Dual Mass Flywheel

[Michael GilliganParticipant @michaelgilligan61133]

Fully understand that, Ches … I merely expressed surprise, not contempt.

MichaelG.

[Howard Lewis]

On Howard Lewis Said:

 

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.

It was an “interesting” car to drive anyway.  The solid rear axle (no differential) gave a very lively back end!

Russell

[Ches Green UKParticipant @chesgreenuk]

Michael,

I merely expressed surprise, not contempt.

Got it.

I wonder if it is a forged part, so perhaps has no sufficiently clockable surfaces?

Also, by the time it is properly seated in to the chuck (3 or 4 jaw) there may be no access to a properly round surface?

Ches

[Michael GilliganParticipant @michaelgilligan61133]

Just to clarify my thinking, Ches

The unit had been bought secondhand, with the specific intention of re-using the female splines … presumably saving $$$ in the process.

I have no idea how commonly these are available, or at what price.

Also, I do not have his workshop or his accumulated experience !

Being ‘risk averse’ in such situations … I would have focused my attention on the splines and tried to ensure the best concentricity possible.

Using a four-jaw; a simple stub-mandrel might have helped … or, as I commented, clocking the splines … but relying on a three-jaw for concentricity was a surprise.

I suspect that he actually knew significantly more about the unit than is shown in the video [the dismantling looked very easy!],  and had probably pre-checked the concentricity.

MichaelG.

 

[Ches Green UKParticipant @chesgreenuk]

OK Michael,

Thanks for the explanation.

Yes, Kurtis probably did a thorough assessment before he took the work on.

Not trying to drift the thread away from it’s OP (….threads tend to have closed loop control anyway 😉 ) but Kurtis and Karen are a good YT team…Kurtis produces the Content and Karen films and edits it.

Sometimes I feel she gets a bit danger-close to the action but that is probably just the camera getting ‘in there’ or use of a zoom. And I don’t think Kurtis would endanger her.

Have a good weekend.

Ches

[Michael GilliganParticipant @michaelgilligan61133]

Returning to the BMW

Here are a couple of quick snapshots of a sheared bolt:

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… That end view probably ‘speaks volumes’ to those fluent in  the language.

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These are nominally M12 bolts and I measured the plain shank as 11.88mm

All of the locking effect seems attributable to corrosion within and/or beyond the tapped hole.

? spoiling the ship for a ha’porth of tar Duralac ?

Yes, I know … they couldn’t produce mass-market cars with that much attention to detail.

MichaelG.

[Vic]

On Vic Said:

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?…

More to do with how much an engine vibrates than petrol vs diesel, though it’s true diesels were historically rougher than petrol engines.  Mine used to thump down the road because it had loads of torque at low rpm, and was noisy until it got to about 2000rpm.

DMFs aren’t new.  Early engines rattled badly and vibration made them very unreliable by modern standards.  Although static balancing of crankshafts is easy enough to calculate, dynamic balancing is far harder because the load varies with speed, road conditions, which piston is firing, what the mix is, and how the timing is set.   Early devices were trialled experimentally to get reasonable performance, but suck it and see engineering takes several years to reveal a problem.   Motor engineers have taken decades to refine engine design and still get it wrong occasionally.

DMFs take a pounding because they exist to absorb vibrations that would otherwise crack the crankshaft, strip gears, break drive-shafts, cause piston slap, and Brinnell all the bearings.   Not surprising DMFs wear out, but in doing so they protect the rest of the car.  I wouldn’t replace a DMF with a solid flywheel as a way of reducing maintenance cost because it’s liable to damage the rest of the vehicle – if that matters.    Sporty types have a good reason for going solid – better performance!  Not a free-lunch though – performance cars are high maintenance, and their owners have to be ready to cough up.

The type and age of engine matters too.  Older 6 and 8 cylinder engines are naturally better balanced and are simplistically managed – naturally low vibration.  Modern cars aren’t simple.  One might be fitted with a 3 or even 2 cylinder engine, and removing the DMF from  is asking for trouble.   More, modern engines are likely to be continually performance, economy and emissions optimised by a sophisticated engine management unit.  For example, an EMU might run the engine at maximum compression for a given load, achieving this by continually listening for knock and backing off slightly.  Replacing the DMF could confuse an EMU; maybe it’s pre-programmed to avoid resonances,  the frequency of which depends on the DMF.

(Entirely possible to deliberately destroy an engine by programming the EMU to do bad things.  Maybe running it very hot with a lean mix and the fan disabled at a speed that resonates the crank-shaft, whilst not displaying any sensor warnings on the instrument panel.  The driver finds out when the engine seizes…)

Modern DMFs should be better than older types because computers can do the enormous number of calculations needed to optimise dynamic design.  Unfortunately I fear the optimisation is more likely to favour the interests of makers than owners.  All the maker wants is a car that’s trouble free for about 100,000 miles or 15 years, after which most customers are trained to replace it.  Planned obsolescence, boo, hiss!   Many people are keen to get their sticky paws on our money…

Dave

 

[Michael GilliganParticipant @michaelgilligan61133]

This is a little difficult to interpret, but I am posting it anyway:

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The black ‘tube’ and the striped fabric are the thumb and palm of the mechanic’s left glove

The smaller “male torx head” is one of several locating screws

Towards the top is one of the heavier M12 fixings … and there is another, higher-up on the bell-housing !!

Hence the need to drop the engine by about 6”

The hairy stuff to the left of the picture is on the inside of the tunnel

I am very glad I didn’t try to do this job on my driveway !

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Maybe the bolts failed in torsion caused by an overload trying to break koose threads that had corroded?

Going back to torsional dampers, they become more necessary as the rating increases.

The P6 was relatively low rated compared to the 6.354, and the Aeroflow combustion system gave lower rates of pressure rise (Compare the sound of a P6 with that of a direct injection 6.354. If you want an engine with a high rate of prssure rise, find a Ford 220 in^3 D4 , 330 in^3 D6, or the 360 in^3 Dorset engine!)

The Rolls Royce C6T and C8T developed 50 bhp/litre so the firing pressures were quite high, especially given the knowledge of combustion processes available in the late 50s. It was only in the early 60s that they developed means of taking cylinder pressure diagrams at high speed (Far too fast for a Dobbies MciInnes indicator to be used)

Even fitting a damper has to be carefully done, since the added inertia will reduce the natural frequency of the system with the risk of bringing resonances within the running range.

I’ve seen a very sensitive governor trying to govern out torsionals, and causing wear in the process!

Howard

[Howard Lewis]

On Howard Lewis Said:

Maybe the bolts failed in torsion caused by an overload trying to break koose threads that had corroded?

[…]

.

Exactly my thoughts, Howard

…

All of the locking effect seems attributable to corrosion within and/or beyond the tapped hole.

? spoiling the ship for a ha’porth of tar Duralac ?

…

Ref. https://www.model-engineer.co.uk/forums/topic/dual-mass-flywheel/page/3/#post-713504

 

MichaelG.

[old martParticipant @oldmart]

My old Fiat Panda Multijet 54 plate 1.3 diesel 70hp had a solid flywheel, but that engine has been used in several different makes of car, including Suzuki and Vauxhall, with versions up to 99hp and some have dual mass flywheels.

[Robert Atkinson 2Participant @robertatkinson2]

The multijet may have had a solid flywheel but it had a torsional vibration damper at the other end of the crank. built into the aux bet pulley.

Robert.

[noel shelleyParticipant @noelshelley55608]

As Robert has said, many engines use the front pulley as a torsional damper. It’s a good idea to scribe a line across the 2 halfs so that any movement can be seen – before it all falls apart. On vehicles with a normal rear axle/drive made to work hard a thin paint line was run down the half shaft, if the line was not straight then the half shaft was winding up – time for a new one ! Noel.

[Speedy Builder5Participant @speedybuilder5]

That link explains the advantages viz:- Increaces fuel consumption …..  That sounds like a benefit?

[Author]

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