12 replies to this topic

[whistler]

Is there any advantage to using the Cooper S 2 piece damper/pulley over the standard 1 piece version as fitted to 1275 and some small bore engines?

[nicklouse]

Easier to buy. Easier to add a timing wheel too. Don’t come with a timing mark on them.

[Spider]

For any street engine, no.

[whistler]

For any street engine, no.

So there must be an advantage at higher revs, is that right?

[DeadSquare]

The reciprocating masses in an engine produce sine waves.  The heavier the rotating mass, the less amplitude unless frequencies harmonise.

 

Harmonic dampeners came from aero engines which need to be as light as possible and in flight, run at a constant speed most of the time.

 

With more than one engine, harmonised frequencies recurring, as each run at a slightly different RPM, can produce periodic drumming, which could go on for hour after hour, rattling the airframe.

 

However, by tuning a dampener to quench a sine wave at the optimal engine RPM, not only was the airframe and crew less stressed, but so were parts of the engine, which could be made lighter.

 

Race car engineers liked the engine to be as light as possible and with constantly changing RPM, tuned a dampener to the RPM perceived to be the most damaging.

 

In a production car, the chief job of the dampener is to quench the most prominent sine wave that the would make the bodyshell drum.

[Spider]

 

For any street engine, no.

So there must be an advantage at higher revs, is that right?

 

 

It depends on the engine, the particular crank (and other spinning parts) and for how long you are making higher amounts of power for.


With each 'bang' in the cylinder, it causes the crank to twist and recoil in torsion.At one end of the crank, we have the flywheel, which will resist much of this torsion and smooth it out. At the other end, it will twist quite a bit. At certain revs and power, they can coincide with the turning parts resonance at which point, the torsional twist becomes violent enough to break the crank. The Harmonic Damper goes a long way to reducing and keeping in check the torsional twist / vibration, in particular at Resonance to keep the crank in one piece.

The usual Rubber dampened type Damper, generally work in narrow-ish bands. Fitting the wrong one can render it useless or even amplify the resonance in the crank.

Here's a graph showing an example the torsional vibration with and without a damper

 

 

[whistler]

Just had a look in the old parts books and the 970, 997, 998, 1071 and 1275 S engines all used the 2 piece one. All have different characteristics and power range.

Has anybody done any research on this?

[mini13]

if your that bothered fit a KAD one, as they are a fluid damper they will work over a wide range.

[Spider]

Just had a look in the old parts books and the 970, 997, 998, 1071 and 1275 S engines all used the 2 piece one. All have different characteristics and power range.

Has anybody done any research on this?

 

And the MG and MG Turbo Metros had the 'single piece' types similar to all other engines, these made more power than the 1275 S Engine did.

Keep in mind here too the while the small block engines in that list had substantially different (lighter) cranks and the smaller of the big bore engines would spin up higher revs then that 1275 S would. In the early days of the 998 Cooper they were fitting the 2 piece dampers but later, they dropped that and went to the 'one piece' type Damper because they were prone to breaking cranks when fitted with the 2 piece types.

As mini13 suggested, if you're worried and not sure which was to go, fit a KAD one, being a fluid type, it covers a very broad range.

[whistler]

My original post was just to ask if there was any advantage in using the 2 piece one over the later 1 piece version. I've only ever used a 1 piece pulley/damper which appear to be in short supply but the 2 piece one seems to be in stock in most places.

[croc7]

My original post was just to ask if there was any advantage in using the 2 piece one over the later 1 piece version. I've only ever used a 1 piece pulley/damper which appear to be in short supply but the 2 piece one seems to be in stock in most places.

I did a quick google check and found plenty of the 1 piece dampers-Moss Motors, Ebay, British Parts Northwest, Mini Mania (hold on to yer wallet), Seven Enterprises.....

Edited by croc7, 24 December 2022 - 07:54 PM.

[whistler]

 

My original post was just to ask if there was any advantage in using the 2 piece one over the later 1 piece version. I've only ever used a 1 piece pulley/damper which appear to be in short supply but the 2 piece one seems to be in stock in most places.

I did a quick google check and found plenty of the 1 piece dampers-Moss Motors, Ebay, British Parts Northwest, Mini Mania (hold on to yer wallet), Seven Enterprises.....

 

I did find new AHU1878 in Minisport and Moss-Europe which were out of stock a couple of days ago. I didn't find any in ebay UK. Minimania and British Parts northwest are not in the U.K. and import duties from North America are far too expensive but I thank you for your input.

[nicklouse]

Some standard BMC/BL/Rover dampers.

No idea what came of what.