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The intricacies of Commando bearings have been well studied and much writ about over the years. !!
The bearings recommended for Commandos are the heavy duty version of the common roller bearings.
It has an extra roller, E being for Extra, in the NJ306E bearings

A big heavy crank like a Commando, suspended between only two bearings, flexes (quite ?) a tad at revs.
What the (roller) bearings need to cope with this is a fair bit of internal clearances.
So the rollers don't dig the very ends of the rollers into their tracks.
This requires the C3 clearance bearings, as RGM so helpfully point out.

This was much discussed after the great Combat bearing saga of 1972.
The operative word splashed about then was 'superblend'.
(Although bearing manufacturers don't really recognise this term.).
Hopethishelps.

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Originally Posted by -BW-
When I received my order from RGM, a gentleman by the name of Paul left a note in the box. He said 'bearings changed to C3 clearance instead of standard. standard not suitable for combat or 850.' or words to that effect,

Yes, C3 (NJ306E.M1.C3) is correct.

https://andover-norton.co.uk/en/shop-details/16253/crankshaft-main-bearing-nm17822-4-

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C3 clearance is used in nortons due to the shrink fit in aluminum cases.
Bearing manufacturers clearly state the bearings are typical clearance speced for cast iron or steel housings................(not aluminum) which in air cooled MC engines expand more than iron.

Even LAB had posted a norton tech sheet with a crankshaft main shaft size change in ?71

To agree with the C3 change I had assembled a 60 manxman with supplied std FAG mains and even that engine could not be tested for end clearance due to drag caused by over tight bearing. It was corrected with a new set of C3 bearings.
So RGM is still not up to speed yet....

Also very old FAG are less clearly marked as to clearance, unlike the modern marking shown by LAB/AN

Commando engine rebuild. How much of a problem...999 more to go!
If it was easy anyone could do it...


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Originally Posted by Dave Comeau
Also very old FAG are less clearly marked as to clearance, unlike the modern marking shown by LAB/AN

C3 is quite a modern spec ?
Certainly not marked on my 850 Mk1 bearings.

I think what you have applied above is termed a post hoc propter rationalization ....

AND, 306 roller bearings were used for quite some decades in Norton dommie twins,
and then in the 650 and Atlas series. With no dramas whatsoever, it would seem.
On the drive side. They all made do with a ball bearing on the timing side.
60hp or less, no problemo.

<this space reserved for a pic of a dommie drive side 306 roller bearing, circa 1950 ish>

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Having read these replies and other threads about C3 bearings on the interweb, it seems somewhat contentious and not completely understood.
I will simply put this back in its box and believe I am being given good advice and move on to the next part...

Last edited by -BW-; 10/29/22 11:34 pm.

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Originally Posted by -BW-
I will simply put this back in its box and believe I am being given good advice

Good thinking 99 !
Bearings have never been better than these days.
What they have sent you (C3 etc) are the best.

The path they took to get here has been a little tortuous however.
The funny part seems to be that Nortons woes have been self-inflicted, to a large extent ?
If they had simply gone to a heavier duty bearing when it seemed advisable, all would have been good ?

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[Linked Image]

thumbsup


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http://atlanticgreen.com

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Originally Posted by Rohan
Originally Posted by Dave Comeau
Also very old FAG are less clearly marked as to clearance, unlike the modern marking shown by LAB/AN

C3 is quite a modern spec ?

C3 is the modern ISO standard for bearing markings and is an industry standard adopted universally, before standardisation it was down to each manufacturer to decide how to mark them. So on old pre ISO bearings for internal clearance identification you can have dots punched on the bearing side or circles etched on the bearing sides and other variations. The engineering design booklets published by the manufacture would detail the definitions for their own markings for engineers to use when specifying the required bearing and all the housing and shaft sizes and tolerances.

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Before you fit the new bearings, it would be worthwhile checking the condition of the bearing housing in the crankcases.

Quite often you can see scoring in the housing caused by the bearing moving around with the crank. With any luck, there will be minimal, if any scoring deep scoring marks are visible its going to need fixing. or the bearing wont be secure.

Last edited by gunner; 11/03/22 6:11 pm.

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Originally Posted by gunner
Before you fit the new bearings, it would be worthwhile checking the condition of the bearing housing in the crankcases.

Aye.
The alloy crankcase bearing housings MUST be heated before bearing fitting or removal.
If they are done cold, the alloy will be stretched, and they will never shrink down again to be able to grip the bearings adequately.

Quite how you measure this beforehand though ??


Originally Posted by kommando
C3 is the modern ISO standard for bearing markings and is an industry standard adopted universally, .

Do we know when this Iso standard was adopted ?


I always quote my attempt to buy some new bearings for an 850, that had been partly dismantled
and then left out in the weather for a bit.

The large Norton Dealer I approached hereabouts trotted out some NJ306.
I said these are for my Dominators, do you have some FAG NJ306E's (aka 'superblends') for the Commando.
(this wasn't all that long after the Combat bearing saga.)
They were really miffed, and I left empty handed.
I was somewhat surprised at this, they had been the biggest Norton Dealer in NSW. (NVT was kaput by then).
And had been helpful for getting my old Dommie resurrected.
All the bearing banter/saga in the weeklies had obviously not trickled down everywhere in the colonies.

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Originally Posted by Rohan
The large Norton Dealer I approached hereabouts trotted out some NJ306.

I often wondered what would have happened if I had simply installed these ?

Was all the 'superblend' banter all just a smokescreen/hoo haa.
Was merely ditching R&M the real solution...

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The Superblend was smoke and mirrors, after looking at the problem R&M saw the edges of the rollers had dug in and so specified a bigger crown on the edges of the roller, all rollers have some crown, they just made it bigger. Then FAG came along with their E for a higher loaded roller bearing which had a larger crown as standard.

The rollers are still parallel, if just the corners are radiused more so with a whippy crank at high revs the edges do not dig in.

An exaggerated diagram of a roller with crowned edges, its never this big in practise.

[Linked Image from researchgate.net]

The start of ISO standard is not a single date, each manufacturer decided when to start the use of ISO but it is now universal.

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Indeed. Those curved edges/ends are only a mm or 2 or so.
If you try and photograph it, about nothing is visible
They are for all intents and purposes just a parallel roller..

I still wonder what would have happened with those NJ306 in an 850
No E for extra roller ...

I wrote the ISO compliance procedures for the Dept of the Co I worked for,
would have been about 1993/94
There was no magic or mystery about it, I read the guidelines and wrote to suit.
It was simply the way we had operated since the year dot anyway.
But engineering guidelines may be a bit stricter ?

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Iso compliance procedures are not the same as Iso standards for a range of products such as a bearing.

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There's a lengthy analysis of the various main bearings used on Norton Commando's in .pdf format Here, including details of roller crown dimensions etc.

It's worth reading the conclusion on page 18 that the author comes to, which seems to be that any bearings with less than 12 rollers are worth replacing and that suitable high capacity bearings were fitted to later 750 and 850 engines.

It seems that the earlier bearings were of lower capacity, hence the failures and that the word 'Superblend' has no real meaning, however bearing capacity did increase in later years with the NJ306E type.

Last edited by gunner; 11/05/22 8:57 am.

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Thanks. I've not seen that summary of the situation before - quite a fair summary of recent stuff.
I've been following this bearing saga, and probably have all the earlier summaries & pics saved !
Not sure they would add much - modern bearings seem to have improved - by quite some margin.
And, this subject has been well flogged to death by now, as you can probably well imagine ...!

As previously/above, Nortons woes seem to have been largely self inflicted. ?
If they'd changed to a heavier duty bearing when it seemed wise, none of this would have developed ??
'Penny wise pound foolish' is the quote ?

I still wonder how those NJ306 would have gone in an 850.
Probably quite well, if the revs kept away from attempting 7000 !

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Originally Posted by kommando
Iso compliance procedures are not the same as Iso standards for a range of products such as a bearing.

So what do the ISO standards for bearings specify.
Enquiring minds would like to know ??

I'd comment that bearings have been broadly interchangeable for quite some years of the past century.
Norton Dommies of 1949 used exactly the same dimensions in their main bearings
through to and including Commandos up to 1977.

I don't think I've ever found the same pairings of bearings in a Dommie when stripped down,
and always wondered if there was a std bearing set.
Or did they use whatever the local bearing factor could supply that week/month/year ?
Hoffman seemed to be the supplier of singles bearings, at some point ?

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I have a question regarding the cam followers... I can't seem to find any affordable replacements so I going to inquire at a machine shop to have them refaced. Is there anything I should be mentioning to the engineer with regard to specific tolerances or requirements? Is this only a job for a motor builder familiar with these engines or is it less complex than that? I just want to have an idea in mind before I approach the motor engineer this week.


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Commando cam followers have a (thin) hard facing layer on the flat base, which may or may not be stellite.
So they can't be ground very far - but I've not had any done, so don't know the specifics.
A shop near me can successfully do the curved dommie variety, but they don't have that welded layer.

So hopefully someone will know and reply here.

P.S. A good operator may be able to add some stellite. ?
BUT, Commandos have a bit of a reputation for shedding some welded stellite feet
so I'm not sure if this is to be recommended ?

There may be a good reason why new ones are big $$, and in demand ...

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Cheers Rohan, thats good to know.
It appears as though getting the followers refaced is a dead-end. The only machine shop that was recommended to me as competent in their work with old engines, have said they will not do the job. To elaborate, the guy looked at the followers and said, 'oh no... well I've done them before but I wont do them again, sorry its too tricky.'
Luckily, I have happened onto a contact who may have found some useable used ones. Which brings me to the next question, if I use old followers, how much wear and tear is acceptable in a set of used ones? At what point should I say, these are ok or not ok?


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That is a good question.
A very good question ...

I see that some of the major Norton suppliers offer 'refurbed' Commando followers.
And all seem to have nil stock ?
There is mention of grinding them on the NOC website.
Again, no actual details of what is involved.
Or examples.
But must be possible - and done.

I think we'd have to see some to offer an opinion.
For my dommies, the followers on the left are a solid NO,
and on the right are good.
https://i.postimg.cc/nh0hVYs3/No-and-yes.jpg

Obviously, any pitting is going to tear the cam to bits ...
Note that these are curved, as dommie followers are.
And no, I don't know how they'd go in a Commando
And probably don't intend to find out !

And I will confess I've reused a couple of sets of Commando followers.
They didn't look 'worn', rather just nicely 'run-in'.
Whether that makes an engine 'rebuilt' or 'freshened' up ... ?

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Originally Posted by Rohan
And all seem to have nil stock ?

?


Andover shows on their website that they are in stock:

https://andover-norton.co.uk/en/sho...-in-ex-for-one-cylinder-nm22771-nm22772-




Miss your presence over on accessnorton, too.

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Ah, these are brand new ones, not refurbed ones ?

There was discussion someplace about these ?
They had some sort of problem(s).
Did they sort that out
Probably a better bet, if they are good.

I wasn't diplomatic enough, I guess ....

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The current "one piece" AN tappets/followers do not have the *Stellite* pad.
https://www.accessnorton.com/NortonCommando/new-2020-andover-one-piece-followers.29725/post-460466

*(The original pads were Delcrome and not Stellite.)
https://www.accessnorton.com/NortonCommando/worn-pw3-cam.25071/post-376539

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Originally Posted by L.A.B.
*(The original pads were Delcrome and not Stellite.)

I have some serious doubts about that claim - and that post.
A quick 0.01 sec google would suggest that Delcrome is a white cast iron, with lashings of molybdenum.
(Although it would seem there are many varieties)

Now, how would one fasten a cast iron pad to the base of a steel cam follower, ala Commando.
Attempting to weld or braze it sounds risky - risky indeed.
As is welding anything cast iron.

Delcrome does sound like it may have been suitable for DOMMIE cam followers though.
Which are cast iron.
Wonder if it was around back in 1947 when the dommie was designed ??

I have this in my collection of trivia.
A broken dommie cam follower.
It can break because it was cast iron ...
Pardon the dust.
Grainy metallurgy at the break immediately screams 'cast iron'
[Linked Image from i.postimg.cc]


As for that guff about cobalt being expensive.
In my farming days, we hard faced the tips of scarifier points (plough like implement)
Kilos and kilos and kilos of cobalt welding rods.
Made the steel points last 3 or 4 times as long - and they were pricey to keep replacing fulls sets of them.
https://static.prd.echannel.linde.c...AS/images/product/en_AU/large/611443.jpg
Welded easily - welds almost never failed.
They are getting pricey these days I see - in reputable brands anyway.

We diverge, muchly !

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