Triumph 2500Cc Harmonic Crank Damper Kit.

[TRTOM2498PI]

Evening All,

 

I have a new, never fitted / installed, Triumph 2500cc harmonic crank damper, complete with water pump, and gasket.

 

Most of the 6 cylinder race cars have these fitted. The long crankshaft in the Triumph six cylinder is especially subject to power robbing torsional vibrations. The stock harmonic damper does not do an effective job of eliminating these vibrations.

 

£500.00GBP.

 

For further information, please e-mail me at:

 

Thomas.key@heavy-weight.com

 

 

Cheers

[GT]

The long crankshaft in the Triumph six cylinder is especially subject to power robbing torsional vibrations.

 

The stock harmonic damper does not do an effective job of eliminating these vibrations.

What on earth makes you come out with such an assertion?

Have you measured this?

Have you ever tried to run a fully balanced crankshaft?

They really are pretty smooth, especially with a proper lightweight conrod and piston assembly.

 

Do you have any idea what the damper is designed to do?

 

FYI, There is no "power robbing" going on whatsoever from the crankshaft.

 

The vast majority of the power losses over say 6000rpm are caused by PISTON SKIRT FRICTION because of the long stroke.

Nothing whatsoever to do with torsional vibration which has an absolutely negligible effect on power output.

[Nick Jones]

My understanding is that the torsional damper is to absorb torsional (twisting) resonances put into the crank by the firing pulses. Being long and fairly flexible the the Triumph six cyl are presumably more than typically vulnerable. Especially so the 2.5 with longer stroke and little overlap between big-end and main journals. Whereas the the 2L is still stiff enough to have it's major resonance frequency above rpms used even in racing, the 2.5 does, according to some at least, have a resonance in an rpm area that might be reached even on hard driven road cars (little above 6k I've seen written?).

 

While this resonance might not rob power directly it can still have unwanted effects - premature fatigue failure of the crank being one - and a busted crank can certainly reduce your output......

 

For my purposes I'm happy with the factory offering - though I'd be happier with one a lot less than 40 years old!

 

Nick

[GT]

If you look at the way such (partial balance) cranks are done, you've got one whopping great weight stuck in the middle of the crank, with 2 more balance lobes added in phase each side.

That part of the crank is not going to move.

The alternative like the "door stop" Farndon cranks are "fully balanced" cranks with dummy mains, but weigh even more, and still are weak in torsion.

 

The power take off end has the flywheel which has high mass and inertia.

In my view the main torsional vibration is between the PTO and the centre of the crank.

This propagates along the crank, increasing as loads increase (the sheer weight of the rods and pistons is the cause making high acceleration/deceleration forces).

The front main is the one with very low loads, but it's almost invariably where the crank breaks.

 

If we look at this a little more carefully:-

In cases where and an electric motor has been substituted with the fuel/air supply to drive the crank assembly the frictional load only increased by 10% compared with when the engine was actually running on petrol.**

 

This proves the majority of the excess forces imposed on the crank were coming from friction and windage NOT from the combustion process.

In the case of a long stroke engine, this is caused by the large losses induced by the long stroke.

 

These high loads as I have just shown are not related to combustion pressures.

 

I would strongly argue, more of the vibration is being caused by decceleration forces at BDC than those at TDC connected with combustion pressures by virtue of the above**

 

It therefore holds, the best way to increase the rev limit of such engines and reduce torsional effects is to decrease the mass of the pistons and rods.

It has been proven, the 2.5L crank is perfectly capable of running more reliably than a purpose made EN40B steel crank at up to 8000rpm, if titanium is substituted for steel in the conrods and the pistons reduced in weight.

This substantially reduces the torsional component at the nose, and from the middle to the PTO point.

It is also cheaper.

 

The damper is there only to try to bring some of the torsional component into control (roughness), but in my opinion plays no role whatsoever in prolonging its longevity.

[Triumph-V8]

The problem with the crank distorsion is not the power of each "hit" that is given to the crank

but it is the time between two following hits.

 

The oldest example for that is the bridge that can not be crossed by the army troops

in marching together bringing the bridge to swing.

 

There are three ways to avoid that crank damage:

 

First is to make the crank that stiff that is does not break.

Many cranks do not have or need a damper,

mostly short cranks or short stroke is good for that.

 

Second is to bring the resonant distortion, that every crank has,

into an rev-area that is not reached. That can be achieved by reducing the mass

towards the free distorting end that is at the front.

 

Third is to dampen the distortion that the resonants can not "collect" the hits to one huge wave

that lets the crank fail or hurts the crank.

 

That means if the distortion is just turning the pulley forward and than the first cylinder fires

an additional load is applied distorting the crank a little bit more

and if the crank manages after that stress to swing back

during the next rotation we must avoid that the same situation happens

after two revs when the first fires again.

That would be the bad situation, where the crank collects hits and swings more and more.

 

As we should not avoid firing the cylinders we can only work on the distortion of the crank.

If we add a huge weight at the front the crank it needs more time to swing back and forward again

and than the firing of the first might meet the crank distortion when it swings back

and than would work against the distortion itself.

But easy to see the problem is only shifted to lower revs but not cured.

 

Dampening can be done with the rubber/metall damper that have their mass calculated to suppress

distortion at special revs. The swing of the crank and the swing of the metall beyond the rubber

work together like bad dancers spoiling the dance because they slap together and prevent each other from swing.

That means rubber damper is made only for that specific crank and purpose.

The damper is cheap and reliable and one can see from outside when it falls apart.

 

The other way (and that is what I try out) is to use a viscous damper.

This damper has a metall ring that can rotate free in a sillicon fluid

sourrounded by a tight metal housing.

 

For moving inside forward/backward The ring needs power that is taken from the distortion swing.

The ring is interested in constant rotation speed but its housing is relatively to him moving forwards/backwards.

These dampers are the secure way for home-users to improve crank

because they work at any rev eating up the distortion by friction

of silicon fluid against the walls and the metall ring.

 

Great disadvantage is that the ring is welded in a even bigger ring housing

and you see nothing. If the inner metall ring sticks, the crank will be without dampening.

That might be the reason that you do not find them in racing engines.

 

Anyway I read about the great advantages of the new dampers,

goodparts claims huge power increase

and ATI is also a supplier of these rubber dampeners.

I do not believe in the benefits concerning power increase but believe in increase of reliablibilty

if you rev into an harmonic distortion area what means beyond 5500 rpm.

 

So I decided not to buy an expensive dampener

but also can not leave that chance for power untested.

Right now I have a sillicon damper from an actual Corvette ready

to accept an adaptor for the TR6.

Will report when finished.

[Triumph-V8]

I forgot:

 

It is not that bad if you only cross a critical rev area maybe in the first gears.

The time in the virtual bad area is somewhat collected until failure.

The problems occure when the engine is driven close to a resonant frequency

with constant revs.

 

Hill climb with a longer straight might be such a problem for a TR6.

[GT]

Anyway I read about the great advantages of the new dampers,

goodparts claims huge power increase..............but believe in increase of reliability

if you rev into an harmonic distortion area what means beyond 5500 rpm.

 

As you know I've been driving a TR6 recently 2000 miles in just over a week, and the engine makes peak power at 6300rpm.

Nice reliable power plant, loads of go at the top end.

 

I have to power test it again very soon, but I have no doubt it will survive all that with no difficulty at all.

If Goodparts are claiming something from nothing it's clearly b..ll..x as per usual.

 

Far too much is made of all these "theoretical deficiencies".

Make an engine with really good torque, have it rev to smiths, and forget all this so called "advice".

[Triumph-V8]

Yes, a friend of mine saw you at Stoneleigh on the ground

with the yellow TR with the extended airbox

but you have been so busy that he did not want to disturb.

 

I would like to agree as my old TR6 in the 80s had to suffer also a lot.

It was the time where one could race topspeed without OD on the highway against the 12 cylinder jags

and although they are pretty quick, more than once I could see oil and water

on the windscreen after a short time from a blown jag engine.....

 

Anyway there is a slight chance that there is improvement from a better damper

and the work to check that out is in limits to adapt the

corvette viscous damper.