GS850GZ crankcase breather leaking oil

[LJR47]

Hello,
Located below the carbs on the crankcase is a crankcase breather plug, this is connected to a small 2mm hose that discharges somewhere ????? maybe to atmosphere.
When my engine gets hot, gear oil leaks from the breather hose ???? is this normal ? I would assume not.
Is the breather plug like a pressure vent? set to a factory pressure level?
Obviously my crankcase is being pressurised as the engine raises in temperature.

I've checked the oil level in the gear box, in actual fact replaced it to the required level, still getting oil out of the breather when engine hot.

Engine recently had full top end rebuild.

Any advice would be greatly appreciated.

Regards

 

[Brendan W]

It's supposed to be routed under the starter motor to discharge via the ' mystery hole ' in the starter cavity. I would expect a small amount even with correct gearbox oil level. Is it possible that it's split or not sealing on the nipple ?

 

[JTGS850GL]

Exactly where are you seeing the leaking oil. If you're seeing at the top of the engine case then your vent hose is broken somewhere.

 

[Steve]

Exactly where are you seeing the leaking oil. If you're seeing at the top of the engine case then your vent hose is broken somewhere.

From his first post:

Located below the carbs on the crankcase is a crankcase breather plug, this is connected to a small 2mm hose that discharges somewhere ?????

.

 

[LJR47]

Hello,
Last night I removed the crank case vent plug from its mounting point, engine was cold, used a piece of wire as a dip stick and inserted it in the hole where the vent plug was mounted, oil level was approximately 40 to 50mm below the top level of the crank case. Started the engine and watched the hole where the vent plug was, after a few minutes as the engine warmed up and got hotter, the oil began to rise and then ran out of the vent plug hole.
Crank case is being pressurised, I've checked all of the oil levels, engine oil on site glass at cold is just below the full indicator, gear box oil is set at a slight drop out the fill hole engine cold, bike sitting level.

The engine has just had a full top end rebuild, hasn't been ridden, still playing with linkages etc, could this issue be blow by?? should this reduce once the rings are bedded in?

As a check, I will remove the oil filler cap and start the motor, I'll keep an eye on the hole where the vent plug went and see if I still get an oil discharge.

Thanks for your advice.

 

[Steve]

On a fresh engine (cylinders hone, new rings, etc.), you will have a bit more blow-by than normal. Be sure to break-in the engine properly (the quick method), you will reduce the amount of blow-by as soon as possible.

Be careful when you open the oil filler while the engine is running, you may find oil flying out of there.

If the crankcase IS being pressurized, check that the breather is still functioning. That is the device on the top of the valve cover that has a hose that runs to the airbox. If the breather cover is blocked or the hose is plugged, the crankcase will not be vented properly and pressure will build.

.

 

[LJR47]

Thanks Steve,
Breather on top of valve cover should be fine, I double checked that prior to bolting up, I will remove and double check its only a few bolts, worth the effort.
Thought opening up the oil filler cap would stop the oil coming out of the vent plug hole, as the pressure should take the line of least resistance, I could cover this with a light rag if oil is going to fly around off the spinning clutch assembly etc.
Even thought of installing a temp vent filter on top of filler cap whilst going through the break in period if the opening up of the fill point works, the cost of a new filler cap is neither here or there.
Could then revert back to the crankcase vent arrangement if pressure reduces once rings seated.
Regards

 

[Steve]

The vent hose on the normal breather cap should handle ANY blow-by, maybe even if you have a hole in a piston, so I don't know why you have pressure building there.

.

 

[LJR47]

Very good question Steve, when I pulled the breather plug out I cut it in half to see how it works, its basically an open hole, no check valve or spring, just a small reservoir with a 2mm outlet, wasn't blocked so it could vent as designed.
But for some reason with it either in position or removed from the crankcase once the engine warms up oil flows from the vent port.
Hence why I thought trying with the oil filler cap off.
Its a mystery .........but I'm a novice hence my post to see if anyone could shed some light on the issue.
Regards

 

[LJR47]

Hello,
Does anyone know if its possible for the engine oil to find its way into the secondary gear oil compartment? Hence filling up the compartment over time and spilling out through the crankcase breather?
If this can happen can you advise of the fix?
Regards

 

[Guest]

Hello,
Does anyone know if its possible for the engine oil to find its way into the secondary gear oil compartment? Hence filling up the compartment over time and spilling out through the crankcase breather?
If this can happen can you advise of the fix?
Regards

It's possible, I have that problem on my '82.
There's a seal between the transmission and secondary gearbox that needs replaced.

Look at this,
http://www.thegsresources.com/_foru...epage-seal-between-secondary-gear-compartment

 

[JTGS850GL]

From his first post:


.

Great, but is it leaking out from the tube, the fitting or down under the bike?

 

[LJR47]

I have confirmed that its coming out of the crankcase breather location.
I actually removed the breather and watched the oil ooze out.
What I've now done as a test is I drained the secondary gear oil, refilled with a measured quantity (350ml) of new gear oil, and have started the bike. I will run it a few times and then drain the oil again into the measure and see if the volume has increased, if so I'd say I have the issue of the damaged seal that AMK refers to.
Obviously I need to see if my engine oil has deceased as well inline with the increase in the gear oil.

If confirmed its the seal between the transmission and the secondary gear box does this mean the engine has to come out or can this be replaced by removing the clutch cover casing?
Please tell me via the clutch case this is the case!!!
Thanks

 

[Guest]

"If confirmed its the seal between the transmission and the secondary gear box does this mean the engine has to come out or can this be replaced by removing the clutch cover casing?
Please tell me via the clutch case this is the case!!!"

http://www.thegsresources.com/_foru...epage-seal-between-secondary-gear-compartment

If you have the same problem as I do then unfortunately this is what we're in for.

 

[LJR47]

Thanks for the info AMK, great link to the job completed by the previous guys back in 2007, will be handy if I need to go down that path, although in saying this my gut feel is that's where I'm heading!
Gut wrenching considering I only put the engine back in the frame a month ago after a top end rebuild, only found this issue whilst test running the engine in the garage, obviously carbs all fitted, new 4 into 1 exhaust, wiring 90% completed. Purchased the bike around a year ago from a guy who never spent a penny on it or cleaned it, was leaking oil from the cylinders covering the engine in crap so to speak, never noticed the leak from the breather, but it must have been there, anyway as they say back to the drawing board!
To confirm this is the issue, I drained the oil from the secondary gear housing and replaced with a measured quantity 350mls of new gear oil, noted engine oil level at exactly on the full indicator on the sight glass.
Have started the bike on two separate occasions since setting up measuring test, only ran engine for around 10 minutes each time as haven't obviously bedded in the new rings as yet, might be over cautious but! No oil coming from breather vent as yet, hard to tell if the oil has dropped in the engine on sight glass, its like the more you look the more you see type of thing.

Will run the engine a few more times and then drain the gear oil and see what volume I get.
I think at lest I might be getting to understand where the oil is coming from and also now what involved in the fix.

Thanks again for your responses, very helpful.
Regards

 

[Brendan W]

Is the breather hose free ?
If it's blocked oily vapour will find the path of least resistance as it heats up in there.
If engine oil is getting in there you should see a colour difference at least when you drain the transmission.
Don't get sucked in by stuff coming out the overflow, the oil will expand a bit when hot.

 

[LJR47]

Hi Brendan, as per my post below, I set up a test procedure, with a measured quantity of gear oil, 350mls in the secondary gear housing, oil level on full in the engine via sight glass, ran the engine a few times, not for long periods as the top end has just had a rebuild and the rings haven't been bedded in as yet.
Let the bike cool, drained the oil from the secondary gear housing into the same measure I initially used to put the oil in with, ( a pyrex glass measure I stole from the kitchen, when my misses finds out I'll be in deep ****!), anyway the gear housing volume had risen by approx 100mls, hence my gut feel is the damaged seals between the two compartments.

Regards