K Model Primary Filler Cap Leak

Production K Models

K Model Primary Filler Cap Leak

Postby BigDen » Mon Oct 04, 2021 9:51 pm

Hi All,
I’m hoping you can help me with an oil leak problem on a K Model I recently got from my brother. My experience with Harleys has been on a 1954 Panhead I have owned since 1969. The K engine was built up by my brother from a mix of parts. From my brother’s notes and my inspection, it has left side 53 K case (belly number 553-1219), right side case is a KR (belly number 223), with KH flywheels, pistons, cylinders, and heads. I have only recently gotten it running, and it has a steady oil leak from the small vent hole in the center of the primary filler cap. There is no oil leaking from the timing case breather tube. As best I can tell, it has no breather valve between the crankcase and the primary case. From searches on this forum, a 53 K should have 25100-53A Crankcase Oil Syphon Tube Assembly. This K has what appears to be the 58-69 XL/XLH primary chain tensioner. Where the lower hole should have the syphon tube assembly, this K has a solid bolt.
I initially thought that without a crankcase to primary case vent, there would be no path from the crankcase to the primary case to pressurize the primary volume, but then I thought there might be a path past the flywheel sprocket shaft and into the primary case. I don’t know what flywheel sprocket shaft and seal system is on this K motor. If crankcase pressure is getting past the flywheel sprocket shaft and into the primary case, with no crankcase to primary vent, there would be no way to relieve this pressure except out the primary filler cap vent hole.
If this is a plausible theory for my oil leak, do you experts have any suggestions for adding a crankcase to primary case vent in this motor? I have found the 25350-37 breather valve on eBay, but haven’t found the 25111-53 crankcase oil syphon tube screw or the 25101-53A crankcase oil syphon tube. Since I don’t appear to have any crankcase wet sumping, would it be a reasonable solution to machine a screw that would accept the breather valve and forgo the syphon tube? Another alternative I have considered is plugging the primary filler cap hole, drilling thru the tool box mounting hole on top of the primary case, and adding a vent fitting and hose.
Any suggestions you experts might have would be appreciated.
Thanks, Dennis
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Re: K Model Primary Filler Cap Leak

Postby wz507 » Tue Oct 05, 2021 12:16 am

BigDen wrote:I initially thought that without a crankcase to primary case vent, there would be no path from the crankcase to the primary case to pressurize the primary volume, but then I thought there might be a path past the flywheel sprocket shaft and into the primary case. I don’t know what flywheel sprocket shaft and seal system is on this K motor. If crankcase pressure is getting past the flywheel sprocket shaft and into the primary case, with no crankcase to primary vent, there would be no way to relieve this pressure except out the primary filler cap vent hole.
If this is a plausible theory for my oil leak, do you experts have any suggestions for adding a crankcase to primary case vent in this motor? I have found the 25350-37 breather valve on eBay, but haven’t found the 25111-53 crankcase oil syphon tube screw or the 25101-53A crankcase oil syphon tube. Since I don’t appear to have any crankcase wet sumping, would it be a reasonable solution to machine a screw that would accept the breather valve and forgo the syphon tube? Another alternative I have considered is plugging the primary filler cap hole, drilling thru the tool box mounting hole on top of the primary case, and adding a vent fitting and hose.
Any suggestions you experts might have would be appreciated.
Thanks, Dennis

There is no need for the crankcase breather if the crankshaft seal is in good shape. Of course, there will always be some small amount of air expelled from the primary as the entire system warms up, but that shouldn’t give the stream of leakage you are describing above. Have you tried removing the felt from inside the filler cap so you don’t have an oil saturated felt wad between the primary and vent hole?

I’d start with a few simple diagnostics and see what you have going on. Perhaps start by installing a tube through the primary filler cap so you can attach a rubber hose and see if there is in fact air continually being pumped out of the crankcase, into the primary, and out the filler cap. The image below shows a filler cap modified with a brass tube so a rubber hose can in turn be attached.

LR filler cap with tube installed.jpg
LR filler cap with tube installed.jpg (68.77 KiB) Viewed 4364 times

Placing the end of the rubber hose in a cup of water and observing bubbling rate with the engine running provides an easy means of monitoring any air entering or leaving the system. If air is perpetually bubbling out of the primary, then the crankshaft seal is shot and needs to be replaced.

20200628_103358.jpg
20200628_103358.jpg (103.4 KiB) Viewed 4364 times

If no air is detected leaking out of the primary cover then you might want to route the open hose to a much higher position, as shown below, and drive the bike in this configuration.

LR K breather test 1.jpg
LR K breather test 1.jpg (47.91 KiB) Viewed 4364 times

If no oil is observed “jacking” it’s way up the clear tube as you drive for a prolonged period of time, then it is simply an issue of properly demisting the oil in the primary to stop the leakage.

Let us know what you see and we’ll go from there.

To your point of venting the primary via the tool box stud/hole, this is certainly a possibility as well as doing similar to one of the rear motor mount bolts atop the transmission. XRs were vented out the top of one of the rear motor mount bolt holes. You could also install a breather fitting on the tranny case under the kick start cover, which would be totally concealed. However, all of these locations are quite active with respect to oil mist/sling, so for sure some means of demisting the output would be necessary to stop oil leakage.
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Re: K Model Primary Filler Cap Leak

Postby BigDen » Tue Oct 05, 2021 2:32 pm

Hi WZ507,
Thanks for the quick reply and diagnostics suggestions. Regarding your first question, I had not tried running without the foam pad in the filler cap. Rather than trying that first, I modified the cap as you suggested with a tight fitting 1/8” diameter brass tube thru the vent hole and a rubber tube into a cup of water. With the engine running, I observed essentially no air bubbles in the water, just an occasional few bubbles, no streaming of bubbles at all, and sucking of water up the hose. Unfortunately, the bike is not currently registered, so I cannot try road testing as you suggested. I did try cleaning the foam pad and reinstalling and running a test without the tube, and there was no oil leaking out the vent hole. I’m not sure what changed, but so far, the test results are encouraging.
This motor was built up in 2003 with used, NOS, repop, and reworked used parts, but it wasn’t started until April 2021. Since then, I have been sorting out carb issues, so the motor only has a few hours of running time. The oil leak was annoying, and was limiting the amount of time I wanted to run the engine.
Thanks for your help. I’ll update this thread as I get more running time on the engine. With these limited test results, do you recommend any modifications to the primary venting system?
Dennis
BigDen
 
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Re: K Model Primary Filler Cap Leak

Postby wz507 » Tue Oct 05, 2021 4:42 pm

Sounds like you may have already solved your problem - yeah! Part of the solution to keeping the tranny oil in the primary is to have the brass tube you inserted protrude into the primary the full length of the filler cap. If the brass tube does not protrude into the cap as described, you should push it on in until flush on the inside and outside and see if this solves your problem.

On my bike the ultimate solution was to press a short piece of hobby shop aluminum tubing into the filler cap, add a small epoxy filet for support and finish the outside smooth. I can’t recall for sure, but believe the tubing OD might have been about 0.156”? (I believe it was a metric size), because a number #22 or #23 drill was just about perfect for opening the hole in the cap before pressing the tube in.

LR inside cap.jpg
LR inside cap.jpg (66.9 KiB) Viewed 4279 times


LR outside cap.jpg
LR outside cap.jpg (58.07 KiB) Viewed 4279 times

The downside to this entire approach is that you no longer have a water and dirt barrier like with the felt pad, but in my case I don’t ride in the rain and stay on hard surfaces so not a concern. I ran without a transfer valve in the crankcase because I wanted to run different lubricants in the engine (oil with friction modifiers) and tranny (wet clutch, so no friction modifiers allowed) and could not tolerate the lubricants mixing.

Please keep us posted on your progress.
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Re: K Model Primary Filler Cap Leak

Postby BigDen » Wed Oct 06, 2021 12:26 pm

Thanks for suggestion regarding the tube in the filler cap, and explaining your reasoning for not running a crankcase vent. It’s good to know that with a good primary shaft seal that the vent is not required.

I did some more running while continuing to sort out the carb jetting, and again, no oil leaking from the primary filler cap vent hole. It will be a while before I get it on the road to see what happens at higher rpms and longer running time.

Dennis
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Re: K Model Primary Filler Cap Leak

Postby wz507 » Wed Oct 06, 2021 12:38 pm

BigDen wrote:It will be a while before I get it on the road to see what happens at higher rpms and longer running time.
Dennis


I’ve got 2500 mi on mine and yet to see any oil dampness around the hole, so I think you’re good to go.
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