Westfield reverse box rebuild

[mr_fibuli]

I'm in the process of fixing the reverse box from my bike engined Westfield, after I found the oil that is normally ejected from the breather had turned a nasty shade of metallic grey.

Inside it looks a bit like this (not my pic):



The culprit seems to be the smaller reverse shaft bearings which sit at the top of the box, well away from the oil, which have gone very crunchy.

I don't have any engineering knowledge, so is there any reason why I shouldn't replace these bearings with rubber sealed ones? Would that solve the lack of oil?

In my box the larger main shaft bearings have already been replaced with rubber sealed ones, I guess last time the box was serviced by the previous owner. These seem okay, but I guess it wouldn't hurt to swap these too while everything is in pieces.

[anonymous-user]

The issue will be with the "max speed" rating of the sealed bearing! The fastest rating will be for the unsealed one (careful of the difference between "sealed" and "sheilded" BTW!) and the grease filled sealed on will be significantly lower.

Work out the max speed of each shaft, measure the bearing sizes and then use one of the many online bearing catalogs / suppliers to find a suitable replacement.

[stevieturbo]

I presume there is oil in the gear casing, therefore there should be no problem with lack of oil

They dont need a constant stream of oil, splash fed is enough.

[mr_fibuli]

Thanks, I've done some quick numbers, I think the max prop speed at 120mph would be about 6300rpm.

The bearings "Limiting Speed" is 28000 for the open ones, and 13000 for the rubber sealed ones.

The box is filled about a quarter full with oil. This is the gear train, so you'd expect the chain and gears to throw plenty of oil around the top bearings.



The other concern is whether sealed bearings might add noticeably to the transmission losses caused by the box?

[stevieturbo]

I'd say any difference would be negligible.

I'd prefer the open oil fed ones if it was mine though.

Heat aside, probably isnt any reason you couldnt use the sealed ones though

[anonymous-user]

I assume the bearings on the "through" shaft must be "one side sealed" (1RS) already to stop the oil leaking out!

Personally, i'd just rebuild it with some nice new std bearings, that match the ones i have in there, fill with some nice new clean oil and enjoy driving it.... ;-)


The only advantage to 2RS fully sealled bearings is that any metallic particles or dirt in the main gear chamber won't be able to make it's way into the bearings, but it should be pretty dam clean in there, and hopefully there is a magnet in the "sump plug" to catch those small bits! (if not, stick on in somewhere!)

[unstable load]

I agree with you that the chain will fling oil around the box, but I can't see much of that oil getting to the bearing on the other end of the shaft.
A quick rummage on Googoo brought this up concerning oil being ejected, maybe it will help your case....
http://forum.wscc.co.uk/forum/index.php/topic/1025...

[anonymous-user]

If you are really concerned about bearing oil flow, then you can get the shafts spark eroded to put a small dia hole down their centre line, and then do the same at right angles from the root of one of the gear teeth. That will then actively pump oil into the bearings as the gears mesh. (it is not without penalty, as any stress raisers in the locality of the gear root can be bad!)

You could also probably come up with some internal "tinware" that screws to the inside of the casing and helps to direct the oil splash into the bearings, a lot of gearboxes use little plastic "gutters" that attach next to the top of the upper bearings in the case (the ones far above the oil level) and catch splash and channel it into the bearing voids



Personally though, if it's worked so far, leave it alone!