Oh that gearbox ?

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nznorton

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Hi Guys,,

I am guessing you would have heard this question many times before but I am going to ask for your indulgence and help...
I have a 1975 Norton Commando and was wondering if there is any chance that Norton was still fitting the faulty main gearbox shaft bearing that failed and locked up when one least expected it .. I do know this was an issue on earlier bikes but did they have it sorted by 75 ?? .. I have read about the serous damage and injury being done to both rider and machine...

Thanks in advance
Paul ...
 
Paul,
The 75 mk3 was the worst of the bunch. They usually failed by 15,000 at the latest. 11,000 on average. Jim
 
Well worth changing. A popular conversion is to a roller bearing, but you lose axial location. Mick Hemmings sells a higher grade roller bearing which works well. Approx. 45,000 miles since fitting and everything is fine.
 
comnoz said:
Paul,
The 75 mk3 was the worst of the bunch. They usually failed by 15,000 at the latest. 11,000 on average. Jim
Click to expand...

Bugger. Almost completed my refurbishment of my MK3 and up to, installing electrics.. Prior the dismantling my motor and gear box felt exceptionally good, now ive got a lump in my throat !!!! My mk3 has 10.5k mls on it .......... Is the bearing/s in question able to be replaced whilst g/box is in the frame........... pleasle, please say it can be done!!!!

Not having researched this issue "yet" can somebody indicate by part # the bearings in question.. Cheers
 
olChris said:
comnoz said:
Paul,
The 75 mk3 was the worst of the bunch. They usually failed by 15,000 at the latest. 11,000 on average. Jim
Click to expand...

Bugger. Almost completed my refurbishment of my MK3 and up to, installing electrics.. Prior the dismantling my motor and gear box felt exceptionally good, now ive got a lump in my throat !!!! My mk3 has 10.5k mls on it .......... Is the bearing/s in question able to be replaced whilst g/box is in the frame........... pleasle, please say it can be done!!!!

Not having researched this issue "yet" can somebody indicate by part # the bearings in question.. Cheers
Click to expand...

Yes, can be done with the gearbox in situ. Remove covers , first couple of gears etc and heat the back of the case (I used heat gun) and pull the layshaft complete with bearing out.
Good luck, I did mine a couple of months ago, bike had 13,000 miles on, and the bearing looked like it was about to implode. I put a superblend in, but there are other choices.

sam
 
trident sam said:
olChris said:
comnoz said:
Paul,
The 75 mk3 was the worst of the bunch. They usually failed by 15,000 at the latest. 11,000 on average. Jim
Click to expand...

Bugger. Almost completed my refurbishment of my MK3 and up to, installing electrics.. Prior the dismantling my motor and gear box felt exceptionally good, now ive got a lump in my throat !!!! My mk3 has 10.5k mls on it .......... Is the bearing/s in question able to be replaced whilst g/box is in the frame........... pleasle, please say it can be done!!!!

Not having researched this issue "yet" can somebody indicate by part # the bearings in question.. Cheers
Click to expand...

Yes, can be done with the gearbox in situ. Remove covers , first couple of gears etc and heat the back of the case (I used heat gun) and pull the layshaft complete with bearing out.
Good luck, I did mine a couple of months ago, bike had 13,000 miles on, and the bearing looked like it was about to implode. I put a superblend in, but there are other choices.

sam
Click to expand...


Superblend ?? is that a UK oil generic name? or a UK generic bearing name ? .... Im continually confronted with unfamiliar terminolgy on the Net as in "wrenches" here in OZ no such thing in a tradie situation.. Thanks for the "relieving" advise re bearing fittment.. Cheers
 
can somebody indicate by part # the bearings in question
Click to expand...
06-7710. Should be available from all reputable Norton dealers. Never had one fail after I put my first one in my first Commando in 1977 after the original ball bearing exploded in the middle of nowhere.
 
ZFD said:
can somebody indicate by part # the bearings in question
Click to expand...
06-7710. Should be available from all reputable Norton dealers. Never had one fail after I put my first one in my first Commando in 1977 after the original ball bearing exploded in the middle of nowhere.
Click to expand...

Now there's a thing. Would I be correct in assuming that this is the 6203-TB fibre-cage bearing?
If so, the Andover price is pretty competitive

I fitted a superblend on my 850 and have had issues due to having to shim up the layshaft to set the end-float - more than once, and I used the 'TB' in the Combat - as Mick Hemmings says; 'THE solution'.
I've now got a 'TB' for the 850, but I'm not sure my bearing puller will fit the outer race of the superblend, so may have to get the gearbox out of the bike to do the job :cry:
 
Code: 
Now there's a thing. Would I be correct in assuming that this is the 6203-TB fibre-cage bearing?
No its the roller so needs shimming of the layshaft.

I've now got a 'TB' for the 850, but I'm not sure my bearing puller will fit the outer race of the superblend, so may have to get the gearbox out of the bike to do the job :cry:
Click to expand...

No need to use a puller or take the gearbox shell off the bike, heat the shell with a propane torch or a hot air gun and a sharp tap from the back of the shell with a stout piece of wood and the outer will move inwards.
 
Sorry, I said Mick Hemmings supplies an upgraded roller bearing, should have said ball bearing.
 
olChris said:
Superblend ?? is that a UK oil generic name? or a UK generic bearing name ? ....
Click to expand...

"Superblend" was a name Norton gave to the high-load capacity R&M/RHP 6/MRJA30 crankshaft roller bearing they introduced during the latter part of 1972 to rectify the high number of premature crankshaft bearing failures on Commandos at that time-so the term "Superblend" is not often heard outside of "Norton" circles.

The high load capacity FAG NJ306E bearing which superseded the 6/MRJA30 is also commonly referred to as "Superblend" and the gearbox layshaft NJ203 roller bearing is occasionally referred to as a Superblend.
 
help me out here. I am looking for one.
Has anybody check for price and availability lately? I think things have changed.

I went through a large supplier. Their catalog showed the bearing but when I went to order it could not be found. Upon further investigation from Applied Industrial Technologies, FAG apparently reclassified this bearing and is now made in Germany and cost around $200 to $300.

FAG ball bearing 6203 TB P63 aka 6203tb p6 c3
 
Mick Hemmings recommends a ball bearing replacement the 6203-TB fibre-cage and not a roller bearing because the shaft flex in the gearbox, like what happened in the Combat with the crankshaft flexing has the potential to tip rollers onto their edges, causing failure like the original roller bearings in the Combat.
I originally got the 6203-TB fibre-cage bearing I used from a state side bearing distributor for not too much but they don't seem to offer it any more. I'd suggest one directly from Hemmings.
If you replace it while in bike I successfully used a cheap electric paint stripper gun inside the box aimed at back of box. After about five minutes shaft with bearing on it came out nicely. Removing bearing from shaft was easy since puller jaws pull on gear on that end of shaft.
Warmed bearing in bag in boiling water while shaft in freezer then slipped on nicely. Put shaft with bearing in freezer for 30 minutes, heat case with gun then push shaft with bearing back in nice and straight with maybe a little tap on end to be sure bottomed out. Be very careful not to paound shaft hardsince wou can crack back side of case! Shaft and gears covered in frost going in so afterward ran heat gun in for a minute to dry out box.
 
More on the ball bearing Mick Hemmings recommends from a couple of sources. Seems the deep groove feature is a plus along with the phenolic cage.


6203-TB-FAG - DEEP GROOVE BALL BEARINGS
In a deep-groove radial bearing, the race dimensions are close to the dimensions of the balls that run in it. Deep-groove bearings have higher load ratings for their size than shallow-groove, but are also less tolerant of misalignment of the inner and out.

FAG 6205TB.P63 phenolic cages ball bearings
FAG single row deep groove ball bearings usually without a cage suffix have a sheet steel cage. The suffix TB behind the bearing NO. means phenolic cages, it has very high mechanical strength, good resistance to corrosion, rust and heat resistance, as well as lubricity. In addition, they are with light weight, high strength characteristics.


The technical data sheet for FAG bearing 6205 TB.P63
Type: single row deep groove ball bearing, with phenolic cages
Dimension: 25mm x 52mm x 15mm
Weight: 0.133 KGS/PC
Radial dynamic load: 14900 N
Radial static load: 7800 N
Limited speed: 9000 1/min
 
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