oil leaves the rockers and drains down through the cylinder wall, and has done its job at the big and little end, what happens next?

[berniej]

Oil enters the sump after:

exiting the big-end bearing
draining down from the top end
passing the pressure-relief valve (at high revs or if you forget to fit the spring  0

If there was a restriction in the return flow between the pump and the 'T' at the tank there would be excessive pressure in the return line - do you have an external oil filter fitted that might be blocked?

If there was a restriction in the short section between the 'T' and the top of the return pipe that you can see in the tank then it would likely over-oil the top end. That could result in oil pooling around the valve guides and getting drawn into the combustion chamber.

Running with the sump plate off should tell you if the oil is getting in there from above or below which might be a useful thing to confirm.

Cheers,
Bernie

[JulianS]

I it if was my bike I would want to check the rings. There are poor quality rings about.

It is the fit of the rings in the bore which is more important than the end gap.

With the barrel off insert each ring into the bore in turn and see if you can see day light between circumference of the ring edge and the bore.

[Mike Farmer]

 

Having had a good read thro all the posts my thoughts are that you probably need a re-bore. It sounds as if the cylinder is worn enough to allow air to pass downward on the power stroke thus pressurising the bottom end and forcing oil out through the breather and the rings are pumping oil upward on the two up strokes.

If your rings sit too far "out" from the groves, oil pumps up past the inside of the rings and into the cylinders. One of the magic restoring additives might be worth consideration but only short term.

Hope all works out for well you

Mike  

[Greenfield]

Thanks everyone.
I replaced  the silencer and tried Bernie's suggestion of running without the sump plate. It was still smoking from the exhaust ( but to be fair this could be oil still in the system) and there was pressure and a spray of oil coming out of the sump hole. What does this mean? Crankcase pressure?
I'll need to strip it to check the rings, but if we're aiming for a rebore the cylinder will need to be lined as its already +60. Can anyone recommend anyone to do it?