Crank dampers
Turbo Mini Forums

All these new pulleys from MED for example. It is basically the same design as the old S damper, but in lighter materials... Will it then do its job? I thought the outer ring needed to be of a certain weight to work?

Quote Sprock -"The only real way to check it is on a dyno with a strobe"

NOT correct - the only way to do it is via calculations - do you think a strobe or your eyes can register at 100+hz with any accuracy?

JK

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

Team Racing

My tonewheel is on the back of my pulley. I didn't like the idea of putting it in my balance mass even 10 years ago. I know folks have done it - but I personally won't, simply because putting it rigid to the crank is a known, wheras putting it on the balance mass is an unknown.

Did I just hear JK actually volunteering to do the math and tell us one way or the other though? LOL

S H Engineering produce friction dampers which are effective at any crankshaft speed. www.shengineering.co.uk
Mini Spares sell harmonic balancers (which are friction dampers) which are also effective at any crankshaft speed. www.minispares.com
Racing Engine Technique produce viscous dampers to order which are also effective at any crankshaft speed, they are expensive too!
A metalastic damper pulley is only effective at its designed speed band therefore you have to know at what speed the crank is going to vibrate & require damping.
It's no use buying an 'S' type because 'if it's good for the 'S' type it'll be the best to have.'
All engines are different so require a damper to suit that particular configuration, the different crankshaft, flywheel, clutch etc etc alters the vibration band so two engines looking identical on the outside could require different damper pulleys so a friction or viscous damper is the way to go unless you've got a calculator to work out your crank vibration band then you can fit a metalastic damper pulley designed for that vibration band.

Baldwin never had a damper on his Swifty motors or SH motors. He told me he never had a problem. Good enough for him - good enough for me

I seriously doubt it!

Stuart Gurr (Vmax-Scart) says most 1275cc miglia racers don't use dampers & they run at 8,000rpm.
'Normally engines require damping at maybe 6750 to 6790rpm and damage can occur in this rpm band depending how long & how often the engine will be held at that rpm.
What's difficult to work out as every engine is different, is when the vibration occurs & how wide the band is'

Any metalastic damper will after a few years be well past their use-by date so it's worthwhile changing them, but if you replace it with another metalastic damper it must be specifically for that engine, the vibration band could only be 40rpm wide (as above) where damage can occur so the damper has to be effective in that rpm band.

Given the cost of one of these really posh dampers, for the extra fatigue life it may give the crank. say maybe 50 miles at 7500rpm, would it not be a better bet to spend your £300 quid on preparing a fresh crank?

I'm not knowledgeable enough to comment to in depth but it seems to me that unless fatigue life is greatly increased they are not worth it. Unless crank failure can be strongly attributed to these frequencies. It would be interesting to know whether those cranks that have broken have done so when resonating at the damaging frequency. That I guess we will never know.

Standard metalastic crankshaft damper pulleys can be bought from £40 to £100 depending on type required. A harmonic damper kit costs £400, once you've changed over to run a harmonic balancer you can buy the pulley wheel for around £340 when you need to renew it.
It's not just the crankshaft which is at risk of damage due to poor vibration control, vibration damage doesn't only snap crankshafts.
Crankshaft vibration damages valvetrain, ignition timing, timing chains & gears, loosens fasteners, fractures engine components, damages main bearings, causes flywheel fretting etc.
EN40/nitrided cranks are at most risk of failure due to crankshaft vibration because of their hardness, they're not flexible enough to allow torsional distortion etc so if you have one of these you'll need a harmonic balancer of some sort.

I'm trying to find a suitable harmonic balancer for my set-up at the moment, I may not be able to because of the supercharger drive requirements.
I have a solid ally pulley fitted which has a vee for the standard alternator belt & a 5pk multi-vee for the supercharger belt & a 36-1 trigger wheel fitted, but after reading all of the above I realise that the crankshaft requires a harmonic balancer.

Team Racing

So whats the thoughts on this then?

http://cgi.ebay.co.uk/A-series-lightened-c...emZ290406792553

Surely lightening the mass will change the effective damping range of this and presumably it is now useless?

If something is worth doing, it's worth doing half of.

Umm, no thanks!

Maybe not useless, but what RPM is this supposed to be effective at? Sureley not at the critical harmonic frequency of an A Series.