N/C Gearbox bearings.

[DBDBrian]

I note that both gearbox shaft bearings in the chain side crankcase are single metal shield Z type. Installed with the shield outermost, this seems a strange arrangement, as Z type bearing shields are not oil tight, and are usually installed with the shield towards the gears, to protect the bearing from debris.
There have been a few posts recently regarding oil leaks from the drive sprocket, has anyone fitted a single side RS type bearing on the layshaft, with the seal outermost, hopefully giving the oil slinger behind the bearing , and it's drain slot, less oil to deal with.

[ranton_rambler]

I’ll try and remember to check my photos, but I think I built mine with a sealed bearing. I definitely blocked the drain slot as recommended by Nigel Lacey. Bearing was sourced from Nigel.

[DBDBrian]

Thanks Ian, I presume the sealed bearing was successful. ?

[blethermaskite]

I havn't worked on a narrow case engine for years but on all the widecase engines I have worked on I always fit a single rs bearing on the gearbox output shaft and never had a leak problem.
Cheers,
George

[Samurai]

I’ll try and remember to check my photos, but I think I built mine with a sealed bearing. I definitely blocked the drain slot as recommended by Nigel Lacey. Bearing was sourced from Nigel.

Same here.

[Bevel bob]

I too fitted a std bearing with a seal on the outside .did not block the drain channel (think its for rear chain lubrication). If I get the oil level a touch high it leaks. But otherwise not an issue.Probably should have fitted the pen steel washer to keep the shimming as was.

[LaceyDucati]

Brian

I've always used a 2RS bearing (contact seals, avoid electric motor bearings) leaving both seals intact. I also seal the oil return groove in the bearing housing. Although at first thought it seems the bearing isn't getting oil feed as such, it's never been an issue in any of my engines. Out of curiosity I've removed the seals from replaced bearings and found them to be adequately lubricated with what looks like oil... Also bear in mind a 2RS bearing is specified in this location on all bevel twins as original.

I also lose the thin 0.5mm shim in the bearing housing that sits between the bearing and sprocket. This is part of the original thrower system and is no longer necessary, it also removes one more potential leak path.

In general for all, other oil leak causes are:

A Loose sprocket.
A poor surface on the back of the sprocket can cause leaks across the bearing to sprocket faces.
A crimped or restricted breather, increases crankcase pressure.
Worn rings, same as above
Too much oil. I always run less oil than specified in the handbook for racing, without issue. 3 and a 1/4 pints (1.875 Litres) in a narrowcase. Can't see that being any different in a road engine, especially as most change the oil more often than specified due to low mileages.

Hope some of this helps

Regards

Nigel

[ranton_rambler]

Thanks Ian, I presume the sealed bearing was successful. ?

No particularly good photos, but in one of them I can read the bearing number as 6204-2RS, which I think means sealed. It doesn't leak from that area, or the clutch pushrod, but the pushrod has the Lacey seal conversion, and I also fitted a new pivot pin.
The drain slot is sealed with epoxy type stuff from memory. I think the drain slot is meant to allow oil which has gone out through the bearing to get back in again, and the scroll on the sprocket helps it to do so rather than sending it flying off.
Ian

[DBDBrian]

Thanks all for the very comprehensive replies. I think I will go for the 2RS approach, this had crossed my mind, but I was concerned about long term lubrication of the bearing, Nigel has put my mind at rest on that one. There is no substitute for experience.

[Ventodue]

There is no substitute for experience.

And the willingness to share it. I'm sure we all appreciate Nigel's exceptional contributions to this Forum.