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Daveys

NJ 205 ECP/ C3 Mainbearing installation

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Hello. I saw some old topics which recommended a NJ 205 ECP/ C3 bearing for the ignition side. This was specific to Bultacos but probably applies to lots of others.

I bought an SKF which was pretty pricey at £30 but the benefits of fitting it sold on the outlay. The SKF has a collar/flange  on one side and the whole outer bearing can slide off the other uncollared side. When I put the bearing on the crankshaft (370 Frontera Mk10) the bearing inner is up against the slight raised section of weight, as should be,  but the bearing outer is free to slide up over this raised section and sit against the weight.  My concern is that in on assembly when I drop the crankshaft plus bearings into the LH case this will push the bearing outer up against the weight and it will rub. 

I could try and put a temporary shim in between the bearing and the weight on assembly so that there is a 1mm gap as per the normal C3s on the other side and then when the case cools down it will grip in in this position.

The other option is to reverse the installation so that the collar sits up against the weight (on the slight raised section) and the outer can slide off.   This might make assembly tricky with the hot LH case horizontal  on bench and the cold crankcase being lowered as the outer bearing will keep falling off. 

I installed the first way because this would still allow me to see the manufacturing number when installed which I though would be the correct way to do it.

The other option is to ditch the NJ 205 ECP/ C3 and use the spare plain C3 I have as installed on the the other side.

I feel I am making a simple mistake which could be catastrophic if I get the bike going.

I am off to In Motion this morning as they showed me the needle bearing they sell which does flex either way on the inner but does not totally come off one end as per the SKF. I could have bought the wrong type.

Any advice gratefully received

 

 

 

 

 

  

 

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Daveys - 

The roler bearing you have has axial location in one direction ( a shoulder on the inner race) - have I got that right ?

Why not heat the inner race and fit that to the crank (shoulder to the wheel), heat the crankcase and fit the outer race ("open" side to crank). Inner and outer parts of the bearing are then located independently and you can simply slide the bearing  parts together when you assemble crankcase halves.

This of course ignores  manufacturer's markings........( and I don't know which way they face on SKF bearing, anyway)....... having NJ series bearing also sets up requirement for the crankshaft width between bearing seats to be controlled to avoid negative axial clearance.

Or maybe I'm completely off beam here.........

Edited by lorenzo

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I'm not technically qualified to comment on the virtues or otherwise of the NJ bearing although it sounds a whole lot of hassle to use, but what's wrong with the usual 6205 C3 ?  I had 6205 C3 in my 360 Pursang when I was racing one and there were no issues 

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I have just tried this on a 350 Alpina, i had no issues with mine. From what you describe you would have the same issue if you used a standard ball race bearing.

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Hi,

a bit confused how using this bearing makes it easier to assemble cases?

- the bearing nj 205 ecp c3 goes into the ignition side case? So does this mean the crank is installed into the clutch side case first?

any help appreciated.,

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Lorenzo. Thanks for the reply and thanks for the other replies

Your suggestion is right. I spoke to In Motion and they suggested the same. Mind you they also said that the original should be the standard C3 and the needle bearing option was just for the Mk10 Pursang.

Before I read your reply I removed the needle bearing and put the standard C3 on. I then read your reply and thought I would be brave so removed the C3 and put the inner race on the crankshaft with the flange on the inside so that the outer bearing can just slide on and off.  I then put the outer bearing in the freezer for a few hrs before heating the LH crankcase with blowtorch and bearing dropped in.

I then put the crank in the freezer again, 2 x C3 on the drive side and the inner race on the magneto side. I then assembled the gearbox put some blue hylomar on the crankcase joints and a new gasket.  I has previously measured the gap between the crankcases and crank as 1.8mm so tried to centre it at 0.9mm each side using a dismantled feeler gauge.  I placed 2 x  0.9mm gauge combinations on the LH crankcase and dropped the frozen crankshaft into the NJ 205 outer bearing so that it sat on these gauges which were retrievable after the cases were assembled. I then used a blow torch on the bearing seat of the RH crankcase and dropped the case on the awaiting crank and 2 x C3. A slight wiggle of the kickstart shaft and they joined up. All appeared very good so I tightened the 12 or so nuts.

After this I tried to rotate the crankshaft and it would hardly move. I was worried but did remember that when I put the gasket on it was slightly proud at the point the crankcase join where the crank sits.  I split the cases and recognised the benefit of the NJ 205 as the cases could be split without me having to heat around the bearing seats. I took the gasket off (ripped to shreds in doing so) and put the cases together. The crank turned as it should. I will used another gasket and trim it back so that it does not touch the LH inner crank 1/2 weight. 

I can definitely see the benefit of the NJ 205 on assembly and disassembly alone. The crankshaft not turning did worry me but thankfully it was simple and I should have trimmed the gasket back.

 

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markg - 

10 hours ago, markg said:

a bit confused how using this bearing makes it easier to assemble cases?

As the inner and outer races of the roller bearing are separate parts, once fitted to crankshaft and crankcase respectively it's then possible to assemble/disassemble the engine without heat.. See above from the o.p. 

Edited by lorenzo
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1 hour ago, lorenzo said:

markg - 

As the inner and outer races of the roller bearing are separate parts, once fitted to crankshaft and crankcase respectively it's then possible to assemble/disassemble the engine without heat.. See above from the o.p. 

Thanks, I understood the post and that the  bearing separates. So your saying to use this type of bearing in both cases or just in the clutch side case? Using the normal bearing in the flywheel side as the gearbox is assembled in this side?

or alternatively assemble crank in clutch side case with normal bearing then lower this as an assembly in flywheel case that has the nj205 bearing installed? 
 

Sorry if the seems a silly question,,,just trying to get my head around it ..

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8 hours ago, markg said:

 

or alternatively assemble crank in clutch side case with normal bearing then lower this as an assembly in flywheel case that has the nj205 bearing installed? 
 

..

Yes.............

Crankshaft needs positive location relative to drive side crankcase half to retain primary chain alignment. Using roller bearing on mag. side of crank also makes crank width and axial location of main bearing less critical.

Edited by lorenzo
missing text
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Daveys - 

Crankcase gasket must stand proud of cylinder base joint face at assembly, to be trimmed after cases are together and all fixings tightened. This should ensure that there are no leaks at cylinder base.

You seem to have taken considerable care to centralise crank within cases ; what happens when driveside nut (for oil seal sleeve and sprocket/weight)  is fully tightened ?

Edited by lorenzo
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Lorenzo,

               I worked out why the crankshaft was not going around. The centralising did not work. I had a 1.4mm gap on the drive side and a 0.7 mm on the magneto.  When I tightened the cases it was rubbing somewhere. The gasket was also slightly proud inside the crankshaft area but that can be moved over when I reassemble.

The centralising technique I used was flawed and missing an important addition. I did not put the oil seal retainer on the RH crankcase side when I heated it and dropped it on the frozen crank where the 2 x C3 bearings sat. I thought my 0.9mm measurement on the other side would be enough and the joining of the crankcases would leave the drive side 2 x 3s in the right position within the crankcase. It didn't work. Perhaps I removed the feeler gauges a bit early and as the magneto crankshaft could move within the NJ205 the whole crankshaft dropped a bit.  Most likely it was down to the omission of the oil seal retainer.

I decided to see if I could put it right by installing the oil seal retainer on the RH crankcase, use a blow torch to heat around the bearing seat and then with the nut installed on the LH crankshaft hit it with a rubber mallet until moved up to the oil seal retainer. It worked. Crank now central ( roughly 0.9mm one side and 0.8mm the other). I tried tightening the cases without the gasket in place but this caused a slight rub. I then put the gasket on and tightened all 12 nuts and the crank now freely moves.

Another Bultaco lesson learned the hardway.

 

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markg,

            Your question re which side the NJ 205 goes was answered by Lorenzo but it did make me think whether you could use all NJ 205s.

This could be an option on cranks which only have one bearing on each side but as mine has 2 on the drive side it would be pointless and an unnecessary cost.

Also on rereading Lorenzo's post the drive side sounds like it needs to be fixed for the primary chain alignment and not have the movement which an NJ 205 provides.

It easy to overthink this which I can be guilty of doing.

 

 

Edited by Daveys
typo

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