Harmonic balancer on it's way out?

[GazCaff]

Well, it's not really a question, I'm pretty sure the harmonic balancer is on it's way out (I'm sure the rubber shouldn't be bulging like that!)

So it's a matter of needing it changed, I've fired a PM to IBW for a price for the job, but I'm just wondering how much longer it will last? The main thing is will it last the 35 miles to Kirkham?

 

[Dieselman]

It will last that long but is well on the way to being dead.

 

[GazCaff]

Well, it's got to get me about 5 miles or so tomorrow as well. It's a good job I happened to have the bonnet up while the engine was running or I might not have noticed it until it was too late!

 

[welland99]

What does a harmonic balancer do exactly? Where abouts is it?

 

[Number_Cruncher]

It is a rotational "tuned mass absorber", which in practice means that it is a heavy steel ring joined to the crank by a rubber layer. It fits on the nose of the crank, and typically also acts as the poly V belt pulley.

The heavy steel ring and rubber layer together form a resonant system, whose natural frequency is tuned to absorb vibration at one of the cranks torsional natural frequencies (the crank has a number of torsional natural frequencies which are operational speeds where the crank is "weak" and suscetible to vibration levels building).

This device absorbs torsional vibrations of the crank which would otherwise build and produce levels of stress in the crank which could cause cankshaft failure.

 

[trapperjohn]

Wow. Now that is one concise answer. GazCaff - Hope you make it to IBW.

 

[grober]

It is a rotational "tuned mass absorber", which in practice means that it is a heavy steel ring joined to the crank by a rubber layer. It fits on the nose of the crank, and typically also acts as the poly V belt pulley.

The heavy steel ring and rubber layer together form a resonant system, whose natural frequency is tuned to absorb vibration at one of the cranks torsional natural frequencies (the crank has a number of torsional natural frequencies which are operational speeds where the crank is "weak" and suscetible to vibration levels building).

This device absorbs torsional vibrations of the crank which would otherwise build and produce levels of stress in the crank which could cause cankshaft failure.

ITEM 23 here http://www.detali.ru/cat/oem_mb2.as...GA=722.607&CT=M&cat=19Y&SID=03&SGR=015&SGN=01

 

[welland99]

So maybe the question should not be " how much longer will the harmonic balancer last", but " how much longer will the crank shaft last"?

 

[GazCaff]

So maybe the question should not be " how much longer will the harmonic balancer last", but " how much longer will the crank shaft last"?

I think it would take someone with a total lack of mechanical sympathy (not to mention strong arms and a good supply of spare batteries) to continue driving their car with a failed harmonic balancer until Crankshaft failure occured!!

 

[welland99]

i think it would take someone with a total lack of mechanical sympathy (not to mention strong arms and a good supply of spare batteries) to continue driving their car with a failed harmonic balancer until crankshaft failure occured!!

lol:d

 

[Dieselman]

This device absorbs torsional vibrations of the crank which would otherwise build and produce levels of stress in the crank which could cause cankshaft failure.

Is this more of an issue because this engine is a V6 but at a 90 degree angle so has natural imbalance, or simply because cranks are weaker than they used to be.

 

[Number_Cruncher]

It's a fatigue issue, and is much worse for longer cranks like those in straight six engines - so, yes, if the vibration absorber is damaged, you're probably doing damage to the crank, but it won't snap until some considerable further use.

The other good thing they do is to reduce the amount of torsional vibration at the crank nose, which means less torsional oscillation in the timing drive and camshafts / injector pump.

The other place on the crank where torsional oscillations are very small is just ahead of the flywheel, which is one reason why some VW engines take their timing drive from that end of the crank (leaving an awful maintenance task to replace them - especially if the toothed wheel is worn). Large MB diesels in trucks also tend to take their timing drive from the rear of the crank, but, these are more usually gear drives rather than chains.

 

[stevesey]

So maybe the question should not be " how much longer will the harmonic balancer last", but " how much longer will the crank shaft last"?

Anecdotal evidence suggests the balancer will fail long before the crank in this case. The balancer is a known issue with V6s (more so in the states - prossibly due to warmer climate) and when it let's go the outer ring is likely to take out the sump, radiator etc. Crank failure on the other hand is not an issue we hear about.

A while since I had a close look at mine - thanks Gaz for the reminder.

 

[BlackC55]

BTW the main nut is VERY tight. You need a special tool to hold the pulley in place.

 

[stevesey]

BTW the main nut is VERY tight. You need a special tool to hold the pulley in place.

Thanks - I was just wondering how it came off in situ - having stripped a couple of engines down over the years it's always been the case of a block of wood between the crank and the block and they figuring out how to stop the whole block rotating on the garage floor.

 

[vijilants]

Older mercs used to have a small cover at the flywheel end, you remove the cover, insert a special tool that locks into the flywheel ring gear and that would stop the engine from turning so that you could get the nut off.

 

[andy27168]

Hi,
This issue is also common on the 430/43 and 55 V8 motors too, when I bought mine, the mechanic (mate) who checked it out for me would,nt even let me drive it away from his workshop till he had changed it, when the engine was running you could see the pulley very badly running out of true.
IIRC the car could of had one of two pulleys fitted one of which was just over £50 the other in the region of £200, luckily for me mine was the cheaper one.

 

[johnsco]

My understanding is that straight-6 engines are naturally-balanced, whereas V-6 engines are not naturally-balanced.
In practice, quality manufacturers fit vibration dampers to most larger engines, as vibrations can occur at the fundamental frequency and at higher harmonics for a number of reasons.

Deterioration of the vibration damper is unlikely to lead to early failure of the crank-shaft, as fatigue is caused by the cyclic stress and is a longer-term problem.
The more immediate problem is the damage that can be caused to the engine front-cover of other local components if the rubber sleeve fails and the vibration damper comes apart while the engine is running.

Fortunately, these things usually tend to fail slowly.
Best to check them regularly though.
They are a known problem on some MB engines.

Johnsco

 

[Number_Cruncher]

>>My understanding is that straight-6 engines are naturally-balanced, whereas V-6 engines are not naturally-balanced.

Yes, that's quite true, but this type of balance is not related to torsional vibration of the crank in any way. If you imagine the crankpin of, say, the front cylinder of a straight six engine relative to the flywheel, owing to the flexibility of the long crank, during the compression stroke, the crankpin will lag the flywheel, and during the power stroke, the crank will twist the other way, and lead the flywheel. Obviously, the angles are truly tiny, but, the stresses associated with this motion cause fatigue failures, with the cracks typically beginning from the corners where bearings meet the webs of the crank.

Modern cranks are much stronger than they used to be - cranks snapping on 3 bearing 4 cylinder engines was quite common, especially on cars like Vausxhall Vivas.

Yes, I fully agree, crankshaft failures aren't seen in practice. But, they might be if people did away with these absorbers, or if they welded the two parts of the assembly together to effect a bodge repair.

 

[johnsco]

Interesting that you mention it NC, but my work involves (from time to time) the inspection of crank-shafts, with particular attention being paid to the radiused corners where the crank-pin journals meet the webs.
I tend to do more cranks for high-pressure pumps rather than vehicle components - although the same principles apply.

Even more interesting is that around 30 years ago I was teaching my mate to drive in a Vauxhall Viva, when he came off the clutch too fast and BANG went the crank shaft at the corner of the No 1 crank-pin (Usual place).
That was a hell of a driving lesson ... How to wreck your engine in one easy lesson.
Lesson No 2 ... Don't buy a Vauxhall Viva !!

Johnsco