Clutch Pushrod O-Rings

[koko64]

I have purchased spares of the little o rings for the dry clutch pushrods at the slave cylinder end of the rod. There are two of them that sit in the grooves on the rod.

Be aware that many of the o rings sourced by both dealers and aftermarket suppliers will leak from new due to their not quite correct dimensions. While some o rings sit proud of the pushrod giving the impression they will seal, they in fact leak because they are not thick enough to fully fill out the grooves, so they flatten out and leak out behind the slave cylinder. You will smell the oil burn as it drips onto the exhaust pipe crossover. Bloody annoying.

Grabbed me mates pushrod out of his '92 Superlight with oem "back in the day" o-rings which were quite worn but fat enough to fill the groove and it worked. You will know if the o rings are not right because you can fit your thumb nail in the gap between the o ring and gap in the groove. So a fat o ring works better than a tall one. I will go to my local bearing shop to see what they have.

I have bag of them from the dealer that dont work. i have tried aftermarket shops and had the same issue. Maybe they work in the newer bikes?

Anyone able to shed some light on this?

[ducpainter]

I could guess...oil travelling into the groove, under the ring, and out the other side?

[koko64]

Sounds good to me. The bad o-rings have too pointy a profile for sure.
I had issues with aftermarket suppliers so got some from the dealer and the leaks were worse again. Originals back in the day might have been an odd, hard to get spec with a round, fat profile.

[ducpainter]

Have any later push rods to compare grooves?

Do you have a dimension on the o-ring you have?

[koko64]

I'll measure the o-rings and compare long later slave and short, early slave rods.

[ducpainter]

They still make o-rings in different sectional dimensions.

I'm wondering if the groove changed on the later rods, something got lost in translation, and the thinner o-ring ended up as the replacement.

[koko64]

They still make o-rings in different sectional dimensions.

I'm wondering if the groove changed on the later rods, something got lost in translation, and the thinner o-ring ended up as the replacement.

You're spot on. The retrofit doesnt work to the old rods as the grooves are wider. I measured black "oem" and brown CCW o-rings at approx 1.74mm in thickness. CCW o-rings appeared stiffer. Both filled the grooves of later push rods but left a gap in the early push rod grooves which were wider and probably need a 2mm o-ring. This makes me think that the spec is based on the later, longer push rods suited to the later slave cylinders, so probably no issue there. I checked the o-rings (both types) on the later push rods and they filled the grooves flush and tight, but would spin loosely on the early push rod. So there you have it. If you still run the early push rod you will have to source wider o-rings closer to 2mm. The gap is quite noticable to the naked eye.


I guess I can swap to a late slave cylinder if I cant find the correct o-ring.

[koko64]

2mm worked

[Privateer]

I had a lot of trouble with leaky orings, replacing them twice a year or so, until I replaced the throwout bearing.  Haven't had a leak or replaced an oring since then.

[koko64]

I change that bearing if in any doubt about its condition.