layshaft bearing-bushing up-grade

rx7171 said:

Since I have a 72 I'm guessing it isn't a "late commando" so should I still think I must replace the bearing?

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Yes, it can happen to any standard Commando layshaft ball bearing eventually-as a few of our members discovered for themselves!

Unclviny said:

As I understood Mick the reason that he does not like Rollers in this application is "side-loading" (Rollers need to run absolutely true and G/B's flex).
Vince

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Rollers need to run absolutely true unless you use a roller bearing with E specification which endures higher axial and radial load (not like Torontonian's "E is for engine applications") Your crankshaft runs on two of those roller bearings (NU/NJ306E) , do you think your crankshaft runs absolutely true without any flex :wink:

Someone in my foggy past said the Superblend bearings were actually a "barrell shaped roller" to allow for crankshaft whip at higher r.pm.'s. Could be true. The roller bearing we need in our transmissions seems to have a slightly looser fit around the rollers to allow for small amounts of layshaft movement. There are a couple others with even greater clearance available and many other types of this size bearing for specific applications such as railroad work stuff and contaninated workzones and other interesting uses.

Mark,

Great to here you are close o back on the road, happy days in Perth mate. You guys have now got the weather, as well. We are hopefully getting our weather over in Sydney now? The roller bearing is the route I took, using shims from old iso's to control layshaft end float to 5 thou. I am not sure how critical the clearance is, as we are only running straight cut gears? But nice to get the clearance the same as old brits site suggested. I made new bushes for the kicker shaft and also the cases, If you purchased a compete new kick start shaft you should be ok, with a nice fresh bush there. Did you eyeball first gear bush, it is a very weak thin walled bush that tends to wear easily?

The bearing designations, as I understand it are normal clearance, not normally stamped on the bearing is c2, c3 is more internal clearance c4 and so forth. At work we run c5 clearance on Thermo King compressor mains, the manufacturer changed to this larger clearances after failures. It is designed to allow for expansion and compression loads on the bearing when fitted to a shaft and housing. So tighter fits demand more C
The NJ bearing refers to the single lip outer race, and the E is regarding the rounded of rollers, or so called super blend style.

Cheers Richard

Bearing was a FAG NJ203E TVP2. My local man said he would not fit a ball bearing. The roller is the way to go.

DogT said:

Good luck Mark, it's downhill once and uphill 3, resulting in at least 2 more downhills? Got it?

Dave
69S

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Dave never a truer word said :lol: But it's the only way to really understand these old girls I reckon. You learn from your mistakes - I only hope I remember my mistakes if I have to do it again!
We're not far off now stockie. Day of today though. Sisters birthday today and new years day party tonight! :wink:

Mark F said:

My local man said he would not fit a ball bearing. The roller is the way to go.

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I don't know who your "local man" is, but it's unlikely he has anything like as much experience of Commandos as Mick Hemmings.
http://www.norton.norvil.net/mickh.htm

Local man is Murray from Cyclecraft Engineering. Anyone who has anything to do with Norton's around here knows him. It's all he does and has been doing it for years so I trust him.

Do all years of 850 s have this issue. 75 mk3s need the mode for new bearings and lay shaft as well?
Thanks

jeffmack said:

Do all years of 850 s have this issue.

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It applies to all Commandos or in fact any AMC gearbox, but due to the extra power output it's more of a Commando problem because of shaft flexing or sideloading (or both?) the standard metal ball bearing cage eventually begins to break up-which causes the bearing to fail.

jeffmack said:

75 mk3s need the mode for new bearings and lay shaft as well?

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Sorry, but I don't understand what you mean? If any Commando still has its original layshaft drive side ball bearing (especially if it is brass cage and made in Portugal) then all that needs to be done is to replace it with either the roller bearing upgrade or the 6203TB ball bearing.

This is a good thread for background, I have a couple of questions. Let me preface this with I am a chemical guy not a mechanical guy, so I am learning. I got the ball bearing (FAG 6203TB.P63) Hemmings suggests for $40 from that place someone recommended in San Fran (my thanks to that dude.) I also got a gearbox rebuild kit from Norvil, and it has a roller bearing in it. Not to start this all up again, I just want to understand this.

Roller bearing: 1) the roller bearing will allow the layshaft to float to the shifter side to the extent that the inner race can move out toward the right hand side (the riders right hand side, toward the kicker shaft side) and that is why one shims the kicker side. This float is probably limited by gears moving over, but needs to be controlled. However, the float to the drive side is limited to the inner race of the roller bearing mating up with the outer race. I think I get this. 2) The roller bearing I got from Norvil is SNH, anyone had experience with this manufacturer? It is marked NJ203.E.M and is a C3 clearance (one C over normal.) 3) The inner race of the bearing I have is a press fit on the layshaft, innner race ID is very close to the layshaft diameter. Also, this bearing has a brass cage that covers up a whole lot of the area one would like lube to get into.

Ball Bearing: Mine was frozen on the shaft; the bearing has about a 69 mil ID, while the shaft is a 69 mil diameter, the new one is the same. - I have about worn my poor old Mititoyo 6" dial caliper out measuring these over and over (caliper is good to .5 mil.) So, I am not great with calipers, but these parts are a darn tight fit, even greased up and ready to go. In the Hemming video, I believe that he shows the bearing slips on and off the shaft of his rebuild. 4) So, does this mean if you use a ball bearing like the one originally in there, or the one Hemmings suggests, there is no end play, the bearing is pressed in and the layshaft rides solid, or does the shaft need to slip in the inner race like in the video and the bearing is allowed some bit of end play? But if the shaft slips on the inner race, would a guy need to shim the layshaft a la the roller bearing?

Side note, on my bike, the first gear bushing on this bike was totally loose, bell mouthed (so the outer end ODs were greater than the inside OD) and the kicker side was really chewed up. But, the kicker bush was loose in the housing, so I think that is what did it. Here is a photo...



I am trying to understand the functional aspects of each bearing type.

My last question is, 5) the cast housing in the gear box that holds the layshaft bearing must have a pretty precisely machined flat that this bearing seats into, so that the run out of the shaft is not an issue, or does this all just seat in with use? Or does the bearing slide into the hole so that the sides of the hole are deep enough and oriented properly to guide the bearing square? (Sorry there must be a term for the bearing socket that I do not know off hand.)

I do not want to mess up this gearbox. I truly appreciate all the help I get on this site, and do not want to over post by thanking individuals - you cats know who you are.

rwalker28 said:

Ball Bearing: Mine was frozen on the shaft; the bearing has about a 69 mil ID, while the shaft is a 69 mil diameter, the new one is the same. - I have about worn my poor old Mititoyo 6" dial caliper out measuring these over and over (caliper is good to .5 mil.) So, I am not great with calipers, but these parts are a darn tight fit, even greased up and ready to go. In the Hemming video, I believe that he shows the bearing slips on and off the shaft of his rebuild. 4) So, does this mean if you use a ball bearing like the one originally in there, or the one Hemmings suggests, there is no end play, the bearing is pressed in and the layshaft rides solid, or does the shaft need to slip in the inner race like in the video and the bearing is allowed some bit of end play? But if the shaft slips on the inner race, would a guy need to shim the layshaft a la the roller bearing?

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The layshaft bearing is often tight on the shaft (when the gearbox case is heated, the ball bearing usually comes out with the shaft).


At 17min. 10secs. into the video, Mick says: "....and this [the layshaft] should be just a sliding fit in the bearing....." so I would guess (as he doesn't actually mention it) that Mick reduces the shaft diameter until the bearing is a sliding fit which is what we are seeing when he slips the layshaft bearing onto the shaft at 27:20 where he still remarks: "incidentally, that's a bit tight".

In John Hudson's NOC gearbox rebuild video, John also encounters a tight D/S layshaft bearing and says: "This bearing was far too tight on the shaft, and at the factory we would have eased the shaft down-so that it was a push-fit into the bearing...."

rwalker28 said:

Side note, on my bike, the first gear bushing on this bike was totally loose, bell mouthed (so the outer end ODs were greater than the inside OD)

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1st gear bush wear is a common problem and it should be replaced as a matter of course.

rwalker28 said:

My last question is, 5) the cast housing in the gear box that holds the layshaft bearing must have a pretty precisely machined flat that this bearing seats into, so that the run out of the shaft is not an issue, or does this all just seat in with use? Or does the bearing slide into the hole so that the sides of the hole are deep enough and oriented properly to guide the bearing square?

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If the layshaft bearing is installed correctly, then it should be up against the machined shoulder inside the recess, therefore it should be square.

To update, Mick does actually say at 49:30: "....make sure that the layshaft is not too-tight a fit in the bearing, if it is, just ease it with Emery cloth because it should be just a nice push-fit...."