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The mkiv Supra Owners Club

Why do lightweight flywheels rattle?


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Lightweight flywheels do not rattle. They make the rest of your engine and gearbox rattle.

 

A flywheel is an energy store which is used to smooth out slight variations in rotational speed at idle. The inertia mass is tuned to certain characteristics of your power- and drive-train. Inertia is a flywheel's raison d'etre. It has inertia, therefore it is.

 

Putting a lightweight flywheel on your engine is akin to having your wheels balanced and then replacing the balance weights with "uprated" lightweight weights. The wheel will no longer be in balance and will vibrate, therefore defeating the purpose of the balance weights.

 

Similarly, if you reduce the rotational inertia of the flywheel, then the rotational variation of the crakntrain will start to have an effect. This will manifest itself as reversing torques in the drivetrain which will make your clutch plate and the gears in your gearbox rattle.

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Originally posted by Digsy

Putting a lightweight flywheel on your engine is akin to having your wheels balanced and then replacing the balance weights with "uprated" lightweight weights. The wheel will no longer be in balance and will vibrate, therefore defeating the purpose of the balance weights.

 

Where can I buy some uprated lightweight wheel weights? Are they polished? Can I choose colours? :D

 

-Ian "Back on stock crank pulley" C

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Originally posted by Alex Holdroyd

So is that a bad thing Digsy?

 

Sometimes it is and sometimes it isn't. At one end of the scale all you have to do is put up with a bit more noise and this BBS has seen plenty of people give up on lightweight flywheels because of this alone.

 

On the other end of the spectrum you have physical damage to the gearbox and cranktrain. The type of noise caused by lightweight flywheels is caused by reversing ,or variations in, loading. Likewise, most "real world" failures are fatigue failures, and fatigue is all about (you guessed it) varying or reversing loads in a system.

 

There's no way of telling what you will get, though, unless you have access to the Toyota development team, or someone with direct experience.

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Can a lightened flywheel/clutch be incorrectly installed and could this cause excessive noise?

 

Just to explain 2-3 years ago I had a brand new TRD twin plate clutch/lighted flywheel and new bearing fitted, the result was a VERY rattly sound at tickover and grating sometime when engaging the clutch.

 

A couple of weeks ago a different garage replaced the friction discs, bearing and clutch housing, the clutch is now silent and no longer rattles or grates. Which has made me think that the first garage didn't fit the clutch correctly which caused the excessive noise.

 

So is there an art to fitting a clutch/flywheel correctly?

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Digsy, Firstly light weight fly wheels do rattle, they rattle because the stock flywheel has a sprung hub in the center and after market light weight ones dont, so they sort of rattle on a spindle.

 

reversing torques in the drivetrain which will make your clutch plate and the gears in your gearbox rattle.

 

So its my gearbox thats rattling is it..........mmmmmm.......

 

Ian C, let me know when you locate those flywheel weights as I think Im in need of some....... ;)

 

The only reason people steer clear of lightend flywheels is the noise (the idle rattle can be got round by raising your idle RPM slightly), some may predict that it can wear your gearbox due to the rattle of the fly wheel, but we havent actually ever seen any proof of this. And on that basis in my eyes theres more +'s to -'s, as a lightened flywheel will have less weight to move so can accelerate quicker, of course it holds less weight so your engine will have to work a little harder to hold its speed, but that means a little more fuel, nothing that you would notice though. Plus most lightend flywheels are rebuildable, another feature I like.

 

On a side note, Digsy, I thought you were a new member of recent times ????? your post count and register date seem to say otherwise......????

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Originally posted by Bobbeh

Haha, he must be having it easy at Lotus, they just use Toyota parts these days :D

 

Nah they work hard to modify the engines to be more British :D

 

Though to be correct Lotus do consultancy work for other companies the car company is just the face the public know about.

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Hi Ash.

 

Digsy, Firstly light weight fly wheels do rattle, they rattle because the stock flywheel has a sprung hub in the center and after market light weight ones dont, so they sort of rattle on a spindle.

 

Not quite following the logic here. When someone says "lightweight flywheel" I asume they are talking about an aftermarket solid job, whithout a sprung hub, which bolts straight on the crankshaft. Nothing to rattle there. Even a dual mass flywheel shouldn't rattle appreciably anyway. The stock dual mass flywheel only rattles when it's knackered. What do you mean by "they sort of rattle on a spindle"?

 

So its my gearbox thats rattling is it..........mmmmmm.......

 

Yep, its a definite possibility. By way of an example, the Renault L7X 3.0 V6 has a sprung flywheel specifically because of gearbox noise. Take this away and you'll have a noisy gearbox. No reason to think that the physics would work any differently on a 2JZ. I suppose that another possibiltiy is that it is the clutch driven plate rattling on its splines.

 

Crankshafts do not rotate at a constant angular velocity - it varies and the crank vibrates torsionally. These variations and vibrations cause momentary torque reversals through the drivetrain. The minute clearances in the gear teeth do the rest.

 

Ian C, let me know when you locate those flywheel weights as I think Im in need of some....... ;)

 

The only reason people steer clear of lightend flywheels is the noise (the idle rattle can be got round by raising your idle RPM slightly), some may predict that it can wear your gearbox due to the rattle of the fly wheel, but we havent actually ever seen any proof of this. And on that basis in my eyes theres more +'s to -'s, as a lightened flywheel will have less weight to move so can accelerate quicker, of course it holds less weight so your engine will have to work a little harder to hold its speed, but that means a little more fuel, nothing that you would notice though. Plus most lightend flywheels are rebuildable, another feature I like.

 

The reason that raising your idle rpm kills the noise is that since adding a lightweight flywheel reduces the energy store which resists changes in engine revs, you have to raise the engine revs to a point where the engine can continue to rotate at a more or less contstant speed without that assistance.

 

Incidentally, apart from the static mass you carry around, the benefits of a lightweight flywheel are mainly when the engine is accellerating or decellerating (because, to re-iterate, the flywheel resists changes in rotational speed, up or down). I would have thought that the primary benefit would be gear change times (changing engine speed while declutched) since the predominating factor affecting how fast your engine can change revs when the clutch is out is the rest of the car attached to it.

 

On a side note, Digsy, I thought you were a new member of recent times ????? your post count and register date seem to say otherwise......????

 

I'm far from a new member. I'm one of the long-standing Norfolk mob. Theres a post in chit-chat revealing my true identity :thumbs:

 

Edited for spelling.

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Originally posted by Ashley Willis

Digsy, Firstly light weight fly wheels do rattle, they rattle because the stock flywheel has a sprung hub in the center and after market light weight ones dont, so they sort of rattle on a spindle.

 

Um, far be it me to step in to what is promising to be an interesting discussion between Ash and the n00b Digsy :D but the flywheel is bolted very tightly to the crankshaft of the engine. About eight or ten bolts IIRC. So it's a one-piece solid bit of metal bolted down - where is the rattle in this equation?

 

So its my gearbox thats rattling is it..........mmmmmm.......

 

That and your crankshaft :D Digsy here has posted before a very intricate and detailed document on dampened crank pulleys and flywheels, and why it's such a bad idea to remove them. I've gone back to a stock crank pulley because of what he's said and I personally wouldn't go near a lightweight flywheel - the fatigue problem seems very plausible to me. I balanced the benefits (nothing noticeable barring slightly less engine braking) against the risks (crank snapping and wiping out the entire engine) and funnily enough took the lightweight pulley off.

 

Ian C, let me know when you locate those flywheel weights as I think Im in need of some....... ;)

 

They are lightweight wheel weights, actually, but I think you've stumbled onto a new niche product!! :thumbs:

 

The only reason people steer clear of lightend flywheels is the noise (the idle rattle can be got round by raising your idle RPM slightly), some may predict that it can wear your gearbox due to the rattle of the fly wheel, but we havent actually ever seen any proof of this. And on that basis in my eyes theres more +'s to -'s, as a lightened flywheel will have less weight to move so can accelerate quicker, of course it holds less weight so your engine will have to work a little harder to hold its speed, but that means a little more fuel, nothing that you would notice though. Plus most lightend flywheels are rebuildable, another feature I like.

 

Um again - the engine uses more fuel because it has a lightweight flywheel? That implies it's working harder, as you say - which means less performance... Does not compute. It would work the opposite - a lighter flywheel does actually have fuel economy benefits as well as lowered drivetrain powerloss benefits, it's just that the fuel benefit isn't noticeable, and the side effect may be a premature engine death.

 

On a side note, Digsy, I thought you were a new member of recent times ????? your post count and register date seem to say otherwise......????

 

I believe Alex has covered this point already :D

 

-Ian

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Aplogies if I have been spurting, but Im limited now on my intranetwork time, so have to read fast and type fast, and I know that leaves you open to be being flamed, I'll chew all this over later........... but I do love an indepth discussion like this......... ;)

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Originally posted by Grazer

I've got a Helix paddle clutch and it rattles like hell sometimes! The flywheel has been skimmed but it's a stock flywheel.

 

Where is my rattle from?

 

No idea. Can you post up a pic of the type of clutch you have?

 

I take it its a single plate clutch?

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I asked Kevin H of Envy fame as to why my RPS flywheel was rattling and if there was anyway to fix it. He got in contact with RPS who said basically it was the idle arm in the gearbox rattling. I've got the e-mail around here somewhere which I could post. The answer was to raise the rpm's a chunk. (I now idle at 1050 RPM at temp)

 

I also asked the gearbox designer at work and Darre... I mean Digsy has basically confirmed everything he said.

 

Hope that helps.

 

Tony

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Originally posted by TLicense

I asked Kevin H of Envy fame as to why my RPS flywheel was rattling and if there was anyway to fix it. He got in contact with RPS who said basically it was the idle arm in the gearbox rattling.

 

Same as the clutch release arm?

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Originally posted by Ashley Willis

Aplogies if I have been spurting, but Im limited now on my intranetwork time, so have to read fast and type fast, and I know that leaves you open to be being flamed, I'll chew all this over later........... but I do love an indepth discussion like this......... ;)

 

No flaming here mate :thumbs: I like a good technical debate too.

 

Not so much that I start spurting, though :innocent:

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