Harmonic dampers on a 998
Turbo Mini Forums

I managed to damage my crank pulley getting it off (don't ask). so I need a replacement.

I have two of the harmonic type, but they're not in very good condition. However, I have loads of the non-harmonic type from the pile of 998s I've taken apart.

Obviously rover never saw fit to fit the harmonic type on the 998 (other than the occasional one and they may have been retro fitted by people like us), so should I use the non-harmonic type?

This is on the TT by the way.

My personal thoughts are that the harmonic dampers are designed for 1275s so may not be any use on the 998 anyway.

opinions please.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

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In my experience 998 A+ metro's had harmonic pulleys. But it may just be luck of the draw?

I would have thought it beneficial especially if your revving hard

Edited by John on 20th Jan, 2011.

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

Only revving to 7k, and had plenty of 998 revving to this over the years and never bust a crank.

In fact the only 998 crank we have bust was running a harmonic damper

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

I think you have just answered your own question, Wil ?

my opinion as you say the harmonic dampers are tuned to the 1275 anyway so pointless fitting one

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I would say that in an ideal world whatever you put on it needs to be balanced. But for the miles we do does it really matter?

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are we sure its tuned to the 1275 and not just a generic resonance absorbant device? The way I see it the pulley absorbs harmonics through the rubber - so shouldn't it work as well on the 998 as the 1275? If its just to stop the resonance, or the point in which the firing freqency from the pistons meets with the frequency that the crank has imparted in it (and we all know that the cranks cannot be the same from rover, they have to be the same mass to have the same resonant frequency). I think it'll work on both the 998 and 1275 equally well.

im 90% sure all Australian standard 1000cc minis had them i know the 997cc & 998's coopers s had them..

i would fit one.

surely a dime a dozzen over in uk? most people i know fit a 1275 later rover one on there older engines as they are in better condition.

i thought it's only purpose is to dampen resonant frequency so it would have to do the same for all cc ranges.

have a read of this thread wil.

http://www.ausmini.com/forums/viewtopic.php?t=68263

Edited by NickG on 21st Jan, 2011.

That is interesting and I will continue to follow it.

But still doesn't explain the fact that many thousands of 998 minis ran without one with no adverse affects, but it was aknown problem in 1275s.

Believe it or not they are not so easy to come across over here. But I'll ask around.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

I've got a couple of 1275 dampers but am keen to keep hold of them. If you are desperate though wil I'm sure I can find one out.

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

The 998 dampers off Metros that I use are slightly thinner than the 1275 ones.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

After some more advice I am definately going to run one.

MS sell a lovely 2-piece one, but too much money. Might be in touch John, but have a few local boys to ask first.

Cheers

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

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

I'm sure I can get one locally. I'll let you know.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Ive never seen one on a small bore (998 or 1098) over here. And ive had the 4 of the buggers taking up room.
I was under the impression the 998 never got bad enough vibrations to cause it.

In boost we trust

I would think rover didn't fit them on the 998 because the torque was insufficient to cause any problem, but as torque increases so does the level (volume) of the harmonic.

I agree that they should be fitted to a 998 when the power/torque level reaches the standard 1275 output.

[X] nail here for new monitor

It seems to me that the BL/Leyland/Austin/Rover engineers had the same conversation as us here and could come up with a consensus either.

http://www.twin-turbo.co.uk
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A man without a project is like a like a woman without a shopping list.

I wonder if a 998 damper would be better suited to 1275's with lightened cranks, flywheels and the like as if they are smaller they could potentially resonate higher up, closer resembing the new position of the resonance.

Sorry, just thinking out loud.

Edited by minimole23 on 21st Jan, 2011.

almichie, im not 100% on what im about to say is true or not, so dont take this as a go, just want to get my facts straight and and or clear up how they work and why

i thought the harmonic dampers are specially designed to numb harmonics at specific frequencies, so id have guessed the 1275 damper was tuned to dampen mainly a specific range of harmonics that the 1275 suffers with (but no doubt will dampen higher and lower frequencies to a certain extent)

so imo its not a case of it being a generic harmonics absorbant device, although id prob think it cant do any harm, and probably will help to some extent?

another thing you mention is that the harmonics are something to do with the torque output of the motor, is it?

i would have thought its rpm related, and as the rpm of the engine goes through the reasonance 'hotspot' of the particular engine, thats when (in my mind) it would start to makes things rock, rattle and roll with potentially disasterous results.

now i dont know if (as you say) a 998 with similar power to a 1275 would kick out the same harmonics,
but i would think that, as all a series are basically the same design, i.e an iron lump of similar shape with a crank spinning inside, i would imagine the harmonic ranges are all pretty similar in any event, but....i would have thought that this would be the case at any power level?
how does harmonics relate to the torque exactly?

if im wrong, apologies for muddying the waters, and please someone put me straight

regards

joey

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

I'm with you joey.

I guess the name 'harmonic damper' suggests what it does. I would presume that the harmonic frequency it is dampening is a vibration setup in the crankshaft at a harmonic of the frequency of rotation.

e.g. 3000rpm = 50hz so maybe at this rpm the crank has an additional vibrating frequency of 100hz set up that if left unchecked wil faill the crank, at best it'll feel horrible.

This will be independant of power. But it will likely be a function of things like crank bearing spacing? I don't know, I'm guessing. But the differnt size 998 crank may suffer less.

Edited by wil_h on 21st Jan, 2011.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Have a read here http://en.m.wikipedia.org/wiki/Harmonic_ba...Redirected=true

This will help you understand the dampener and what it does.

And this is a good one too

http://www.pro-race.com/faq.htm

The damper just absorbs the peak harmonics that cause crank failure.

Al

Edited by almichie on 21st Jan, 2011.

Yes it does help, nowt to do with increase in torque. Just the crank vibrating, and at certain rpm (frequencies) this will become resonant, the damper reduces this.

And any article that wants me to take it seriously shouldn't use the word 'torques' as its a Top Gear bastadisation that has no place outside of an entertainment show.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

My only thought about Joe's thoughts, is that the 998 would have a different rotating mass to the 1275 as everything is that bit smaller, so chances are it will wobble about in a different manner...

In the yellow bible uncle David writes on page 366 that it should be use at all times, though it can be machined down on light weight 850 and 1000.

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