MKIII Drive Chain Sprocket/Speedo Drive

Deets55 · Nov 6, 2014

1975 MKIII

Just had to disassemble the rear drive sprocket on my MKIII and ran into some problems. Hopefully I can get some help. First off I would like to replace the large speedo drive seal. I can not find a part number for it. Drive still works fine, just needed to be cleaned and lubed (Jewell Amber Oil per Comoz?). I am guessing the felt side of the drive seal faces into the the drive unit?
I looked at Old Britts parts breakdown page, is part #06-5562 (Group 23 part # 25, http://www.oldbritts.com/nor_mk3_75_23.html) the seal for the drive, or is it the bearing seal shown in the wrong location? I only see one seal shown. I need to identify both of those seals, their locations & positions.
I would also like to replace the double row bearing (bearing type 4203) with a sealed unit, but it looks like machine work needs to be done for that to take place. Am I correct in assuming that, or is there another option?
Thank you in advance for the help.

Pete

comnoz · Nov 6, 2014

I do not believe the large felt seal is available separately. There is a smaller felt seal that keeps the birds out of the original unsealed bearing that is available.
If you want to keep the original bearings load capacity when you install a sealed bearing you will need to machine the bearing bore deeper and shorten the spacer by that amount.
There is a sealed bearing available to fit in the original bore but it is not rated as high as far as load capacity. Jim

Deets55 · Nov 6, 2014

Jim,
Is that small felt seal in the gear box, looks like the spacer rides in? If so how do I find a part number.

I guess this is the lower capacity sealed bearing:
http://www.fairsparesamerica.com/find.asp
part number 06-7688

I have a roadster, ride solo, no luggage. Will that be a problem with the lower rated bearing?

Thanks,
Pete

comnoz · Nov 6, 2014

Deets55 said:
Jim,
Is that small felt seal in the gear box, looks like the spacer rides in? If so how do I find a part number.

I guess this is the lower capacity sealed bearing:
http://www.fairsparesamerica.com/find.asp
part number 06-7688

I have a roadster, ride solo, no luggage. Will that be a problem with the lower rated bearing?

Thanks,
Pete

I have a part number 06-5562 for the small seal.

I have never used one of the lower capacity bearings so no real experience. It would probably work fine but with a shorter lifespan. Jim

L.A.B. · Nov 7, 2014

Deets55 said:
I looked at Old Britts parts breakdown page, is part #06-5562 (Group 23 part # 25, http://www.oldbritts.com/nor_mk3_75_23.html) the seal for the drive, or is it the bearing seal shown in the wrong location?

Yes, it is the 06-5562 seal, drawn on the wrong side of the bearing in the parts book diagrams (but not in the factory manual drawing, this has been mentioned a few times, previously).

The drive gearbox felt seal is available from various Brit part suppliers : http://www.rgmnorton.co.uk/buy/felt-for ... s_2204.htm

comnoz said:
If you want to keep the original bearings load capacity when you install a sealed bearing you will need to machine the bearing bore deeper and shorten the spacer by that amount.
There is a sealed bearing available to fit in the original bore but it is not rated as high as far as load capacity. Jim

What is the actual difference in load capacity between a sealed 4203 (17x40x16 4203 2RS) and an open 4203, could you please give more information, Jim, as I have been unable to find any relevant data or any reference to '2RS' bearings having a lower load capacity to an equivalent open bearing?

Deets55 · Nov 7, 2014

http://www.bendasrulmRe: MKIII Drive Chain Sprocket/Speedo D

Les,

Thanks, I recall reading about an incorrect drawing but I could not locate that thread, and wasn't sure if it was MKIII related. The large felt seal I have does not resemble any I have seen shown. Instead of being convex (viewed from outside of gear box) with numbers stamped on it, it is flat with a raised lip on the O.D. edge. There are no numbers stamped on it.

Les and Jim,

I found this bearing ( http://www.bendasrulman.com/42032rs-bearing) but I can't decipher the specs, perhaps either you or Jim (or anyone else) can figure out this bearing's rating compared to the SKF sealed bearing, or in fact how it compares to the stock RHP 4203. The factory bearing is marked RHP "4203" outer race, and "4203 1 11-02" inner race.

Pete

Edit,
Les just found this:
smiths-speedo-gearbox-repair-t5646.html#p53976
That is my felt seal retainer, same as Dog T first picture. Bottom right of photo. Also looks factory to me.
Pete

L.A.B. · Nov 7, 2014

Re: http://www.bendasrulmRe: MKIII Drive Chain Sprocket/Spee

Deets55 said:
The large felt seal I have does not resemble any I have seen shown. Instead of being convex (viewed from outside of gear box) with numbers stamped on it, it is flat with a raised lip on the O.D. edge. There are no numbers stamped on it.

What you appear to be describing isn't the seal, but the retainer, these are two separate parts, however it does sound as if somebody may have either replaced the retaining plate-or reversed it?
Photo?

Deets55 · Nov 7, 2014

Les,
Top picture shows close up of outside of retainer, bottom shows seal and retainer. There was so much crude in there I wasn't sure what was suppose to come apart or stay together. Can't say if it is original or not but I have had the bike since 1990. There is a little ridge where the stub axle shaft goes through the gearbox housing. Not sure if that is suppose to look like that.
Pete

L.A.B. · Nov 7, 2014

Deets55 said:
,
Top picture shows close up of outside of retainer, bottom shows seal and retainer.

Unfortunately I can't see an enlarged image of the bottom photo which I think, shows the inside view of the retainer (even if I go to your Photobucket album), but what I think I'm seeing is (yet another) MkIII retainer that has been crushed against the sprocket boss, (from the dummy axle nut being tightened) and then the boss has spun against it and removed the numbers. I found my own MkIII's retainer to have been similarly afflicted which prompted me to add a shim washer on the inside (between the 06-5547 spacer and the sprocket bearing) to move the drive gearbox further away from the sprocket boss, as basically, the 06-5547 spacer seems to be too short.

Deets55 said:
,There is a little ridge where the stub axle shaft goes through the gearbox housing. Not sure if that is suppose to look like that.

No, I don't think so. There is usually a large diameter washer (06-5549) outboard of the drive gearbox, was it there?

Deets55 · Nov 7, 2014

Les,

Yes large washer was installed

Here are some better pictures. I see what you mean about the crushed retainer.

I can't seem to locate that felt seal in the States yet. I may have to call some people up, can't find a part number that works. I wonder if there is a rubber seal that might cross over with the correct dimensions.

Pete

Gearbox Ridge

Gearbox Ridge

Retainer Sprocket Side

Retainer Felt Side

L.A.B. · Nov 7, 2014

Thanks, they're better photos.

There was a recent thread that has photos showing similar damage.
another-speedo-question-t19889-30.html#p255829

comnoz · Nov 7, 2014

L.A.B. said:
What is the actual difference in load capacity between a sealed 4203 (17x40x16 4203 2RS) and an open 4203, could you please give more information, Jim, as I have been unable to find any relevant data or any reference to '2RS' bearings having a lower load capacity to an equivalent open bearing?

The sealed 4203 [4203rs] and the open 4203 have the same load capacity. However the sealed 4203rs is .047 wider than the open 4203.

I no longer have the part number for the narrow sealed bearing that is a drop in but I recall checking the specs and finding it had a lower load rating. Jim

L.A.B. · Nov 7, 2014

comnoz said:
L.A.B. said:

What is the actual difference in load capacity between a sealed 4203 (17x40x16 4203 2RS) and an open 4203, could you please give more information, Jim, as I have been unable to find any relevant data or any reference to '2RS' bearings having a lower load capacity to an equivalent open bearing?

Click to expand...

The sealed 4203 [4203rs] and the open 4203 have the same load capacity. However the sealed 4203rs is .047 wider than the open 4203.

I no longer have the part number for the narrow sealed bearing that is a drop in but I recall checking the specs and finding it had a lower load rating. Jim

All the available info I can find lists the same width (16mm) for both 4203 and sealed 4203 2RS?

http://simplybearings.co.uk/shop/p50026 ... _info.html

http://www.bearingoptions.co.uk/angular ... 5110-p.asp

http://www.feked.com/ball-bearing-4203-2rs.html

Wouldn't the wider (17 x 40 17.4-5) double row bearing be a 5203 or 3203?

comnoz · Nov 7, 2014

L.A.B. said:
All the available info I can find lists the same width (16mm) for both 4203 and sealed 4203 2RS?

http://simplybearings.co.uk/shop/p50026 ... _info.html

http://www.bearingoptions.co.uk/angular ... 5110-p.asp

http://www.feked.com/ball-bearing-4203-2rs.html

Wouldn't the wider (17 x 40 17.4-5) double row bearing be a 5203 or 3203?

Yes you are right, the bearing I use is a 3203-2rs with a load rating of 14800N

The original open bearing is a 4203 at 15600N

The 4203-2rs is the drop in with a load rating of 11840N

So either sealed bearing is rated lower than the open bearing. Jim

Deets55 · Nov 7, 2014

Jim,
Just saw your last post. Good info. Thanks.
Now the million dollar question. Seeing how there are 3 bearing on that axle do you think that even the lowest rated 4203RS bearing will be an issue of concern?
Pete

comnoz · Nov 7, 2014

Deets55 said:
Jim,
Just saw your last post. Good info. Thanks.
Now the million dollar question. Seeing how there are 3 bearing on that axle do you think that even the lowest rated 4203RS bearing will be an issue of concern?
Pete

Probably not. But I haven't tried it. Jim

L.A.B. · Nov 7, 2014

comnoz said:
The original open bearing is a 4203 at 15600N

The 4203-2rs is the drop in with a load rating of 11840N

So either sealed bearing is rated lower than the open bearing.

Maybe as much to do with quality or specification than anything else, perhaps?

http://www.vxb.com/page/bearings/PROD/17mm/Kit20615

4203 Double Row Open Ball Bearing

Dynamic load rating Cr: 11840 N

comnoz · Nov 7, 2014

L.A.B. said:
comnoz said:

The original open bearing is a 4203 at 15600N

The 4203-2rs is the drop in with a load rating of 11840N

So either sealed bearing is rated lower than the open bearing.

Click to expand...

Maybe as much to do with quality or specification than anything else, perhaps?

http://www.vxb.com/page/bearings/PROD/17mm/Kit20615

4203 Double Row Open Ball Bearing

Dynamic load rating Cr: 11840 N

Click to expand...

Very possible, the specs I quoted were from my old FAG catalog. Jim

850commando · Nov 7, 2014

i just checked my fag bearing catalogue for the 4203 brg, and you can get this online direct of SKF, just by googling the bearing #

Fag gives dyn C of 14.6 kN, and static C0 9.5 kN, and rpm limit of 13000 with grease or 17000 with oil.

its been a long time since i've had to think open bearings on vehicles...

comnoz · Nov 7, 2014

850dunstall said:
i just checked my fag bearing catalogue for the 4203 brg, and you can get this online direct of SKF, just by googling the bearing #

Fag gives dyn C of 14.6 kN, and static C0 9.5 kN, and rpm limit of 13000 with grease or 17000 with oil.

its been a long time since i've had to think open bearings on vehicles...

I don't believe SKF or FAG supplies a sealed 4203 anymore. It is in my 1978 catalog but doesn't come up on their site. Jim

MKIII Drive Chain Sprocket/Speedo Drive

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