750 crankshaft rollers stuck on crank

Status
Not open for further replies.

Drummer99

VIP MEMBER
Joined
Oct 18, 2013
Messages
148
Country flag
Hi guys just split the cases on a 73 750 commando and as the cases came apart the roller portion of the main bearings has stayed on the crank. The roller bearing outer shells are still in the cases. They are tight on the crank and turn easily I would have thought they would just pull out off the inner roller sleeve however they are tight on there. Not sure how to proceed from here I have a puller for the inner races but it will not fit in behind the rollers and I don't want to damage them. Any guidance here would be appreciated
Thx Drummer 99
 
If the bearings are the R&M/RHP 6(etched) MRJA30 "Superblend" then they are NF type where the rollers and cage are held captive by a double-lipped inner race, unlike the later FAG NJ306E bearings which are NJ type with the roller cage held captive by a double-lipped outer race.

750 crankshaft rollers stuck on crank
 
I think you'll need to buy / borrow a bearing separator / puller:
http://www.harborfreight.com/automotive ... 93980.html

There should be a .030 shoulder that leaves a gap behind the inner race allowing you to slip the puller wedge in from behind.
You'll have to pop out the rollers and remove the cage first. I doubt you'll want to save the bearing however.
Best to fit new Superblend's, but even then the inner race stays attached to the crank.
 
How many rollers does this bearing have ?

If someone has fitted the older dommie type roller bearing, with 11 rollers, which is not a 'superblend' at all,
then the rollers stay with the inner race on the crank.

They often get damaged if you try and remove them.
Thats why its strongly suggested they only be removed if you intend to discard them and thus intend to replace them.
 
Thanks the bearings are marked MRJA3 dot and MRP they have 12 rollers ? would these be original bearings?
Thx
I have sourced a bearing puller at Harbor Freight my son is bringing it up for me should have it by Christmas day
Drummer99
 
Drummer99 said:
Thanks the bearings are marked MRJA3 dot and MRP they have 12 rollers ? would these be original bearings?

As it's a '1973' model the original bearings should be the R&M/RHP 'Superblend', and marked '6' (this is often faintly etched) 'MRJA30'.
If the bearings had been changed, then it would be more likely (and logical) they would now be FAG NJ306E.

jimmytwin said:

I believe the standard MRJA30 had 13 rollers:
pierodn said:

http://www.norton-parts.com/a-36386700/ ... hp-mrja30/
 
Hi that's the bearing I couldn't see the 0 etched into it So I should assume these are original bearings as they look exactly like your picture and on recount have 13 rollers. I have a set of lightly used superblend bearings that I took out of an 850 they are NU306E fag bearings out of a 74 commando. Will they fit the 750 and what do you think about reusing a set of main bearings?
Thx Jack
 
Drummer99 said:
Hi that's the bearing I couldn't see the 0 etched into it

I would have expected the etch mark to be "6" rather than "0", however....?

Drummer99 said:
So I should assume these are original bearings as they look exactly like your picture and on recount have 13 rollers.
After 40+ years I suppose it isn't safe to assume anything.

Drummer99 said:
I have a set of lightly used superblend bearings that I took out of an 850 they are NU306E fag bearings out of a 74 commando. Will they fit the 750 and what do you think about reusing a set of main bearings?

Yes, they should fit, as the FAG NJ306E (although the outer race may be marked "NU") became the standard replacement main bearing for all Commandos (part number 064118).

As for re-using them, it's got to be your decision.
 
Drummer99 said:
I have a set of lightly used superblend bearings that I took out of an 850 they are NU306E fag bearings out of a 74 commando. Will they fit the 750 and what do you think about reusing a set of main bearings?
Thx Jack

New Superblend's aren't cheap. Like $200 a set? I can understand wanting to reuse them if you're on a tight budget.
Superblend's seem quite stout and and should last a long time in normal usage.
If your used ones have low miles on them and turn silky smooth without any trace of roughness then they should be ok.
Who knows. Maybe they're better quality than the new ones you can buy now. But it is a gamble.
Just be prepared to split the cases again in the future if they start making funny rumbling noises.
 
L.A.B. said:
Yes, they should fit, as the FAG NJ306E (although the outer race may be marked "NU") became the standard replacement main bearing for all Commandos (part number 064118).

Care to elaborate on this a bit? Are you saying that some replacement bearings were mislabeled?

If the bearing was a true NU then it could only be used on the drive side and it would be necessary to constrain the crank on the timing side with a ball bearing. Is this what they did with earlier big twins?
 
I am just looking at the boxes of the bearings that I replaced them with I was going to reuse them in the 850 bike showed 18,000 miles but I decided to replace them The bearings I replaced them with were NJ306E .M! the original bearings were made in Germany and are single dot . The new bearings were made in India Would you think that the NU306E's were what they put in the 74 at the factory ? They are quite different from the bearings in the 73 750 the MRJ30 ?
Thx
Jack
 
Drummer99 said:
where are you located

Sill in Norfolk, UK.


Dances with Shrapnel said:
L.A.B. said:
Yes, they should fit, as the FAG NJ306E (although the outer race may be marked "NU") became the standard replacement main bearing for all Commandos (part number 064118).

Care to elaborate on this a bit? Are you saying that some replacement bearings were mislabeled?

Not exactly.
"NJ" and "NU" outer components are identical, only the inner races differ, NJ inners having a single lip, and "NU" having no lip.

It's certainly not the first time we've heard of owners reporting finding apparently NJ306E bearings-but with an "NU" marked outer and an "NJ" inner.
superblend-bearings-fag-nu306e-original-t18382.html


who-has-fitted-superblend-bearings-early-commando-t20664.html
Time Warp said:
 
Don't be such a tight arse and replace the bearings, yes they are expensive but look how much it will cost you in the long run if one fails, do the right thing and never reuse bearings, you want the rebuild to last as long as it can, you say the bearings only have 18K on them but do you know the history of those 18K.

Ashley
 
Ok I know you are right I'll lose up the purse strings and give them to me for Christmas
Thx for all the feedback
Jack
 
The ONLY so called 'superblend' bearing specifically designed for Commandos was, im my opinion, the R&M (Ransom and Marles) 6MRJA30 bearing.
The ORIGINAL roller bearing which did NOT have so called 'superblend' rollers as used in Dommys and Atlas and which failed at around 4,000 miles in Commandos due to various factors was a R&M 8MRJA30. It worked perfectly well in Dommy and Atlas motors...
Both had a brass cage but the 8MRJA30 bearing employed 11 rolling elements of apperox 11.12 mm width and diameter. The actual parallel working width of each roller was approx 10mm. The load capacity of this bearing was Dynamic 41,900 Newtons and Static 35,200 Newtons.
The 6MRJA30 bearing employed 13 rollers approx 9.53mm in width and diameter but the working parallel width of each roller was approx 6mm tapering down to 9.46mm at each end. The load capacity of this bearing was Dynamic 35,800 Newtons and Static 31,000 Newtons.
It was interesting to note that the load capacity of the 'superblend' bearing was LOWER than that of the bearing it replaced.
Ransom and Marles became part of Ransom Hoffman Pollard (RHP) many decades ago and for nearly as long have been owned by, I believe, a Japanese company. (NSK.)
The 'E' part of a bearing designation simply denotes it is a higher load calacity bearing. IT DOES NOT designate that it has 'superblended' rollers. Many years ago one London dealer bought a pile of FAG NJ306E bearings with brass cages....as I went to put them into stock I opened one up, took the outer raceway off and looked at the rollers under a good light to see the slight tapering at the edges of each roller...there was non. I phoned FAG who suggested they must of been old stock as their bearings now had 'crowned' 'superblend' rollers. The dealer flogged them to Commando owners...wonder how long they lasted??...... DO NOT ASSUME a bearing has crowned /superblended rollers. If you cannot see the 'crowning' / 'superblending' on the rollers 1 phone the bearing manufacturer and ask or even 2 pull out a roller and run a micrometer over it....assuming you can use a micrometer or even that you have one....
A FAG NJ306E bearing is shown in my olde FAG book to have load capacities of Dynamic 51,000 Newtons and static 48,000 Newtons. When I measured a roller many decades ago it was approx 12mm wide and 11mm outside diameter with a parallel portion width of appreox 8mm tapering down to approx 10.97mm at each end.
Looking over the years at a few manufacturers bearings taken from various Commando motors it was interesting to note that on the old R & M 6MRJA30 bearings the wear markings on the rollers stopped short of the very edges of the rollers whereas on FAG bearings wear showed right out to the very edges......Of course these FAG bearings could of been used by people who ran their motors to 7,000 plus rpm as often as possible causing the cranks to flex rather seriously although I suspect the greater crowning of the R & M rollers might have something to do with it..........
So do Indian and Chinese manufactured these days NJ/NF306E bearings have 'crowned' /superblend' rollers?? In my experience thier quality can vary .....however even the bad ones will probably perform perfectly well IF used as per the bearing manufacturers design data but in a Commando motor do we do that?? I suspect NOT. Whats the design life of a bearing? I know its a minimum of 15,000 hours for a Renold chain and in the order of 20,000 hours for one major toothed belt manufacturers products (because the big boss told me so during one of our converations. ..Maybe i should follow my own advice and pick up the phone and ask as few bearing manufacturers thus storing away more useless info!
It could be expensive to assume your new bearing is 'superblended' AND PLEASE while you have your crank in bits check there is no stress raiser inside the drive side half directly beneath the big ends outer 90 thou radius......if it has get that half checked for cracks BEFORE shoving the crank together. You may find it is well on the way to failing BIG TIME. A friend and I many years ago had all our 'spare' DS halves checked and 2 went straight in the scrap bin..... The factory drawings showed the stress raiser left by the drill that cleaned out the inside should of been left inside the web but clearly that was more time consuming to do and what did it matter if peoples cranks failed big time just as long as it occured outside the warrenty period!(Triumph cranks also failed....) I guess the same applied to can shafts failing prematurely due to leaving out the oil bath Mr Hopwood had so carefully designed INTO his original Dominator motor crank cases to ensure the cam was CORRECTLY lubricated especially during the engine start period.
 
J. M. Leadbeater said:
Many years ago one London dealer bought a pile of FAG NJ306E bearings with brass cages....as I went to put them into stock I opened one up, took the outer raceway off and looked at the rollers under a good light to see the slight tapering at the edges of each roller...there was non. I phoned FAG who suggested they must of been old stock as their bearings now had 'crowned' 'superblend' rollers. The dealer flogged them to Commando owners...wonder how long they lasted??...... DO NOT ASSUME a bearing has crowned /superblended rollers. If you cannot see the 'crowning' / 'superblending' on the rollers 1 phone the bearing manufacturer and ask or even 2 pull out a roller and run a micrometer over it....assuming you can use a micrometer or even that you have one....

Again JM, you have to destroy the race to 'pop' a roller out - on the bearings I have seen anyway. ?

And, the 'crowning' you mention is described in the literature as the VERY SLIGHT ROUNDING on the VERY END of the roller.
There is no way to use a micrometer to measure this, it is only a mm or 2 on the very end of the roller.
The rest of the roller is a perfect cylindrical shape - as you would expect in a cylindrical roller bearing !

Also, I have had a quick look at the rollers on a Hoffman bearing in an early dommie engine.
They appear to have rounded edges on the rollers - and this would be a circa early 1950s bearing.
When I get a chance, I'll take another pic - the one I did in a hurry the other day was blurry, focussed on the wrong area,
when I had a chance to review it.

They (Hoffmans) didn't come in a C3 clearance option though (?).
Which is the important bit these days to ensure they don't crush when installed...

Maybe the FAGs you saw had missed a stage in the manufacture ?
 
ashman said:
Don't be such a tight arse and replace the bearings, yes they are expensive but look how much it will cost you in the long run if one fails, do the right thing and never reuse bearings, you want the rebuild to last as long as it can, you say the bearings only have 18K on them but do you know the history of those 18K.

Ashley
What he said. :)
jug
 
Status
Not open for further replies.
Back
Top