Gearbox mainshaft bearing upgrade? (2017)

fiatfan

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There´s loads of threads on the layshaft bearing upgrade here, but is there an upgrade for the mainshaft drive side bearing as well? Or is the old ball bearing type good enough?
Just realized it´s called sleeve gear bearing....To quote the great Danish comedian Viktor Borge; it´s not my language, I´m just trying to use it..... :D
Tommy
 
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No upgrade I am aware of, it's a odd size which limits volumes so less scope, there may be sealed versions around but not looked as never had an issue with it unlike the layshaft which did fail.
 
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When I refurbished my gearbox this summer, someone on the UK NOC forum helpfully suggested getting a sealed bearing and removing one seal, on the side that would face into the gearbox - a bearing with one seal is available for this purpose from AN: https://andover-norton.co.uk/en/shop-details/18011 – AN call the seal a 'shield', but I believe it's the same thing. I went for this, as gearbox oil residue on the inner diameter of the inner race of the old bearing contained rust. Whether fitting a bearing with a seal/shield on its outer face could be considered an upgrade, or would make any difference to my issue, I don't know, but it seemed like a good idea and couldn't hurt. HTH
 

L.A.B.

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NortonMKIIA850 said:
a bearing with one seal is available for this purpose from AN: https://andover-norton.co.uk/en/shop-details/18011 – AN call the seal a 'shield', but I believe it's the same thing.
'Sealed' (RS/2RS) and 'shielded' (Z/ZZ) bearings are not the same.

http://www.ebay.co.uk/gds/Ball-Bearing- ... 758/g.html
Essentially, shields are non-contact metallic (carbon or stainless steel) devices which allow high-speed operation but offer limited protection against the ingress of moisture and dirt.
Shields have no contact with the bearing inner ring, hence their low torque qualities. This structure also means that they are generally unsuitable for applications where the ingress of moisture is possible. But shields are better than seals at resisting damage from solid airborne contaminants, such as small flying stones.
Seals can be either contact or non-contact types. The former provide better protection than shields, but with reduced speed capabilities, while the latter can be used at higher speeds as well as offering the improved protection.
http://www.astbearings.com/bearing-closures.html
 
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Interesting – so the bearing I fitted is unlikely to make any difference to what I found at all! Oh well – why might AN be selling that bearing, then? I can't imagine any flying debris hitting that shield – er, fingers crossed!
 

L.A.B.

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NortonMKIIA850 said:
Interesting – so the bearing I fitted is unlikely to make any difference to what I found at all!
As far as performance or reliability is concerned I don't think it makes any difference.......


NortonMKIIA850 said:
Oh well – why might AN be selling that bearing, then?
I believe the shield on the outside of the bearing was intended to reduce the amount of oil thrown at the sleeve gear oil seal. According to Mick Hemmings in his gearbox rebuild video, he says the early bearings were the shielded type but that the shield isn't really necessary.
 
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2 years ago i aquiered a "not runner" 750. not actually a good buy. also the gearbox main bearing seat was damaged - lots of free space to the bearing due to a gear wheel failiure. the guy doing some mashining on the motor said, he can reinforce the case by deposition welding and rebore the main bearing seat in order to use a needle bearing, leaving more meat between the bearings.

this is what i am ended up with. the gearbox is working fine for the last 1200 miles, hopefully i can tell you in 10 years this was a fabulous approach.
 
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Iv'e got a MK 111 gearbox in my pile of stuff that has a roller bearing fitted in place of the large mainshaft ball type. It's outer diameter is less than the shell hole size , so the machinist made up a sleeve to take up the difference and fit it. Worked well when I last ran it 30 years ago. It also runs the roller layshaft bearing . Overkill maybe but I had extra cash 30 yrs. back. Hope that helps. :)
 
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L.A.B. said:
I believe the shield on the outside of the bearing was intended to reduce the amount of oil thrown at the sleeve gear oil seal. According to Mick Hemmings in his gearbox rebuild video, he says the early bearings were the shielded type but that the shield isn't really necessary.
Ah ok – thanks again – well, I'm a fan of anything that helps keep oil where it should be!
 

fiatfan

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Thanks, great input as usual. So I´ll just buy a good quality bearing then, hope my usual bearing supplier can find one, even if they are an odd size. Don´t Think that´ll be a problem. If so I´ll take one from RGM or the like. I will have to find a good compound to lock the bearing both on the sleeve and in the housing. There were signes showing that the bearing had turned on both in and outside.
Tommy
 
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Whatever large bearing you choose I would make sure it does not rock about it it's shell bore. I hope this is not a concern. Heat and cold.
 

fiatfan

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Torontonian said:
Whatever large bearing you choose I would make sure it does not rock about it it's shell bore. I hope this is not a concern. Heat and cold.
I hope so too! :wink: I´ll try find the best locking compound for the job, as I wrote there was small signs that it had turned both in the house and on the sleeve. I´ll clean the surfaces and measure the new bearing, the sleeve and the bore in the shell, hope it´s enough with locking compound.
Tommy
 
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the factory used both dot 2 and dot 3 clearance bearings.. there is quite a lot of play with a dot 3 -just think about those bronze bushes the main shaft can wiggle in .. could not get dot 2 when i replaced mine but it turns out a lot of 850s where fitted with these and made in japan.. and they failed much to the amusement of we xenophobic Brits. Truth is just pull the primary outer start the engine and blip the throttle. the amount of flex on the shaft is terrifying

no wonder there was a problem under racing conditions and recourse to outrigger bearings- the bodge for we the punters was dot three ,lets the shaft flex
presumably. if there is one thing that does not impress me about the commando... this is it. Good tip when replacing them is to put soap on the alloy casing when it goes brown under your torch flame-you are approaching the temp you want... i made up a jig out of thick dural which bolts on to shell so as to ensure bearing starts straight when replacing them
 
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In the past many of the sleeve gear bearings were ground, this was done as the correct size was not available for sometime. The availability of the correct size bearing is now far better, as for a roller, it maybe possible to get one that size. I know of one manufacturer that supplies alternative roller and needle bearings as direct replacement for most of the standard sizes.

Bearing fit will work, but it can cause the bearing to close up, but considering the temps involved when in use, I would not consider it an issue provided it is checked when fitting of the bearing and the sleeve gear is complete.
 

jimbo

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In the past many of the sleeve gear bearings were ground, this was done as the correct size was not available for sometime. The availability of the correct size bearing is now far better, as for a roller, it maybe possible to get one that size. I know of one manufacturer that supplies alternative roller and needle bearings as direct replacement for most of the standard sizes.

Bearing fit will work, but it can cause the bearing to close up, but considering the temps involved when in use, I would not consider it an issue provided it is checked when fitting of the bearing and the sleeve gear is complete.
If you use a roller type bearing on the sleeve gear what locates it? Anybody know the special correct OD dimension of the SG bearing?
 
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