Harmonic Balancer

[andrea]

My mechanic balanced all engine component and crankcase very well -with a lot of accuracy- when was the point to assemble the damper, tell me -better nothing - five years of car life, and long trips NO problems

 

[John Turney]

My take: Get your damper rebuilt. I've seen what happens when they self-destruct, and it ain't pretty (start with a new or repaired radiator).

The damper, well, damps because there is a layer of rubber between two concentric rotating masses. Rubber is probably the most perishable substance on cars; AFAIK the rebuilders all use silicone (it looks different than original, but I don't know if even the concours judges know or care).

I absolutely agree - it ain't pretty.

 

[John Turney]

My mechanic balanced all engine component and crankcase very well -with a lot of accuracy- when was the point to assemble the damper, tell me -better nothing - five years of car life, and long trips NO problems

Are you saying you or your mechanic didn't install the damper?

 

[andrea]

[QUOTE = John Turney; 1113314] Stai dicendo che tu o il tuo meccanico non avete installato lo smorzatore? [/ QUOTE]
YES
My mechanic are experienced and specialized in racing cars and gearbox rebuild

 

[Healey Nut]

Are you saying you or your mechanic didn't install the damper?

If all the rotating mass is dynamically balanced then you dont need a dampener .
Dynamic balancing takes time and therefore expense , so put on a balancer they are cheap and ship them out .

 

[John Turney]

If all the rotating mass is dynamically balanced then you dont need a dampener .
Dynamic balancing takes time and therefore expense , so put on a balancer they are cheap and ship them out .

My understanding is that the firing of individual cylinders causes a rotational vibration in the crankshaft three times a rotation. If the the vibration occurs at a harmonic frequency, it can cause crankshaft failure due to twisting. On an Austin 6-cylinder engine, the harmonic frequency may be above the redline and not an issue. On a 4-cylinder engine crankshaft failure is a frequent occurrence and is likely an issue.

 

[Bob_Spidell]

My understanding is that the firing of individual cylinders causes a rotational vibration in the crankshaft three times a rotation. If the the vibration occurs at a harmonic frequency, it can cause crankshaft failure due to twisting. On an Austin 6-cylinder engine, the harmonic frequency may be above the redline and not an issue. On a 4-cylinder engine crankshaft failure is a frequent occurrence and is likely an issue.

Excellent technical explanation here:

http://www.netbug.net/blogmichael/2017/01/03/austin-healey-100-crank-failures/

 

[andrea]

i AGREE with Bob- the procedure followed by my mechanic produced a better result that the use of one damper
Damper is a rustic solution to obtain the crankcase balancing -
on oldest engine the balancing of weight and rotation engine was reserved at few engines not certainly to a large mass production engines
on the engine rebuild for a oldest sport cars a right total balancing is essential
On SIX in line engine aren't hard to obtain -
I remember that at the beginning of the engine rebuild my mechanic maniacally observed and measured all the engine dismantled pieces
two con-rod suspected to be bent or torn was rejected, and the two new (used) was lightened to have the same weight to all six- one of it
have more than +130 gr difference !!! (a TAXI engine con rod???)
NOTE :The instruments and machinery (and abilities) for crankcase balancing (especially revolving engine mass)are uncommon on a normal mechanic shop probably can be find in one specialized in works on race car
The real problem are the limited number of "supporti di banco" crankcase holders?? used by GB engineer
on our motor - probably for economical reason -or for block fusion problems-

 

[Novamonte]

The C-series derivative engine used in the MGC had seven main bearings (which I believe is the term Andrea refers to). Maybe one of these can be installed in a Healey offering a better balanced and sturdier design?

 

[andrea]

The term are correct - and also the number of 7 main bearing are the good number for the 6 cylinder engines
If I right remember our six have FIVE - the gap is evident -
a lot of the GB engine of this era have few main bearing supports
I don't know the reasons of this project choice ???
And I don't know if MG C six cylinder engine have also a damper-I doubt

 

[Dandare]

The original C-Series is 4 main bearing. The 7 main C-Series certainly has a crankshaft pulley with damper.

Danny

 

[andrea]

The RADICAL solution are to change our cars with a Porsche 911
http://epi-eng.com/piston_engine_technology/torsional_excitation_from_piston_engines.htm
After two pages-of deep technical considerations, this is the conclusion

One crankshaft manufacturer described torsional absorbers / dampers as "a great hoax", based on two observations he has made in his experience: (1) A crankshaft which has an absorber tuned to the wrong frequency has a very short life expectancy, and (2) Certain aftermarket absorber / damper products installed on a crankshaft pose extreme difficulties in balancing the assembly.It is obvious that modifications to an original engine design which affect crankshaft stiffness and / or system MMOI (stroke, counterweights, bobweight {therefore counterweight} mass, clutch and flywheel MMOI, etc) will change the system resonant frequency. In order to determine the correct solution for a particular engine combination, the engine designer must a) do the measurements to determine the critical frequencies in your application and (b) and design or obtain an absorber tuned for the correct order or frequency, as fits with the application.For any application which operates at high power and a relatively constant speed for long periods (unlike a race engine which typically cycles up and down quite rapidly and only has to live a few hours), it is critical that the major orders of crankshaft torsional vibration be attenuated.Whatever device is used to absorb crankshaft internal torsional vibrations, it has an effect (usually small) on the excitation produced at the loaded end of the crankshaft around resonance. That device, together with the Mass Moment of Inertia of the devices attached to the output flange of the crankshaft, will affect not only the value of the crankshaft resonant frequency, but also will influence the longitudinal location of the torsional node on the crankshaft.

 

[Healey Nut]

Just to get this thread back on track I still have had no answer from damperdudes so they wont be getting business from me .
I was in the shop today working on the engine rebuild and the existing damper looks good when you compare it to Steves pics of his so its going back on the car .

 

[Bob_Spidell]

Just to get this thread back on track I still have had no answer from damperdudes so they wont be getting business from me .
I was in the shop today working on the engine rebuild and the existing damper looks good when you compare it to Steves pics of his so its going back on the car .

Wow. They were responsive when I had mine rebuilt (same story with Rocker Arms Specialists--maybe the heat up there gets to them).

I'm not sure you can judge a balancer by appearance; 50+ years will do a number on rubber.

 

[Bob_Spidell]

The RADICAL solution are to change our cars with a Porsche 911 ...

And deal with IMS bearing failures? No thanks. Ant just replaced one with an upgrade in a recent episode of 'Wheeler Dealers.'

 

[andrea]

And deal with IMS bearing failures? No thanks. Ant just replaced one with an upgrade in a recent episode of 'Wheeler Dealers.'

intended as my ex- 911 2,4 S 1972 Targa, LEFT flap oil tank - the recently water cooled engines aren't worthy of the company name

 

[kozelding]

So rather than perseverate, last weekend I dove in and pulled my harmonic damper out... Sure enough, the outer rim was >1/8" off-center and the two discs were separating.

A shout out to Damper Dudes: I called, and he promised - then delivered - a 1 day(!) turn around on the rebuild. He even apologized for not being able to get the rust-pitted surface smoother.

Anyway, I'm excited to get it back on the car....

 

[Healey Nut]

So rather than perseverate, last weekend I dove in and pulled my harmonic damper out... Sure enough, the outer rim was >1/8" off-center and the two discs were separating.

A shout out to Damper Dudes: I called, and he promised - then delivered - a 1 day(!) turn around on the rebuild. He even apologized for not being able to get the rust-pitted surface smoother.

Anyway, I'm excited to get it back on the car....

Lucky you , I guess they know only how to answer the phone and not emails ?

 

[Bob_Spidell]

Lucky you , I guess they know only how to answer the phone and not emails ?

I've found that to be the case with a lot of small businesses.