leaking oil from vent on crankcase

[Anonymous]

Hello all, I have a problem with my 82 GS850 (38,000 miles) and any suggestions would be appreciated. If I go for a ride for about 10 miles or more, the bike will spew oil all over the top of the crankcase (underneath the carbs). I'm guessing it leaks (or "spews" may be more accurate) at least 2 or 3 ounces of oil (at least) on a 10 mile ride. The oil will rest on top of the crankcase, and spill from the left side of the bike, and partially onto the left side of the back tire. Not fun.

There is what appears to be a vent on top of the crankcase near the starter with a very thin tube (about a foot long and about .5 mm thick) that is not hooked up to anything. It appears that oil is coming from this tube (oil is in the tube when I look into it). Oil was also seeping from the clutch rod seal that goes into the right crankcase cover, I changed that, and for the most part no oil is leaking there anymore. A small amout of oil also appears to be coming from the oil pressure sensor (even after changing the o-ring).

I do not have a compression tester, but I pulled the plugs and they do not show any sign of oil on the plugs. The oil is not over-full, if I changed the oil, if anything its running maybe 1/2 pint low based on the oil glass view.

If anyone has any ideas where that thin tube hooks up to, if anywhere, and any ideas why it's blowing oil I would greatly appreciate it.

Thanks!

[daveo]

the tube in question is a pressure relief (breather) for the bottom end, and should attach to the airbox(if you still have one). Generally, oil spewing from this tube means your crankcase is becoming pressurized, usually from ring blow-by, this doesn't necessarily involve the oil control rings and you may notice no oil fouled plugs, but, more than likely, you've got a worn or broken compression ring or two. A dry, then wet, compression test will confirm this, as would a leakdown test

[martin]

I think your kind of right Daveo, especially as the bike in question is a shaft drive like my GS1000G.
I have the same problem and was just about to do a search on other posts on this question.
according to the bikebandit parts diagram, what looks like a breather is called the "plug bevel gear"
I assumed that it was the breather for the bevel gear case, and that the breather tube goes down into the starter cavity and drains out that weird hole near the gear change lever.
I recently did an oil change and thoroughly degreased the crankcase. This morning I noticed that there was oil around the base of the bevel gear plug.
I don't have a workshop manual, but for any one who does, a couple of questions.
is the "plug bevel gear" actually a breather?
how is it sealed to the crankcase, and can I remove it?

I'm going to change my bevel drive gear oil, and see if I can't get some new tube for that 'breather'. it may be tht it has become gummed up, so pressure builds and then spurts out oil when the bike is stopped. anyone else with a view about this?

Martin
GS1000G, z650B, z650SR
Melbourne, Australia

[saaz]

Hi Martin, greetings from Canberra.

Checking the operation of the breather would be a good idea, as it may not be venting properly, leading to pressure buildup that dumps the oil. Unfortunately my chain GS1000 does not have the vent, so I have no experience with it. I would be interested in any solutions you find

[martin]

ahh, Canberra. spent a couple of years up there, working in the public service. i used to think Melburne was cold in winter...
I think you're right about it not venting properly. I'm going to get hold of some new tubing and try that as a first step. I really want to know how it's attached to the crankcase so i can feel confident about yanking it off!

Martin
GS1000G, z650B, z650SR
Melbourne, Australia

[Anonymous]

Daveo, Martin and Saaz, thanks for your posts. A friend of mine also suggested rings (ugh), so a compression test is in order. I'm replying from work, and don't have the bike with me, but a couple of points to refine it a bit. I still have the original airbox, but I can't find where that tube hooks up to. I 've pulled the airbox a few times, but it doesn't seem that the vent tube goes there. I bought the bike used, and I'm sure the hose was disconnected since I bought it. I'm sure I'm just overlooking it, but where does it go on the airbox?

Martin, I went to Bike Bandit, that is the "plug bevel gear" as they call it. Kind of an odd name for what looks like a breather vent. It appears from mine that it is blowing out motor oil, not gear oil. I'll check the gear oil level tonight to verify that.

To me, it does seem to work as a breather, otherwise, why would there be a hose attached to the end of it? Of course, sometimes the obvious isn't the answer.

Thanks again everybody!

[bwringer]

I'm not clear on what it is, but on the non-leaky, non-oily GS850 engine I have handy, the strange little tube you describe is routed through a notch in the wall of the well where the starter sits, then under the starter and into a rectangular hole at the bottom of the starter well. I think can see gearbox innards through the hole.

Hope this helps. It looks like it's some sort of breather/separator that routs oil back to the crankcase.

I'd still try to do a compression test if possible.

[Dave_A]

I had this happen on my GS850

Turned out to be caused by a crankcase full of GAS...

Drained gas/oil mix from crankcase, re-built the carbs -> no more problem...

[Dave_A]

Daveo, Martin and Saaz, thanks for your posts. A friend of mine also suggested rings (ugh), so a compression test is in order. I'm replying from work, and don't have the bike with me, but a couple of points to refine it a bit. I still have the original airbox, but I can't find where that tube hooks up to. I 've pulled the airbox a few times, but it doesn't seem that the vent tube goes there. I bought the bike used, and I'm sure the hose was disconnected since I bought it. I'm sure I'm just overlooking it, but where does it go on the airbox?

Martin, I went to Bike Bandit, that is the "plug bevel gear" as they call it. Kind of an odd name for what looks like a breather vent. It appears from mine that it is blowing out motor oil, not gear oil. I'll check the gear oil level tonight to verify that.

To me, it does seem to work as a breather, otherwise, why would there be a hose attached to the end of it? Of course, sometimes the obvious isn't the answer.

Thanks again everybody!

There should be a nipple on the top of your airbox (underneath the main frame tube, directly in line with the nipple on top of the engine) where the hose attaches...

[Anonymous]

hi all, just following up, gear oil level looks ok, its leaking oil. Bweringer, thx for your post I'll look down the starter cavity and see if I can hook it up. I hope to have a "non-leaking" GS850 again soon!

Dave A., the fitting you describe I believe is for the crankcase breather that comes off of the cam cover, and I have that one hooked up to the top of the airbox. From what I gather on these posts, only the shafties have this "plug bevel gear" breather that is behind the cylinders and below the carbs, near the starter housing.

Going back to Martin's post, does anyone know how to remove the "plug bevel gear"??

thanks all...

[Anonymous]

thebear, The info you got on blow-by (which is the oil coming out your crankcase) is correct. It is mostly likely poor ring seat due to wear, a broken ring or a cracked piston. I have had a chunk between the piston lans come loose and I got a ton of blow-by while the rings were just fine. Time to look at taking apart the top end.

[Anonymous]

Hi Wiredgeorge, I'm slowly coming into reality here and realizing that it is the rings I'm going to run a complression test(s) as soon as I can score a compression tester and some free time. I appreciate your reply...

I see that you're a carb rebuiding guy, a fine art...I don't know what this site allows, maybe you can give more information about your services on here. I'm sure people here would be interested in knowing more.

Have fun!

[martin]

I think I fixed my problem. it was easy - the previous owner had filled the bevel gear case to the top! no wonder it was blowing out the breather!
anyway, I'm not so sure about the rings being the cause - maybe someone with a workshop manual can confirm this, but I would have thought that as there is a seperate oil fill for the bevel gear, it is actually seperateed from the crankcase, so increased pressure in the crankcase wouldn't lead to increased pressure in the bevel gear case?
just a thought (and make sure you haven't overfilled the bevel ger case!)

[Anonymous]

Martin, thx for the post, I'll double check the bevel gear oil level, but it looks like its blowing motor oil to me, and I've put over 4K miles on it before it started to spew oil all over the place. It's worth a shot tho.

Thanks!