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?
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
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.
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.
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?
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.
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.
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.
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.
:) :)
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 8) 8) 8)
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?
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 :o 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
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.
:) :)
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 8) 8)
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?
The oil you see spraying into the sump is probably from the pressure relief valve opening, it discharges excess oil into the sump. That is normal.
forgive me if wrong but arent Italian piston rings poor quality, and Australian? , newer Hepolite are not as good as the originals.
as for reboring over +.060 have a word with your local reputable motor engineer, my ,Bristol, engineer can usually come up with an alternative and he does fit liners as an alternative then you might pick up cheap zero standard pistons that others cannot use. He does do work outside Bristol mail order and does offer advice.
:) :) :)
Hi Agen. I obviously don't know where you are but I have just spoken to "the boss" at Owlesbury Crankshafts in Winchester Hampshire. They carry out this type of work. Relining single cylinder approx. £170 + VAT. You supply the piston. I have had a lot of jobs done by this company and can recommend them.
You might also try AD Engineering at North Scarle just to the north of Newark on Trent. Speak to Adrian. Again had a lot of work done by him. But he is usually bunged up with work and quite slow. He relined an A65 engine for me last year---good job.
Good luck. If you want fone no's etc, just ask.
Mike 8) 8) 8)
Correction to my last reply - running with sump plate off won't indicate if the problem is from oil passing either valve guides or rings as there won't be any return flow to the top end - doh! Also, running like this there won't be any crankcase pressure at all to speak of.
Hope you make some progress in your diagnostics soon - it does sound like rings/bore. If the rings you're using are tapered check that they're fitted the right way up (typically marked 'top').
Regards,
Bernie
You say that oil is passing through and spraying onto the rear tyre, I have had this and it turned out after a long battle that the oil was in fact coming from the rocker box nuts on the covers, to sort this I fitted copper washers underneath the nuts, like you I was concerned as the oil was lying on top of the cylinder head and going all over the place but now sorted, HTH
TTJohn
I've now had the oil pump out and everything looks good. All the oil pipes are clear so there shouldn't be any pressure build up. The breathers on top of the gearbox, at the rear of the timing case and at the bottom of the inner timing cover and next to the camshaft nut are all clear. There are no leaks from the engine surface. The piston rings are the right way up. So by elimination I think the only thing left can be the bore. Yes there are some lines and I can only think that these together with new rings that aren't bedded in must be the root of the problem. So its bite the bullet time. I've sourced piston sets and a couple of engineering shops have been recommended, so I'll call round to see what they say.
Bikes of this age with little documented history can have many issues. Whatever I work on, I find evidence that someone has been there before. When I got the bike, included were several used head gaskets. I suspect that a previous owner thought as I did, that the oil could be entering the cylinder via the head. Hence one of my first jobs was to deal with the worn valves. All good fun!
second attempt at posting, French internet dosnt like the forum!!
have you done a compression test?
or if you have the head off, try pouring some oil on the top of the piston to see if it leaks past the rings