N9181C 576208 Mainshaft Rear Brg Options Bushing

[Lovel]

Currently working on the overhaul of my 3500S manual box. The rear mainshaft bearing does not seem too bad on close inspection, however there may be an ever so slight roughness to it when turned, hence I am looking to replace.

The component in question has Rover part number 576208, and the bearing is inscribed with N9181C RHP MJ11/8.
I estimate the dimensions to be 2.813" OD x 1.000" ID x 0.813" Wide

The nearest brg I can find is the same dimensions as above apart from the ID of 1.125"

http://www.bearingstation.co.uk/Product ... J1-1-8-RHP

Has anyone machined a spacer collar bushing to make up the difference, and if so was it long lasting and what material was it made from? or should I just bite the bullet and purchase the original bearing which seems to be available from JRW at an eye watering price.

Gary.

 

[harveyp6]

The only place I've found that has the OE bearing is JRW as you say, and the price is eye-watering. You will get suppliers who will say thay have the bearing you want, but send one with a sleeve inside the inner track. These don't work. As you tighten up the rear flange nut it pulls the sleeve rearwards and locks the mainshaft up. The only way to make a sleeve that does work is to machine one that is like a tophat, with the brim of the hat shape on the rear of the bearing, and the same outside diameter as the speedo gear and about 1/4" thick. You then need to machine that 1/4" off the front end of the speedo gear to get it all back in line again. I've not done one yet, but see no reason why it wouldn't work.
The last one I came across that had one with a sleeve fitted had been "reconditioned" and their cure was to leave the rear flange nut loose.....

 

[Lovel]

The only place I've found that has the OE bearing is JRW as you say, and the price is eye-watering. You will get suppliers who will say thay have the bearing you want, but send one with a sleeve inside the inner track. These don't work. As you tighten up the rear flange nut it pulls the sleeve rearwards and locks the mainshaft up. The only way to make a sleeve that does work is to machine one that is like a tophat, with the brim of the hat shape on the rear of the bearing, and the same outside diameter as the speedo gear and about 1/4" thick. You then need to machine that 1/4" off the front end of the speedo gear to get it all back in line again. I've not done one yet, but see no reason why it wouldn't work.
The last one I came across that had one with a sleeve fitted had been "reconditioned" and their cure was to leave the rear flange nut loose.....

I decided to roughly sketch things out with the 1.125" ID bearing with a bush design something the attached photos. There seesm to be a lot of space in side the worm gear for the speedo drive, maybe this is catering for the 2000cc models too, versioning as such?

Oil pump worm gear should of course say Speedo drive gear

 

[harveyp6]

The way you've drawn it up you'll find that the extension of your bush inside the speedo gear will distort as you tighten the flange bolt. It will act like a collapsable spacer in a rear hub. If you make one up like I said, and shorten the speedo drive gear to match it then it won't.

It's quite possible that the 4 pot and V8 speedo drive gears are the same item.

 

[Lovel]

The way you've drawn it up you'll find that the extension of your bush inside the speedo gear will distort as you tighten the flange bolt. It will act like a collapsable spacer in a rear hub. If you make one up like I said, and shorten the speedo drive gear to match it then it won't.

It's quite possible that the 4 pot and V8 speedo drive gears are the same item.

I left a small clearance with the overall length of the bush when the speedo drive is torqued up, of approx .010" so that the inner bush would not compress

Need to decide which grade of ball bearing race to use, as there are different running clearances to specify. Possibly C3 grade ?

 

[harveyp6]

I left a small clearance with the overall length of the bush when the speedo drive is torqued up, of approx .010" so that the inner bush would not compress

All that will do is allow your bush to move backwards until it hits the speedo gear, at which point it will start to deform, and also it will increase the preload on the mainshaft. Try it by all means if you want, I'm just trying to save you the trouble of finding out it won't work that way. That's exactly the same thing that happens with the bearings that you can buy with the sleeve already fitted.

 

[webmaster]

All that will do is allow your bush to move backwards until it hits the speedo gear, at which point it will start to deform

Sorry to jump in here, but I don't understand how the sleave will deform if it's not under compression from the flange nut ?, are you saying that the speedo gear compresses, leaving less room for the sleave ?

And is this your proposed solution Harvey ?

 

[harveyp6]

All that will do is allow your bush to move backwards until it hits the speedo gear, at which point it will start to deform

Sorry to jump in here, but I don't understand how the sleave will deform if it's not under compression from the flange nut ?, are you saying that the speedo gear compresses, leaving less room for the sleave ?

And is this your proposed solution Harvey ?

That's exactly what I would do. (Why can't I do things like that on the computer?) The sleeve is under compression from the flange nut, because the mainshaft is smaller than the sleeve in the gear, so it gets pulled backwards, moving the sleeve, as you tighten the flange nut, and that in turn pulls it (the mainshaft) through the collar on the rear that retains 1st gear, which then locks up the shaft altogether.

 

[Lovel]

I have still not decided which way to go with the bush design, but once I obtain the new 1 1/8" ID bearing, I'll have a bit more thought on it and then see from there.

The last few nights I have been removing the old bearings from the shafts/housings and inspecting the components closely to establish what else I need to replace. Reverse gear is definitely one thing that will need replacing, and I'll replace the selector for that too.

The overall appearance of the mainshaft gears and layshaft look to be in remarkably good nick considering there is more than 100k on the box. Now based on the percieved poor image of the 4 speed manual box weakness, I expected lots more wear and tear, tbh but it not as badly worn as a 5 speed box that I pulled apart years ago from my TR7.

One thing I have noticed is that on FRC180 (Cover plate oil pump & gear assembly) the oil pump has picked up a sharp edge from the speedo gear drive, which may be due to wear in the rear roller bearing??. This has possibly affected the old pump as the rivets holding it to the gearbox plate are loose and I can get a feeler gauge underneath. Would it be wise just to nip up the rivets again and polish out the sharp edges that have built up over time? The speedo gear has slight wear marks on it too from rubbing against the oil pump. Should I just replace the oil pump with new? What would be the costs to replace these parts if available?

 

[Lovel]

One further question I have is on the front input shaft ball bearing race. It is inscribed 5/6306 RHP, the inner of the race has what appears to be 3CM or 3OM ? 72mm OD x 30mm ID x 19mm Wide. Maybe its simply just 3cm ID ?

Would the coding on the bearing be related to the running clearance as it seems real close to the term C3 which is used to indicate larger clearances?

The rear bearing is STD running clearance afaik, but for some reason would the front bearing be C3 spec or not?

Front Input Shaft Bearing

 

[harveyp6]

I doubt that you'll find a NOS oil pump, and TBH they never worked very well anyway. There aren't a lot of NOS parts for those boxes at all really so I'd be surprised if you got a new reverse selector as well. Although there are differences, parts can be interchanged with the 2000 box. First motion shaft bearings are readily available from normal bearing suppliers. It's an Imperial bearing. I may have a speedo driven gear that's in better condition than yours, and I also have an oil pump but I'd be surprised if that was any better than the one you have already.

 

[Lovel]

Looking closely at FRC180 (Oil Pump plate hsg) I noted that there is some wear from the outer race of the rear mainshaft brg. Now this raises the question that there seems to be movement against the plate. What concerns we is that the original gasket (FRC1214) I removed was 0.004" thick. The replacement gasket is 0.015" thick which means there is even more space for the rear bearing race to move under load.

 

[harveyp6]

I always remember the gaskets as being thick when I was doing them back in the day, but a lot I've seen recently are just thin paper gaskets. I think you'll find that all the pump plates have marks like that. Have you measured to see whether it's just a mark or whether it's worn a groove? That outer track shouldn't be spinning in the casing, and if it moves backwards and forwards enough to be the cause of the marks on the pump plate then eventually it's going to get loose in the casing.

 

[Lovel]

I always remember the gaskets as being thick when I was doing them back in the day, but a lot I've seen recently are just thin paper gaskets. I think you'll find that all the pump plates have marks like that. Have you measured to see whether it's just a mark or whether it's worn a groove? That outer track shouldn't be spinning in the casing, and if it moves backwards and forwards enough to be the cause of the marks on the pump plate then eventually it's going to get loose in the casing.

The wear circle groove at it's deepest would be at the most 0.001" around 120deg of the top. The bottom of the wear circle has no wear. The bearing is not loose in the alloy housing when cold, maybe loose when hot though? Probably application of Loctite for the outer bearing housing just in case.
If I fit the thicker gasket I am considering shimming the out the bearing race by the difference to make the clearance between bearing to a minimum, however this will have the knock on effect of pulling the mainshaft rearwards away the the front input shaft a wee bit. Maybe make no differnence in the end :?:

 

[harveyp6]

I don't think that the bearing will be loose in the casing when it's hot, (although that's obviously difficult to prove in use) and TBH I think that you're looking for solutions to problems that aren't there. We all know that they're not a reliable box, well overstretched behind the V8, and for that reason I've done loads of them, and all of the things you mention have never caused me any problems.

 

[Lovel]

Would anyone have advice on where to obtain layshaft shims from? I have shopped around but they seem to be an obsolete part.

I calculate I need thicknesses of shim greater than .107", .108", .109", .110" and maybe even thicker than this?

The shim measures 49.5mm OD x 42.5mm ID

 

[harveyp6]

I have one gearbox in bits so in theory there should be a shim in amonst those parts so I'll see if I can find and measure it over the weekend. I'd be surprised if new ones were still available.

If you can't get one it won't be difficult just to make a few so you can get the preload right. Time consuming but not difficult.

 

[Lovel]

I have one gearbox in bits so in theory there should be a shim in amonst those parts so I'll see if I can find and measure it over the weekend. I'd be surprised if new ones were still available.

If you can't get one it won't be difficult just to make a few so you can get the preload right. Time consuming but not difficult.

Thank you very much for the offer Harvey.

I'll place a wanted ad in the relevant forum section, to see if I can clear out any P6 owners of superfluous gearbox shims.

I have now narrowed it down to a requirement for a (FRC1618) 0.124" or (FRC1619) 0.125" shim by using a process of numerous shim materials and achieving a 4 to 6lb rolling preload reading.

 

[harveyp6]

I answered you're wanted thread for the shim. While searching for that I looked at the speedo driven gear, and the oil pump plate and they both look marked just like yours which goes some way to confirming my thoughts that they're all like that.

 

[Lovel]

Looking closely at my new replacement bearing and bush I can see an issue with the arrangement. The new replacement bearing has too large a lead-in on the inner race. Hopefully from the pics attached you can see that when all is tightened up the spacer ring on the mainshaft will move inboard causing lock up or high internal loadings. There may be other manufacturers of bearings where the lead in is less as this surface is not normally critical except in this case unfortunately.
Looks like I will contact JRW to establish if the bearing that they supply is original design manufacture or if they simply use the larger ID brg with a bush.

I have attached two sketches showing the layouts with the original and revised arrangement