TWIN CAM transmission oil transfer.

[guydoc77]

Yes you read that right.
2015 Rooad Glide.
Mueller clutch actuator (which I highly recommend by the way).
Otherwise stock setup except for I replaced the trans top cover with the "old style" with the bigger diameter vent hose, which didn't change a thing as far as trans oil loss.

I discovered late last season that my trans was 16 oz low.
So I have been OCD about checking it and I'd estimate that around 4 oz disappears every 400 miles.
No it's not leaking.
Engine oil is not overfilling.
Primary is overfilling.

What I've ascertained researching this is that a very small number of the Rushmore Touring Twin cam bikes with the hydraulic clutch also had this problem.
The internet is replete with the M8 issue and all the "fixes". But I have found essentially nothing on the Twin Cam bikes with this issue.
It seems that the inner trans cover for the Twin Cam bikes and for the M8 bikes has the same part number as do other key components.
I ordered an inner trans cover from Ronnies and it will be here tomorrow.
A poster over on HD Forums who goes by "Stonecold" was central to many threads on the M8 bikes with oil transfer going back to 2018ish. Various "fixes" including milling the trans cover and placing lip seal as well as, more recently, milling the trans cover to allow oil to drain out the bottom in one section. For the $60 bucks I paid for the inner cover I'd consider doing that second mod.
I realize HD is now placing the primary vent on the M8s but the Twin Cams don't have that little cavity in the back upper corner. Placing a pipe fitting/vent doesn't seem like rocket science but I wonder it oil splash wouldn't cause oil to splash out that fitting as there is no cast rib in that are of the Twin Cam primary.
I also picked up one of those "fat rods". Let's just say there has been a considerable amount of controversy and pissing match discussion on a couple of forums regarding whether the "fat rod" works at all or whether it holds up.

Anybody have any first hand experience with this annoying issue on Rushmore Twin Cams? I have days off next week and plan on riding to Wisconsin for King of Baggers race with my son in a few weeks.

Thanks in advance.

Guy

[jsachs1]

I tried to vent my inner primary back in the day. I installed a fitting, in the rear of it, as high as possible. Oil found its way out in spite of it. Had to plug it.
John

[HogMike]

Only thing I've heard about this issue is,

Transmission is vented to atmosphere, primary case has a hollow main shaft and will relieve pressure + or - out the trans vent.

Speculation is the primary will go into a "negative pressure" under certain conditions and draw any splash oil at the end of the main shaft at the slave actuator area.

Factory guy we had here knows about the problem and has tried different sprocket shaft seals, double seals, reversed seals, etc.
I think they gave up and just slapped a vent to the primary and called it a day!

Couple of the new bikes here STILL have the primary vent but now all the clutches are cable operated so I guess it was not a problem with the hydraulic clutch?

Curious 🧐

[guydoc77]

Only thing I've heard about this issue is,

Transmission is vented to atmosphere, primary case has a hollow main shaft and will relieve pressure + or - out the trans vent.

Speculation is the primary will go into a "negative pressure" under certain conditions and draw any splash oil at the end of the main shaft at the slave actuator area.

Factory guy we had here knows about the problem and has tried different sprocket shaft seals, double seals, reversed seals, etc.
I think they gave up and just slapped a vent to the primary and called it a day!

Couple of the new bikes here STILL have the primary vent but now all the clutches are cable operated so I guess it was not a problem with the hydraulic clutch?

Curious 🧐

Well that does make you wonder about the root cause. I just figured that, since this issue only first became apparent on the Rushmore bikes (with hydraulic clutches), it must have something to do with the hydraulic clutch. Hmmmmmm. I even priced out all the parts/pieces necessary to convert mine to cable clutch (the '14-'16 Road Kings had cable clutches) but that is spendy. I have decided to use the M8 primary vent kit, which I picked up the other day, in my Twin Cam inner primary.

I talked to a very helpful guy at BDL yesterday as I have their "ball bearing" pressure plate installed. He suggested placing the vent on top of course, in front of the starter. If it pushes or pulls oil out of the vent hose once installed, I have imagined fashioning some sort of tray of deflector around the vent to shield it from oil. I know the M8 inner primary has a little "chamber" like area cast into the inner primary way in the back on top that the vent tube gets installed into. I figure it's worth a try and I can always put a brass plug into the small hole if the experiment is a bust. I also have my eye on an inner primary on an auction site. It may remain stock and I'll use mine for a guinea pig, or it may serve as the guinea pig itself. It seems reasonable to conclude that the trans to primary oil transfer on a Twin Cam is due to the same root cause as on the M8s. And, from what I have read, and I've read a lot, Harley's little hose seems to fix the problem.

Guy

[guydoc77]

I can tell the interest in this topic is earth shattering LOL.

I vented the primary today.
Used the HD hose for the M8s. Placed it on the flat just in front of the starter.....with some modification.
The placement In the M8 inner primary is in the little chamber on the upper rear of the primary so results in oil splash shielding for the hose. Well the TC inner primary has no chamber. I was worried before I started that the lack of oil shielding provided by the chamber on M8s would result in puking oil out the hose on the TC. It did. With some 1/4" brake line with a few strategic bends such that the heighth of the breather is higher, I came up with a setup that hopefully works. We shall see. Although the forecast calls for possible snow flurries here tomorrow.

Guy

[Appowner]

Got Pics?

[guydoc77]

I did snap a few pics.

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[JSD]

What sealer is that?

[HogMike]

If you're talking about a sealer on the HD hose, it's made to install without, just a little lube to pull it through.
The primary case thickness should be the same from the M8 and earlier twin cams I think.
 I never had any oil transfer issues with the twin cam clutch systems.

[HogMike]

Here's another version that has the vent tube in front of the starter.You cannot see attachments on this board.

[Deye76]

"I never had any oil transfer issues with the twin cam clutch systems."
My experience as well, 2015 RG or 2014 RK.

[guydoc77]

"I never had any oil transfer issues with the twin cam clutch systems."
My experience as well, 2015 RG or 2014 RK.

Well I did.
Looking into it, there were occasional Twin Cam Touring bikes that had this problem. HD had a "tech bulletin" which suggested installation of a new sprocket side engine crank seal and spacer. That was really the beginning of HD trying to figure out this "vacuum must be developing in the primary and pulling trans oil through mainshaft" theory. Even now, when you read posts on forums, some are fairly convinced that the "vacuum" has to be coming from the upstroke of the piston pulling air through the primary. Most importantly, the trans ---> primary oil transfer issue only occurred in bikes with hydraulic clutches.

Obviously the issue became far more common on M8 bikes, which had their own evolution of "solutions" from HD culminating in the vent kit. I suspect there is an inherent design issue with the hydraulic clutches as, even on M8 bikes with cable clutches, this oil transfer was not an issue. Interestingly enough, HD now has gone back to cable clutches on touring models. The other thing to note is that the inner primary was considerably slimmed down on M8 bikes as compared to Twin Cam bikes ?maybe augmenting the "vacuum" issue?

So it was a fairly uncommon but known issue on Twin Cam bikes with hydraulic clutch '14 and up. HD actually was aware and came up with the "tech bulletin". Not sure though if the crank seal "fix" was actually a fix.

I have only 100 miles since my redneck vent install but, 1)it is not puking oil and 2)trans oil level didn't move a millimeter on the dipstick. And this included a stretch of undiscloseable distance on an undiscloseable road at 120-130 mph. My plan was to put a few hundred more miles on it and report back here. I still will. A few days prior to the vent install though, I can say that in 200 miles I was down four ounces in the trans.

Guy

[guydoc77]

If you're talking about a sealer on the HD hose, it's made to install without, just a little lube to pull it through.
The primary case thickness should be the same from the M8 and earlier twin cams I think.
 I never had any oil transfer issues with the twin cam clutch systems.

Correct about the no sealer. Drill a specific size hole and push/pull vent hose through. The vent hose has a "flange" in its body that pulls in and seals both sides of the primary.

Incorrect however about the primaries being the same on TC and M8 bikes. They are definitely different. Which makes selecting a location on a TC bike a bit of an experiment. There is a flat to the rear of the starter on the TC bikes but considerably less room there to work with primary on bike plus, I was concerned about oil puking as mentioned and placing the vent behind the starter results in the vent hose placement directly over the drive belt. Didn't want to chance that.

If there were ever a "next time", I would move the hose slightly rearward from where I have it now. A sharp eye will note that I had to trim the flat on the vent hose to get it to follow the contour of the inner edge of the inner primary.


Guy

[guydoc77]

Here's another version that has the vent tube in front of the starter.You cannot see attachments on this board.

That appears to be an M8 bike. The TC primaries don't have those convenient "chambers" which provide a kind of built in oil splash baffle. I thought about coming up with something to glue in (like the oil tray for the compensators a few years ago or maybe a piece of sheet metal glued in). I figured the more complicated I made it, the more stuff to fail/break down the road.

Guy

[HogMike]

I wouldn't expect the primary to have a positive pressure situation to "push" oil out the breather tube.

He M8 bikes went into a "negative" pressure "pulling"
the oil into the primary from what they told me.
That being said, I'm guessing there could be a pulsating effect that may push some vapor out the tube causing the issue.

I never did get a definitive explanation from the engineer that visited us.

I've had other hydraulic clutches since 2003 and never had a problem until the M8 on 2 of bikes.
 

[HogMike]

I know the primaries are different but I'm wondering if the thickness where you drilled the hole for the hose is the same as the "new" narrow cover?
Looks like the hose is seated properly?

[guydoc77]

I suspect the thickness is essentially the same. The vent tube itself fits like a love really. No issue there.

As far as "puking oil", I don't think its being pushed per se by a significant positive pressure. I just think that, wherever you put the vent in a TC, splash from the chain and possibly the pulsing you mention results in puking oil. Either way, by basically extending the length and heigh of the vent assembly this is not an issue as I have it now. Again, the "chamber" on the M8 provides sort of a built in oil baffling and it is no surprise HD places the vent within that chamber. Still vents but no oil gets near the entrance to the hose.

Guy

[guydoc77]

Well 300 miles on the experiment.
Prior to the vent, I would have been off the dipstick in 300 miles.
Just got back and checked the trans oil.
It hasn't moved a bit.
I'm gonna call this a win. For now....
 

Guy

[guydoc77]

Just got back from a 1400 mile trip with my son. So roughly 1800 miles total since the primary vent install. Zero loss of trans fluid in those 1800 miles since the vent. 

[HogMike]

Just got back from a 1400 mile trip with my son. So roughly 1800 miles total since the primary vent install. Zero loss of trans fluid in those 1800 miles since the vent. 

I'm still not clear on what caused the initial problem with transmission oil ending up in the primary. I have my own theory.

Anyone have a definitive answer?

[guydoc77]

There doesn't seem to be a widely accepted cause.
Lots of theories.
I suspect it does have something to do with the hydraulic clutch and its hard parts as the hydraulic clutch is the common denominator in Twin Cam bikes and M8 bikes that suffer(ed) the trans oil transfer issue.
And, after multiple "fix" attempts, Harley eventually went with the primary vent on the M8 bikes and that seems to work, which is why I decided to try it on my '15.
I think it is also significant that HD has gone back to cable clutches on the new touring bikes.
What the root cause is though?
That remains speculation by many of us.
Please share your theory. I'm interested.

Guy