Dual Mass Flywheel

[VicParticipant @vic]

I haven’t read this whole thread but I was under the impression that DMF’s were originally only deemed necessary on Diesel engined cars? I then read somewhere that commonality of parts between petrol and diesel suited car manufacturers. Not least because these parts cost more and that’s a good revenue stream?
I actually begged the question of whether my Petrol car had a DMF before I bought it and was told “no, don’t worry it’s just a plain one!” I asked because of the bad stuff I’d read about them. I never heard of ordinary flywheels needing replacement, apart from exceptional circumstances. I was tasked with replacing the ring gear on one though when I was a mechanic years ago.

[Michael Gilligan]

On Michael Gilligan Said:

[…]

[‘though one can never predict what might be found]

 

.[…]

I am not a superstitious man; but I rather regret making that remark

The ‘phone call at about 17:15 yesterday was to inform me that, after working all day, they had not yet separated the gearbox from the engine.

 

I walked down this morning to have a look

Several high-spec bolts hold the two together and a wide range of failure-modes have been demonstrated.

The really bad news was that the least-accessible bolt [which has moved a little, but is now seized] needs its head cutting-off … and the engine will have to be dropped about six inches to give sufficient access to do that.

So … today is scheduled for doing that; repairing the damage done so far; and putting the engine back in place.

Tomorrow is then scheduled for the ‘simple’ job of installing the new clutch and flywheel; and putting various bits back in place.

MichaelG.

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Note: Feel free to add all the “could-a, would-a, should-a” comments if you like.

BMW apparently chose to use bolts sufficiently long to extend beyond the through-holes tapped in Aluminium Alloy … and 20years exposure did the rest.

[Tim StevensParticipant @timstevens64731]

A long time ago I was discussing shakeproof washers with a Landrover engineer, and expressed my view that they don’t work, but they do destroy the flat surfaces on which friction depends. His response was that in his experience, they did work, but only because the gaps in the star washer let the rain and salt in, where it could do its mischief and lock everything together. I wonder if the same idea is in use by BMW?

Cheers – Tim

[Michael GilliganParticipant @michaelgilligan61133]

No idea, Tim … but I do know that one of the fancy bolts failed by shearing the driving head from the integral flange !

[ sorry, I probably don’t have the correct terminology there ]

MichaelG.

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[HillclimberParticipant @hillclimber]

Coming late to this, I used to race a Ford Focus and had some experience with this stuff.

Yes, you’re right to switch the DMF. Although for my application, I quickly swapped in a billet aluminium wheel. Which was not going to explode.

In that car, a straight in/out box swap took two professionals six hours with the car up in the air. Which is one reason why I now race historics, that I can handle myself.

And lock washers are filthy things. I threw them all away and use Schnorrs (see below) or Loctite.

Cheers, Colin

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for the comments, Colin … much appreciated.

I am perfectly happy with the local garage and their advice

… just [more than a little] upset by the state of the car.

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Quite possibly, serviceablity was low, if even present, on the list bof priorites for the new design.

I suspect that Profit, probably on aftermarket parts was top of the list

Often a new product will be sold for a small matgin, in the expectation of greater cash flow from sales of spares.

Not a mindset which gets my approval, but having spent years testing for reliability and durability, I’m biased, as well disliking scrapping anything!

Howard

[Grindstone CowboyParticipant @grindstonecowboy]

An old mechanic friend told me that, to prevent propshaft bolts loosening – this was in the days before Loctite et al – they used to degrease the nuts and bolts thoroughly, then dip them in water just before reassembly. The resulting corrosion did the trick perfectly.

Rob

[Michael Gilligan]

On Michael Gilligan Said:

No idea, Tim … but I do know that one of the fancy bolts failed by shearing the driving head from the integral flange !

[ sorry, I probably don’t have the correct terminology there ]

MichaelG.

.

The problem is that sometimes mechanics use impact wrenches if an air ratchet isn’t man enough. I nearly bought a little 3/8” impact wrench when I was a mechanic.

[Russell EberhardtParticipant @russelleberhardt48058]

Not sure about Lanchester but I used to own a pre war Fraser Nash fitted with a 1936 BMW 326 straight six engine.  That had damper consisting of a friction mounted flywheel mounted at the front of the engine.  Much easier to get at!

Russell

[Andy StopfordParticipant @andystopford50521]

Straight sixes suffer crankshaft torsional vibration at around 4000 rpm so any engine which can reach this speed is fitted with some sort of vibration damper. Bus and truck engines with maximum speeds in the 2000 – 3000 range don’t experience the problem and are not fitted with dampers.

Is this part of the reason Michael’s engine has the DMF?

The LuK paper I linked to above says this:

The DMFW permanently alters the vibration system of the crankshaft. In
the conventional system, the heavy flywheel including the clutch is rigidly
connected with the crankshaft. The large inertia of the flywheel generates
high reaction forces on the crankshaft.
The DMFW system behaves more favorably because the secondary
flywheel mass can be disregarded for the bending load. It is only very
loosely connected via the torsion damper as well as via the roller bearing to
the primary flywheel mass and therefore generates practically no reactions.
The primary flywheel mass is much lighter than a conventional flywheel and
is also elastic, like a flexplate for a torque converter.
Inherent bending and torsion resonance forms change with the DMFW in
comparison to a conventional system. The crankshaft is mostly relieved.

[VicParticipant @vic]

Thanks for that Andy, that’s interesting. 😉

[Andy Stopford]

On Andy Stopford Said:

Straight sixes suffer crankshaft torsional vibration at around 4000 rpm […]

Is this part of the reason Michael’s engine has the DMF?

The LuK paper I linked to above says this:

I found that paper very interesting, thanks Andy

My BM has its torque peak at a little over 3,000 and the red line is a 6,500 so your torsional vibration may well be very relevant.

I did also wonder whether the [very clever] ‘dynamic stability control’ system might be inputting its own vibration from the other end of the drive train in some situations. … It’s almost imperceptible in action, but the car definitely feels different when I switch it off.

Whatever the logic … it all appeared to work beautifully, and I’m just hoping everything will be right when I finally get it back !

MichaelG.

 

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, nothing to do with MichaelG’s DMF, but in my last job, one of the office guy’s had a probe that was screw into a threaded port on part of the exhaust pipe that the catalytic converter was attached too, on his BMW. The probe had become faulty and so needed replacing, however, when in the garage and removing the faulty probe, it sheared off, resulting in the garage saying that he needed a new exhaust pipe as well as a new probe. Well as you may guess, the new exhaust pipe was a real eye-watering amount of money, so this guy brought it into the workshop and asked me if I was able to get the old one out which the garage said wasn’t possible to do. The first thing I said leave it with me and I’ll have a go, but couldn’t guarantee a success, but at least I wouldn’t make matters worse for him. All the while, I believed that I would be able to remove the old probe without any further damage and his new probe would fit in without any problems. It was a bit of a fiddly job, and needed a bit of care and attention, but I did get the old one out without any damage to the threads, and the guy was well chuffed and couldn’t thank me enough.

Regards Nick.

[Michael Gilligan]

On Michael Gilligan Said:

No idea, Tim … but I do know that one of the fancy bolts failed by shearing the driving head from the integral flange !

[ sorry, I probably don’t have the correct terminology there ]

MichaelG.

.

Just re-read this posting and it has left me amazed.

If that is the same type of bolt as the one that failed then (whilst I’m not a metallurgist) I would be interested to know what scenario could separate the male Torx protrusion from its flange, or was it that the Torx just got complete chewed or rounded off?

There is an art or skill required to undo seized fasteners which one would like to think garage mechanics have learned by experience. I think power driven spannering has removed any ‘feel’ from the task with the result that Michael has experienced.

Ian P

[Michael GilliganParticipant @michaelgilligan61133]

I didn’t get the chance to discuss it in detail, Ian

[ the poor bloke was about to start a potentially difficult day’s work ]

I might get the opportunity to gather more facts [and maybe some evidence] when I eventually pick-up the car.

MichaelG.

[Ches Green UKParticipant @chesgreenuk]

On a slightly related subject Kurtis repurposes a well used ‘flex plate’ into something shiny and new….

Making an Adapter Plate for Transmission Dyno – https://www.youtube.com/watch?v=SGoVgQ5Cx2o

The springs are well past their use-by date.

Ches

 

[Howard LewisParticipant @howardlewis46836]

Andy Stopford will be interested to know that 6 and 8 cylinder Diesel engines that do not run to 3,000 rpm ARE fitted with torsional vibration dampers.

The Rolls Royce C range engiens were rated at 2100 rpm maximum, so with vehicle governing would hardly eceed 2350 rpm

The C6 used a Holset 11″ viscous damper, the C8 would use two two 1″, or one 15″

The Gardner 6LW which had 8 main bearings(!) used a friction damper consisting of two cast iron plates calmped to a steel disc on splines on the nose of the crankshaft.

From memory, the Leyland 0600 and 0680 engine used viscous dampers.

The Perkins 6.354 used either a rubber bonded damper, or a viscous damper, (depending upon rating) and in vehicle form the maximum no load speed was 2950 rpm.

The problem is that as the number of cylinders increases so does the crankshaft length, and even more as the number of main bearings increases. The longer carankshaft has a lower natural frequency, and stiffness than a shaft with fewer main bearings.  But the main bearings are needed to increase crankshaft stiffness in planes at right angles to the crankshaft axis.

Consrquently care has to be taken to damp any resonance that might occur within the running range.

An undamped resonance within the running range would easily cause failure. As the resonant speed is approached, the dynamic magnifier causes the ampltude of vibration to increase dramatically. 50 rpm either way and life will be rosy, hit the resonance, and then watch out!

I can think of a number of instances where a resonance within the running range caused rapid total failure.

In one instance it was warned that a particular vehicle driveline configuration would result in excessive torsional vibration, with a node just inside the rear main bearing. The warning was ignored and the carkshaft broke exactly where predicted!

Tuning a system so that any resonance is above or below the running range will ensure survival. Quickly running through the resonance would give acceptable life. But running on the resonance will produce very rapid failure.

Garrett Air Research said that  if the maximum allowed speed for a turbocharger was exceeded, even slightly, it would bring the blade passing frequency close to the resonant frequency of the blade, with a life expectancy measured in seconds.

There was Frazer Nash that used a BMW engine and the valve events of the engine, combined with the induction and exhaust systems poduced a ram effect. It was a difficult car to drive since the torque suddenly and violently increased close to 4,000 rpm.  Probably at 2,000 rpm, the ram effect would be reversed and the engine would be pretty powerless.

Apparently, the 1.5 litre V16 BRM was similar, in that it could spin its wheels at a speed close to the maximum of its rivals.

Unless carefully controlled, it could tear the cluch asunder, although relatively biddable at other speeds.

Howard

[Michael GilliganParticipant @michaelgilligan61133]

I am re-united with my little grey hatchback … and she feels fine so far.

No idea what level of ‘expedient engineering might have been needed to re-fit the bell housing but I have been assured that it is all sound.

Frankly: There is no way that I could have done it myself, and no way that I could have afforded BMW prices to do whatever they thought appropriate [!]

… so “we are where we are”

Unfortunately: The mechanic couldn’t find the remains of the bolt that the driving head snapped-off, but I do have one that simply sheared in the stress-raising area where plain shank meets thread. … I may photograph that surface tomorrow.

He has assured me that no power-driver of any description was used … just the trusty socket set with long extension. [there is not room for anything bulky]

MichaelG.

 

[Howard Lewis]

On Howard Lewis Said:

Andy Stopford will be interested to know that 6 and 8 cylinder Diesel engines that do not run to 3,000 rpm ARE fitted with torsional vibration dampers.

…

I had a feeling when I wrote that, that someone would say otherwise! (thanks for an interesting post, by the way).

I suppose that if they could get away without one, then they went without and saved the expense. Most of the (older) 6s that I’ve had experience of didn’t have dampers, e.g Perkins P6 (interesting that they changed their minds on that for the 6.354), Bedford 27hp and 300, etc. I don’t think the AEC 410 and 470 did, but I might be wrong there.

 

[Michael Gilligan]

On Michael Gilligan Said:

I am re-united with my little grey hatchback … and she feels fine so far.

 

MichaelG.

 

Glad you have the car back which is the main thing.

I cannot confess to having much confidence in garages whether main dealers, highly recommended independents, or  backstreet lock-ups, whilst I have had some good experiences from all of those, it’s only a tiny fraction of mostly bad experiences.

Ian P

[Ches Green UK]

On Ches Green UK Said:

On a slightly related subject Kurtis repurposes a well used ‘flex plate’ into something shiny and new….

.

Nice video, Ches … and a very sensible ‘Make-From’

’though I was surprised to see him just pop it in the 3-Jaw rather than using a 4-jaw and clocking it on the splines.

I salvaged my old ‘Dual Mass’ from the garage and will be contemplating whether it can become something else, in due course.

MichaelG.

[ChrisLHParticipant @chrislh]

Years ago I had a Wolesley 6/80 straight 6, the sort used by the police with a very nice harmonious exhaust note and a bell on front. As a result of, in succesion, a cracked cylinder head and a thrown connecting rod I had occasion to get to know its internals rather well. There was very strong evidence of dire troubles with torsional vibtration problems not in the crank but in the drive to the single overhead camchaft. One of each of the pairs of crossed helical gears driving the vertical drive shaft was spilt and spring loaded to take up backlash and the free end of the camshaft carried a large friction type torsional vibration damper. The latter no doubt fitted in desperation after a series of drive train failures during development.

[Ian P]

On Ian P Said:

On Michael Gilligan Said:

I am re-united with my little grey hatchback … and she feels fine so far.

 

MichaelG.

 

Glad you have the car back which is the main thing.

[…]

Thanks, Ian

MichaelG.

[Ches Green UKParticipant @chesgreenuk]

Michael,

clocking it on the splines

Kurtis seems to be a well trained and capable chap. I’m sure he could figure out a way to adequately ‘clock the splines’, but time is money to him 😉

Ches

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