Need for Crankshaft Harmonic Balance Pullys
Turbo Mini Forums

I was told the 1275 engine required the subject crank pulley to minimize vibration to the engine internals.

Does anyone know if this mean that the guys like myself running the Vmax / JonSpeed SC kits that no longer have a harmonic balancer will be experiencing certain engine failures????

Its possible, but my thought is that the extra load of the supercharger on that end of the crank may well have a damping effect on the harmonic vibration that the balancer pulley is supposed to suppress.

Supercharger belt drives don't do the same as a harmonic damper.

There is plenty of documentation around the internet on 'torsional vibration'

While you can use a crank without one, is service life will be shortened. How much shorter is anyones guess, but cranks do break, and I don't thinks just as a result of overload.

Me personally, on an engine that needs a reasonable sevice life, IE a road engine, I wouldn't run without one. If its a race engine and its going to get a new crank every 500 miles, then you could most likely get away with it.

I was afraid of that prognosis Sprocket. If you are correct then a whole bunch of us Vmax & Jon Speed guys are going to experience main bearing and or Crankshaft failures. I hadn't thought of this issue until my trigger wheel sheared off the aluminum SC & Alternator pulley and it dawned on me that none of us have the steel damper pulley any more.

My car is primarily used for Autocross and sees less than 100hours per season. We are currently improving the trigger wheel attachment to the aluminum pulley, but I'am thinking if it fails again...it may be due to crank vibration, not a poor attachment of the trigger wheel????

On the Aus kit I bought, it has the grooves machined into outer part and the belt runs from there.

I remember a post from the guy at the ML motorsport forum has done some rather large mileages 10K I think, have a search on their forum

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Theres another topic on here somewhere with my thoughts on crank dampers - I'm not up to speed on these m45 charger conversions - is there any reason the mpi bottom pulley couldn't be used as its poly v type with a damper? If for any reason a damper couldn't be used my thoughts would be to make the crank damper out of steel in en16t- and make it heavy and strong to keep the keyway in one piece and offer a mass for the vibrations to act against opposite the flywheel.

JK

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

You were correct! There is another thread but they refered to as a crank damper and I hadn't used that serch term before I started this tread. Much info .......it sure seems like those of us that don't have a crank damper are in for a future failure ^&&

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=343561

If I'am not mistaken both Stuart and Jon Speed purchase their all in one solid but machined aluminum crank pulley for the serpantine SC belt and alternator V belt from the same maker. It does have a fair amount of mass, but there is no "Isolation material" between the shaft and the mass...

you need that isolation material really,

I've been looking into making a proper cam belt drive with a proper cam belt (apbellamy you can fuck right off before you start lol) with a proper fluid damper.

It wont fit with a charger though...

Me?

The theory of having a solid damper and supercharger inertia may be ok - there are enough people out there putting lots of miles on them without breakages - though if we were to do a single piece pulley it would be made from a very good grade of steel not ally and probably a full length keyway in the crank.

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

Thank you John K for those words of support - I thought I had been dismissed out of hand. I know it cant be as effective as a "proper" harmonic balancer, but part of the problem is the effect of a large lump on one end of the crank (the flywheel) allowing the crank to flex torsionally at each firing stroke -more when no 1 fires, obviously.Having a weight or some inertia at the other end may well help to alleviate some of this problem and a steel pulley may be better than an alloy one, both because of its greater weight and durability/reliability.

Just a theory, I have no maths or practical experience to support it so please dont crucify me.