Rocker Lockers offers new centrifugal oil seal to stop the transfer
As some of you know the new M8 bikes with the hydraulic clutch and some of the twin cams are experiencing oil transfer from the transmission into the primary side. This transfer is through the tunnel where the clutch push rod goes through the main shaft in the transmission.
Most owners do not even know they are having a problem since very few check the amount of fluid being drained from the transmission and primary. There have been reports of only a few ounces of fluid left in the transmission and the primary overfilled, this can lead to transmission problems and hard shifting problems.
The previous bikes had a different clutch release and the shaft had a oil slinger to prevent oil transfer, in the new design there is not enough room.
There have been several attempts to eliminate this problem, Harley has tried several but had limited success at this time. One was a plastic slinger that went on the push rod between the main shaft and the hydraulic actuator. I do not believe they still offer this and it was a dealer only part. Another factory fix is a vent on the primary, so far the vent looks promising and word is the new bikes are coming with it. Their theory was that the primary was forming a vacuum as it cooled and sucking oil from the transmission.
Harley is now offering the primary vent to the general public, it runs about fifty dollars plus installation. It is covered under warranty. The primary cover needs to be taken off and a hole drilled for the vent. We have been contacted by owners who are still having bikes transfer with the HD vent and we are furnishing our kit and they have been successful in stopping the transfer.
We feel even if the oil is being sucked into the primary by a vacuum we feel the cure is to keep oil out of the main shaft tunnel.
Once oil is inside the spinning tunnel since there is nothing to stop it is pushed into the primary by centrifugal force. (The main shaft spins as long as the motor spins)
One solution from the aftermarket has come from a poster on the HDforum, $tonecold. His solution is to install an oil seal on the end of the shaft to prevent oil from entering in the tunnel. It involves removing the side plate on the transmission and having it machined for a seal and installing a machined nut on the end of the shaft to go inside the seal.
His solution has had very good results, however he has stopped offering the kit.
Another solution is to install a fatter clutch push rod.
Results on this have been good but mixed since the tunnel diameter varies in different bikes. They are using 9mm rod, or .354, the tunnel on the main shaft run from .376 to .382 so you can see there is still a gap and nothing inside the tunnel to stop the flow. There are a lot of guys using the Factory vent fix and the fat rod with good results.
You can read more at
Our concept works on a different principal using a tapered bushing inside the main shaft tunnel that acts as a dam using centrifugal force to keep the fluid from migrating through the shaft, we feel that our kit is easier to install and less complicated. We have several kits being tested at this time and so far had a 100 percent success with the centrifugal seals stopping the transfer.
We have waited for these result before offerings any other kits, and now we are looking for more testers to try the kits.
How Our Centrifugal Oil Seal works
The centrifugal seal works exactly as it sounds, the insert is tapered so that as the main shaft turns centrifugal force acts as a dam, the oil can not climb the ramp and pushes the oil back into the transmission
The insert also is a snug fit on the clutch push rod and wipes oil off the shaft as it tries to pass. The insert is a medium hard brass so it will not wear the steel push rod shaft. The seal is not airtight against the push rod shaft so it will still let the primary breath.
The holes in the main shaft run from .376 to .382 so the inserts are designed as a press fit but the brass will press in fairly easy no matter what size the tunnel.
The kit also has an oil slinger that slides over the push rod shaft, and sits just outside of the tunnel, this keeps oil from entering the tunnel on the shaft.
The inserts are installed on the transmission side of the bike and the transmission side cover and inner side cover need to be removed in order to expose the transmission main shaft. Please refer to your service manual for this procedure. (installation should be done by a qualified mechanic)
Remove your clutch push rod.
The small end of the insert goes in first, start with the 5/16 bolt and gently tap the insert in until the bolt head hits the shaft end.
(We are just showing the installation in the main shaft of the transmission, but procedure on the bike is the same.)
Then use the installation tool to run the insert in an additional half inch. (This is what I feel will do the best for keeping the fluid from moving into the tunnel past the insert). It is also enough room for the oil slinger to clear inside the tunnel when the clutch is depressed.
To install the oil slinger, one end is larger than the other, slip the big end over the rod (all the push rods that have tested are .312 so the slinger is designed to be a press fit.) I use my lathe, with the push rod chucked up, the aluminum block against the end and press it on. Or place the aluminum tool in a vice then tap the push rod down into the tool pushing the slinger onto the rod.
I use my lathe to press the oil slinger on the push rod.
You will need to use your judgment on how far up to put the oil slinger. I would like to see it just at the edge of the main shaft so any oil will drip/be slung off before it goes into the tunnel. A lot will depend on the position of the hydraulic actuator for the clutch. .
One Word Of Caution
One disadvantage that I can see is that once the oil slinger and insert are installed the push rod can only be pulled out on the trans side, I don’t know if that is going to be a problem but want to mention it. (The oil slinger will not go through the insert.)
At this time we are not even sure if the oil slinger is needed so we want you to know that you need to be aware of this for future work.
If you need to remove the insert you should be able to make a wire with a hook and pull it out, worse case pull your adjuster out of the clutch side and put the installation tool inside the tunnel and push it out with a 3/8 dowel rod.
We Are Looking For Testers
We are looking for experienced techs that understand the problem and have a problem bike. If you are going to take the bike somewhere to install this kit, we ask for your tech to contact us so we can explain the concept.
This kit is experimental and we are not charging for it during the testing period, However we would appreciate help on shipping and the cost of making the tool to install the seal. This is voluntarily and $20 would be appreciated, contact me for more information on this.
Testers need to be aware that this is experimental and that they are responsible for any possible problems.
Installation is fairly simple but any work on a transmission needs caution.
This concept is new and we are writing the instructions as we go, so any suggestions would be appreciated. We would also like feed back from our tester both positive and negative.
We make these kits as they are requested so there is sometimes a short delay in response and shipping.
Thanks Steve Jones, Harley Cruiser, Rocker Lockers.
You can contact me at Harley_cruiser@yahoo.com