72 commando resto

splatt said:

I got some bearings recently,FAG, the box was marked nj306e, the inner race was marked nj306e,but as foxxy said the outer race is marked nu306e??? I have been meaning to question bearing supplier on the number difference.

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Maybe the FAG factory uses the same outer bearing part for both NU and NJ bearings?

As it's only the inner race that is probably different, the NJ version has a single lip inner race and the NU inner does not.

I'd find that very easy to believe since that's how a lot of our bus hub bearings work. The same race can be used in several applications. A quick phone call to a supplier should clear it up.
I'd love to have a bearing interchange book again, the one we had were huge but I wish now i'd saved an old copy.

hi lab,in your earlier reply post to foxxy you said,(the NU bearing probably works just as well but it does,nt have the lip on the inner race so i would expect the inner race slightly more difficult to extract from the crankshaft) so without the lip will the inner race slide in one side out the other side of the outer bearing.if that is the case how would you set the endfloat, the crank would be free to run up against whatever it came into contact first, or have i missunderstood something

Gday again, yes the inner race of the FAG bearing has the # NJ 306E stamped on it and is only single lipped allowing the crank to move. I have removed my (ebay)850,s mains and they have only done 3000 miles with slight water marks from sitting for some 30 years under a work shop bench. Ive dismantled a bearing to measure the rollers and they are perfectly cylindrical, .433 thou or 11 mm right across! I believe this kills the myth about the bearings being slightly (wine) barrel in shape.Im about to order my bearings and will be definately quoting both numbers to make it clear as to what I want.

On some old main bearings I have looked at that seems to be true but look at the outer race, Does yours look to be slightly tapered on the ends? Maybe I am nuts here or mine could just be wear.

Ive checked out the bearing races and they are nice and square with no signs of wear.So yours Horton could be wear? Seams a shame to dismantle mine but seeing Im fitting a 920 RGM kit and off set crank, mains are not something to cut back on after what Ive spent!

Well here's the polished rod. It actually came up OK! I will probably get the little end bushed tho. Before, during and after pics...










opinions welcome, Jim.

looking good jimmy,just a couple of minor points i would polish out the numbers and blend the steel end caps to the rods, other than that great job

chris plant said:

hi lab,in your earlier reply post to foxxy you said,(the NU bearing probably works just as well but it does,nt have the lip on the inner race so i would expect the inner race slightly more difficult to extract from the crankshaft) so without the lip will the inner race slide in one side out the other side of the outer bearing.if that is the case how would you set the endfloat, the crank would be free to run up against whatever it came into contact first,

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Yes, I'm sure you're right, it would be difficult to set the end float without lipped inner races.

somebody should make plexiglass engine cases so that we can see the polished con rods in action!

We once had a training 6/71 Diesel with a plexi crank window. It got boring after a bit.

hi cookie, boring maybe but not for BSA i read it somewhere that they did exactly that to see what was happening inside A7 and A10 engines to solve the problem of drive side big end and conrod failures

That's interesting Chris. I wonder what Norton did to figure out what was going on? BMW had already run into the same problem a few years before with crank flex requiring the barrel roller type bearing, but that may well have been top secret at that time.
A lot is going on down there in a engine under load, first the alloy crankcase is going to expand increasing clearance, the crank is going to expand at a different rate and then under high RPM the crank is going to be driven sideways by the load and flex up and down. No wonder those cases cracked and stock bearings died. The beautiful alloy rod with a dissimilar metal cap has to be a weak point for high RPMs too. On top of that they had inadequate scavenging.
A window in the case would have shown some of that stuff at least.

hi cookie,norton did,nt have to resort to such measures,they knew what was going on, the roller bearing on the drive side was( digging in) due to crank flex at high rpm , and as foxy has destroyed the myth of barrel shaped rollers i wonder what did cure the bearings from( digging in) regarding the alloy rod with a steel end cap why would it be a weak point,and who had inadequate scavenging, and to jimmytwin sorry for highjacking your excellent thread but it looks like we,ve kidnapped it as well lol

Here we go with another one that should stir up some controversy. Generally when you go with two different metals on a rod you have a high RPM weak point, when folks started doing that the rod was not subjected to the kind of revs we see today and the lighter rod worked fine. The steel cap was a fix from the full alloy rod as it helped to keep the bearing from spinning and reduced rod flex. I think you'd probably want custom forged steel rods if you were going to really rev one of these.
Around 72 the case was changed and according to old Britts it won't scavenge enough oil at sustained high RPMs. They have a fix for it on their website.
That said, there are probably a lot of engines running around for which that will never be a problem. I don't think in my use that I can run my 72 engine out of oil, but if I ever have it apart I'll have the case mod done. I was worried about it when I frist got the bike and a few guys with similar equipment assured me they had no problems.
My feeling is that if you run one of these with good stock equipment, the bearing fix, perhaps dumping the rods that some folks say are worse than the early ones (I forget the type, I've never had them), one of these things can run a long time and do a fine job.
I'm a bit surprised that the "superblend" might not be what folks told me it was, barrel rollers like bMWs used. I suppose wider flat rollers might just prevent crank flex just enough to get by, whatever they are they work. My last Norton ran for years and never gave a minute's trouble with them.
I'm still scratching my head over these bearings.

My problem with having a perspex window in my crankcase would be,

"What sort of curtains would I fit?"

Interesting that BMW had the same problem with bearing failure, Im wondering if the bearings used today are C3 clearance to allow the flex or float required? Also the J in the FAG bearing NJ306E denotes single lipped inner race(Im slowly learning) The article in Britts about the oil scavenging fix mentions the blocking off of an oil hole using Araldite! Not a good idea as araldite becomes soft if heated(read the fine print)! On the subject of conrods, Ive purchased MAP rods for my project and they come with no topside drilling for the oilway, any thoughts? Also appologies for my part in the current highjacking of this thread, rgds FOXY

Years ago when I was mixing and matching rods I found my Atals rods (maybe late Atlas) were identical to my Commando rods except for the piston cooling hole. Since I had been advised that it was better I drilled it on the rods I used. I think I still would because I ran that sucker hard for years with no problems.

Fullauto said:

My problem with having a perspex window in my crankcase would be,

"What sort of curtains would I fit?"

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ha ha - I like that weird humour :lol:

Well its time for an update. Ive had a 13 day shift recently hence no news but after such a nice weekend I finally got back to it. I got the gearbox out and cleaned up the number. I stripped the rear wheel, cleaned up the brakes and painted the back plate and arm. I carried on polishing the frame and there seems to be little round marks on it, they wont polish out nor will a soft chemical like white spirit remove them but they will come off if I scrape my fingernail over them?? Probably gonna have to grow my nails then lol. I also have half cleaned the casing, i think im going to polish it but leave the little scrapes and nicks in the casings to give it the nostalgic feel, I can always do them properly in the future. I'm going to buy all new shiny nuts and bolts as well but Ive used the old ones in the pics. Here's some pics....oh does anyone know a reputable rim and spoke supplier in England??


Thanks, Jim.