lightened flywheel

[ChaosAD]

I think I remember reading something about the cast flywheels having a hard surface but being softer inside.

Also, being 20 years old could have a few tiny cracks in it. They would usually be fine, but when the flywheel is machined down significantly they are more likely to cause problems.

Unsure if its true or not, but im sure you would have covered it if it were true.

Could probably get it xrayed or something but dunno what thats worth.

There was a big thread on club 4ag about a flywheel exploding that was lightened by a very well know tuning shop. But that seems to be gone now.

[crispy'86]

i remember the guy at the clutch place where i got my flywheel skimmed for the new clutch i got , that flywheel was very slightly machined, the guy said i wouldn't want anymore taken off it.
(bluetop flywheel weighing at 7.3kg according to the vivid marker on it) so i guess whoever did it may have known what they were doing, had vivid lines where they wanted to machione more off it to make it aimilar to 20v

[RS13]

I think I remember reading something about the cast flywheels having a hard surface but being softer inside.

Its' called case hardening, its' a similar idea to shotpeening. The outside surface has been hardened, but the inside material is considerably softer, allowing for thermal expansion and shock loads. When you machine a flywheel, you're removing the hardened surface and removing the element of strength, and creating a lot of stress risers in the softer material which may develop into cracks.

You can get the flywheel heat treated again to case harden it back to perhaps factory strength.. but personally, I wouldn't mess around, to do it properly you'd be spending a fair bit, and would be better off buying an aftermarket alloy one.

Could probably get it xrayed or something but dunno what thats worth.

Yeah, if you've lightened it, I would suggest taking it in to an engineering or similar shop that specialises in NDT, and get it x-rayed or dye-penetrant tested. Once again though, this wouldn't be the most cost-effective.. moral of the story, buy an aftermarket one!

[Jdawg]

From what I was told about Cast/forged crankshafts once
Cast, think toast, Forged, think dough

[jondee86]

Some good info here, from guys who do it professionally.....

http://www.roadraceengineering.com/clutchandflywheeltech.htm

As can be seen, surface cleanup only near the centre, controlled
thickness in back of the friction face, and take out whatever you can
at the outside edge. Front surface is already pretty much fully machined,
and cleaning up the back gets rid of any casting irregularities. All angles
nicely radiused to avoid causing stress risers.

There is nothing inherently dangerous with lightening stock cast iron
flywheels, if it is done professionally by people who understand what
they are doing. Problems with lightened flywheels are caused by people
who don't know what they are doing, taking out too much material from
the wrong place. This reduces both the strength and the thermal capacity.

Used in stock or mildly modified vehicles, a correctly lightened OEM
flywheel will give a more responsive engine and improved gear
changes.

But, if you plan on abusing your flywheel with full throttle launches, or
running it to 10,000 rpm, do yourself a favour and get an aftermarket
steel unit. Almost certainly, you will be installing a stronger "racing"
clutch, so why not upgrade the flywheel at the same time ?

Cheers... jondee86

[Grrrrrrr!]

As i suspected, there is no real reason for not machining a standard flywheel if you have a clue as to what you are doing.

as for the case hardening arguement.. 90% of the surface of a standard flywheel is machined anyway so not much of that skin is left to start with.

And if the 20v flywheel by my feet is anything to go by they are sandcast so the rough finish that sandcasting gives is less than helpful in terms of fatigue strength. A light skim to take the roughness off the back can only help from what i can see.

[Flannelman]

making stuff lighter is ok to a point. as removing casting lines from cranks and conrods aids in strength (failure can be traced back to these areas) but, grinding them to they are nearly seethrough for the name of weight loss is silly.
Be it anything in motion, it is built to last. when you start attacking it with the intent of weightloss, it is cheaper in time, easyer to do, and both satisfying in the result AND knowing that it will hold together by getting your eftpos card and buying TRD or other well known and used brands.

even if the flywheel you have is perfect, and is safe as original. And to you it would be a shame to throw it away. But, perhaps if it is as good as it looks, then wouldnt every one have one too?

[Grrrrrrr!]

It is cheaper in time, easyer to do, and both satisfying in the result AND knowing that it will hold together by getting your eftpos card and buying TRD or other well known and used brands.

If I have free access to a mill, a rotary table and a lathe all it costs is my time, which i sometimes have a lot of to spare, however being a student means spare $$ are somewhat harder to come by.

[/quote]
even if the flywheel you have is perfect, and is safe as original. And to you it would be a shame to throw it away. But, perhaps if it is as good as it looks, then wouldnt every one have one too?[/quote]

Most people would have to pay for someone to do the work, i don't.

[jondee86]

Car manufacturers build engines to suit mr and mrs Joe Average, who
commute to work and fetch the groceries. They want their cars to be
smooth and quiet and easy to drive. Heavy flywheels help in this respect.

Petrolheads want responsive engines, and don't mind a little vibration,
or having to be a bit more skilful with the clutch to avoid stalling. Reducing
the flywheel moment of inertia helps engine response.



This is my flywheel with some mass removed at the outside edge. No
other machining was done, as removing material closer to the centre has
much less effect. The flywheel was dynamically balanced after machining.

Cheers... jondee86

[Dell'Orto]

FWIW, it cost me $450+ gst to get a custom steel flywheel made up. Weighs 5kg, looks all shiny and is pretty near guaranteed not to shatter and cut my feet off.

[Grrrrrrr!]

The benefits of a FWD.... your passenger gets to play catch with high velocity flywheel fragments instead of you

[jondee86]

As a matter of interest, how many people do you actually know who
have had their feet separated by an exploding flywheel ??

This is as opposed to some guy who was a friend of my girlfriends ex
flatmates dog, who knew a bloke that lost both his legs when he missed
a change in his monster turbo/mega modified 105E Anglia van.....

Goodonya for choosing to use a steel flywheel. I would too if I was
building a race car. But I'm not, so I'll keep my $100 modded stock
flywheel until I feel the urge for more power

Cheers... jondee86

[frost]

sounds like email time to myth buster....

[Jdawg]

As a matter of interest, how many people do you actually know who
have had their feet separated by an exploding flywheel ??

This is as opposed to some guy who was a friend of my girlfriends ex
flatmates dog, who knew a bloke that lost both his legs when he missed
a change in his monster turbo/mega modified 105E Anglia van.....

Cheers... jondee86

Don Garlits

[jondee86]

Its cool that you know Don Garlits... he is an outstanding guy, true
gentleman, and quite possibly the greatest drag racer ever.

Garlits suffered a broken left leg and had his right foot severed at the arch
when his transmission exploded at Lions Drag Strip in Long Beach,
California.

But as suggested above, there is a whole bunch of bullsh1t floating
around about exploding flywheels.

Cheers... jondee86

[TRD Man]

jondee86, I totally agree with you. And if I was to "fess up" I'd admit that much of the hysteria on this forum probably began with a posting I made some years ago about a Mini flywheel failure and the consequences for the driver - much along the same lines as Craigt has written.

In reality, in the 70's & 80's, and even the 90's, machining stock flywheels was commonplace and proportionately we heard of very few failures.
Like you, I doubt that many, if any, members would have either experienced or witnessed a flywheel failure.

The point of the post that I made all those years ago was that there are options available today that are worth exploring whereas 20+ years ago there were not.

A chrome moly flywheel from TOM'S or TODA is likely to cost $800ish new and there are now a few available 2nd hand for around half this amount.

There is a benefit in many applications to 'measured' lightening of the flywheel.
If you don't want to spend $400 and prefer to have your flywheel machined ensure you use somebody who knows what they are doing and where to remove metal.

[RS13]

In reality, in the 70's & 80's, and even the 90's, machining stock flywheels was commonplace and proportionately we heard of very few failures.
Like you, I doubt that many, if any, members would have either experienced or witnessed a flywheel failure.

To that I would say, cars these days have considerably higher technology, and with the progress of variable valve systems they're doing nearly 9,000rpm factory. Not the same as your old 70's/80's sohc or pushrod motor. I have seen a pics floating around of a vtec civic that had a flywheel failure at high rpm, wasn't pretty.

[pureadrenalin]

Quick search on youtube.
I was expecting to find more

http://www.youtube.com/watch?v=ZhLDAc_H-xc

[Bling]

that video alone backs up (in my mind) the reason to NEVER run a lightened flywheel.

sure its a slim chance of it exploding if done right, but ya never know!

[jondee86]

Hmmmm...... let me take a wild guess. That was a highly modified
car in a drag race and the flywheel exploded cutting the drivers feet
off !!!! Fcuk... if you are a drag racer you should be using a
scattershield... they are mandatory in many classes because they
are always blowing clutches. Not to mention diffs, engines and
transmissions... they also break drive shafts, axles, cranks and pretty
much every other moving part !!!!

I can't get the whole video clip to play, so you'll need to help me out.
Was it the flywheel or clutch that exploded ??? And was it a standard
unit, modified or aftermarket race unit that failed ??? Did an engineer
inspect the damage and make a diagnosis, or did the commentator
make the call from 100 metres away ??

Cheers... jondee86