76 replies to this topic

[stretch tech]

Evening all,

 

First things first, i haven't really been on here in ages since passing my test last year and starting work so hello again TMF 

 

right then, i bought an 1100 pre A plus engine the other day ready to start building a low comp turbo daily motor (more on that to come soon). Anyway, i've been weighing up helical vs straight cut drop/transfer gears for my build and after a bit of digging around i've decided i hate straight cut noise   

 

However, i've seen the notion of chain drive as an alternative but no one has developed such kit... this got me thinking. 

 

I actually work as a CAD designer for a company specialising in power transmission (gears, chain, pulleys etc among other linear motion products http://www.wmh-trans.co.uk/ ) and we are a uk distributor of IWIS chain - THE best quality chain money can buy and is also the stuff that MED has recently started using for their timing chains. We also have a sister company that is much better equipped to make pretty much any gear thinkable.

 

So, it seems that i have access to pretty much everything needed to produce the parts for such a conversion. Unfortunately i currently lack the time to develop such a kit  ​ (various projects at work etc)

 

Anyway, if you guys could post any ideas and constructive criticism regarding a chain drive kit/conversion that would be great. Pros/cons of chain vs gear drive, feasibility etc - Chain is a more efficient power transmission after all !!

 

If there are people who can talk technical/design proposals with me, please get involved   

 

Cheers

Rhys

 

PS: Dear admin, please forgive my company advertising 

[mini-geek]

The original design was to use a chain...

Why it wasn't used I can't remember..

[Cooperman]

That is an interesting proposal.

The chain(s) will need to transmit a working load represented by 130 bhp (nominal) via fairly small diameter sprocket(s). A tensioner will not be possible because the chain has load reversal 'power-on' - 'power-off', so chain stretch might be an issue.

A power transmission expert is what we need and it looks as though we have one.

[stretch tech]

The original design was to use a chain...

Why it wasn't used I can't remember..

 

maybe it was the chain technology back then ? modern chain drives have very high tolerances on the parts and old English engineering (especially on the mini) didn't quite have the accuracy 

[stretch tech]

That is an interesting proposal.

The chain(s) will need to transmit a working load represented by 130 bhp (nominal) via fairly small diameter sprocket(s). A tensioner will not be possible because the chain has load reversal 'power-on' - 'power-off', so chain stretch might be an issue.

A power transmission expert is what we need and it looks as though we have one.

 

Unfortunately i'm no expert on the A series engine, is there much scope to increase the size of the sprockets on the crank and the err bottom one (name escapes me), it's been a while since i had my engine apart (thankfully !)

 

Going on your reputation, we also have an engine expert 

 

We do sell chain that is maintenance free (self lubricating and resists stretch/wear although it does still wear) 

 

Regarding the tensioner, why could you not use one ? more over, what would be needed to make one work ? i might have a look into a design to compensate.

 

Rhys

[Cooperman]

Hi Rhys,

 

It would be difficult to fit larger sprockets, but a triplex chain might be possible.

The transfer train is highly loaded in one direction with full power/torque loads, but on the over-run there are the engine braking loads and a tensioner would have to withstand these. As I always understood it, a tensioner can normally only take the catenary loads, which are always low whilst engine braking can be much higher. However, a chain transmission specialist might be able to fit a suitable load carrying tensioner.

It's all a tight fit in there, but why not pull it to pieces and see what the special limits are and see if a duplex or triplex chain might fit and carry the loads and very high chain speed around those small sprockets.

In the end, the possible gains might not be worth the costs. After all, the helical drop gears are very effective and don't suffer from chain stretch making a replacement of the chain necessary after relatively few miles. It's bad enough having to change the timing chain every few thousand miles in high-revving units.

[Dan]

Didn't the Princess gearbox have a chain driven input gear in the same arrangement as the Mini drop gears? Good place to start looking.

[stretch tech]

Cooperman: i'm picking my new engine up sunday so i think i'll whip the transfer case off and have a look at the space available and measure up my center distances and available depth for the du/triplex sprockets. Then i can have a play on solid works.

 

might have a look at putting a tensioner either side of the assembly so each one works in the opposite direction. that's if the size of a single tensioner would be too large. Iwis do a range of motorcycle style chain that might be perfect for such an application.

 

Dan: thanks, i'll have a google...

 

Rhys

[Cooperman]

Any idea what the gain in reduced power train loss might be in percentage terms? This needs to be a comparison with helical gears as straight cuts are really only for competition (unless you want to suffer from tinnitus in later life) so that the overall gear ratio can be changed easily for different circuits.

 

Look under the current 'Missing Bearing' thread on this page and you'll see a great view of the inside of the transfer gear casing.

Edited by Cooperman, 06 February 2014 - 10:40 PM.

[stretch tech]

blimey, off the top of my head no unfortunately, i'll have to stick it in the calc software we have a work... in my office 

all that i can say at the minute is that it should be significant reduction.

 

thanks for that , there's less room than i remember !

[Cooperman]

I do seem to recall that one of the original reasons for helical drops was because to fit sufficiently large sprockets would mean a much larger transfer gear case.

Any chain drive would have to take a maximum safe sprocket speed of 7500 rpm, have a chain life of a minimum of 60000 miles, have no tensioner (due to reverse loading and space) and take high shock loading e.g. when coming from mud onto dry tarmac at high rpm with wheel-spin being suddenly killed by the grip on the dry surface and where such loading, in extremis, will snap a driveshaft without damaging the transfer gear train.

That's a tough specification and to warrant it would mean the saving in power loss would need to be very significant.

[tiger99]

This is extremely interesting, as I have been wanting a chain drive for a very long time. My investigations took me to several manufacturers web sites, and I found that the torque was easily feasible, but the maximum rotational speed was not, because centrifugal force lifts the chain away from the sprocket, and the contact points move too high up on the teeth. So, that is as far as I got.

 

But now we have an expert on the job, so I am hopeful of progress. I think there would be many takers for a conversion kit. Also, the possibility exists of introducing a step up or step down ratio, without the unsatisfactory bodge that is currently used, which compromises correct meshing of the gears.

 

By the way, I wanted  a chain drive just to remove some of the power loss in the drop gears, and solve the reliability problem caused by the helical gears causing the idler to try to tip sideways (yes, I know there is another way of addressing that, by taper roller bearings), without using intolerably noisy straight cut gears. I want driving a Mini to be a pleasant experience!

 

Herringbone gears, which cancel all side thrust and run quietly, were another idea that I looked at, but thin herringbones (limited by the depth of the transfer case) can't be machined in one piece, and I could see immense difficulty in bolting the two halves back to back. The cost would also be considerable.

[carbon]

I think space will make it very difficult to fit in a reliable roller chain as alternative to the drop gears.

 

Might however be worth taking a closer look at the HY-VO toothed driveline chains.

[Dan]

A tensioner in the centre, positioned into the idler gear location, could tension both runs equally and so the load direction wouldn't matter. I believe I've seen large machines working with chains running loaded both ways using this kind of tensioning. It would also fit the available space better.

[Mr Joshua]

Could you envisage the carnage that occur if the chain failed! Reason enough.