Crankshaft Dampers

[CP120]

Hi All

While working in the LF wheel well of my car ('53 XK120 DHC) I happened to look at the rear of the crankshaft damper and noticed that a small chunk of the rubber had obviously detached itself. After 60 odd years I suppose I should not be surprised, clearly the rubber has become brittle over time. Checking the usual sources I note that they offer units that are rebuilt and require a core charge. Has any lister actually used the services of companies who rebuild these units such as Damper Doctor and others?

Tadek, sometime back you were looking for a company to rebuild your damper as you wanted to retain the original, did you find someone and if so was it in Europe or did you, as Rob suggested, try the above named company or Winslow Manufacturing?

One thing I read from one of the sources is that the engine would need to be re-balanced after fitting their rebuilt damper. Would this be necessary if one had the original unit rebuilt? I have noticed that there are several drilled areas on my existing unit, clearly balanced at the factory. As a neophyte in this area, if one simply gets a rebuilt unit then how does one then balance the engine?

Any responses from those who have gone through this experience would be appreciated as I plan on removing the damper once the driving season ends.

Regards,

Chris.

[Mike_S (Mike Spoelker)]

That does not even sound right. Jaguar XK crankshafts and rotating assemblies are internally balanced by drilling the crankshaft counterweights, not the damper. The damper on a Jaguar six should have zero influence on the reciprocating and rotating assembly balance.

[Terry_McGrath]

the dampers do have minor holes drilled in them like a brake drum to balance the unit itself?

[Rob_Reilly]

Yes, the damper itself is balanced by drilling little holes.
That’s probably what they meant by rebalancing, not the whole engine.
Damper Doctor was great for me.
I punched three marker holes inline in my inner and outer steel parts, sent them a labeled picture explaining these, and told them to line up the marker holes when they put it together again. They did.

[Roger_Payne]

Jaguar in their day, were very advanced when it came to balancing their engines, albeit the equipment used at that time, seems very primitive by todays standards, albeit produced an excellent end-result given their highly skilled technicians - and that’s what they need to be called, not just unskilled assembly line workers with robots and computerised controls as in todays car factories.

But everything was balanced and matched individually, then balanced again as an assembly.
So both the harmonic-balancer and the flywheel and the clutch-assembly were individually balanced, then the whole assembly of harmonic balancer/ (prebalanced) crankshaft/ flywheel and clutch assembly were balanced as an assembly, the added overall length of coarse impacting on torsional vibration and dynamic-balance.

So any good engine rebuild will do the same.

But if you just replace the harmonic balancer or just the Clutch assembly the best you can do is ensure they are individually balanced as they were originally, and hope that does not compromise the overall crankshaft/engine balance, which indeed would be most improbable. But just bolting on a reconditioned harmonic balancer, without ensuring its individual balance first, will most certainly compromise the overall balance, albeit to what degree is a guess, and chances are not detectible to the average driver unless extremely bad and that’s unlikely.

But having said that - an old harmonic balancer with rock hard/embrittled 60+ year old rubber has stopped doing its job anyway, and is there only for the free ride.

There are many places that can re-rubber old harmonic balancers, and as with all engineering jobs - of greater or less competence/knowledge, but the one thing I do warn is that its best to get your original harmonic balancer reconditioned, rather than seeking a core-exchange. And note, with XKs, there are different Harmonic Balancers, not all the same.

See attached picture of an XK140 C.8241 Harmonic Balancer after reconditioning - look closely and you will see the original balance-holes, and some now extra holes required to rebalance after reconditioning.

Second picture shows substantial difference in an XK140 versus XK140MC Harmonic Balancer - make sure you note correct manufacturers Part Number stamped in, and that’s what you get back - note the relative thicknesses (and thus mass) of the outer mass which is what does the torsional damping!