oil leak from airbox?

[steve_wicks]

I noticed a few drops of oil under my bike and on closer inspection it appears to be coming from the airbox then running down the back of the gearbox. Not really a stream of oil, but an oily, sweaty film of oil.

Was too busy to take a better look and tomorrow I go away until Monday.

Any quick ideas, theories, suggestions etc

[Bob_Roller]

The crankcase breather is connected to the air-box, you can get an accumulation of oil in the air-box because of it, and it exits through a 'fish-mouth' looking rubber valve at the back of the air-box.

[steve_wicks]

Okay. Will look when I get back next week. But what would be the cause of that. Worn rings or could it just be an accumulation over the years?

Its an 81 model which I bought in January and have put just over 3000 km on it since. Mileage is now almost 50 000km, but no idea if that's genuine.

I changed oil & filters (inc air filter) shortly after getting it. I also had to do gearbox seals and clutch which cost more than I paid for the bike!

[trolle]

Probably the crankcase vent hose has a small crack somewhere. Get a new one.

greetings from a foglifting, sunny north

[nhmaf]

I'd open up the airbox and see how much oil was collected in the bottom, and clean it out well.  If you end up with more than a tablespoon of oil in there by the next oil change then I'd start to think that maybe there was excessive blow-by the rings.   It  is not uncommon for there to be a little bit of oily film in there especially if running at high RPM for a extended intervals.  As trolle suggests, check the hose.

[Bob_Roller]

I reduced the amount of oil in the air-box, and from seeping out of the carbs, by placing a portion of a copper pot scrub pad into the area above the crankcase ventilation reed valve.

It gives the atomized oil a place to collect, and then drain back into the oil sump.

A lighter weight oil may contribute to an excessive amount of oil in the air-box.

When you remove the top cover of the air box, and air filter the breather hose is at the front of the air box, then a plastic  'tee' fitting slides into it, then there are two rubber hoses that go from the  'tee' fitting, to rubber 'air horns' before they exit the air box, could be that some parts have been  omitted by previous owners.

[steve_wicks]

I washed the engine then went for a ride and left it for a day only to discover serious oil leaks from sump gasket, cylinder base gsasket, pushrod seals.

I bought it in Jan and the only oil leak was onto the shelf which ended up as replacing gearbox, crank seals as well as the clutch. At the same time I asked for an oil & filter change and didn't notice a problem until last week.

I left it standing for 3 days and there was quite a few drops of oil left on my driveway whereas it's never left oil on the bricks before.

Could new oil do this?

[Bob_Roller]

You could try re-tightening all the fasteners that secure these parts, but remember that the oilsump bolts are threaded into aluminum, and won't take much over torquing before stripping, so if they are snug ,looks like replacing the gasket is the only real solution to eliminating the leak.

Same goes for the cylinder base seals, , there is an o-ring doing the sealing, so if torquing to the specified amount, doesn't cure the this and the push rod tube seal leakage, replacement of the seals is your only real option.

I don't know what year your bike is, but a lot of these bikes are in the 30 year old range, and the leaks, are not uncommon at all.

[nhmaf]

If the bike has been using dino-oil all its life and you've just switched to a full synthetic engine oil it could start doing this multi-orifice leaking thing.   If so, swapping back to dino oil may cause it to "cure" itself in time.   But if a switch in oil type didn't just happen, then I'd echo the previous recommendations to  carefully backoff and retorque the sump/base pan bolts and do the same with the cylinder head bolts.  You'll want to recheck the valve clearance adjustments after adjusting the head torque.

Good luck, let us know how it turns out .  Post some pics if you can and we might be able to decipher something else or provide other ideas.

[steve_wicks]

Okay, getting somewhere. When I got the bike it had oil on the shelf!! and because I didn't know its history I decided a good service was in order so I sent it to a BMW specialist (expensive). Apart from seals and new clutch, all fluids were changed along with oil filter, air filter etc.

Now, I don't know what oil was in it and I don't know what oil was put in so that could be an explanation. There also seems to be a sort of silicone around the base of the cylinders .... and on tappet covers!

[Justin B.]

Silicone sounds like someone was trying to "hide" stubborn oil leaks...

[Yikes]

A thin coating of sealant at the cylinder base is called for on the engines that use O-rings instead of gaskets.  When I pulled my jugs to replace my push rod tube seals, the old guy at my local bike shop recommended I use a non-hardening silicone as the sealant.  It's worked fine, so a little silicone squeezed out around the base of the jugs may not indicate a problem.  But if it's slathered on like caulk around a window frame, it may sure enough be covering something up.

That big fat paper gasket on the valve covers should be fine without any sealant unless they are old and compressed hard.  

[Justin B.]

He used the term "around" the base of the cylinders so I took that to mean a bead laid on in an attempt to stop a pesky oil leak...

[steve_wicks]

I think after 28 years it needs some affection .... I know I did!!

So new sump gasket, tappet cover gaskets, cyl base & pushrod seals it will be.

I just had the seat recovered and swapped the hand guards over from my Honda XR, so it's starting look like an urban adventure bike.  

[steve_wicks]

YIKES ....The oil leaks get worse with each kilomete I ride!

Seeing as though it first appeared under the airbox I was wondering if it had something to do with the crankcase vent. Then I was looking at the boxer engine animation on the Moto-Bins website and noticed how the pistons come down together and it dawned on me. Surely that must increase the pressure in the crankcase which will make oil spurt out of the weakest points?

Is there any sense to my toughts ....?