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DickyM

Bearings

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Hi again all. Back again so soon.

I am literally about to order all the bearings and seals for my 198a and I thought what the heck why not fit a roller bearing to the timing side like many others have already successfully done. An extra £30 or so in percentage terms is not much.

So my question is what type of roller bearing to buy? What type have you all fitted? I note that DaveyS posted a similar question back on 26th June and he has used an SKF NJ205 ECP/C3. This type of bearing allows free float in one direction but not in the other and fitted with the flange against the flywheel means that if the crankcase expands more than the crank itself, which it probably does, it is free to float. If for some reason the crank moves more than the cases then the bearing would resist, as a ball bearing would do. Personally I was thinking of an NU205 series which can float in either direction. With the double bearings located with a circlip on the drive side I thought this arrangement gives the most flexibility. Also I note that the P in the designation ECP means that the cage is made from plastic. Reinforced polyamide (Nylon). Is the cage being made out of plastic likely to be an issue or am I  fretting about nothing, again. SKF NJ205 ECJ/C3 and NU205 ECJ/C3 with steel cages are available at yet more cost if required.

I would be interested to hear your experiences. It never crossed my mind that bearing cages these days could be plastic so maybe plastic cages are being used on ball bearings as well. All the old bearings I removed are steel cages though.

As a by the way I had a go at calculating the differential movement between crank and cases just to see how much they can move. Aluminium crankcases will move almost twice as much as the steel crank but with an engine temperature of say 120C from say a 20C ambient  the movement is around 0.1mm with the cases moving outwards relative to the crank. (According to my calculations that is) Not much but enough to stress ball bearings. Can't see the crank/cases getting much hotter than 120C otherwise the nitrile crank seals would break down and the gearbox oil would be boiling!

I would be grateful if you would let me know your thoughts.

Thanks

 

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Not sure why everyone seems to overthink this issue, C3 bearings are standard and don't cause any problems that I am aware of, so why fix something that isn't broken it's a trials motor after all not a motocrosser or road racer where it's getting flogged to death

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Hi Dickie, I use the SKF bearings you mention in all the motors I build, and to date not one has failed. It is interesting to note when a main bearing does fail, it is nearly always on the ignition flywheel side. A roller bearing such as this has far more strength than an ordinary ball bearing of a similar size. One thing that is a benefit, no need to heat up that case when you are ready for assembly, just pop it straight on. Hope this helps..........

 

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DickyM,

Hello. I fitted the SKF NJ205 ECP/C3 on the ignition side as you mention,  with the flange against the flywheel. I am happy with the arrangement,  more from the ease of assembly and disassembly than the other benefits whihi I haven't experienced yet.  Johnjsy confirms this ease. When I was reading up on this bearing the main benefit as I saw it was the ability to use some loctite (641) on this side alone as the bearing I took off was a little loose and I figured i would fix it with the loctite and allow the float to take up the movement which had caused the slight wear on the crankshaft in the first place. Apparently this side is prone to such wear. I have retained 2 x C3 on the other side and they are not fixed with any loctite.

When I was speaking with Inmotion they did have a bearing which  could float in both directions and stated this was for a Mk10 370 Pursang.  It is here that Sherpa325's comment has merit and it is clearly for a motocrosser. My bike is a frontera 370 so I'm nearly a motocrosser but I will generally be driving miss daisy when i get it going.

If I had been aware of the plastic I would have bought one with a steel cage the reason being if I need to take the bearing out of the crankcase then I have been using a blowtorch which will likely damage the plastic.

I had to swap some bearings between clutch baskets and one had a plastic cage which slightly singed when removing it. I will stay away from P in the future.

Thanks 

Daveys 

 

        

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You can see quite clear photographs of the C3 and its alternative roller bearing. Ease of assembly is good with the roller bearing but friction is increased due to greater surface area covered by each individual roller, unlike a ball bearing which has a significantly smaller contact area. If you are going to be stripping the engine down on a regular basis then go for the roller bearing otherwise save some dosh and stick with the C3 type which has designed in free play for sideways movement. As mentioned the reason that the flywheel side (ignition) main bearing usually fails first is that it runs hotter as there is less cooling due to the shrouding action of the timing cover and the fact that the crankshaft can dissipate more heat through the primary gear/chain and of course oil. Too much side play wont do the crank seals any good either, unless you like changing them regularly.

Edited by section swept
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Section Swept. Like your explanation. When I have eventually got everything sorted, which may involve further strip downs, I will return to straight C3s.

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Hi all, thanks for your replies. Choice of bearing seems to be a matter of personal choice as there doesn't seem to be a consensus point of view. I take on board and acknowledge the different views people have and recognise the merits of the different points of view. But I have now decided and rightly or wrongly, bought a steel caged N205 roller for the ignition side with free float either way. I shall see in due course how it works out.

Johnjsy and section swept make the comment that the ignition side bearings tend to go first due to generally running hotter. I wonder if this is also true of the ignition side seals? The outer seal on this side must vertually run dry as well as hot. Any evidence of more failures on this side?

Daveys I'm sure your loctite solution will work fine. I have used it in numerous situations in all sorts of applications and personally never known it fail.

Thanks again everyone.

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On 7/18/2020 at 7:48 PM, johnjsy said:

Hi Dickie, I use the SKF bearings you mention in all the motors I build, and to date not one has failed. It is interesting to note when a main bearing does fail, it is nearly always on the ignition flywheel side. A roller bearing such as this has far more strength than an ordinary ball bearing of a similar size. One thing that is a benefit, no need to heat up that case when you are ready for assembly, just pop it straight on. Hope this helps..........

 

Concur with ease of assembly/dis-assembly using a pair of roller bearings as opposed to 2 x ball bearings or 1 x ball and 1 x roller brg.

Back in a previous life i built Brit parallel twins for a living in my own workshops.

Norton came out with a fix on their Combat Commandos in the early 70's which were a pair of FAG bronze caged 3 piece rollers, set up and run with end float.

No more bottom ends and crankcases exploding, and comfortably able to handle much more torque and bhp.

We fitted these with machining of crank or cases wherever possible on various bikes, mainly Meriden Triumphs, and a big benefit was ........... ease of assembly/dis-assembly...

Sorry, carry on Bultaco's - back on topic.....

 

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