Harmonic balancers...AGAIN!

[b_have]

Ok, I know that this has been done to death, but I'm on a mission to reduce my rotating mass. Have just made a torsion link to replace my a/c pump (what a heavy lump of luxuory that is!) I use a PE high stall TC that is substancially lighter than the oem.

So, while its in a million pieces, I'm considering making a slightly underdriving lightweight crankpulley (need to source new belt anyway now the a/c pump has gone).

Bearing in mind this engine will not see huge mileages, has anyone heard of ACTUAL experiences of doing this. (not the usual "read somewhere it might break the crank/cause huge vibration/make the indicators go twice as fast...")

[Digsy]

I have direct experience of an I4 engine snapping its crankshaft due to a failed torsional damper.

 

The failure was due to the rubber hardening over time and changing the damping frequency. The damper in question was for torsional vibrations only.

 

The Supra has a 6-throw crank (i.e. 50% longer in terms of cylinders) so it will be more susceptible to torsional vibration than an I4. Also, the Supra pulley has a bending damper in it as well.

 

I wouldn't do it. Go for a reduced-inertia flywheel instead. Bigger bangs for your buk and less risk.

[Guest Terry S]

As stated before a long time ago I ran and Unorthodox Racing underdriven, non dampened pulley for approx 30k without any issue. Having said that I now run a BL pulley and that was also what the UR one was changed to on the old car, and I couldnt be happier, still dampened, lighter than stock, and uses a stock belt.

[Gamer]

I have a BL crank pulley and UR pulleys for the rest ready to go on.

 

Also removing the stock fan and running dual electrics...

[Guest Terry S]

I have a BL crank pulley and UR pulleys for the rest ready to go on.

 

Also removing the stock fan and running dual electrics...

 

 

Not a fan of the electrics personally. Hope they work out well for you mate.

[Ark]

I have direct experience of an I4 engine snapping its crankshaft due to a failed torsional damper.

 

The failure was due to the rubber hardening over time and changing the damping frequency. The damper in question was for torsional vibrations only.

 

The Supra has a 6-throw crank (i.e. 50% longer in terms of cylinders) so it will be more susceptible to torsional vibration than an I4. Also, the Supra pulley has a bending damper in it as well.

 

I wouldn't do it. Go for a reduced-inertia flywheel instead. Bigger bangs for your buk and less risk.

 

I have a used Cyn_R_G flywheel for sale

[JohnK]

I use a PE high stall TC that is substancially lighter than the oem.

 

Sounds like an auto to me, so a lightened flywheel isnt much use.

[Digsy]

Sounds like an auto to me, so a lightened flywheel isnt much use.

 

Good point.

[Lucifer]

But a lighter TC is!

[b_have]

I have a BL crank pulley and UR pulleys for the rest ready to go on.

 

Also removing the stock fan and running dual electrics...

 

Been using twin electrics for >5years now with no probs.(fully ducted fmic to rad with no a/c condenser)

[b_have]

I have direct experience of an I4 engine snapping its crankshaft due to a failed torsional damper.

 

The failure was due to the rubber hardening over time and changing the damping frequency. The damper in question was for torsional vibrations only.

 

The Supra has a 6-throw crank (i.e. 50% longer in terms of cylinders) so it will be more susceptible to torsional vibration than an I4. Also, the Supra pulley has a bending damper in it as well.

 

I wouldn't do it. Go for a reduced-inertia flywheel instead. Bigger bangs for your buk and less risk.

 

What is an I4 engine? What I want to know is does a 2JZ engine suffer?

Terry, interesting feedback, why did you change to the BL dampened if there were no probs? Did you notice any evidence of crankwalk or unusual wear?

[Lucifer]

Charlie, How did you do your ducting? is it an air tight seal. We use expanding foam and a binliner then trim and spray.

[b_have]

Charlie, How did you do your ducting? is it an air tight seal. We use expanding foam and a binliner then trim and spray.

 

Did exactly that. Bloody messy job!

[RICHARDA]

Inline 4?

[Digsy]

What is an I4 engine? What I want to know is does a 2JZ engine suffer?

 

I4 means inline four. The longer the crankshaft, the more pronounced the effects of torsional vibration, so the 2JZ (an I6 engine) will be 50% more likely to suffer fatigue stress than an I4.

 

So if an inline 4 can snap a crank just because the TV damper isn't working, then an inline 6 certainly could.

 

The real problem is that without access to the people who designed the 2JZ, you will never know why it was fitted with such a complex damper. The reason could be anything from simple NVH and refinement all the way to protecting the crankshaft.

[b_have]

I4 means inline four. The longer the crankshaft, the more pronounced the effects of torsional vibration, so the 2JZ (an I6 engine) will be 50% more likely to suffer fatigue stress than an I4.

 

So if an inline 4 can snap a crank just because the TV damper isn't working, then an inline 6 certainly could.

 

The real problem is that without access to the people who designed the 2JZ, you will never know why it was fitted with such a complex damper. The reason could be anything from simple NVH and refinement all the way to protecting the crankshaft.

 

Thanks Digsy, any idea how the damper design is calculated? I often wonder if the TC /flywheel is mass is involved in the calculation, but as the mass's are very different why would the damper be the same on auto/manual? Also, by reducing the rotating mass in a substancial way by using a light highstall TC, does this effect the calculation?

I would imagine that a fluid filled TC would in itself have an effect on harmonic balance.

[Ian C]

I had an Unorthodox Racing underdrive lightweight crank pulley on mine until Digsy put me off it and I put my stocker back on One of the main reasons I swapped it back was because I noticed absolutely sweet FA difference in the car after installing it - so if the seat-of-the-pants dyno isn't affected one jot, why chance the whole engine on it?

 

-Ian

[Guest Terry S]

Terry, interesting feedback, why did you change to the BL dampened if there were no probs? Did you notice any evidence of crankwalk or unusual wear?

 

I was going built engine, bigger power, and had read all the horror stories so seemed like the right thing to do. The crank was used by Leon in his car afterwards and he had it check and there was nothing untoward. Just lucky I guess

[Wez]

How much are these BL crank pulley?

[Gamer]

$420 on the other side of the pond.... No idea on the cost if bought here. I got mine (Brand new, black anoidised) in a private sale via Supraforums.com

[Guest Terry S]

Wez PM me if you want one, I owe you a favour.

[Wez]

Wez PM me if you want one, I owe you a favour.

 

PMed

[Digsy]

Thanks Digsy, any idea how the damper design is calculated? I often wonder if the TC /flywheel is mass is involved in the calculation, but as the mass's are very different why would the damper be the same on auto/manual? Also, by reducing the rotating mass in a substancial way by using a light highstall TC, does this effect the calculation?

I would imagine that a fluid filled TC would in itself have an effect on harmonic balance.

 

The damper tuning is usually done by the damper supplier as it is a pretty specialist area. There is some fairly simple (i.e. not requiring a supercomputer) code that will work out the resonant frequencies of the cranktrain and tell the damper supplier what to aim for, but they will usually do their own analysis. For a mass-produced car they will also probably have their own engine specifically for damper tuning work.

 

In short, I wouldn't like to have to do it myself!

 

I used to be of the opinion that the whole cranktrain mass (i.e. rotating inertia) would affect the TVD tune. This used to make me rail against light flywheels and clutches in the same way that I rail against removing the damper. I did learn enough to make me retract my comments on flywheels when I learned that the flywheel effectively "decouples" the cranktrain from the rest of the driveline.

 

To use an analogy, if you fix a ruler to the edge of your desk and twang it, it will wang up and down at its natural resonant frequency. If you now fix the rule fairly loosely to the table and balance a coin near the fixed end, the coil will bounce off when you twang the ruler. The ruler will, however, still wang up and down at the same rate. However, if you fix the ruler firmly it doesn't matter how hard you twang it. The coil will stay nice and still.

 

Now to liken this to the cranktrain, the ruler is the crank, you twanging it are the inputs from the pistons going up and down, the place where it is fixed is the flywheel inertia, and the coil is the transmission. The flywheel inertia's job is to keep that end rotating at a fixed speed (i.e. no torsional vibration) so if your flywheel is heavy enough you can assume no vibration at all. No vibration at the transmission (coin) end means no transmission rattle. Lightening the flywheel is akin to loosening your grip on the ruler. The transmission (coin) will rattle because some of the vibrations get past the flywheel.

 

Also, in a dual mass flywheel the fact that one half is connected to the cranktrain and the other half to the transmission via a series of springs also helps the decoupling.

 

No lets assume that you have a particularly weak ruler (one of those horrible shattery ones you had at school). In order to safely twang this on your desk you need to add a magic gizmo to the end of it that limits the amount of vibration - a damper in other words. Using your magic ruler damper you can twang away at your brittle ruler with the other end firmly fixed and it wont break because the damper is taking teh ooph out of the vibrations.

 

Now imagine the school bully comes along during break time and steals your ruler damper.

 

Of course you still want to twang your ruler, but now you are frightenend it will snap, so what can you do? Obviously you can twang it less hard but where's the fun in that? An alternative might be to not hold the fixed end so firmly.

 

Now, going back to the 2JZ, "not holding the fied end so firmly" caring less about having zero vibrations getting through the flywheel, or in other words having a flywheel with less inertia.

 

Therefore having a lighter flywheel might even help make your cranktrain last longer.

 

Part of me still thinks that the whole cranktrain acts as a tuned system and that changing any part of it would mean that the torsional damper would be less effective. Certainly I still think that changing the damper and leaving the stock flywheel in place is a bad idea. The 2JZ must have a vibration problem to have both torsional and bending dampers on the front and a dual mass flywheel on the back.

 

However, if the flywheel or TC is heavy enough to completely decouple the crank from the rest of the driveline, then the damper could be the same for both manual and auto, because it only has to compensate for what happens inside the engine.

 

I would bet that the NA and TT dampers are different, though because the inputs from the gas loads would be different.

[JohnA]

... I'm considering making a slightly underdriving lightweight crankpulley...

Just to pick on this one, you do realise that the water pump will be turning slower right?

Same as the alternator --- will your fuel pumping be a happy bunny?

 

Alternatively you may already know of the old track 'trick' that was to keep the auxiliaries in principle but have them disconnected during full throttle.

[b_have]

Just to pick on this one, you do realise that the water pump will be turning slower right?

Same as the alternator --- will your fuel pumping be a happy bunny?

 

Alternatively you may already know of the old track 'trick' that was to keep the auxiliaries in principle but have them disconnected during full throttle.

 

How does that work then?