64 replies to this topic

[tiger99]

You really need something like taper roller bearings to resist the complex thrust on the idler gear, which is trying to twist the gear around a vertical axis. There should actually be no significant thrust on the thrust washers, the main loads should all be taken by the needle rollers, yet as we all know, the thrust washers will chew into the casing, which suggests that the needle rollers are not stiff enough.

You may have significant problems getting taper rollers in there, and adjusting them correctly, but if you could solve the problems the results would be well worth the effort.

Or, I do like the idea already suggested of herringbone gears, but they are extremely difficult and expensive to manufacture in small sizes. In larger installations they are machined in one piece, with a groove between the opposing sets of teeth to allow for the tool radius, but there is no room for the extra width so they would have to be made in two halves and solidly joined, with correct tooth alignment. Also, only one would be axially located, most likely the gearbox input shaft, so the idler and primary gear would run without thrust washers, the torque loading automaticaly centering them axially. If you fitted thrust washers, there would be an unpredictable axial load due to tolerances, and all the same problems as the existing design.

I like the idea, as long as someone competent makes them, but there is also the possibility of chain drive, which has a similar number of problems to solve, although could be expected to be much cheaper than herringbone gears.

[freshairmini]

You really need something like taper roller bearings to resist the complex thrust on the idler gear, which is trying to twist the gear around a vertical axis. There should actually be no significant thrust on the thrust washers, the main loads should all be taken by the needle rollers, yet as we all know, the thrust washers will chew into the casing, which suggests that the needle rollers are not stiff enough.

You may have significant problems getting taper rollers in there, and adjusting them correctly, but if you could solve the problems the results would be well worth the effort.

Or, I do like the idea already suggested of herringbone gears, but they are extremely difficult and expensive to manufacture in small sizes. In larger installations they are machined in one piece, with a groove between the opposing sets of teeth to allow for the tool radius, but there is no room for the extra width so they would have to be made in two halves and solidly joined, with correct tooth alignment. Also, only one would be axially located, most likely the gearbox input shaft, so the idler and primary gear would run without thrust washers, the torque loading automaticaly centering them axially. If you fitted thrust washers, there would be an unpredictable axial load due to tolerances, and all the same problems as the existing design.

I like the idea, as long as someone competent makes them, but there is also the possibility of chain drive, which has a similar number of problems to solve, although could be expected to be much cheaper than herringbone gears.

Am I over simplifying this, or would it just be a case of trying to find the correct size taper roller bearing for the idler to replace its existing bearing type?

[Cooperman]

The difference betwen ID and OD of the existing nneedle rollers is where the problem comes. There is simply not enough room to fit taper bearings and it is probably not possible to bore out the two casings to take a taper with the same ID.

[freshairmini]

The difference between ID and OD of the existing needle rollers is where the problem comes. There is simply not enough room to fit taper bearings and it is probably not possible to bore out the two casings to take a taper with the same ID.

Would it be possible to add material around where the bearing is positioned? Maybe TIG some more aluminium around it then bore it out to a larger size?

I ask this because the workshop that belongs to my friend, which I will be using for my mini, has a big old milling machine and loads of different welding equipment (which includes a TIG welder). He's a pretty proficient welder and knows how to use the mill.

[tiger99]

It would be nice if you could do it that way, and I guess that very many Mini owners would be interested. One big problem is setting up the end float for the taper rollers, and I think that you would need to bore right through the clutch casing and fit an adjuster of some kind, which would be accessible with teh flywheel removed. The adjuster would of course have to be sealed to prevent oil leaks.

I suspect that it is doable, with difficulty. Making a new clutch casing casting is not impossible either, but you would want to keep the main gearbox casing and just machine it, I would imagine, to keep the cost down.

It is disappointing that none of the usual Mini suppliers has seen fit to develop such a modification, as some of them have the engineering resources, although others (no names, but many of you know various bits that break) manifestly do not....

[freshairmini]

It would be nice if you could do it that way, and I guess that very many Mini owners would be interested. One big problem is setting up the end float for the taper rollers, and I think that you would need to bore right through the clutch casing and fit an adjuster of some kind, which would be accessible with teh flywheel removed. The adjuster would of course have to be sealed to prevent oil leaks.

I suspect that it is doable, with difficulty. Making a new clutch casing casting is not impossible either, but you would want to keep the main gearbox casing and just machine it, I would imagine, to keep the cost down.

It is disappointing that none of the usual Mini suppliers has seen fit to develop such a modification, as some of them have the engineering resources, although others (no names, but many of you know various bits that break) manifestly do not....

so if taper bearings are an option that is a little to complex, for me at least, then would a better needle roller bearing a different option? As I wouldn't have a problem with spending more on the individual part if I know that's its going to be better.

[Cooperman]

The needle rollers don't normally break, the problem is the thrust loads on the thrust washers.
There really is no easy way to cure this without going to straight-cut gears and putting up with that absolutely horrible whining noise which means ear plugs on normal road journeys.

[tiger99]

It occurs to me that another problem is that the two bearings will not be aligned pefectly. The clutch housing is dowelled to the transmission case, but even so, there will be some residual misalignment. What I said about taper rollers might best be applied to self-aligning roller bearings instead. If one bearing was fully located and designed to resist thrust in both directions, the other could be floating axially, so more need for adjusting clearances to suit the gasket thickness. There now, two problems solved, if only a real expert would come forward to make the bits.

Theoretically, if there is a sufficient market for something and the technology exists, someone should make it. That is fundamental to how new business develops. So maybe we are missing something, and the market is far too small to support the investment?

[freshairmini]

It occurs to me that another problem is that the two bearings will not be aligned pefectly. The clutch housing is dowelled to the transmission case, but even so, there will be some residual misalignment. What I said about taper rollers might best be applied to self-aligning roller bearings instead. If one bearing was fully located and designed to resist thrust in both directions, the other could be floating axially, so more need for adjusting clearances to suit the gasket thickness. There now, two problems solved, if only a real expert would come forward to make the bits.

Theoretically, if there is a sufficient market for something and the technology exists, someone should make it. That is fundamental to how new business develops. So maybe we are missing something, and the market is far too small to support the investment?

I'm surprised that someone like MED or the like haven't developed something, they have the know-how and the tools, surely this kind of fix would be great for motorsport minis?

[tiger99]

Maybe it is just too difficult? In theory it is easy, but if you have to make new castings, and maybe don't have enough clearance behind the flywheel, the scope of work necessary would escalate out of proportion to the benefit. Real transmission designers may have seen the major snags that we have not.

I am more surprised that no-one is making a chain drive conversion, which would seem to need only three new parts, primary gear, input gear and chain. There would seem to be no need to modify the castings. If a wider chain proved to be necessary, a spacer plate could be fitted between clutch housing and engine/gearbox, but it might then be necessary to use an automatic subframe to get some extra width.

[Cooperman]

Perhaps the reasoning is that standard helical gears are good for up to c.120 bhp without the side loading giving any real problems. Even a 100 to 120 bhp engine is going to be stripped fairly regularly so the thrust washers can be changed then if required. At over 120 bhp it might be expected that the car will be a competition vehicle and as crash helmets will be worn, the whine from straight-cut drop gears won't be an issue. The number of Minis used as road cars with much over 100 bhp is really minimal, so there is no real market for any sort of helical gear side thrust modification.

[mini-luke]

As above I think the reason it's not been solved is that it's not a problem that exists for the vast number majority of people

[tiger99]

Probably correct, and I guess that there will not be much more development of the A series now, so if it was going to happen it would have been when Minis were more plentiful.

I still would like a chain drive, because the power loss would be less than with the idler gear, and so it would benefit everyone by slightly improved economy and performance, regardless of power output of the engine. But I guess I just have to accept that it is not going to happen now.

[mini13]

just for you!

Edited by mini13, 18 January 2013 - 04:29 PM.

[Ethel]

That's some fancy chain.

Would it be any quieter though, and what about drivetrain inertia - the reason for using the idler in the first place?