HarleyTechTalk

I have a 2021 sporty that has consistent oil from the breathers,  i did change it to vent to atmosphere but the drips continued and makes a mess on the engine cases, even if i routed it to the ground it would still leave oil stains when parked. My question is has anyone ever plumbed the breathers back to the oil tank to catch the oil or would this over pressurize the oil tank, the bike is used for long highway rides mostly. TIA

Quote from: FDT on June 03, 2023, 09:06:41 PMI have a 2021 sporty that has consistent oil from the breathers,  i did change it to vent to atmosphere but the drips continued and makes a mess on the engine cases, even if i routed it to the ground it would still leave oil stains when parked. My question is has anyone ever plumbed the breathers back to the oil tank to catch the oil or would this over pressurize the oil tank, the bike is used for long highway rides mostly. TIA

What comes out the crankcase breather is exhaust that went past the rings instead of out the exhaust port. In it's travels through the crankcase, it picks up oil and water both. So it's a mixture of exhaust and oil and water. Not something you really want to send to your oil tank. And unless you vented your oil tank, you'd create a closed, unvented system, which would then cause gaskets to start leaking. The blow-by has to go somewhere.

Being a 2021, it seems unlikely your bike would have poor ring seal, contributing to excess blow-by. But it's possible, and a leak-down test would be useful for diagnosing it.

Another thing that will cause a lot of oil out the breathers is ineffective check valves. On a 2021, these are on the floor of each rocker box. These are variable volume crankcases - the volume is constantly changing as the motor turns, due to the 45 degree common crankpin design. When the volume increases, it tries to suck in air. When the volume decreases, it blows that air back out. If it's successful, you get an inhalation/exhalation thing going on through the breathers. That inhalation/exhalation tends to pump oil out the breathers. An effective check valve gets rid of the inhalation/exhalation and instead what you get out the breathers is just the blow-by and the contaminants it's carrying.

Again, it's hard to imagine on a 2021 that those check valves are already failing. But who knows.

Being in the engine kit business, one of the common mistakes we see customers make is to accidentally put the front rocker box onto the rear and vice-versa. This effectively bypasses the check valves and causes a lot of oil to come out the breathers.

Anyway, external check valves are available. You can even buy a breather filter with a check valve built into it. Breather filters are really used not to filter air, but to absorb the moisture component of the blow-by and keep it from dripping on the ground.

Another common solution is to use a catch can. It's just a vented can that catches the moisture component, and you periodically drain it.

It's also possible to route the breathers out the exhaust. But it's not simple to do in a way that generates a vacuum. A check valve is advisable near the connection as well. You don't see this a lot on motorcycles. Google the Moroso crankcase ventilation system to see what it takes to do it effectively.

Quote from: aswracing on June 04, 2023, 07:08:26 AM

Quote from: FDT on June 03, 2023, 09:06:41 PMI have a 2021 sporty that has consistent oil from the breathers,  i did change it to vent to atmosphere but the drips continued and makes a mess on the engine cases, even if i routed it to the ground it would still leave oil stains when parked. My question is has anyone ever plumbed the breathers back to the oil tank to catch the oil or would this over pressurize the oil tank, the bike is used for long highway rides mostly. TIA

What comes out the crankcase breather is exhaust that went past the rings instead of out the exhaust port. In it's travels through the crankcase, it picks up oil and water both. So it's a mixture of exhaust and oil and water. Not something you really want to send to your oil tank. And unless you vented your oil tank, you'd create a closed, unvented system, which would then cause gaskets to start leaking. The blow-by has to go somewhere.

Being a 2021, it seems unlikely your bike would have poor ring seal, contributing to excess blow-by. But it's possible, and a leak-down test would be useful for diagnosing it.

Another thing that will cause a lot of oil out the breathers is ineffective check valves. On a 2021, these are on the floor of each rocker box. These are variable volume crankcases - the volume is constantly changing as the motor turns, due to the 45 degree common crankpin design. When the volume increases, it tries to suck in air. When the volume decreases, it blows that air back out. If it's successful, you get an inhalation/exhalation thing going on through the breathers. That inhalation/exhalation tends to pump oil out the breathers. An effective check valve gets rid of the inhalation/exhalation and instead what you get out the breathers is just the blow-by and the contaminants it's carrying.

Again, it's hard to imagine on a 2021 that those check valves are already failing. But who knows.

Being in the engine kit business, one of the common mistakes we see customers make is to accidentally put the front rocker box onto the rear and vice-versa. This effectively bypasses the check valves and causes a lot of oil to come out the breathers.

Anyway, external check valves are available. You can even buy a breather filter with a check valve built into it. Breather filters are really used not to filter air, but to absorb the moisture component of the blow-by and keep it from dripping on the ground.

Another common solution is to use a catch can. It's just a vented can that catches the moisture component, and you periodically drain it.

It's also possible to route the breathers out the exhaust. But it's not simple to do in a way that generates a vacuum. A check valve is advisable near the connection as well. You don't see this a lot on motorcycles. Google the Moroso crankcase ventilation system to see what it takes to do it effectively.

Thanks for the reply, i have already done both the leak test, and had the rocker covers off to check the check valves, both were fine, and the leak test passed. I did drop the oil level in the tank closer to the minimum level and it did help but eventually i was seeing oil again. Could i run the hoses from the breathers to the throttle body on the otherside of the throttle plate or would that act like a vacuum leak and give me an erratic idle ?

Quote from: FDT on June 05, 2023, 11:59:32 PMThanks for the reply, i have already done both the leak test, and had the rocker covers off to check the check valves, both were fine, and the leak test passed. I did drop the oil level in the tank closer to the minimum level and it did help but eventually i was seeing oil again. Could i run the hoses from the breathers to the throttle body on the otherside of the throttle plate or would that act like a vacuum leak and give me an erratic idle ?

Well, assuming "otherside" means downstream of the throttle plate, you wouldn't want to do that. These check valves in your rocker boxes are not PCV valves, designed to allow a slight bit of flow when under heavy vacuum. They'll just open up and be ineffective and you'll pump oil right out of the motor into the intake tract. If you want to send it into the intake tract, do it into the upstream side of the throttle plate, i.e. the way the factory does it.