FJ - chain drive drop-box?

[rbm]

this is a technical type post so may be in the wrong place but has historical content.

so in our obscure, one off, over weight, under powered, French Canadian, front engined Formula Junior we have a chain drive drop box bolted to the front of the diff housing to lower the height of the prop shaft and therefore lower the seat.

Anyway this thing screams away - a quick clip of how noisy at L-J Sjoberg last FJ invite https://www.youtube.com/watch?v=86PRfud0o_g

also the drop-box is way way to hot to touch by the end of a race.

anyone got any experience with chain drive drop-boxes?
the box has a sprocket on the nose of the diff so uses the diff pinion bearings at the top and has a sprocket on a shaft running on sealed bearings at the bottom - yep I know it is upside down!

so the oil which is ep90 is only lubricating the chain and this is like stirring treacle, so the question is would I be better with an ATF or similar?

[Dave Brand]

I have no experience with boxes like that, but I have some experience of industrial power transmission products.

I assume the box is filled, or partially filled, with EP90? If so, part of your problem could be oil churning. EP90 is not, in my opinion, a suitable lubricant for chains - you need a specialised chain lubricant.

I'd be looking at a grease which can be applied direct to the chain & which has anti-fling properties to ensure that it stays where it's needed; that could well be nothing more than a motorcycle chain spray! If you want something more high-tech, look at the products of specialist lubricant manufacturers. I've had very good results from a Kluber grease in a troublesome gearbox application, Rocol also has a wide range of lubricants for many different applications.

[Geraint Owen]

I would doubt you need any oil in the box at all. You need to check the spec of the chain. It may well be "o ring" chain with seals to keep the EP90 out of the bearing area!

The chain is going far faster than it is designed to, but the chain load is, I bet, far lower than the designed maximum

Can you adjust the tension. check it isnt too tight.

But basically you have there a mechanical oil heater. Half fill that with oil and I bet it is consuming 4bhp at 6000 rpm

[zefarelly]

The whole thing may work better with a smaller pitch and a duplex or triplex chain.

A Lambretta runs a long chain drive with a light tensioner on the slack side ( usually uprated with a PTFE block these days)

There is but a puddle of ST90 to keep the clutch plates and gearbox wet. the chain is 1/2" pitch ( as a Ford FJ cam drive) and duplex, the same is available as a triplex also, that may help.

[L-G Sjöberg]

I am not 100 % sure, but I think Ingvar Malm has a chain drop-box in his Elva 100, or at least that he has tried it. I will check with him.

[Dave Brand]

Originally Posted by Geraint Owen

It may well be "o ring" chain with seals to keep the EP90 out of the bearing area!

I doubt it, as FJ predates O-ring chains by a couple of decades!

An O-ring chain would not, in any case, be of much benefit in this application. They are intended for use in harsh environments, where the chain is exposed to contaminants such as dirt & water; their main use is for motorcycle drive chains. They do also incur a small power loss - one of the claims for DI's X-ring chains is that the power loss is less than for a comparable O-ring chain.

[GORDON STREETER]

Personally I would use a much thinner oil, all timing chains on engines last for years and most run on 5w30 oils now. I would also use some ZX1 mixed with it and only half fill it.

[wnut]

I don't know whether your rules allow it, but you may be able to substitute your chain drive for a silent type chain drive, they are smoother, quieter, more efficient and can run at higher speed than your sprockets.

Have a look here http://www.ramseychain.com/prod_sc.asp and speak to them.

[zefarelly]

you could probably run a belt drive dry.

These have been around for a few years now, can run dry or in oil

http://bristollambretta.webs.com/BELT%20DRIVE.jpg

its only a small belt, but even the well tuned motors are only putting out 35 ish HP

Modern Hardley rideables for Midlife crisis consultants run belt drives.

[L-G Sjöberg]

Originally Posted by L-G Sjöberg

I am not 100 % sure, but I think Ingvar Malm has a chain drop-box in his Elva 100, or at least that he has tried it. I will check with him.

Ingvar Malm confirmed that he has experience of both a gear drop-box and a chain drop-box in his Elva 100. He says that the box with the chain does not run any hotter than the one with gears. Rather the opposite. He is using a normal hypoid oil in both types of box, i.e. something around SAE90. One thing he has done, though, is to make sure that there is a good flow of air around the drop-box. He has a scoop to get air in and has hole to let it escape. Before he did this, it was running too hot (both the gear type and the chain type).

[zefarelly]

So it needs wind to cool it.

Where is the seat exactly?

[L-G Sjöberg]

Ingvar Malm just called with some additional info which he forgot to mention yesterday. Most important: the casing for the chain is connected to an oil tank of about 1 litre in volume. The tank is installed at a height which results in the chain casing being filled to about one third. The tank is ventilated to the atmosphere to prevent over pressure.

[wnut]

Originally Posted by rbm

this is a technical type post so may be in the wrong place but has historical content.

So, what did you decide to do, and how is it working?

[rbm]

having pulled it all to bits, and found that the top sprocket was welded to an original diff flange that had been spun down on a lathe so we had a seal between the drop box and the diff, this gave us the ability to use different oil.

the chain is a modern o seal type chain and the bearings on the drop box input shaft were sealed bearings.

in theory there should be no need for any oil and the box could be run dry.

but there are some witness marks where the chain has come into contact with the drop box casing and whilst this shouldn't be a problem obviously this will cause friction with the resultant heat.

having re-assembled the diff with the new crown wheel and pinion (a more sensible ratio we hope) we put the drop box back together and have added a small amount of AFT as a splash lubricant.

so in the first test down the road, the only problem is the ATF not wanting to stay in the drop box - it was running down the splines on the input shaft and coming out between the flange face and the prop shaft! a bit of sealer and try again sorted.

not much more to say, the little motor is in a big tin box heading towards a test session/free practice/ for the end of Jan at Zwartkops.

Richard

[wnut]

Thanks Richard good to know.

Good Luck at Zwartkops in Jan, it is a great little circuit.

[Dave Brand]

Originally Posted by rbm

the chain is a modern o seal type chain and the bearings on the drop box input shaft were sealed bearings.

in theory there should be no need for any oil and the box could be run dry.

You still need lubrication between the chain & the sprockets.

[rbm]

Originally Posted by Dave Brand

You still need lubrication between the chain & the sprockets.

yep sort of meant running in oil rather than chain lube

cheers

[rbm]

update on the chain drive drop box

well it broke

not actually sure if the chain broke jamming the sprocket on the diff which caused the drive shaft to snap and the resultant suspension failure

or

the drive shaft broke up causing suspension failure, jamming on the rear upright and snapping the chain

anyway if you want a laugh this is what it looked like:

https://www.youtube.com/watch?v=EUbqT1tZqXY

Richard

[delta]

Yesterday was first time I had driven a car with a drop box . Tell me are they always that noisy

[rbm]

well the one in the Autosport howls, but that the only one I have experience of - it is than noisy I have to wear ear plugs.

Richard