64 replies to this topic

[freshairmini]

hello,

I've researching for my mini project, more specifically about turbocharging. One thing I have come across is the suggestion that straight cut drop gears would be needed at engine power over 120hp (as a guide).

The main reason that has been said is that the side loading in helical gears can cause problems with the thrust washers.

So my question is how can this be combatted? is there any way of stopping this and get the benefit of much quieter drop gears over the very loud sc ones.

Any insight into this would be great!

Thanks.

[ACDodd]

I have looked at this in the past. If you can work out how to pressure feed the idler gear bearings with oil, I think this would help a lot.

AC

[Gr4h4m]

Robert on turbo minis run high hp with std drop gears. Sites down at the mo.

[Ethel]

I'm sure there was some info online where someone in Germany had created a feed by drilling into an oil gallery. It does seem amazing no one's engineered a commercial solution - an idler with taper roller bearings, like you could get for straight cuts.

[Gr4h4m]

I know of two people with the mod, below is one

http://www.minifreun...oilpressure.htm

[jakejakejake1]

What about using double helical/ herringbone drops, best of both worlds!
Could manufacture two thinner gears and mount together to get around the manufacturing issues, possibly with a small gap between the sets to allow for alignment/tolerances.
Very expensive, yes, but I'm sure there are people out there who would pay the extra for these type of gears.

[Ethel]

That's probably the one I remembered, badly.

It must have been hard drilling through the gear. I'm not sure what the advantage would be as it's the gearbox side that takes the thrust off the helix. I wonder how effective it'd be to screw the standard shim down & feed oil through it?

[Ethel]

Jake,

I think a beefed up idler would be more practical, set against a set of straight cut drops you'd only need to produce 1 gear instead of 3, and that'd just be bringing together existing products. Somewhere all the tooling already exists.

[Gr4h4m]

Try this thread for some thoughts about the issue at hand


http://www.turbomini...d=248104&fr=100

[Ethel]

Ta for that, interesting reading. Suppose the bit about axial load is obvious when you think about - if you didn't get nearly as much torque out of the idler as you put into it, it'd be screwing it's way through the gearbox more than moving the car.

Would it be worth turning the idler bearing housing in the box casing into a blind hole to help retain the oil? Maybe that's why They seem to fair worse than the tranny casing one?

[freshairmini]

excuse my ignorance, but unfortunately I'venever seen the idler gear assembly in the flesh. So from the pictures in the link that Gr4h4m posted up, does the idler normally have those kind of bearings? Or is it that the german guy has created that washer that will allow oil to be passed around the bearing under pressure from that feed pipe? And is it that which makes it more reliable?

[Wil_h]

Assuming everything is in the same condition, you'll break the gearbox before you break the drop gears.

And 120bhp is a pretty arbitrary number, at this power you WILL need a cross pin diff, but everything else will be ok standard.

A standard box will still last beyond 120 bhp, but once at 150 I think mechanical sympathy will be the order of the day to keep it all together.

as stated above, Robert is running 230bhp, and gives it death down the dragstrip on standard drops and all is well. this is of course the later drops with the larger idler bearings. But the standard size first motion bearing, not the larger Metro turbo one.

[freshairmini]

Assuming everything is in the same condition, you'll break the gearbox before you break the drop gears.

And 120bhp is a pretty arbitrary number, at this power you WILL need a cross pin diff, but everything else will be ok standard.

A standard box will still last beyond 120 bhp, but once at 150 I think mechanical sympathy will be the order of the day to keep it all together.

as stated above, Robert is running 230bhp, and gives it death down the dragstrip on standard drops and all is well. this is of course the later drops with the larger idler bearings. But the standard size first motion bearing, not the larger Metro turbo one.

When you say later drops, from when year or model fo you mean. Mines a 1990 rover cooper. Can they be retrofitted to earlier minis or at least my year mini?

Also

I had read on Keith Calvers site that the main reson for people thinking helical drops to be not that great for higher power applications is they have been unreliable, but due to poor end float setting in the factory, which cause them to wear prematurely.

Edited by freshairmini, 13 January 2013 - 05:26 PM.

[Wil_h]

All A+ Boxes/transfer cases had the larger bearings, so your 1990 will.

Yes you need to check the end float of both the primary and idler, different size thrusts are available for both. Key to getting the idler correct is using the orange gasket, these are the correct thickness. the only way to measure the float on the idler is to dry assemble the transfer case on the gearbox with no engine attached. when checking, us the gasket you are going to use.

[mini13]

Also it is alleged that the MPI gear is made for a better material, and the bearing on the MPI wis a better quality torrington one, I belive robert is using both these items.