B31 Oil leaking? Primary case filling up

[Fraz]

Hi.
On my '54 B31 (just removed the primary chain cover to renew the leaking cork gasket) and after thoroughly cleaning the area out, I thought I'd start the bike to check that the large amount of oil that I drained out of there, was either a previous owner filling mistake or a leak somewhere.

Upon starting, oil started to drip quite heavily from the bottom of the case and was "sprayed" around the bottom portion of the inner case.
This oil kept leaking through from what looks like, behind the clutch area. Within a minute of running, there was about 10ml of oil on the floor.

The new engine oil in the tank has slightly emulsified but this "leaking" oil wasn't, it was clearly used, non-emulsified oil.

I'm guessing it's gearbox oil so I removed the oil filler, expecting it to have been over-filled but there was no sign of oil in the gearbox.

As a total novice owner, should oil be coming in to the primary drive chain case area?
Does the amount sound excessive? (It would fill up fairly quickly I guess - potentially leaving the gearbox totally dry?)

Any suggestions as to where the problem lies please?
Many thanks

[Rog1]

Oil should not be coming in. Stick a finger into that oil and take a sniff; gearbox oil (at least the sort I use; my M33 is the same age as yours) stinks.

If there was a lot of oil in the chaincase, your clutch plates will have got oily. It would be a good idea to dismantle the clutch and clean the plates, having taken note of how many threads were showing through the lock nut on each of the six studs (on a standard clutch) to aid in reassembly. You might find some more evidence of your original problem, too.

It would still be a good idea to set up the clutch again so that it lifts squarely, as you don't know how well or how long ago it was done last time. Each stud has a spring, and you adjust the nuts so that, when you hold the clutch lever in, the outermost plate is the same distance back from the edge of the clutch basket all the way round. The depth measuring bit of a vernier caliper is ideal for this job.

I haven't had this oil problem myself (famous last words!) so I don't know the exact causes. But the gearbox oil should be just below the edge of the inspection cover hole on the right hand end of the gearbox, with the bike upright on the centre stand. You want GL4 oil; do not use GL4/GL5 oil as it harms the gearbox bearings. It can be surprising how little oil needs to be added, to top of the gearbox when the oil isn't visible through the hole.

I wonder if the bike has spent a lot of time on the side stand, so encouraging oil along the shaft and out.

[neil1964]

Most likely scenario is that the excess oil in the chaincase came from the engine crankcase.

During a period of layoff oil leaks past the oil pump into the crank case and then into the chaincase.  `People will top up the oil in the tank as a matter of routine.  When the case is full of oil and you start the engine the crankcase becomes pressurised by the down strokes of the piston and oil will follow the path of least resistance which is typically past the drive side main bearing into the chaincase.  This oil will not be frothy like that in the return feed to the tank.

- I suggest you do as Rog1 advises and clean your clutch plates.
- drain the sump (after cleaning the crank plug surroundings meticulously) into a clean container.
- measure what is in the chaincase.  If it is more than 100mls or so (bearing mind you have run the engine and some oil will have been pumped into the oil tank (the level may rise) then that is likely the problem.

The main solution is to at least start the engine to running temperature once a week.

Someone told me a good trick (maybe a joke) was to use different colour oils for engine, gearbox and chaincase!!

[Fraz]

Thanks.
When I first got the bike, it was dripping oil from the chain case so I drained the sump and removed the chain case cover (which dropped about a litre of oil)
I then thoroughly cleaned all the chain case area and added new oil to the oil tank (about 2 months ago)

Before starting today, the chain case was totally dry.
After starting (with the cover off) it was leaking oil quite badly whilst running.

[rhyatt]

You mentioned "2months ago" above.
Did you drain the engine crankcase before starting it?

If not, then 2 months worth of oil tank oil could have dribbled through the oil pump into the crankcase.
This would then come through the main bearing into the chain case.

[Fraz]

I drained the engine when I got the bike (two months ago) and then re-filled it with new oil (which has now gone emulsified a bit in the tank)
The oil that's leaking out of the primary drive case is not emulsified.

I didn't drain the engine before starting the bike - I presume that would lead to catastrophic failure?

I'm confused

[rhyatt]

These engines are a dry sump , where the oil to lubricate the engine is stored in the oil tank and is pushed around the engine by the oil pump (there are 2 halves of this pump , feed and scavenge)
All this oil then whizzes around the inside of the engine lubricating everything and then drops down by gravity into the bottom of the engine, from where the scavenge side sucks it up and sends it back to the oil tank ,
Then it starts all over again on its journey round and round.

During idle periods when the bike is not running, oil by gravity dribbles through the gears inside the pump and gathers in the engine.
It is this collected oil that is stirred up and dribbles into the chain case BEFORE the scavenge side of the pump can suck it back to the tank.
I hope this helps you understand the oiling system.

Your car is a WET sump whereby the oil must be in the sump

[Fraz]

Thank you for taking the time to explain this.
As you'll gather, I'm totally new to this.

So am I right in thinking that if I drain my engine from the sump plug, I'm still OK to start the bike and then hopefully, no oil will escape in to the primary case?

Many thanks for your patience

[rhyatt]

no problem , i hope it helped you understand the bike.


in answer to your question, if you drain the engine sump(from the plate under the engine) then all you are doing , is removing the oil that gravity has dribbled down whilst standing.

BUT BUT BUT - check that there is still oil in the oil tank before you start the bike AND when started, check that oil is being pumped back into the tank by the little pipe inside the top neck of the tank.

whatever you take out of the bottom of the engine, you can put it straight back into the oil tank - recycle it !!

the oil in the tank will eventually take on a slightly "frothy" look as the suction side of the pump sucks up air as well as oil(only doing this when it has sucked all the oil out of the engine sump)

if you don't use your bike regularly - some people leave the bottom plate off with a small container to catch the oil dribbling down - but obviously replace and tighten before starting your bike.

at least, if you do the above, then you can at least start to establish where the chaincase oil is coming from.

also - if you leave the bike on the side stand, it has been known for the gearbox oil to dribble along the shafts into the chaincase - so keep it on the centre stand

[Fraz]

Again, thank you for clarifying - it makes sense now.

I'll drain the oil and start the bike.
If I still get oil appearing in the chain case, I guess I've got some problem?

The oil tank is full to correct level and it's being pumped back via that little pipe within the tank (so that's good news that it's working)

I wish I had a side stand but I don't and can't see where one would fit.

[neil1964]

As per my post above

Run it every week to get it warm and you should have no problems.

You can get anti-wet sumping valves to fit on the inlet pipe (I had one on a B31 without issue - other people  may have different opinions!).

[Fraz]

I'd just like to say a huge "thank you" to everyone who helped / advised me with this issue.

Today, I drained the sump and started the bike (still without the primary cover fitted) and no oil was coming from behind the clutch or anywhere in to the primary cover - so I steps I don't have a major problem 
Though it had lost a fair amount of oil in to the sump (see image)

The bike will only be ridden very occasionally and it's stored where it's difficult to access it to regularly start the engine so the "anti-dry sumping" gadget mentioned would be of great interest.
Does anyone have a link to where I could get one please?

Next issue is the headlamp wiring but I'll start a new topic 

[cdsdorset]

I would recomend an anti wet sump tap which has a switch to isolate the ignition /magneto.

[rhyatt]

Glad you got to the bottom of it.
Warning, if you do fit a tap then have a switch to kill the engine, otherwise there is a danger of starting the bike without the oil turned o
Some taps have switches built into them.

FEKED sell these things

At least you can wrap up the chain case now

[neil1964]

I have heard horrible stories of bikes being started by absent minded owners who forget the manual tap.
I used the automatic version on mine without problems, although I understand people have had issues with them, but no personal issues. The B31 is a v lightly tuned machine with minimal oiling requirements (fresh clean oil is priority imo).