Ball bearing mains
- Thread starter Fast Eddie
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comnoz said:
Norton Dominators had a roller bearing NJ306 * on the drive side and a ball bearing on the timing side, right from the 1st dommie engine back in 1948.
As far as I know, that was standard fitment all through the dommie and into the Atlas engines.
And quite when/if it stopped I know not...
They are ALL interchangeable with so-called superblends too.
* or equivalent, I think they started with Hoffman bearings. Who may have had a different/abbreviated numbering system.
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Rohan said:
Well, that last bearing I measured was an NJ306. It came from an old dealer who said it was supplied by Norton to replace the bearings that were failing at the time. It had been on his shelf since the early 70's.
Hand written on the box was "superblend" but there was no engraved number on the inner race and the outer race was missing.
I have torn down a few 72 and earlier motors with NJ306's in them -but who knows how they got there.
A Norton Dealer tried to sell me some NJ306's for an 850 in the late 1970s.
He was offended when I refused, and I said they should say NJ306E.
That bit was certainly well publicised back then, the E was said to be critical for use in an 850.
The NJ306 was just fine for dommies.
Has one less roller in it.
He was offended when I refused, and I said they should say NJ306E.
That bit was certainly well publicised back then, the E was said to be critical for use in an 850.
The NJ306 was just fine for dommies.
Has one less roller in it.
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comnoz said:
Is this a different bearing to the one you measured in your video, as that was an RHP MRJA30 (an NF type bearing)?
comnoz said:
How can an "NJ" bearing be missing its outer race? Why would you expect to find an engraved marking on an NJ306 bearing?
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No idea but it is on their first Service sheet when they attempted and failed to cure the premature main bearing failure, its in a list of approved replacement bearings along with the NJ306E, it does not say what they fitted at the factory at that time but they are least told dealers they could fit them to replace failed original fit mains.
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OK, thanks. Will soon be reassembling the motor on my 68 Commando.comnoz said:
MF
o0norton0o
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I have a 70 commando. I recall reading that the 70 cases were weaker than later model cases, so they flexed more with the pressure from the spinning crankshaft. Anyone hazzard a guess as to how much more those cases are subject to breaking or spinning a main bearing???
btw, I changed my original bearings to superblends, but I still have my original bearings in my parts bin for my '70. The part # on the ball bearing is SKEFKO - 165133B, and the original roller bearing part # is R&M - MRJA30
btw, I changed my original bearings to superblends, but I still have my original bearings in my parts bin for my '70. The part # on the ball bearing is SKEFKO - 165133B, and the original roller bearing part # is R&M - MRJA30
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o0norton0o said:
I don't think you need to worry about the cases unless you are racing or running extended highway miles over 5000 rpm. Just use good cradle mounting hardware and keep them tight. I would suggest grade 8 bolts or better for the 3 rear mounting bolts.
If that MRJA30 bearing you have has a hand engraved number by the part number I would like to measure it. Jim
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There does look like there's a faint number lightly hand engraved into the bearing next to the R&M. Maybe it says "e121"??? it's hard to read.
I'll send you a PM Jim...
I'll send you a PM Jim...
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