There has been a lot of discussions on this forum and others about venting the primary to fix the transmission to primary oil transfer. It has also been discussed that the transfer might be happening because of a vacuum coming through a defective oil seal in the crankcase. I am not sure what causes a vacuum in the primary in order for the oil to be sucked from the transmission, but the MoCo is convinced that venting the primary is the answer. From what I have read it appears that the oil tank, cam chest and crankcase share the same air space and some aftermarket companies are selling products to vent the oil tank in order to relieve the pressures inside the engine. Is the transmission transfer related to pressures inside the crankcase? I don't know but I can't see how a spinning chain inside the primary creates a vacuum.

Feuling sells a vented dipstick that they claim "removes unwanted build-up of blow by, which is found in engines with excessive leakdown through the rings/cylinders which is a common issue with large displacement big bore engines. Test results show a decrease in engine sump oil levels."

T-Man performance sells a permanent mount oil tank vent to release crankcase pressure by drilling a hole in the side of the dip stick spout. TR has a video on You Tube detailing the installation of the vent.

I don't know how much T-Man sells his kit for but Feuling sells their vented dipstick for $279 so I decided to try my own vent for about $20. I don't have a problem with my bike other than a small transfer from the transmission. If my transfer is caused by a vacuum created from the crankcase, then this should fix it. It's cheaper and easier than drilling a hole in my primary or replacing the oil seal in the crankcase. And it's totally reversible. This will only work on bikes with twin cooled heads.

You will need to add an oil return fitting found on bikes that have oil cooled heads, part number 62700146, $4.96 from New Castle. The fitting is for the return oil from the heads back to the oil tank. This fitting is 1/2" so you'll need a filter and some hose the same size to hook it all up. I used about 36" of 1/2' heater hose and a K&N filter from Amazon for $7.99.


Parts I used minus some 1/2" heater hose. The fitting is made of plastic and I cut off about 2" just in case it was submerged below the oil level.




Remove item 35 and install item 34 in its place. Item 34 comes with O-ring installed


Use a 3/16" hex bit. Reuse the same bolt


Oil return fitting with 1/2" hose attached to top of transmission


I routed the hose under the ABS module and strapped it to the fender struts.

After hooking up the hose to the fitting I verified that it shares the same air space with the dipstick by blowing into the hose. You could use a smaller filter and hose with a 1/2" to 3/8" adapter but this works fine for me.

Since my transfer problem is small right now it could take all summer to find out if this has any effect. Otherwise venting the crankcase can't be a bad thing.

 

Edited, I see you mention this will only work for water cooled.

 

That's correct. The oil cooled bikes are already using this fitting as a oil return path to the oil tank. Oil cooled bikes would need to use a solution like T-Man uses or a vented dipstick.

 

5-7 bucks is all i did on twin cooled bike..... I did it because i believe the breathers need to be vented to atmosphere ( so i did) oil tank needs to go to atmosphere ( so i did) and primary needs a vent. I dont think i own anything thats not vent other than the engine because of epa.....all cars / trucks have vented trans ..differentials .
2017 now uses not a drop of trans,engine or primary oil. Or for that matter coolant. 5 k oil changes so thats 4 times a year.

 

I have a 2018 Limited with about 30,000 miles on it. I'm just now seeing oil coming out through my air filter. Could this be from the crankcase not being vented? If you don't mind my asking, how has your venting solution worked for you so far?

 

Last December I bypassed the breathers from the rocker boxes to the ground so I wouldn't have any oil going into my throttle body. I never see any oil on my garage floor from the bypass so I'm probably not getting much. As far as my vent goes I don't know how much it has helped the rocker breathers because I never noticed much oil on my air filter before the modification. I mainly did the vent because I thought it was a good idea. When I had my 2012 Limited dyno tuned 6 years ago the first thing my tuner did was check my oil and he pulled out about a half quart. He told me to always run it a little low and since then that's what I have done. I've read in other threads in these forums if you run your oil level low that it will help with oil puking in your air cleaner. If you haven't done that yet I would try it first.

 

Larry. Were did you get that plastic oil tank vent tube with the screw flange that you used to vent your oil tank. You showed photos and diagram but I am having trouble finding the part you showed

 

Might need to PM Larry, as post is old. I’ll do that for you because I think forum requires more posts than you have in order to PM.

 

I bought it at my local dealer. In my original post I listed the part number and the cost from New Castle.

62700146, $4.96 from New Castle

You can drill a hole in your blank plug, part # 35 in my diagram on post #1, and put in a barbed adapter.

https://www.lowes.com/pd/B-K-3-8-in-...ing/1000504941

 

If you have an external breather mod to your air cleaner, is this still beneficial to do? If you already have a primary vent installed, is this still beneficial to do? Is this one of those “it can’t hurt so just do it” mods, or “if it ain’t broke, don’t fix it” deals?