Crank dampers
Turbo Mini Forums

I have been thinking about this today.

Having bought a trigger wheel for the megajolt that will be going on my new engine, what is the quality of the original damper like compared to a number of the fancy offerings by the likes of Med, KAD, and Swiftune.

Do these really have that much benefit to the longevity of other engine components, or are they more of a belts and braces approach to engines turning massive revs and strokers.

I guess its hard to quantify the effectiveness of them really given the number of variables involved in a peformance engine.

The reason I ask is that looking at the standard crank pulleys in my pile, they are looking past their best so will probably replace the standard item anyway, as the next engine for my car will be turning to 8k.

Put a new one on it. If you're not sure then replace it is my rule.

-James

I rang MED the other day for some advice on exactly the same question...the dude on the blower (steve?) told me that provided the rubber is in excellent condition, they should all do the job (even standard, apparently!) for a street motor.

That last comment makes me laugh

What defines a 'street motor'?

Not a clue, but he asked me wether it was for street or race...

Well I have a race motor then built like a street motor

I spoke to my machinest about this the other day, took the standard pully down and he said it should be fine.

Thats good enough for me!

If a race motor is built well, as in balanced properly, then it doesnt need a damper (as much). Swiftys and Slap Heads Miglias dont run dampers and win many races after thumping round a track flat out for 20 mins.
A street motor is more likely to need a damper.

As far as I can work out

Paul

I seriously doubt it!

4cyl in line motors generate lots of torsional vibrations along the crank, ending up atthe crank damper whose job it is to ease the pain on the crank - how does it do it?

a little science - the rubber element in the crank damper, its length width, thickness and shore hardness/damping along with the mass on the outside of the damper are tuned to generate a reasonate - natural frequency - at the precise rpm points which are going to be giving the crank grief. The properties of rubber as an engineering material are extreme as are the dynamic stiffness's it can produce. In essence the rubber compound along with the mass generate massive forces at the point of resonance which counteract the forces the crank is producing.

lightening the crank/rods/pistons/flywheel will push the problem rpm points of the crank up the rpm scale - but they'll still be there.

racers may choose not to run a damper and give their cranks "lives" in hours - why take the risk. My rule of thumb on something like a tuned (lightweight internals) K which turns up to 8k or so is to use the A+ damper with the small mass on the outside as this wil lresonate higher in the rpm band compared to the large mass A+ damper

lesson over!

If Carling made Mini engines
it would probably be like this one!

John,

So based on that, what is your opinion on using a machined damper as a crank trigger both from the perspective of timing accuracy and damping effectiveness?

Jean

http://www.jbperf.com/

Jean - I know many many people have done it and are happy with it but be in no doubt you will get random and varying spark scatter - especially just before and after the natural frequency of the mass, I'd have to do the maths but I'd expect the mass to rotate easily 5 degrees on its outer edge this is quite a distance.

JK

If Carling made Mini engines
it would probably be like this one!

Yes i moved to the darkside

Instagram @jdm_brett

There are a few posts discussing it on page 1 of this thread:
http://www.turbominis.co.uk/forums/index.p...t&tid=7423&fr=0

As I've mentioned I'd have to do the maths to work out how much it moves but I did design chassis/drivetrain mass dampers for Nissan/Ford/Audi for a living for a number of years,believe me you can expect more than 0.5 degrees of movement at 5000rpm or so when a 0.5/0.75kg mass reaches resonant frequency - truth not fiction or guess work

JK

If Carling made Mini engines
it would probably be like this one!

Funnily enough John, I had thought about this, and was consdering the posibility of moving the crank picup to the flywheel at some point.

I had no idea of the effect but was thinking how many picups do you see on the dampers of production cars...

When you consider our poor little 3 bearing cranks probably twist, end to end, at least 2° in stock oem applications never mind you boys throwing 250+bhp through them or 8500rpm and the frces involved- makes you appreciate how hard that little crank damper has to work (by oscillating) to keep it all in one piece!

JK

If Carling made Mini engines
it would probably be like this one!

So what causes the taper on flywheel to vibrate and pickup on the crank?

Mine is all balanced, and yet again its picked up on the taper? My thoughts are that its the crank damper at fault.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

Edited by evolotion on 16th Feb, 2010.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Matty - the root cause is all the same - torsional vibration

JK

If Carling made Mini engines
it would probably be like this one!

John,

Thank you for this information. Even without hard numbers, it does confirm my feeling that this was not a good thing to do. Especially if you use this with a relatively sophisticated ECU where the trigger is not only used for position but also for engine speed variation to predict engine position and to perform tasks such as traction control.

With such an essential input, getting data that is affected in an unknown way in both absolute position and instantaneous speed doesn't make much sense to me.

Jean

http://www.jbperf.com/

How many degrees of movement do you think could occur on the crank damper?

The only real way to check it is on a dyno with a strobe

While I have my trigger mounted on the outside of the pulley, against my own better judgement, its better than what I had previously. There is still room for improvemnt

Edited by Sprocket on 17th Feb, 2010.

i got the trigger wheel and damper for med, i asked then if i needed the damper and they said deffo put it on it will pro long the crack life so i got one