This is in regards to La Bala, a middy.

Having recently aquired an FJR1300 engine that's shaft driven I am in research phase and thinking about different ways of getting the power to the wheels.

Since I have very little experience with the different car differential units available, I am hoping that I might get some advice about it here.

Should I assume that a limited slip unit will not run backwards and/or upside down? Am I limited to runing an open diff?

Any suggestions for a common lightweight unit with a very short snout? I am in the USA, but I see a ton of BMW E-series diffs on ebay... Suggestions?

Mounting: Since my engine bay space is not infinite, I was thinking about making a strong cradle that holds the engine and the differential together as one solid unit. I want to eliminate the u-joint and mate the output from the bike shaft directly to the input flange of the diff. Bad Idea? Any suggestions for the shortest possible solution?

Thanks, Graber

Oh yea, I almost forgot. The Yamaha rear diff is a 3.66:1 unit. My cars tire height will be close to the bikes at 24". Should I assume that the car diff ratio should be close to this number?

[Edited on 4/11/05 by sgraber]

You might want to check out the Legends race cars which use the FJ1200 motor to see how they get power to the back wheels. Dont know about the FJ1300 though.

Alternatively didnt some early RWD honda diffs run the wrong way?

Cheers

Jim

[Edited on 11/4/05 by jimgiblett]

Steve:

Why not run a chain setup? It would be easier and not much more money. You would also worry less about getting the rear ratio right because you could always change the sprocket.

--Chris

I can`t see why, any diff should`nt run upside down.
Provided you stop the oil running out and fill it to the same relative height of oil over the gears, I cant see the difference?

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Originally posted by ReMan
I can`t see why, any diff should`nt run upside down.
Provided you stop the oil running out and fill it to the same relative height of oil over the gears, I cant see the difference?

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Originally posted by chrisf
Steve:

Why not run a chain setup? It would be easier and not much more money. You would also worry less about getting the rear ratio right because you could always change the sprocket.

--Chris

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Originally posted by ReMan
I can`t see why, any diff should`nt run upside down.
Provided you stop the oil running out and fill it to the same relative height of oil over the gears, I cant see the difference?

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Just give it a try. Flip the diff, plug the breather, relocate and see what happens running it upside down. If it's knackered after a few hundred miles, it might become costly. If it's knackered after a few thousand miles, treat it as a consumable and get another one. They aren't too expensive after all. You could pick one up for the same cost as one tyre. Then we'd all know once and for all whether it's a viable option or not. Go for it...............

I'm not too worried about the ring and pinion. I used to be very hung up on the issue, but I'm over that. I am more interested in the effects of limited slip internals being run backwards...

The most common LSD has ramp pieces, which angle gives the amount of locking effect, and they are sometimes different in accellerating and in engine brake situations. So maybe your diff will work strangely if run backwards. Need to unmount it and check the ramp angles to be sure.
About the layout I suggested: it's easy to add an intermediate axle, behind the diff, with two chains. On this axle you can put an electric motor to sort the reverse gear problem. By the way it becomes easy to place the engine in the body's centerline.
I will make a sketch because I feel that my writing is confused.

Hope this pic is a bit more clear..
Rescued attachment FJR1300-.JPG

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Originally posted by Aloupol
Hope this pic is a bit more clear..

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have you heard of a phantom grip diff its USA made it fits where the sun gears go and gives a limited slip action for half the price.search the web for info.

The reverse gear: I was thinking of that too but I wonder if it's strong enough. It's designed to be driven by the gearbox torque, and the sub axle has a little bit more.
Efficiency: I don't know the exact numbers but I don't think it's a lot. If it was some cooling system should have been developed by bikes tuners ;-)
Maybe by replacing the chains by straps (like the Harley Davidson bikes) it's possible to save something.
The Phantom diff: is it the stuff I saw, using the axial reaction of the diff's gears to press clutch discs, without ramps? Is it worth? Which car uses it?
Compactness: I plan to use this kind of jack axle in my car, with a standard (transverse) bike engine, in order to minimize the wheelbase, and to have half axles of equal lenghts.
LSD: The guy who tested the R1ot said it's not that important to have one in a middy BEC, due to the good weight balance and reasonable power. I won't sell my children to buy one, if an open diff is good for that great kit car it will suit for mine.

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Originally posted by Aloupol
Compactness: I plan to use this kind of jack axle in my car

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Is the engine the wrong way round in the drawing? The drive comes off the side of the gearbox. If you've taken the shaft drive off it will it still be driving the wrong way?

No problem. They are on the streets everywhere. The front diff in a small four wheel drive truck rotates backwards. If you use a clutch type limited slip you should be able to build-up what you need by using one from a rear unit of the same make and size. For example. One could use an Ford 8.8 front diff and use the LSD carrier from a 8.8 rear diff. The difference is in the gears and case. Not 100% positive what fits what in smaller sizes but this might give you a place to start looking. Now finding the right gearing may be a whole other story, but this excel spread sheet might be of some help there: http://members.lycos.co.uk/alister667/speedcalc.xls


[Edited on 12/4/05 by madman280]

Had another thought. If you were to use a racing type quick change you can rotate them backwards since they are bevel type gears not spiral bevel like most diffs. I've seen Winters and Halibrand midget diffs used this way. If you do a bit of a web search on midget or speedway sprint cars you should find a couple sources. They make IRS type diffs as well as the live axle variety. Not usually listed in a catalog. Call and telling them what your doing. I'm sure they can offer a couple sugestions.

[Edited on 12/4/05 by madman280]

Aloupol:

My idea was to use an inline reverse box as the jackshaft. The whole unit could be slide fore/aft to tighten the chain.

Actually, I suggested to Steve that he use a standard size inline reverse box (scroll down), he could decide later if he wanted to go with a Quaife unit or use a standard jackshaft. Alternatively, he could put a toothed gear in the middle of the jackshaft and run an electric reverse off that. All three solutions could be designed to act interchangibly.

Moreover, using the jackshaft means an easier final gear ratio. At any rate, the chain drive seems much easier than having to flip heavy differentials. Just my ideas...

--Chris

The clutch type has spring loaded clutches which will slip when a certain torque differential occur between the two wheels. This will function in either direction.

Viscus uses silicone fluid in place of the springs. When the difference in speed between the two axles heats the silicone it expands and causes the clutches to bind, locking the axles. This type will also work in either direction.

The ring and pinion gears should be fine turning backwards otherwise downshifting and engine braking would kill them on a regular basis.

Looking in my "Machinists Handbook" 1941 edition gears typically have a symetrical profile, therefore the direction of rotation is mute.

Now one thing we haven't examined is lubrication. Now I can say from personal experience that a rearend, turned on it's side, with one axle pointed straight-up, has run lightly loaded in a mill in our plant for decades. In fact we did just change it out due to a failure, but it has amassed over 2,000 hours of operational time before it failed.

I believe, firmly, that a rearend will work just fine in a small car in an upside down and running backwards orientation. The windage effect should give plenty of lubrication to the bearings.

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Originally posted by sgraber
Where will you fiind your jack-shaft components? ... This a likely a part that will be best made by a qualified machine shop.

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Originally posted by Peteff
Is the engine the wrong way round in the drawing? The drive comes off the side of the gearbox. If you've taken the shaft drive off it will it still be driving the wrong way?

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Originally posted by chrisf
Aloupol:
My idea was to use an inline reverse box as the jackshaft. The whole unit could be slide fore/aft to tighten the chain.
--Chris

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Originally posted by The Shootist
The clutch type has spring loaded clutches which will slip when a certain torque differential occur between the two wheels. This will function in either direction.

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Steve, what is the estimated weight of La Bala? I doubt if the type of electric reverse Locosters are familliar with would cope with the weight of your car. If you ran a more powerful motor, then you'd be getting into power-sapping alternators and heavy duty batteries.
I would look into either a diff with a built in reverse, or possibly a canabalised transaxle to provide a mechanical reverse. Basically, what you need for a compact reverse is a set of planetry gears.
As The Shootist says, any diff will perform OK in any orientation as long as it's suitably lubricated.
With the engine orientated as in Aloupol's drawing of the Busa, an industrial reverse mechanism in line with the engine's output shaft may be worth considering. Some are made with aluminium housings which would help keep the weight down.
What about one of those reverse transaxles I posted recently? I know they're a bit pricey, but I believe it may be a cheaper solution in the long run.

La bala is fairly light. The car weighed 1,126Lbs with the 1.6l 4AGE. and that was in driveable condition, but without bodywork, windshield, etc. My finished estimate was 1,400Lbs (or around 650Kg). The new drivetrain is (est) 150Lbs lighter than the old. So at 1,250Lbs (560Kg) la bala is still heavier than the typical locost BEC, but not extremely so. FWIW - My weighing was done using 4 bathroom scales so there is probably a margin of error, but not significant to the SWAG calculations we need to do here.

Why not eliminate the jackshaft completely but still use a chain driven differential, an intermediate shaft to the longer side, and two equal length short half-shafts like the newer front wheel drive cars use to eliminate torque steer? I might be able to use the entire drive assembly from a Honda, starting from the differential outward to the hubs.

Rorty, I haven't completely discounted the mini-transaxle, but want to pursue (discuss) all other non-comercialized ideas to their logical conclusions.

Rorty et al,

This is what I have in mind. Just a quick sketch in Max.


Chain Driven diff render 1

Note that the red blob in the middle with the little gear is an automotive style gear reduction starter that would be a reverser unit. The large green blob in the back is the engine, the purple blocks would be the bearing blocks and the blue sticks are portions of the car frame....

I intend to take the entire half-shafts, intermediate shaft and differential from a Honda FWD transaxle since that centers the engine mass in the correct location relative to the centerline of the car.

In my opinion, that is the best idea yet. But just a thought...If the driveshafts are dissimilar lengths, will they really cause torque steer? 1.) You're not steering in the rear with a deDion and 2.) you won't have that much torque.

At any rate, your idea would be the easiest to fabricate/machine and lends itself well to your deDion rear. This is something you can sort out between GRP work. Might break things up a bit.

--Chris

I would have a good look at the bearings on the output shaft of the bike box before going further. They would be designed to take torque, but not the thrust that a chain will put on them.

I only say this because we have a drier barrel similar to a concrete mixer truck running with a truck box with a chain on the output, and eats bearings regularly. The salt does not help though.

The recent fix was to mount the sprocket with bearings both ends on a cradle, with a flexible joint between the gbox and sprocket shaft. This means the gearbox now only provides torque as designed and no chain thrust on the output bearing.

So far, no new bearing trouble.

quote:

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Originally posted by Neville Jones
I would have a good look at the bearings on the output shaft of the bike box before going further. They would be designed to take torque, but not the thrust that a chain will put on them.

I only say this because we have a drier barrel similar to a concrete mixer truck running with a truck box with a chain on the output, and eats bearings regularly. The salt does not help though.

The recent fix was to mount the sprocket with bearings both ends on a cradle, with a flexible joint between the gbox and sprocket shaft. This means the gearbox now only provides torque as designed and no chain thrust on the output bearing.

So far, no new bearing trouble.

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Placing the sprocket between two bearings, and a CV joint to dissociate is the beter but increases the off-axis of the sprocket, maybe too much?
There's a mounting point on the block near this area, maybe possible to add a bearing after the sprocket, keeping this one at the same place?

Steve, that's the basic layout of 95% of rear ends I've seen/done myself, albeit the engine's orientation is different. Should work perfectly well.
I would look closely at the pinion shaft bearing cover in the photo above with a view to re-machining it or making a new one to take a more substantial bearing.
If money wasn't an object, I would machine a billet sump for it to position a new output bearing and extension for the output shaft, thus bypassing the whole bevel gear set-up. You could dry sump it while you were at it.

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Originally posted by Rorty
Steve, that's the basic layout of 95% of rear ends I've seen/done myself, albeit the engine's orientation is different. Should work perfectly well.
I would look closely at the pinion shaft bearing cover in the photo above with a view to re-machining it or making a new one to take a more substantial bearing.
If money wasn't an object, I would machine a billet sump for it to position a new output bearing and extension for the output shaft, thus bypassing the whole bevel gear set-up. You could dry sump it while you were at it.

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Originally posted by sgraber
For cost savings - If I were to retain the bevel gear, and attach a sprocket onto the splined shaft (where the u-joint currently attaches in the photo above), should I definitely support the outer portion of that shaft with an additional bearing? What would Jesus do?

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In your place I would let it like this, simply mount the sprocket in place of the CV joint. If the bearing lasts more than 10 000 km then it's good, it's just a service part. If not it's still time to consider an expensive option.
If you are too affraid of possible dammages to other parts than the bearing you can build a short axle with the splines and the sprocket in one end and a secondary bearing in the other, which sits on the engine mounts.