WRX wrx WRX

Ok, just been out in my wrx and admittedly had been giving it some stick, calmed down a bit and 3rd gear seemed funny (crunch, presume the syncro), turned stereo down and there is an awfull noise which sounds like something metal rattling about in the gearbox, all gears still select/drive fine apart from the crunch in 3rd which as above i presume is a syncro but would this cause the noise in the box ? other than that there was a little jump whilst reversing.
Anyone any ideas please ?
Car is a late 95 (260bhp) wrx import model.
I'm presuming its another gearbox job or a rebuild, does anyone know what other years/model gearbox's will be a straight swap, i've heard the type R box is excellent for acceleration, is it a good idea and how much work involved in fitting it.
Any info / help / advice will be greatly appreciated

911

I think you are right, duff 3rd sync.
The Type R box is great if your engine can rev, ie 8000 rpm as gears are very short.
same goes for the Sti box (easier to find)
You must be sure the rear diff you have matches the box. There are ratio changes everywhere, so beware.
If you want to steer through all this painlessly, call David at www.apiengines.co.uk and you will get a rational sensible answer at the right cost.

Swopping boxes (and maybe rear diff) is not for the faint hearted if it is your first time.

Good luck, 911

STI5300

iTrader: (4)

API have helped me in the past in sourcing a 4.444 diff and are very helpful. For spec. try www.rallispec.com go to transmissions - spec and you get a massive chart of all the gearbox codes and ratios ever fitted by Mr Subaru

WRX wrx WRX

Cheers folks, yeah it will be first time swapping box on a subaru and i know it will be a headache as i aint no expert mechanic but i'm confident in giving it a shot.
Could anyone tell me whats involved with putting a lightened & balanced flywheel on while i'm down there ? and is it worth it ?
Matt

911

To change the flywheel is dead easy if youv'e got that far on your own!
Most people will say this and that in their opinion, so very hard for a straight answer.
PERSONALLY, I would go for an 8Kg wheel from a very reputable source, NOT someone with a big lathe! Fit a good clutch (ie AP Organic) and a new h/duty release bearing for peace of mind.
Put good synthetic oil in the box too.

If you search the Drivetrain threads there were some really good advice/tips threads on the job, Greasemonkey's were truly excellent.

911

APIDavid

iTrader: (4)

David APi Engines / API Impreza

Neilo

what are you referring too david?? (im a thickie).....as i will be lightening my flywheel on my UK WRX03 at some point soon..

Andy.F

Front pulley

Andy

Darbo_wrx

I though the front pulley would be ok as it is because its rubber mounted crank damper?? Designed to stop a torsional vibration in the crankshaft
How does lightening the flywheel affect this?-genuine question!
i would have thought it beneficial to keep the crank damper as it is or am i missing somthing reguarding the scooby engine?
By rights I would suggest balancing the full flywheel/crankshaft/frontpully/clutchcover assembly if you are doing the job properly
but saying that it would most likely be ok anyway

please feel free to answer my questions

DuncanG

Surely your not seriously saying that the crank pulley has to have the same mass as the flywheel? What are you on about?

911

David is correct.
The stock wheel, crank, and the crank pulley is a calculated and proven balance to stop vibrations fatiguing the assembly by harmonic vibrations occuring through the rev range. It is a precise job, and an exercise Subaru and all the other car manufacturers do to give a reliable engine in all conditions.
You will find such balancing acts every where. Look at the rear diff front cross member on the Impreza. On the lateral cross beam are 2 dampers, steel cups, about 45mm in diameter and with a rubber mounting bolted to the member. They kill off the vibrations due to movements in the subframe and stop them from getting into the cabin of the car.
If you removed them you may not notice, but there will be a difference. Same goes for the flywheel/pulley.
I am no specialist in this field, but I did enough to know that David is right.
Depends how 'fine' you want to be.
I know and have seen Mini's have their flywheels either fall off or 'weld' themselves to the crank due to these torsional vibrations.
That's IMHO anyway.
911

Darbo_wrx

911 Don’t agree
The crank damper is put there to stop torsional vibrations in the crankshaft so removing it to put a lighter alloy item i can see as only being a bad move!
For what weight you would save i cannot see the point
Not having the front crank damper removing the effects of these vibrations and increasing the risk of the flywheel being spat from the rear of the crank
Unless the Subaru engines design is one that DOES NOT suffer from these torsional vibrations to a great degree (I wouldn’t know) then I could only follow the evidence at hand which is that the Subaru technicians deemed it necessary to fit one to the car as standard
mabee the lighter flywheel reduces the whip effect but possibly it increases it!!(who understands harmonics and all that ....)
So i just have this feeling removing the damper would be a bad idea

Darbo

Danny Boy

iTrader: (2)

APi Davids explanation of a see saw seems to make good sense to me, the mass of the damper and the mass of the flywheel on either end of the crankshaft are totally linked in the effort to reduce unwanted harmonic vibrations. In the standard set up there is a balance between the two.

If you then reduce the mass of one end of the system (Ie: the flywheel) this whole balance goes out of kilter and your see saw analagy literally falls over!

So for the see saw to be in balance and for the dampening system to work properly the ratio of masses at either end of the crank have to be within stock parameters.

So say for arguments sake the standard fly wheel is 12kg and the dampener is 6kg, i would have thought that if you reduced the mass of the flywheel by half to 6kg, you would have to do the same to the dampener to reduce it to 3kg to keep the ratios the same.

Don't know if this is complete bo11ocks but it seems to make sense to me, im sure there are far more variables than this and if APi David is about im sure he will fill us in, and i for one would love to learn!

Dan.

911

As I said before, I'm no expert, but you do pick things up as you go through automotive life.
I am saying much as Dan above.
Alter the flywheel weight/change (in the same direction) the crank pully weight.
If you simply change the pully and not the flywheel you are in the wrong again!
It is the balance.

The Impreza flat 4 has a very short crankshaft so will be very stiff torsionally, but the engine's pully is a bit substantial, so is the flywheel; maybe the need is more critical on a 'short' engine.

My old 911 is a flat 6, and the flywheel is about 6Kg from Porsche as standard and the 'pully' is just 2 pieces of steel to allow the drive of the fan cooling belt, no mass in it relatively speaking. If you use a lighter flywheel most leave the steel flywheel alone and fit an RSR aluminium clutch cover for the same effect, reducing the rotating mass.

Maybe someone will read this who is an expert and put me/us right!

911.

Danny Boy

iTrader: (2)

911 i hope so too, would like to know for sure.
Seems sensible to me to do this now it has been mentioned, not something i would have thought of on my own though!

I wonder what sort of pully would be required? are theese readily available and how much of a weight saving do they give? That would prob then give us an idea of a sensible weight to reduce the flywheel to.

Is the harmonic balacer the one infront of the cambelt covers that drives the altenator and PS pump? Or would you need to replace the pulley behind it as well, making neccesary a cam belt change?

Dan.

APIDavid

iTrader: (4)

The two weights of the crank counterbalance [ flywheel / front pulley ] are sympathetic to each other - thus if you reduce the weight of one end it requires a balancing reduction at the other end to prevent whip effect over the length of the crank.

In a six cylinder inline engine the effect would be much more pronounced that in the relatively short Subaru crank. However, anything that spins has a balance / whip issue.

The weight of the crank pulley is calculated by Subaru to counterbalance the flywheel. If you halve [ or more ] the weight of the flywheel then you really should reconsider whether the crank pulley is now the correct weight to match your flywheel counterbalance requirement.

In practice, there is little choice in alternative weights for front pulleys so it would make most sense to rebalance the whole assembly to be sure of the result. In case of a simple clutch / flywheel replacement then stripping and rebalancing the whole thing isn't going to happen. In the case of a proper engine rebuild then it is most advisable.

My original point was to draw attention to the longer term issues of just bolting on a 4.2 kilo flywheel and expecting it be automatically better. Equally, just bolting on a lightweight set of front pulleys has a [ lesser ] similar effect.

David APi Engines / APi Impreza

911

Wish I could express things that simply!
The aluminium pulleys are readily available from Roger Clark Motorsport, Scoobymania Graham Goode Racing etc.
The front pully that is exposed for the alternator is the one to change. I don't think they come off too easyly, API zapped mine off in an instant with an air driver where my socket set failed.
911

APIDavid

iTrader: (4)

The aluminium pulleys are readily available from Roger Clark Motorsport, Scoobymania Graham Goode Racing etc

AND API ENGINES !!



David APi Engines / APi Impreza

Jay m A

iTrader: (2)

Hope this doesn't sound stupid, but doesn't this light flywheel/light pulley balance get thrown out of the window when the car is in gear? Since the clutch plate is now hanging off the end of the flywheel?

APIDavid

iTrader: (4)

A good question and not stupid at all. Theoretically?!?, the clutch plate is centri - something - al and is circular and in balance at all times. Thus it doesn't matter where in the 360 degrees of a rotation circle it ends up. If it did, ALL cars flywheel assemblies would be out of balance for 359 degrees.

The flywheel is a casting and due to casting flows you can get greater or lesser density of the cast, therefore it is necessary to balance out the heavy bits from the light bits. [ Same as a tyre really ]

David APi Engines / API Impreza

Jay m A

iTrader: (2)

Now I'm even more confused!

I would have thought that a flywheel is balanced in the rotational plane even before it gets put on any engine. Isn't that why theres the balancing holes drilled into it?

So why the pulleys? Is it to balance the load across the bearings? (along the length of the crank)

APIDavid

iTrader: (4)

So why the pulleys? Is it to balance the load across the bearings? (along the length of the crank? Yep !!


David APl

Danny Boy

iTrader: (2)

so David If i were to install a lightweight front pully that is readily available from stock from a number of reputable dealers ;-) then how far should a standard flywheel be lightened in your opinion? Obviously the weight of the clutch cover has to be taken into account also, would this vary hugely from a standard to a mildly uprated item?

Dan.

DuncanG

I'm with Darbo on this one. The Subaru crank pulley is also a torsional vibration damper. David (API) do your lightweight alloy pulleys incorporate a damper? A solid pulley without rubber or some other damping material provides no damping at all.

This is nothing to do with balancing though. Of course any replacement flywheel (and any other parts) should be balanced irrespective of the weight of the crank pulley.

The see-saw analogy is complete bunk. There is no see-sawing motion or balancing involved.

The crank damper is tuned to reduce a specific torsional vibration frequency but its probably not strongly tuned (ie low Q). Its been sugested that a lighter flywheel will cause it to be out of tune. I don't think that's the case.

On first sight you might expect the flywheel weight to have an influence on the damper tuning, but that is not the case. As far as the torsional vibrations are concerned the flywheel end of the crank is effectively fixed (or grounded to use an electrical analogy) by the mass of the flywheel + clutch + drivetrain + car inertia. The torsional vibrations (due to crank springiness and power pulses) if undamped will build along the length of the crank from the fixed end to the 'free' crank end so it makes sense to combine the damper with the crank pulley as that is where it needs to be.

If you could get a virtually massless flywheel and clutch you might have a problem when revving hard while de-clutched - the flywheel end would in effect be free, but in practice even lightweight flywheels have significant rotational inertia so its not a problem.

Can you ditch the damper - well do you feel lucky (well, do ya punk)? Whether you do or not has little to do with fitting a lighter flywheel or about reducing rotational inertia.

I'm sorry if this has been a bit more long winded than saying its like a see-saw with a fat thing on one end.

Danny Boy

iTrader: (2)

Arent resonant frequencies directly related to the mass and compsition of an object or system of objects? Hence changing the mass of the system would change the resonant frequency the object?

Dan.

APIDavid

iTrader: (4)

This post is getting boring !! I was merely trying to advise that putting an extremely light flywheel on one end of a crank is poor engineering practice.

The analogy of a seesaw holds good, to stabilise the crank balance, if you take weight off one end you should ideally do a similar thing on the other end.

None of the aftermarket pulleys have a rubber insert in them.

Anyway, I'm bored by all this; theorise till you're blue in the face.

Good luck all. I'm off.

David API

DuncanG

Yes they are - but.

If you were to constrain the pulley end of the crank 'spring' to a fixed rotational speed or slowly changing one then the flywheel mass would affect the resonant frequency, but that doesn't happen. Even with the lightest flywheel available and ignoring the added inertia of the clutch and drivetrain etc, and keeping the heavy crankshaft pulley-damper, the inertia at the flywheel end is much (>10 times) that at the pulley end. So for all practical purposes its the flywheel end thats grounded with respect to torsional vibrations and the pulley end thats (relatively) free to be affected by them. If the flywheel were so light that were no longer true then it would cease to be a flywheel.

If you prefer to think of a system of oscillating masses then you will realise that the flywheel end will have a much lower resonant frequency than the pulley end, or more importantly vibrating nodes along the crank, due to the large difference in inertia. That means that for the harmonic that the harmonic damper is tuned for will be at a much higher frequency than the flywheel resonance. So again for practical purposes the flywheel mass is not important, it just has to be sufficent to act as a flywheel, its not part of the 'tuning'.

I'm sorry I haven't been able to explain this more clearly but I'm just working it out for myself. I'm happy to be corrected.

Danny Boy

iTrader: (2)

Not convinced either way now, need to do more reading to satisfy my curiosity, i knew i should have listened in a-level physics!

Dan.