the wiki item states "even though it technically does not dampen or balance the crankshaft".

whomever wrote this doesn't know what they are talking about. Pull up any engine design engineering textbook or SAE pub and you will see lots of verbiage about torsional vibration in cranks and the need to dampen this torsional vibration to avoid crank failure.

If, as the wiki says, the device neither dampens or balances, then what the hell does it do? whistle Yankee Doodle ?

This remark in wiki is absurd on its face and not credible.

Anyone can write a wiki item. Some are well written by credible authors. Many are not. Wiki does not do a good enough job at vetting their authors.

Wiki does not vet the authors - it is self regulating - YOU can edit it if you feel it needs it

_________________
David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

So would you say that the people who wrote this are using incorrect terminology? If so why would you use it on your side of the arguement?
Also please look at the name of the business.........
BHJ Dynamics Inc
Precision Engineered Harmonic Dampers




It is not a balancer as you are thinking eg wheel tyre where you add or remove weight, it is a balancer of.....vibrations which creates various noises at different pitches that need to be tuned to one level so the noise level is in Harmonious continuity.

1 part 2 different names......points proven on both sides of the arguement, no one person is correct and no one person is incorrect, even though there are many other websites etc that has further information that can be quoted all saying basically the same thing etc and things can be rephrased its not going to make an ounce of difference to the outcome, if there ever was to be an outcome. It will continue to be like a puppy chasing its tail...(or a harmonic balancer, harmonic damper, torsional damper, torsional balancer, damper or balancer).......going around and around and around in circles getting no where fast.

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OK Lets get back to the topic.
From the original posting I belive that the following happened.

A "thingy" on the front of a engine" failed" and a crankshaft broke.

ALL internal combustion engines suffer from torsional vibration. From a single cylinder to a 32cylinder. The vibration varies between engine configeration IE number of cylinders, the bigend configeration of the crank, 2 or 4 stroke[6 insome engines] diesel,petrol fuel, displacement, and so on.

torsional vibration has 2 major componets when doing the calcs on a engine.
1 the design of the engine and the type of fuel used. This influences the MEP [the explosion pressure/force when it fires]. Diesel engines are higher due to the compression ratio.
2 the accerleration and de-celleration of the rotating mass.ie crank.pistons flywheel etc.
As it rotates and the firing sequence/MEP is increased and the force causes the crank to accelerate then de-cellerate. This combined with the fact the crank is rotating[RPM] sets up a "frequency" vibration in the crank and connected componets. With any rotating mass the frorces will at certain RPM create a critical frequency magnitude.[force X magnitude is the harmonics of a vibrating body]
Now the "thingy" absorbs the fluctuations of the crank to reduce the magnitude [force generated] to remove the stress or force applied to the componets.

ALL engines have different critical rpm and if you want to do the calcs on a "A"series the 3 critical RPM ranges are around 3100 , 6300, 9400 rpm.
The one that has the highest magnitude is 6300.

Now with crankshaft failure breakage is due to a stress exceeding the tensile strength of the material. The stress can be either a long term thing IE small force over a period of time, like bending a piece of metal repeatly until it breaks
OR and instantaniously failure, like a componet attached breaking.ie rod,piston, or a" thingy" and suddenly throwing the whole assembly out of balance.

We do not know if the crank broke first or the "thingy" broke first.

Now a couple of questions
1 was the crank shaft crack tested ,stressed relieved and then normalised before installation if it was a used unit. Were all the componets individually balanced before assembly.

2 If the crank was brand new what grade of material was it made from, and was it balanced and check for running true before assembly.

3If the whole assembly was "balanced" what maximum rpm was balanced to and what were the original "out of balance" readings before and after.

I would be interested in seeing a picture of the "thingy" after it failed and where the crank broke and as I asked before what the other engineers you have spoken to what their ideas for the failure were.

I have conducted many investigations into to engine/ componet failure over the years and have found in many cases that "other causes" apart from the original item failure have contributed to the breakage.

PS If anyone is interested in looking at the formulas and calcs to work things out for this topic and stuff like piston acc/deccl. [angular to linear motion] flywheel stess, air velocity/flow/pressure etc, etc I am happy to scan from my old text books and post them.[If I can work out how to scan/post ]

_________________
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WOW, just back from a holiday and all this has appeared!!

On-topic, I went for a tour through the ROMAC factory before the bloke who started and owned the company sold up. Production is now by a competitor and has moved from Brisbane to SA I believe. I don't know if the product has been changed since the buy-out.

Being nosey, I spent a lot of time asking the owner how the designs came about, how he sized the various parts and how he measured the results, plus many more questions. I was there for literally hours learning all about the place, the dampers, timing chain sets, timing belt sets and his drag car. Here are some answers:

Q: How did the designs of crank dampers come about?
A: The designer was a tool-maker/machinist with an interest in drag racing. He had huge trouble with spark scatter on race engines and noticed that fitting a better damper reduced this and gave more power (he quoted 40 Hp on an old v8 ). He was obviously talented and came up with his various designs over the years. The race ones are the best because the outer ring doesn't drive any accessories. It just does it's thing.

Q: How are they made?
A: All fully machied from billet in CNC machines. No forgings and no castings. The inner and outer parts are knurled and press-fit together with a strap of rubber in between. Then a circlip is inserted to keep them together. Then they are balanced on a digital balancing machine. Various additional elements are incorporated, anodising of alloy bits, laser engraving etc.

Q: How are they sized for various engines?
A: Basically they aren't. All have the same rubber thickness and width. There are just two diameters for road versions. The biggest that will fit is selected. There is no calculation of harmonics, the need to form a two-mass spring/damper system. No calculation of the damping required or rubber hysteresis. The only calculation is the counterbalance required for certain v8 engines. (see some are "balancers"). In-summary, there is no engineering design in these at all. I bet someone from Illmore, Renault or Cosworth would really chuckle at the way they are sized. Maybe they are hugely over-designed. They certainly are heavy. I asked how much different the performance of the allow-outered to steel-outered ones was and the response was no difference.

Q: Why are they better than the competition?
A: The designer showed me the competitor's products. Some have circlips that aren't balanced and can walk around the damper making it go out of balance. Some have poor circlip grooves so they can crack and fail. Some have bonded-in rubber and the outer and inner halves are not concentric. Many aren't USA drag racing (I forget the organisation) approved which means they may explode at high revs.

Q: How do you know they are working better than another one??
A: Engine dyno testing and looking for spark scatter and cam follower bounce that occurs when the crank is really twisting. This was not routine when I was there. I gathered it had all been done in the 80's and 90's and no more was planned. One visual way of checking this is to use a timing light to see how much the timing marks dance around. He also listeded to drag racing team feedback. They always looked at units returned for new rubber to be re-inserted.

From what I saw, the only way one of the ROMAC dampers should fail would be if there was a very strong torsional excitation that generates enough heat in the rubber (as it damps due to hysteresis) that the rubber overheats and the outer slips or the rubber is destroyed. Any other failure really would be mis-use like machining the unit to accept accessory belt drive rings, damage during fittment, incorrect installation with mounting face or keyway damage. The other one may be trying to balance the unit with a balancing machine that isn't calibrated.

I hope this helps the OP with the question.

M

From what I pick out of the Q and A above (and very interesting reading it is thank you Mokesta), Romac seem to treat the "harmonics" to be dampened as rotational speed oscillations. It makes sense to me because of the need to prevent timing scatter which in my mind would be caused by the sudden acceleration and deceleration of the crankshaft as it rotates through the stages of load. A similar issue is noticed in electric motors, and the use of dampener windings is used to prevent the oscillation about the synchronous (operating) speed.

I lost ya's all a little while back, but was interested in the geometry of the vibrations these things are supposed to absorb... are they along the axis, across the axis or in the direction of roatation?

_________________
SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

At long last.....Thank you, Mokesta !!!

Some of your findings are the same or similar to what I have found in my conversations with damper manufacturers/engineers/vendors or in my readings of their technical papers.

I especially liked, and can relate to, this Q/A you listed:

Q: How are they sized for various engines?
A: Basically they aren't. All have the same rubber thickness and width.
In-summary, there is no engineering design in these at all. I bet someone from Illmore, Renault or Cosworth would really chuckle at the way they are sized.

I won't say that this is true of all damper manufacturers and sellers, but I have heard this often enough to make me wonder just how many dampers are doing something beneficial.

As I saw mentioned in one of the websites/papers, the equipment and tests needed to assess damper performance are both very expensive. I have heard the same thing from a friend who has access to some of the equipment that can be used to evaluate damper performance. He has tested several dampers, including some for the A-series. He found at least one damper to be completely ineffective at damping crank torsional vibrations.

In particular, since the market for A-series crank dampers is relatively small, it's hard to see many folks conducting these tests for the A-series dampers. Thus, the answers provided by Mokesta, above, are the same answers that I came to after asking several engineering firms' knowledge leaders, point-blank, these questions: 1) how are the dampers designed and 2) how are they sized for an application?

When I also asked just how they could tell if a given damper was doing anything to improve engine performance or longevity, the replies were less than satisfying.

Mokesta has disclosed some very important findings regarding dampers. I hope this will cause people to be more discriminating in their damper purchases. Once again, it's caveat emptor.

so where is the mans medal

I could tell you where it is... but then he'd tell me to grow up again

All jokes aside, it's good the thread got cleaned up and some clarity/light has been been shed on the subject and people are getting their answers ...it's an interesting read without all the BS.

Now I know it's not an A Series, but it is a 1.3 four cylinder for the sake of this discussion.

The Suzuki G13b as found in the Mk1 Gti had no harmonic damper, just a plain crank pulley.
In the Mk 2 & 3 Gti Suzuki had added a HB, however the consensus is that it was done primarily to reduce the NVH levels that customers found unacceptable in the Mk 1.

Even 25 years down the track, Mk1s do not have a higher crank failure rate than the Mk2/3, not do those with aftermarket alloy underdrive pulleys fitted instead of HBs.

Disclaimer These engines have a high quality 5 bolt crank which are renound for their toughness (unlike the A Series).

_________________
Too many cars, and too little time.

Out of curiosity 850's never even had a harmonic/torsional damper/balancer did they? Pretty sure I've got a block in the shed with just a steel pulley... in similar vein to awdmokes example, is there any comparisons of A series engines with no dampers vs dampers?

I DID have a Womac and Womac failure once. The cassingle got stuck in the tape deck, oh the 'teardrops'

MICK, The answer to your question on the way the crank deflects is
How long is a piece of string.
I will try to explain in simple terms as it is a very complex thing.
Basically the crankshaft twists every time a cylinder fires. The twist is from the crankpin of the firing cylinder either direction along the crank.
At the same time the crank also bends from the force of the cylinder firing.
As each bending moment occurs there is a reflex return motion. It's like a spring that is compressed and released, it returns to it's original position. sometimes the bending force is too great and the crank will not return to it's original position.
So think about the amount of twisting and bending that occurs when a engine is running at 6000 rpm.
The problem with any engine is that due to the rotating mass and firing pressure any engine due to it's construction will have certain rpm where all these forces combined create a critical stress.
It's like a car wheel that is out of balance. as you drive along and increase speed the wheel wobbles then when the speed goes above that point it stops.
On big marine engines they have either a optical or electric sensors set-up inside the engine. These accruately measure the crankshaft "twisting" and give a read out. The maximum load force is calibrated and the computer control will automatically reduce fuel to individual cylinders until it settles down or changes RPM.
Another thing that creates harmonics in the engine is the valve gear. IE the springs . This is transmitted thru the engine aswell.

In regards to 850's not having a "balancer" they were only designed to a max of 5500 rpm and had a shorter stroke crank and some little granny puttering around. The torsional was not a big problem, this only occured when the engines had longer stroke , higher MEP and were reved more.

Bottom line is the condition and balancing the internal componets. A balancer will help to a certain degree but will not help a stressed crank that has had a hard life from breaking

_________________
Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com

and you admit that in public

I spoke to a tech person at ROMAC yesterday afternoon and the info he gave me was basically the same as Mokesta has stated.

So in the broken engine what is the assesment of the damage?
Where did the crank break
did the balancer/damper recieve an impact etc?
was the flywheel loose or did the flywheel bolt come loose?
Did a bigend, main or thrust bearing fail?
Any idea of the condition of the timing gears and the chain?
When did the failure occur ?(eg load conditions etc, like a "snap shot" you can get with problems in a modern car from the ECU, PCM what ever the manufacturer calls it)

_________________
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