Drag on transmission mainshaft excessive?

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springs75 said:
Ok, you guys are convincing me I need to start taking things apart. L.A.B, given your post, can you comment on the following taken from the Oldbrits article on taking apart and inspecting the transmission, which seems to indicate that you need to remove the trans to replace the layshaft bearing and that it's more of a pre-MKIII problem. Is the Oldbrits article not entirely accurate? Thanks

"You can perform limited work on your gearbox in the frame, but any serious work like replacing the lay shaft bearing, which is recommended for all pre-MK3 gearboxes, should be done on the bench"
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The OldBritts technical articles are an excellent 'how-to' reference, however, there does seem to be the occasional error or odd statement included and that is one example.
As others have said, the layshaft bearing can be replaced without having to remove the gearbox and that's the way I did it, although having the bike raised on a bench or bike lift makes the job easier instead of working on your knees!
I'm not sure why the reference to "pre-Mk3 gearboxes" either as replacing the layshaft bearing applies to all Commandos especially the Mk3.
 
I had owned my MKIII about 6 or 7 years before I opened up the gearbox, the seller had told me everything was gone through and it was ready to go. Well when I did open it up you could clearly see the layshaft had gone out in it and the damage was easy to see. The case was chewed up by two of the gears and the gears were also in very bad shape, as the mainshaft was bent and wear on the layshaft also. Someone just changed out the layshaft bearing and put it back together, and the layshaft bearing was loose in the bore, I mean really loose as in it just could fall out and the case had a crack were the bearing rides. And to think I rode this bike around for years like this, It never sounded funny or gave me any indication anything was wrong. I would suggest anyone that buys an unknown machine should take a look at what condition the gearbox is in.
 
Update: I disassembled the transmission and my initial impressions are that if it were not for the fact that you guys educated me on the layshaft bearing needing to be replaced regardless, I would have thought I disassembled it for nothing. Everything looks really good. All bearings and bushings seem fine, although 2nd gear main's bushing is floating in the gear. The others are fixed in their respective gear. The dreaded layshaft bearing with the brass cage is in excellent shape, i.e. cage intact and spins freely. If I didn't normally replace ball bearings and wasn't aware of it being problematic, I would have considered reusing it. Fourth gear has some slight wear but probably OK. I need to wash everything and inspect more thoroughly and also put the mainshaft in the lathe and check the runout. I'll report back on what I end up replacing. Thanks
 
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springs75 said:
Update: I disassembled the transmission and my initial impressions are that if it were not for the fact that you guys educated me on the layshaft bearing needing to be replaced regardless, I would have thought I disassembled it for nothing. Everything looks really good. All bearings and bushings seem fine, although 2nd gear main's bushing is floating in the gear. The others are fixed in their respective gear. The dreaded layshaft bearing with the brass cage is in excellent shape, i.e. cage intact and spins freely. If I didn't normally replace ball bearings and wasn't aware of it being problematic, I would have considered reusing it. Fourth gear has some slight wear but probably OK. I need to wash everything and inspect more thoroughly and also put the mainshaft in the lathe and check the runout. I'll report back on what I end up replacing. Thanks
Click to expand...
My experience was similar. Gearbox working fine except I had an issue with the kickstart pawl plate. So while in there, decided to replace layshaft bearing. I thought that since I was 2nd owner and had bike since it was 2 years old, it would have the original bearing. When I got it out, it was not the original Portuguese bearing, and had probably already been changed out before I bought the bike. But, since I don't plan on taking the gearbox apart again soon and since it has 23,000 miles on it, I went ahead and renewed a lot of the usual suspects. So, even though it turns out I probably didn't need to do all that and the bike was down for a few weeks, I now have peace of mind knowing what is in there. And soon you will have that as well.
 
Update for those interested: I washed everything and finished the inspection. The only thing I found that might explain the drag I was feeling was that the bushing on 3rd lay had a very light ridge on the kicker side where there is an oil groove on the layshaft. 3rd lay gear would drag when turning depending on where it was floating on the layshaft. I had to tap the bushing off the layshaft due to the small ridge. Runout on mainshaft was acceptable. Looks like 2nd gear has some fairly significant wear and should be replaced. The wear on 4th is much less and only on a couple of teeth and I will run with it. So besides gaskets and seals I will replace the following:

1. Both mainshaft ball bearings
2. Layshaft ball bearing with a roller bearing
3. 1st, 2nd and 3rd bushings just because I'm in there. The long ones in 4th are fine.
4. 2nd gear set


12E9C3D4-4AE3-4640-AB01-263C31B74EAF.jpeg
2nd gear. I will replace this set.


9135BD0D-EA3A-49B3-ABDD-7DD59B927771.jpeg

4th gear. This is the worst tooth. The photo makes it look a little worse than it is. I think this will be OK for a casual rider.


B11A84E5-148E-4FF7-9FE0-B2F00E85EFEF.jpeg

Is this the"exploading" Portuguese layshaft bearing?
 
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You may find that the new floating bushing are a bit tight and won't slip in freely. Mine were that way. Polish with some emery cloth until they are a sliding fit both on the shaft and into the gear.
 
'Sploding' bearing Lucy. I believe the very same one resides in mine. Perhaps I'll poke a stick at it sometime this winter.
 
L.A.B. said:
It certainly looks like it as it has the dangerous crimped brass cage although it seems not all were marked Portugal.
Click to expand...
Were there different bearings installed at the factory, or are they all likely to be the same?
 
maylar said:
Were there different bearings installed at the factory, or are they all likely to be the same?
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The 6203 layshaft bearings in 750 gearboxes were usually British-made (SKF etc.) with riveted steel cages. Some later layshaft bearings seem to have been Japanese NTN, again with riveted steel cages. It seems that later pre-Mk3 850s and all 850 Mk3s had the Portuguese/FAG brass-cage bearing.
 
L.A.B. said:
It seems that later pre-Mk3 850s and all 850 Mk3s had the Portuguese/FAG brass-cage bearing.
Click to expand...
So, it's likely that my Aug 74 MKII has one? I have 40,000 miles on it, how often do they fail?
 
maylar said:
So, it's likely that my Aug 74 MKII has one? I have 40,000 miles on it, how often do they fail?
Click to expand...

It might not be, as they often fail well below that mileage (unless it has already been replaced) but if it does have a Portuguese bearing then you've either been lucky or the bearing has had an easy life but if it has a standard 6203 ball bearing of any type then it should be replaced with the roller upgrade.
 
My October 74 MkII had the Portuguese bearing. I replaced it 2 years ago with 23,000 miles on it. It appeared to be in fine condition.
 
lazyeye6 said:
My October 74 MkII had the Portuguese bearing. I replaced it 2 years ago with 23,000 miles on it. It appeared to be in fine condition.
Click to expand...

This one has 22K miles and as mentioned before, layshaft bearing seems fine. Regardless, in the bin it goes. The right side mainshaft ball bearing says "England" and left side "GT Britain". Both have steel cages. I am fairly positive the trans has never been apart before.

Ordered the parts from Old Britts and should get it back together next week.
 
My March '74 MkII has 24,000 on it and to my knowledge hasn't been gone into.... I got it with about 7500 on the clock. Anyway I'll take a peek soon.
 
My 73 850 had the Portuguese bearing. 17k, still looked good. Replaced with a roller last winter. Peace of mind.
 
Same as the last few people's comments, I pulled the layshaft bearing of death at 20,000 miles and it still looked good... piece of mind..
 
I'm sure most of them are good up to the point they aren't. And at speed that may happen quickly.
 
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