Transmission Oil Seeping Into Engine Side On My 2012 Montesa

[12mont]

Hi, I'd greatly appreciate some help with this issue. If I fill the engine oil to the first line on the dipstick and have about 3 rides totalling about 12 hours, the engine gains about 100ml of oil and the transmission side is down 100ml. I pressure tested the engine and transmission side with about 3 pounds of pressure and no leakage detected.

Once transmission is down 100 ml it is very difficult to shift and find neutral. Recently changed clutch frictions. Running Belray 85 in transmission. Thanks

[jrsunt]

Is the oil definitely getting through? Before doing anything drastic, I'd be tempted to do a full oil change on both sides then you know the quantities are correct rather than going off the dipstick.

[12mont]

Thanks for the input. I've done that twice already and each time there is approximately a 100ml more in engine oil and 100ml less in tranny.

[jrsunt]

Thats a tough one, There aren't many oil seals in the crankcases. Kickstart and gear lever shaft seals, Very unlikely. Oil pump seal, again very unlikely and the 2 crankseals, could be. Then there's the crankcase gasket or a defect in the cases. Is the bike under warranty?

Edited July 21, 2016 by jrsunt

[12mont]

Thanks for the differential diagnosis. I pressure checked both compartments and they stayed pressurized, but maybe oil can seep through where air can't? I will recheck the seals you suggested. It's a 2012 so no warranty.

[sportsawyer]

Seems like the most likely location for transmission oil to get into the engine oil is the right (primary drive gear) side crank seal. See frame E-11 in the parts book, part reference number 31.

 

Note there's a reed valve (reference number 12) at the crankcase bottom. And the reed valve opens to the stator / timing chain side when there's positive crankcase pressure (piston going down) to purge oil from the sump. So when the piston is going up, and the reed valve is closed, there's some vacuum in the crankcase. The vacuum could be pulling oil in past a bad right crank seal until the transmission oil level gets below the bottom of the seal. That might be about a 100ml drop.

[2stroke4stroke]

There was a thread a while back where someone had solved this by replacing a seal but I can't remember the detail. Worth a search?

[jimmyl]

I recall a post were the opposite had happened when overfilling the engine oil - pushed a seal out but seems strange to go from gearbox to engine - sports lawyer seems a good explanation though especially if at some point had be overfilled pushing right crank seal out.  

Might just need right cover taking off and se if you can get access to the seal.

Best of luck

[12mont]

Thanks for all the excellent information. Sportsawyer's explanation sounds very plausible. Is it hard to change the crank seal? Looks like it may be able to be reached by just taking the clutch basket out? The bike doesn't have many hours, so you wouldn't think it would be a crank seal. I'll change it out and see:)

[tman427]

Thanks for all the excellent information. Sportsawyer's explanation sounds very plausible. Is it hard to change the crank seal? Looks like it may be able to be reached by just taking the clutch basket out? The bike doesn't have many hours, so you wouldn't think it would be a crank seal. I'll change it out and see:)

 

How did you make out? Was it the seal?

 

I also use the Belray Gearbox oil. Thinking of using the dimpled clutch plates. When the bike is cold the plates stick together a bit until they are lubed with oil.

 

Thanks

Tom