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Sick to death of 50 years of cursing every time I have to remove a Mini flywheel, I have tried another route.

Modifying a Cooper S front drive flange and bolting it to the flywheel on splines is very simple, but does it work? So far mine did 4 race meetings but sheered last Sunday.

I have seen splined flywheels and cranks before, but they are uncommon.

I think the big problem is controlling the wear between the male and female splines and getting the tolerances tight enough to start with

this is why the taper method is so good, as long as everything is correct its a far superior method of locating rotating things like flywheels onto shafts

That is quite a job!

As Rich says, it has been done before, but is very rare. You must have a great machinist to reply on.

The biggest advantage of the taper is that there is a MASSIVE contact area when everything is a perfect fit making a really good firm, self centering joint. Using the spline method the contact area is reduced as is the self centering effect. I reckon that crank failures after 3 or 4 events in an engine as powerful as yours could become a regular occurrence.

Beautiful job though.

I take it that the splines were heat treated and that causes the crank end to shear off.

Perhaps a large radius where the crank tail turns into the splines would help cut down on failures (there might be one I just can't see it )

In one of my previous jobs we fabricated godet rolls for handling textile fibers. All those rolls attached to their drive shafts using Jarno tapers. They could transmit huge amounts of torque due to the amount of contact area (as mentioned above).

I am afraid that any shaft modification you attempt that involves reducing the diameter of the crank is going to reduce the shaft area and introduce stress risers. Both changes will contribute to earlier failure than the taper lock.

Hey, some great ideas and work done there for sure, I always like the 'outside the square' thinking and let's face it, if none of us tried these things - success or failure - we'd all still be sitting around the fire in a cave.

I would think though in this case, the Torsional Vibrations would kill it, as being on a parallel spline, no matter how tight it is done up, it can still move, where as the taper is a low enough angle that it is self locking and even then, we have all seen them fret and come loose.

What is about the taper locking that you don't like?

I've had a good look at the whole thing now, and can describe things better.

Firstly, yes, i would have liked a bigger radius where the splines end. That would certainly have helped. But what I hadn't noticed earlier was that the flywheel/crankshaft 5/8 bolt stops in exactly the same spot the splines end, thus that point is not only weakened by the step, but also by the hollow.

I plan to take another chance. There is plenty more tread in the crank - at least another 3/4 inches, so I shall be making a longer bolt, and welding the splined nose back on, building it up nicely in the process. We'll see how long that lasts.

From past experience, nothing ever breaks from the weld. Plenty of locktite on both the bolt and the splines, should keep it all rigid and centred. This is an 86mm billet crank, so i'll try everything to save it.

I'll keep you posted. I'm taking th lot to the engineer tomorrow morning and see what he thinks.

I already had someone who had a crank taper welded up. Like yours a specially made crank, in that case a short stroke Gordon Allen crank. Right on the weld edge was where the crank broke. If I can work out how to post a photo, I will show the remains.

As Spider says, there will be movement of the spline, due to the clearance.
-You'll probably see galling/polishing of the end clamp faces (which quickly loses your clamping force).

Spline "clicking" is common on high-powered drive-lines, and is usually coped with by using tapered, or partly spiral splines that lock.

As everyone says, I would think that splines on a crankshaft are always going to be a problem due to the vibration/shock-loading (that is normally damped by the clutch)

If you Loctite the splines won't that put you in the same situation as having a standard taper?
-Difficult to remove the flywheel
-(I would hate the idea of heating the crank to 200 degC plus to remove the flywheel each time....).

A few clarifications / replies.

Apart from the splines, which were a nice tight fit, and were also locktited, I also had the standard pinned plate at the end of the crank. This was an MED one which was a very tight fit on crank and flywheel. Now that I have dismantled it all and studied things I can tell you that the splined bit remained completely intact. The crank sheared at the point where material thickness was reduced - for 2 reasons: 1) there wasn't enough of a radius, in fact far too little radius, and 2) just my luck, the standard crankshaft bolt stops at exactly the same point. With hindsight it could so easily have been avoided.

Now for the solutions: Again there are 2. Firstly I could throw away the crank and flywheel and start with new items, but this will cost an arm and a leg. Secondly, with what we have learnt I can try a similar system but without the flaws. What I plan to do is clean up the treaded hole at the flywheel end of the crank - there is still over an inch of hole. Machine a new end with males either end and the splines in the middle. One end will press fit into the hole in the crank and then be welded up solid. The other end will be treaded and take a nut to tighten up the flywheel, complete with standard pinned plate.

As an other alternative to the machined bit, I could simply machine an old CV joint to press fit into the hole in the crank, but I don't know if the material is strong enough. Can anybody answer this one please? WHAT MATERIAL ARE COOPER S CV JOINTS MADE FROM?

All very interesting, but I would like to have a few opinions before going ahead. Thanks.

This is a very interesting technical thread.

I certainly look forward to seeing how it develops.

John Bull wrote:A few clarifications / replies.

Apart from the splines, which were a nice tight fit, and were also locktited, I also had the standard pinned plate at the end of the crank. This was an MED one which was a very tight fit on crank and flywheel. Now that I have dismantled it all and studied things I can tell you that the splined bit remained completely intact. The crank sheared at the point where material thickness was reduced - for 2 reasons: 1) there wasn't enough of a radius, in fact far too little radius, and 2) just my luck, the standard crankshaft bolt stops at exactly the same point. With hindsight it could so easily have been avoided.

Now for the solutions: Again there are 2. Firstly I could throw away the crank and flywheel and start with new items, but this will cost an arm and a leg. Secondly, with what we have learnt I can try a similar system but without the flaws. What I plan to do is clean up the treaded hole at the flywheel end of the crank - there is still over an inch of hole. Machine a new end with males either end and the splines in the middle. One end will press fit into the hole in the crank and then be welded up solid. The other end will be treaded and take a nut to tighten up the flywheel, complete with standard pinned plate.

As an other alternative to the machined bit, I could simply machine an old CV joint to press fit into the hole in the crank, but I don't know if the material is strong enough. Can anybody answer this one please? WHAT MATERIAL ARE COOPER S CV JOINTS MADE FROM?

All very interesting, but I would like to have a few opinions before going ahead. Thanks.

Hey John,

As I said before, I really love this thinking outside the square stuff, it's awesome and gets the brain juices flowing.

What I would like to say in regards to this proposed modification is for you and your machine shop man to read up on Torsional Vibrations and Crankshafts. It is a very 'deep' and 'intense' field and you guys will really benefit HUGELY from getting a grip on all the forces that a crankshaft is being subjected to and it will enlighten thing like why we have harmonic dampers, how and why they are 'tuned', it's effect on the flywheel, the real reason why crankshafts break, what are the true benefits of heat treatment and of different types of treatments, correct crankshaft materials etc etc. I went through this a number of years ago and it was like someone just turned on the light.

A college has CV manufactured, I did go though some of that with him. I know there are various grades of steels used, depending on application and quality, but in general look to some of the tool steels. I'll ask him what he ended up settling on.

Here's a technical one for you all.

WHAT IS THE STRONGEST WELDING ROD AVAILABLE. I want to weld a nose made from M300 steel to an EN40B steel crank?

Thanks in anticipation.

Hi Joe,
Be careful with using a nut to hold the flywheel on.
-The clamping force to stop the flywheel/splines moving relies on the amount of stretch between the clamping face of the nut (it's in the first threads, but let's say the face of the nut) and the end of the threaded portion where the diameter increases to the spline.

This gives 2 potential problems:
1. the corner radius that you are aware of
2. the very short section that is available between the nut and the change of section.

This short section makes it difficult to achieve a reliable and consistent clamping force. And as Spider points out, the vibrations and loads in the crankshaft make this clamping critical.

You (everyone! ) gets a much better joint with long fasteners.

I'm not sure whether you could bore and tap the end of the crank after welding, and install a longer bolt that goes past the splines, so as you have found, they don't both finish at the same point.

Good luck, and keep us all informed.

Spider wrote: I'll ask him what he ended up settling on.

4340, heat treated where required (including the splines) to 55 Rc.

IMO, while ideal for a CV, this wouldn't be wise for a crank.

Andy1071 has also made some good points regarding fasteners.

John Bull wrote:Sick to death of 50 years of cursing every time I have to remove a Mini flywheel

http://www.minifreunde.at/harry/links/flywheel.htm

Now that does look like a good idea!

John,
Most people can manage to get the power they have through a standard taper (lapped or not), but I understand your frustrations at this level of getting flywheels stuck on the crank.
Unless you go to tapered splines I really don't think you'll ever get splines to work in parallel form, it's simply never tight and crank vibrations will play hell with it.

A friend of mine's father held a patent for an item he invented for mining equipment applications, it's a hydraulic taper lock.
Assemble components, pump up taper lock with tiny amount of very high pressure oil and it locks, BLOODY SOLID! by distorting the metal.
Disassembly is by pumping into a different passage of the taper lock that has the affect of slackening it all back off.
Might well be worth a look if it is produced at that small size.
Best of luck with breaking the mould.

Roger

John,
Take a look at Abssac.co.uk
Plenty of hydraulic bushes there that you should be able to adapt flywheel and crank to suit.

Roger