Clarity re: main bearing history

My bike is April 1972 ... the first owner had less than 1000 miles when he hit a fence as a 17 year old .... Rick bought the bike as a barn find ( 1987 ) ,the bike hadn't turned a wheel since the fence .... he fixed the cosmetics and did the top end , said he checked the bottom and it was fine .... the bike now has 7800 miles ( true ) .... in the Norton service notes it say " July 1972 ... models subsequent to engine # 201197 incorporate a nominal increase in bearing housing diameter to overcome any significant tendency to excessive closure of the single lipped outer series of roller bearings"... I talked to Rick at his living wake just before he passed on ... he maintained there was no worry , to continue to ride and I would know when I was having a problem .... my bike is # 207384 it runs great ,I have had two different experienced Brit mechanics ride it and listen and they say same ... though , they both surprised still original bottom end .... Does anyone have any thoughts on this .... the Super Blends were not mentioned in Notes until Aug 1972 " from engine # 211891 super blend would be fitted ( Part # 063906 ) " I am wondering what if anything I should do ... Rick was kinda frugal when it came to running his bikes and I know he would have had no problem running it till he was forced to stop ... where as Me , not so much .... I must say I have no reason at all , yet to think I have any troubles just wondering in the dead of winter .... thanks for any comments
Craig

Based on the info you have given you will not have superblends fitted, how long your current setup lasts will depend on how you ride the bike. If you ride it like a 17 year old then you have maybe 5k to 10K miles left in it, ride it like the Pope and it will last for many more miles. The main tell tale of failing mains is a rumble, so as long as you know what it sounds like ride until you hear the rumble, then strip down and apply all the fixes for 72 engines.

1. Superblend mains

2. Relocate sump drain to the rear of the crankcases. Do not follow the Old Britts scheme but the later scheme with smaller holes to act as a crude filter.

3. Fit reed type breather valve

Plus if its a Combat

4. Check and adjust pushrod length (40 thou too long as the factory forgot to change for the 40 thou skimmed from the head)

5. Check the pistons for the full slotted type and replace

Depends on your circumstances, I would ride and enjoy.

Overtime you pull it down you will find many things you want to do with it, especially if it an original 72. Isolastics, head steady frame paint, new loom etc etc etc. Things you never thought of. It will then be off the road much longer than you expected. You will have missed a season.
Just saying!!

Oh yeah ... most of all mentioned mods have been done and then some ... 'bout only thing left is the bottom end Rick like I had mentioned , did cam, rods , pistons,rings and bored out to first oversize, all other mods improvements have been looked after ,shocks ,forks with lansdowne kit , wire harness , all bearings,electonic ign, new alternator , single mikuni34vm, all new cables , clutch, gearbox rebuild ,swing arm refurbish with nuts welded for extra bolts,18" rear wheel, new rear brake drum , new CNW front brake master and on and on ... just looking for confirmation that I will know when mains are giving me trouble and was interested how good the improved bearings in my bike were/are ...
Craig

Leave it be, when you hear the rumble then look at it, unlike a broken con rod other than replacing the bearings there should be no other damage other than the oil pump return side passing some small bits of steel bearing which will get trapped in the return line oil filter (if you do not have one fit it now).

That's done too ... thanks
Craig

I was mostly interested in the history of this short run bearing , that was installed in a small number of Commandos ...

Craig

My 1972 combat had 16,000 when purchased as a barn find. I guess you have some more miles if you don't rev it too high.

Craig said:

I was mostly interested in the history of this short run bearing , that was installed in a small number of Commandos ...

Click to expand...

From October 1971, a roller bearing was fitted on the timing side, replacing what had up to then been a ball bearing, (see Service Release No.68).

http://www.nortonownersclub.org/support ... e-releases

68

Explanation
We are introducing a new roller main bearing arrangement in production almost immediately. The fitting of this bearing arrangement reduces overall width between the main bearings and increases timing side main bearing journal diameter....

......The new bearings are 2 dot single lip roller bearings and should be assembled with the lip into the crankcase in both cases. Main bearing Part No. 063114 is of the Ransomes type (R&M) MRJ A30.

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In July '72, an alteration was made to the bearing housing diameter after 207197 (Not 201197) because:

N2/6

Field experience with the 1972 models (incorporating two single lipped roller main bearings) indicates a small but significant premature roller main bearing failure rate.....

........Models subsequent to Engine No. 207197 incorporate a nominal increase in bearing housing diameter to overcome any significant tendency to excessive closure of the single lipped outer series of roller bearing.

Click to expand...

N2/9 (August 1972)

Explanation
In order to extend main bearing life, a change of roller main bearing specification has now been authorized and fitted on production engines from Engine No. 211891. The new roller bearing is designated 'Superblend' with an increased load carrying capacity and is supplied under Part No. 063906 (manufacturers part number R&M 6/MRJA30).

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N2/10 (January 1973, introduction of the FAG NJ306E)

Extra high capacity main bearings
All Commando
DISTRIBUTION: Worldwide (Trade only)
EXPLANATION: A new main bearing capable of carrying a much higher load than any offered before, has been introduced.

The new bearing, part number 064118, supersedes the old type 063906 and will be supplied in lieu by our Parts Division. The new bearing should be fitted in pairs.
This bearing may also be fitted to advantage to engines of 1971 and earlier models (originally fitted with a ball bearing as a timing side main bearing).

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Thank you Les .... does anyone else still have these short run bearings installed and what is your mileage ?

My combat which is a Jan 72, 2026..had 26000 on the clock when I last rode 20 years back. Bought it with 5000 on her. Never so much heard any sort of rumble. And yes rode like the pope. Changed oil religiously. I am in the middle of a complete restore at this time, and very curious as to what I will find inside the cranks. I will be posting my teardown saga soon. And yes guys lots of pics!

great please keep us all in the know ...
Craig