14 replies to this topic

[The Matt]

Well, I have been reading a few engine specs and came across the different types of crank dampers.

My question is,

What do the high performance ones offer and are they necessary for my rebuild?

[The Matt]

like this

[Oldskoolbaby]

When I was speaking to John Lee about the motor I was building up, he advised me to get one as close to the flywheel weight as possible. Very hard I know but this is why he designed THE lightest clutch and flywheel assembly I have ever seen for the A seires.
He found that the crank tails on the 1300s would crack or break up completely at long periods above 8500rpm because they twist when accelerating. I know you wont be taking your engine to these hights but the whole point of having a crank damper is for reliability so this science still applies just on a smaller scale. Check his website for some pretty 5h1t hot products.


http://homepage.ntlw.....20wheel 2.jpg


www.lynxae.com

[Sprocket]

The Cooper S damper is the performance item when it comes to the standard ones, but does need balancing because its a two piece item. Be suspicious of second hand items as the isolating rubber perishes and they then become useles for purpose, this could also true for the one that's on your engine now. And that purpose is to reduce torsional vibration in the crankshaft thereby increasing fatigue life of the crank and bearings. If you have rebuilt and changed the spec significantly of the engine then good practice says you should fit a new one if your old one is showing signs of deteriation.

The ultimate in crankshaft damper is the viscous type, but could set you back 200 notes

[Oldskoolbaby]

When I get my milling machine and lathe, Im gunna try and make my own. Im going to make parts of it hollow so I can fill it with fluid so it will be perfectly balanced at high rpm.

MiniSprocket is right though. A brand new damper is really what you want.

[Sprocket]

When I get my milling machine and lathe, Im gunna try and make my own. Im going to make parts of it hollow so I can fill it with fluid so it will be perfectly balanced at high rpm.

MiniSprocket is right though. A brand new damper is really what you want.

You are aware that these are tuned for the engine they are on. Also they are not solely filled with fluid, there is a steel ring that floats in this fluid and the toleremces to which these parts work together is very close.

http://www.fluidampr.../howitworks.htm

[Oldskoolbaby]

Yeah I know. I'd do my research first and final designs on CAD.

[Dan]

Yeah, I wouldn't try to make your own. Crank dampers are quite complicated machines really, even though they look simple.

The Mini Cooper S two piece one is the best according to very many rce engine builders who have tried many different types. The friction clutch type one even seems to give problems in Mini's when they are the best available for many other engines.

It's not got anything to do with the flywheel mass AFAIK. As far as I'm aware it's balancing the flex caused by the cylinders firing. The crank spinning at high RPM without the fuel and ignition running (being driven by a balancer for example) won't really flex or twist at all.

The genuine Cooper S item is still available new from Minispares and costs about £40.00 more than the final price of the second hand one on E-bay. If you get this do get the locktab for the screws that hold the two together.

Edited by Dan, 14 November 2005 - 09:16 PM.

[Sprocket]

The genuine Cooper S item is still available new from Minispares and costs about £40.00 more than the final price of the second hand one on E-bay.  If you get this do get the locktab for the screws that hold the two together.

[Edit]
My mistake, i found reading that statement a little difficult and i miss understood. sorry for the confusion.

That is for the damper only, you still have to buy the pulley which is about another 40 notes.
[ Edit]


Torsional vibration is as Dan said generated by the firing of the cylinders generating bending loads. This causes the crank to flex and if left un checked will cause localised work hardening of the metal and then failure. This is more of a problem in the A series engine because its only a three bearing crank. The damper changes the frequency of the vibration resulting in a more satisfactory fatigue life.

Leave one off a heavily modified high reving 1275 will lead to the crank breaking all depends how the engine is used as to how soon it'll break.

Edited by Mini Sprocket, 14 November 2005 - 11:27 PM.

[The Matt]

Well, I am looking into it. I am due to have my crankshaft reground and the bottom end fully balanced. So was wondering if it was needed for my engine really (as it will have to be on when the bottom end is balanced).

I am not going to be absolutely revving the nuts off the engine, or really racing it all the time. It will be a weekender and the odd track-day. So I guess a new crank pulley (a standard one) will suffice.

Once again, cheers for the advice peeps! :wink:

[The Matt]

I think I will order one of these bad boys tomorrow then:

Pulley

[Sprocket]

[The Matt]

It would, of course, be nice to go to a cooper s style damper and a poly vee belt set up.

But the coinage won't allow at the moment! :sad:

[Sprocket]

It would, of course, be nice to go to a cooper s style damper and a poly vee belt set up.

But the coinage won't allow at the moment! :sad:

Ben after the TPI set up my self to go with my high tec 16valver

[Dan]

You'll need to buy the Minispares version of the poly-vee system, which although it uses belts designed for machine tools and not engines is still a good item. The standard set from a twin point won't be much use to you. The alternator pulley only really fits the twin point alternator (the internally cooled version) and the belt will be far too long as the alternator is meant to sit up above the head. The set uses the standard twin point crank and water pump pulleys along with a custom alternator pulley and comes with shims to align the pulleys.

Sadly there isn't a poly-vee crank pulley which will accept the Cooper S damper ring at the moment AFAIK, if there was I'd already have it!