Kickstart leak

htown16 · Nov 26, 2019

When I built my 72 750 I had an oil leak on the kickstarter using the oem oring so I replaced it with a SKF 9815 seal that was recommended by someone on this forum. That was 8 years ago and it hasn't leaked a drop since. I recently finished my 74 850 build so I installed the same seal since it had preformed so well on the first bike. In less than a thousand miles I've had 3 of them go bad and start leaking. I've done some very careful measuring and the seal lip is riding well in board of the splines and the slight tapered part down to them. I can even see a slight witness mark. There doesn't appear to be any damage there and it measures out to almost exactly 1.00" so I don't think it is worn much. Because I'm using a roller layshaft bearing I also shimmed the kick start shaft per Old Brits instructions so there is very little lateral movement. I'm getting tired of pulling the cover off. If anyone has any suggestions I'd love to hear them.

baldy · Nov 27, 2019

Try polishing the kickstart shaft to remove any corrosion or scratches.

RoadScholar · Nov 27, 2019

baldy said:
Try polishing the kickstart shaft to remove any corrosion or scratches.

+1

I went through this effort less than a week ago. The k/s shaft will mount securely in a relatively small lathe; I set the lathe's gearing up to run the chuck as slow as possible. I started with 600, went to crocus cloth and finished with gray compound on my polishing wheel; I polished the shaft from the end of the k/s splines back about 3/4". I am pleased with the results, but until the motorcycle has some miles on it the jury is out.

I suspect that running ATF may present the seal with a greater challenge than running a traditional heavy weight gear oil, but I can't say for certain as I don't run ATF.

Best

comnoz · Nov 27, 2019

No, ATF doesn't leak any easier. Of course if there is a hole it may leak faster when cold. Hot there isn't much difference in viscosity.
In fact ATF has seal conditioner in it so it keeps the seals pliable -cause if the seals in an automatic transmission get hard, it stops working.

But I have always skipped the v-ring seal and just gone to real seals -and polished the shaft.

jseng1 · Nov 27, 2019

I have no leaks at the kickshaft - I use the next larger diameter O ring (viton) and work it into place with an oily wooden dowel rod. Its a tighter fit.

I tried some fancy oil seals but ended up with the technique above. No modifications.

htown16 · Nov 28, 2019

Okay, I will polish the shaft with finer and finer grit paper. I have a choice to make. I have the skf9815 lipped seal and an andover quad ring seal on the work bench. Need to decide which one to try. It's not a huge job changing the seal except I like to use 3 bond on the cover gasket and it's a pain to get the cover loose and then scrape the old gasket off.

baz · Nov 28, 2019

htown16 said:
Okay, I will polish the shaft with finer and finer grit paper. I have a choice to make. I have the skf9815 lipped seal and an andover quad ring seal on the work bench. Need to decide which one to try. It's not a huge job changing the seal except I like to use 3 bond on the cover gasket and it's a pain to get the cover loose and then scrape the old gasket off.

Just use grease on your gearbox gasket

eskasteve · Nov 28, 2019

baz said:
Just use grease on your gearbox gasket

Not to hijack this post but I've used grease on gaskets for the last 40 years with no problem. I use a hi temp grease that's designed for use on brake calipers.

rvich · Nov 28, 2019

I bought a 9815 off eBay and developed a leak right away. I then ordered one through NAPA and have not had an issue. It makes me wonder if that first seal had been on a warehouse shelf for twenty years.

Torontonian · Nov 28, 2019

Also it could be the seal outer bore of aluminum itself. I'd clean it with thinner/cleaner , then put a thin layer of Hylomar on both surfaces then squarely and evenly tap the seal home. If you feel the seal where it rests on the shaft it should be pliable. Not hard.

Danno · Nov 28, 2019

Mask the splines with tape for installing the outer cover, especially with a vintage kicker shaft.

htown16 · Nov 28, 2019

I've done a bit of careful measuring and with the bushing installed the gap between it and the inside of the cover is more like 3/16" while the seal is only 1/8" thick. The oem o-ring is listed as 1/8 thick also. I was think about putting some sort of shim behind the seal which would also move the lip a little further in board on the shaft. I'm not having any luck finding a shim that size though.

texasSlick · Nov 28, 2019

htown16 said:
.......... I like to use 3 bond on the cover gasket and it's a pain to get the cover loose and then scrape the old gasket off.

Use one of jseng's fiberglass reinforced silicone gaskets on the cover. No sealer required and reuse indefinitely. These type gaskets are the only gaskets that finally stopped a persistent weep on my timing cover.

https://jsmotorsport.com/product-category/gaskets-norton-motorcycle-bike/

FWIW .... I am using the quad type O ring on the K/S with no leaks ...... yet.

Slick

justin scroope · Nov 28, 2019

A hydraulic backing ring with the standard oring fitted in the groove after putting some RTV gasket cement in the groove works for me. The RTV can be left to partially or fully cure before fitting. If you can,t source a backing ring you could use a piece of inner tube to fill the space in the groove.

htown16 · Dec 10, 2019

Thanks for the replies. I ended up using the Andover x-ring instead of the Skf seal. I put a smear of hylomar on the inside the groove before installing the seal. I polished the shaft and smeared grease on it. I didn't use any gasket on the cover just a smear of hylomar on both faces. Idea being the seal would ride a little more inboard on the shaft. Took it on a road test yesterday and everything appears dry. We will see how long it lasts.

dynodave · Dec 11, 2019

My take on this topic
Kick start shaft .996"
outer KS bush 1.000" new/hard as tool steel/ if worn, may grow .001+ on bottom from kicking wear.
Inner shaft and bush similar but larger nominal diameter.1.125"-KS shaft 4 thou smaller.1.121"

KS outer floats/supported to center by oring, normally while running does not touch bush.
Inner KS shaft is pressed to the bottom of the bush by the KS ratchet spring.
KS always show way more wear marks than bushes.

When kicking the oring, quad X, lip seal, is deformed and if old/hard may open a slight gap temporarily.
Also as the KS shaft ages in the weather a light rust sheen appears and it can grind on the seal when kicked since the KS shaft is not IN/OUT precision held in place.

The "me too" statement...
My combat rebuilt in 1988 with normal oring, did not leak until 2002. Oring test completed.
I then put in a quad X- still OK for gear box pressurization experiment. Still have a bag of 99?? left over for other jobs coming up.

jbruney · Dec 11, 2019

Those reinforced gaskets spoken of earlier are truly wonderful as they are the only ones I've come across to stop my PITA tappet cover oozing for any length of time. Great stuff there if not over tightened.

jseng1 · Dec 11, 2019

I tried the quad type oil seal for the kickstart but I'm having better & longer lasting results just using the next size larger diameter round O Ring.

Here's the Oring break down to eliminating leaks:

Tranny kick shaft – use wooden rod and oil to force in a oversize 1/8×1-1/8 ID viton Oring (take your time).
1/16th by 3/8th OD hard viton Oring clutch push rod seal (after-market oring nut item for belt drives).
Oversize 3/32 x 11/16 ID viton O ring shift lever – force into place with a wooden rod.
Tranny cam & shift pawl – force in oversize 3/4 OD x 3/32 viton Orings.

Kickstart leak

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