Are flywheels getting too light?

[mk1]

I agree with some of what has been said above. But for me the salient bit of evindence is that the back plate also supplied by MED is perfectly OK. If it was JUST caused by lots of starts I would expect the backplate to be looking similar..

I am currently speaking to someone at the universities metallurgy dept to see if I can get the material spec tested.

[Peter Laidler]

The crazing is the immediate giveaway here to any metallurgist. The material simply cannot cope. with what was asked of it

[mk1]

Here are a few pics of the back plate that was working with the flywheel. As you can see it has also got hot, but hasn't turned into a piece of 1000 year old bog oak.

I have contacted MED about it, all they will say is that it has got hot. No explanation as to why the flywheel is close to breaking up but the back plate isn't. Despite both parts being claimed to be EN24T.

Sadly, I can't afford to get it analysed, but will draw my own conclusions as to what has been happening & why.

M

Images of the backplate.

[MiNiKiN]

As opposed to anybody else here, I am not shocked at all. This is not a great matter of concern as long as:

• the depth of the cracks is not deeper than a few tenths of a mm (i.e. it's surface crazing)
• the cracks do not radially expand over the entire width of the friction surface

So why am I saying so? Such crazing is pretty common on railway brake discs, it comes from sudden local increase in temperature ("heat shock"). Hence manufacturers have thresholds of crack lenghths and distruibution in place, i.e. what is acceptable and what not.

I'd skim the flywheel and check how deep the cracks go.

[mk1]

That's a great insight MiNiKin.

TBH, The flywheel has already been consigned to history as has the backplate. I have never seen one do that before & I value my nads somewhat higher than a flywheel & backplate

Have replaced them with the Minispares items. They are a bit heavier, but will hopefully give a superior heat sink.

[MiNiKiN]

The evidence would suggest that they probably are!

This is an MED featherlight that has done just a light couple of seasons in my Hillclimber, TBH I was pretty shocked when I saw this!

I have emiled the pics to MED & will post any developments here.

M

EDIT: the cracks that should IMHO be looked at are the ones which go over the inner edge

[MiNiKiN]

I suppose my post was not in favour of promoting to use of trains, was it?

[mk1]

I suppose my post was not in favour of promoting to use of trains, was it?

Ha, ha, Maybe not

The red highlighted cracks certainly do go right through to the other side. There is a sort of flange there which is about 3 or 4mm deep.

[Julian Harber]

As commented on the facebook post for these photos it has the hall marks of the clutch being slipped when paddle clutches are not designed to be used in this way, they like to be on/off hence why people push cars in paddock line-ups and winch car on to trailer, the heat that is developed by slipping is incredible I have used ceramic paddle clutch (with the MED x-lite and it has not been anything like these photos) personally prefer AP racing organic for hillclimbing but still avoid clutch slipping style of driving and winch on trailer. KAD do an Alloy flywheel which I know some of the circuit lads use so maybe this will didpense the heat better and there is replaceable surface plates that can be changed

[GraemeC]

I’m. It shocked either - been there done that but not quite as extreme. That backplate will be warped which just exaggerates things - viscous circle.

As Tim says, it is the slipping of the clutch at slow speed or what you think are sympathetic starts that does it - boot flummox revs, side step the clutch pedal and then drop the revs slightly as the car launches, then feed them back in.