1980 GS1000G oil breather leak
 

I picked up a 1980 GS1000G project bike. I got it running and developed an oil leak from the crankcase breather. (This is the small nub behind the starter and under the #2 carb.) The breather is part #24821-45100 and #51 on the "crankcase" diagram from Suzuki. When I got the bike, the breather had a short length of hose attached that was plugged up. I removed the plug and after a few minutes of running the motor, oil started coming out of the breather. Every time I start the bike, within a minute or two oil leaks out of the breather. I tried an 18" length of hose mounted vertically with a filter on the end and oil still climbed to the top and poured out of the filter. If I plug the breather, the engine doesn't run as smoothly. Seems like there is too much crankcase pressure to leave this plugged. I don't want to start blowing seals. Should this be venting to atmosphere or connected somewhere? Can I "tee" this into the oiler cooler line, or will that not solve the problem?

The airbox was replaced with pod filters. The valve cover vent has pressure pulsing out of it when the motor is running. It has a short length of hose with a filter.

I am stumped.

I'm just realizing that the oil cooler may not be am OEM part. Any idea if it is worth removing and restoring the original oil switch cover? I don't see how, but could this be contributing to high crankcase pressure?

Hi Kawboy636,Reply
Did you ever solve this problem? I have the same issue, trying to figure out why oil is coming out of this part #51. I am thinking it is the secondary gear oil breather, I have not changed the gear oil yet... LMK Thanks

Part #51 is definitely a crankcase breather - engine oil comes out of it. It is NOT a gear case breather. I researched this to death and came up with the conclusion that the thin hose attached to this breather is meant to vent to atmosphere, it does not connect to anything at the other end. I could not figure out why there was so much crankcase pressure in the bike I was working on to force oil out of the breather. I rigged up a catch can and routed the breather hose to dump into the can. The tiny diameter of the hose restricts the amount of oil being forced out. You may want to check for restrictions on the breather on top of the engine going into the air box. Couldn't hurt to do a compression test on the cylinders too.

After further research of draining the oil and performing a filter change and only putting 3 quarts back in, it is still doing the same thing. the bike will run, but it appears to be leaking oil on the front exhaust head gasket seal. Could the head gasket leak be causing the bike to push oil out of #51 breather?

When you're dealing with a bike this old, leaky seals/gaskets are not uncommon. Rubber and cork dries, shrinks, and cracks.

Excessive crankcase pressure can cause an age-compromised seal to finally leak, as well as cause oil to force its way out of the breather. However, it's most likely just a bad seal. Clean and degrease the motor, then start it and watch carefully to determine exactly where the leak is. I experienced leaks from the rubber plugs on the sides of the valve cover gaskets. I also cleared an obstruction from a decomposed gasket on the valve cover breather.

40+ year old bikes are not turn key. They are projects. Even if they are low mileage, the fact that they were sitting unused for many years adds to the decaying process of wear and tear parts like seals and gaskets.

And double check your oil level. If you have too much oil in the engine, then it may find a way out through lowest open point - that #51 breather.

Here is a video link of what it is doing:

https://photos.google.com/share/AF1Q...JONlRsMHRpdFhR

I figure out what is going on. The guys at GS resources helped.

https://www.thegsresources.com/_foru...ember-question

So if I got this right, that breather is for the gear box and there is a bad seal internally allowing crankcase oil into the gear box. The pressure in the gear box, due to the compromised seal, is forcing the crankcase oil out of the gear box breather. That makes total sense.

However, when I drained my gear box, only gear oil came out. And only motor oil discharged from the breather.

I no longer have the bike or I would test this theory. Lmk if you have any luck proving that this is what you are experiencing.