strange vibrations

[l1ttle_d3vil]

ive got a reasonably bad vibration on the corolla (4age turbo / w55) but only after 4000rpm in any gear including neutral. seeing as its the same rpm it wouldn't be the driveshaft. most obvious thing is the flywheel, but before I pull everything apart...

how likely is it to be the gearbox? it was run without oil for a bit (not by me!) and now whines so bearings obviously aren't 100% but its still definitely driveable, changes smoothly etc.

or the engine is running an alloy pulley kit, if any of these are out of balance is it likely to cause a noticable vibration throughout the car? not exactly large pulleys of any great mass or anything. I could pull the waterpump belt off to bypass the waterpump/alt pulleys if it could be these though...

definitely starts at the same RPM in any gear. anyone else got ideas?

cheers
-matt

[Lloyd]

Neutral with the clutch in or out?

[l1ttle_d3vil]

definitely with clutch out... pretty sure with clutch in too, but can check tomorrow if it makes any difference?

[matt dunn]

from what I have read and the story's I've heard,

I'll never run an aftermarket alloy crank pulley on anything.

Matt

[l1ttle_d3vil]

Its exactly the same clutch in or out.

I'll never run an aftermarket alloy crank pulley on anything.

How come? What sort of problems have you heard? Could the crank pulley cause vibrations like this?

[xsspeed]

Gunna take a stab and say "no harmonic balancer"?

Was reading something about this the other day, will try dig it up

[Dunny]

Does it drive through it?

reason being as I have a similar problem although it's only at certain revs and it drives through it (different in each gear 3rd, 4th & 5th) which points to d/shaft however after having a brand new one made in a larger diameter tube it only made the vibration far worse, so we changed back to the old one. Also the gearbox mount made a difference, old mount not as severe, new mount more severe

Our next step was to put a standard gear box back in and try that which would totally eliminate the c/r kitted box I run now, this is yet to be done.

Unfortunately it's a process of elimination

Car companies spend a heap on eliminating harmonic vibrations so when parts start being changed things can turned pear shaped

[jondee86]

Harmonic balancer aka harmonic damper. A device fitted to the
crankshaft of an engine to reduce the potentially damaging effects
of excessive torsional vibration.

Torsional resonance. The point at which the frequency of an exciting
torsional impulse coincides with the critical torsional resonant frequency
of the rotating system. Operation at this frequency can result in torsional
oscillations many times the magnitude of the displacement resulting
from the same impulse at other (non-resonant) frequencies.

Or if you prefer, undamped torsional resonance can snap your crank
like a carrot

But usually, the critical frequency is higher than the operating speed of
the engine, so all that is felt is some annoying vibration at one of the
minor harmonic frequencies.

There ya go... an answer to a question no-one had got round to asking

Cheers... jondee86

PS: I just make this sh*t up when I get bored....

[xsspeed]

epic answer, basically what I would have written if I had time lol

[l1ttle_d3vil]

...............
PS: I just make this sh*t up when I get bored....

i take it that is a serious answer though? from what i've just read up on the net about a harmonic balancer, sounds like you're right say this is the cause, how long would it take for the said crankshaft to snap? are we talking 100km or 2000km of racing at the track?

and does the 4age actually have a harmonic balancer, or is it sort of incorporated into the standard crank pulley? from what i've read they sound like a separate thing all together fitted to the crank...

[cat007]

The front crank pulley IS the harmonic balancer

[xsspeed]

The front crank pulley IS the harmonic balancer

From what I know this is the truth, and installing an alloy or aftermarket pulley should also have a harmonic balancer installed.

This is very common on v8s with blower setups etc

[l1ttle_d3vil]

The front crank pulley IS the harmonic balancer

ah right, from what i'd read it sounded like the balancer was a separate thing on the crank, generally made from a rubbery substance.

i'll pull the crank pulley off and try the factory one again. if its a twin belt pulley, is machining the front pulley off going to effect the balance or anything?? done this to my old engine and never had any problems, but that may've just been luck??

[cat007]

The main crank pulley is in two pieces with the inner bein held to the outer with a rubber sleeve

Cutting off any of it would cause it to do itS job worse so don't

[AceSniper]

Iv been running a alloy pulley for awhile and just run into troubles that can only be pointed to the pulley.
Alot of random unloaded metal parts are cracked (oil pickup/sump baffle/rear oil pump plate/ clutch plate)

All the parts were balanced before been assembled, New parts are in getting balanced now and the workshop is also going to check my old setup to confirm clutch/flywheel/crank are not to blame they also think its due to harmonics.

[l1ttle_d3vil]

Alot of random unloaded metal parts are cracked (oil pickup/sump baffle/rear oil pump plate/ clutch plate)

interesting...

any idea what sorta km you've done since fitting them? i doubt i would've done 1000km, possibly 150km on the dyno, and about 350km open road driving.

just wondering if I'm likely to have damaged anything already...

[AceSniper]

about 20thou or just under, so you should be safe... just ditch it

[jondee86]

Harmonic dampers use one of several methods to "dampen" torsional
vibrations in much the same way as shock absorbers (dampers to your
old man) dampen the oscillation of the suspension components.

Some, as on the 4AGE, use a layer of rubber and an external inertia ring.
Others use an internal inertia ring sliding in a highly viscous silicone fluid.
Either way, some of the energy of torsional vibrations is dissipated in
overcoming the internal friction of the rubber or fluid.

The effect of removing the harmonic damper/balancer, will range from
none at all up to disasterous. It really depends if a critical frequency
occurs within the operating rpm range of the engine, and how much time
the engine spends at that frequency. For what its worth, I was told that
the crankshafts in the FWD GT hatches raced by TTNZ way back, had a
life expectancy of 20 hours under race conditions.

But for every person who has a tale of woe about the effects of using
lightweight crank pulleys, there is another who has "used them for years
without any problems". You pays your money and takes your pick

Cheers... jondee86

[l1ttle_d3vil]

Does it drive through it?

right I've swapped the alloy pulley for the original factory one again.
waterpump and alternator are still running the alloy pulleys for now...

took it for a thrash, still vibrates at 4000rpm.
Hard to tell, but it might be a bit better than before.

But I did notice if I keep revving it stops at about 6000rpm onwards, just the gearbox vibrating from doing 7000rpm in 1st gear but the car itself doesn't vibrate after 6000rpm.

Is there anything else I should look at? Would it be worth taking the waterpump and alternator pulleys off? Seeing as the gearbox bearings are pretty shagged, it is at all likely the vibration is coming from the gearbox itself??

[jondee86]

If the vibration only occurs between 4000 and 6000 rpm, I'd be looking
for some non-rotating part that can vibrate. Something that runs real
close to some other part, loose brackets, shagged centre bearing, exhaust
touching the floor...

I'd be surprised if it was coming from the gearbox. All the parts in there
are fully machined and inherently in balance. If a bearing had collapsed
you would be hearing all sorts of ugly rattling and rumbling noises.

Cheers... jondee86