Crankcase breather

[Idealistmeb]

Hello, I'm hoping someone can help me figure out what to do next with my 1980 SG. I have it running well but I am getting what I think is exhaust fumes coming out of the crankcase breather tube. It has sat for over 10 years before I got it and I have put maybe 100 miles on it since I got it running. I did a leak down test on it and it is leaking through the crankcase about 20% on all 4 cylinders. Do I have a big problem or something else? Also the oil light does not work. Is it possible to replace the switch or sensor and where would I get one?

Any help would be appreciated. Thanks

Mark

[dbeardslee]

That's going to happen with a breather tube - it's crankcase ventilation. If you've got the stock air box on it the breather tube hooks up to it and the carbs suck the fumes back through the engine and you don't notice it. If you've got pods then the tube dumps the fumes under the seat, and you really notice it when you're sitting at a stop light. I've got a pcv valve topped with a tiny little pod filter wired up under the seat on mine, but that's really just to keep little critters from crawling down in the line. I still get the fumes at a stop light.

As far as the leak down test, I'll leave it to others to weigh in on that.

[Idealistmeb]

I do have pods on there and a smaller pod filter on the crankcase breather tube wired under the seat. I smell it going down the road but it is stronger while sitting still. Would the PCV valve help?

[dbeardslee]

I put the pcv valve on to keep it from burping oil through the line, although that was never really a problem. It's a one-way valve (sort of), and it's not going to stop the fumes. It's supposed to let the fumes through so you don't get pressure inside the crankcase.

[TopCatGr58]

Hey Mark,

The crankcase vent tube used to go into the OEM airbox to get recycled and reburned. You have POD filters, so that doesn't happen. However, you have the end of the vent tube under the seat. If you were to route it a lot closer to the carb pods....then they might suck in more of the fumes into the carbs instead of just wafting upwards into your helmet.

But secondly, the bike has sat for 10 years, and now you have only put 100 miles on it. Did you do anything like treating the topend/piston rings with a dose of tranny fluid or Mystery Marvel Oil to help dissolve any gum/varnish that might be holding the rings stuck into the pistons?? Also, you probably need to just put several more hundred miles on the engine to help RESEAT the rings....then recheck your compression and leak down, and you'll probably find that the comp will go up and the leak down % will go down.

T.C.

[TADracer]

The 20% leak down would be bothering me. As a rule of thumb this should only be 10% or less for a well broken-in motor.

Did you identify if the leak down is from a particular cylinder and/or valve? If you are getting the leakage across the board and into the crankcase then it might be time to service the rings if this does not change after running it in again like TC said above.

[Idealistmeb]

Thanks for the information. I will try and move the breather closer to the pods.

All 4 cylinders were showing around the 20% leak through the crankcase. So I hope the rings just need to be reset. I will also put some MMO in the spark plug holes and put some mile on. Thanks again.

[dbeardslee]

Thanks for the information. I will try and move the breather closer to the pods.

All 4 cylinders were showing around the 20% leak through the crankcase. So I hope the rings just need to be reset. I will also put some MMO in the spark plug holes and put some mile on. Thanks again.

Just be ready when you use the MMO. When I put it in Betsy, and fired her up a week or so later, she looked like a destroyer laying a smoke screen for the D-day invasion.

If you're getting that much leakage past the rings, I doubt whether moving the breather closer to the pods will make that much difference. What you're probably smelling is all that blow-by past the rings. Get the rings squared away and the fumes shouldn't be so bad.

If I was going to move the breather closer to the pods, I'd want it up towards the top of the pods so as not to get anything else puking up through the breather tube. JAT