crankshaft pulley

Why would a crankshaft pulley have a damper?

I have no idea...

In message , Stuffed writes

Ford Zetec engine also has a damper on the crank pulley.

To damp out harmonic vibration? Pretty well all straight sixes have had this for many years - although I'm not sure how much benefit it would have with a four, as the second harmonic occurs at much higher RPM. Balance shafts tend to be the answer with those.

You'll actually find that most manufacturer's class them as torsional vibration dampers. They're designed to absorb the flexing of the crankshaft, so that the auxilliary belt doesn't get shredded (without the damping, the constant accelerating/decellerating of the pulley, especially under load, would quickly shred any belt).

I just can't recall ever seeing one on the straight sixes I used to work on. Admittedly we're going back 20 years now and "Ye Olden Technology" so it's quite possible it wasn't a requirement.

Alot do, in particular the PSA HDi's crank pulley /damper is now regarded as a service item to be changed with the timing belt at 60k making it a

250quid+ job now. :op

Tim..

As does the 1.8 engine in a Mitsubishi Galant. Had to replace the one on my guvs car after the bonding started to give way. £130 for just the pulley alone. Mike.

On a 1990-1991 Mazda MX-5, it means the crankshaft keyway has worn and the pulley is about to fall off (cure: new engine).

I'd check the tightness of the pulley bolt.

Effectively the same thing.

I'd say that gets the prize for the most novel answer of the year...

Do you want me to scan the relevant pages from my college notes, and the various text books, regarding torsional vibration dampers and crankshaft whip/wind-up?

The bit about it causing belt shredding, yes.

I'll go along with you on that, but as far as being designed to not 'quickly shred any belt'. I'm with Dave on that one. The sheer mass of an engine is enough to prohibit the sudden change in speed that could cause a belt to slip, or strain it enough to cause it's premature failure. Mike.

Loctite cure for MX-5

Peter Hill Spamtrap reply domain as per NNTP-Posting-Host in header Can of worms - what every fisherman wants. Can of worms - what every PC owner gets!

On Mon, 26 Jun 2006 14:59:25 +0100, "Mike G" wrote:

The primary and secondary forces act on the whole engine mass suspended on the engine mounts which are rubber springs and dampers. The forcing function is the piston's acceleration up and down the bore. On a 4 cylinder all the primary force is fully balanced at the crank and reacted by the bearing into the crankcase. None of the primary force reaches the engine mounts. The secondary force is 1/4 the primary and can't be balanced in the crank. It can be balanced in the crankcase by balance shafts running at twice engine speed. This was invented by Dr. Lanchester. It's usual to not bother with this on engines under 90mm stroke as the force is lower and doesn't become big enough to be intrusive until crank is at high speed. Also high frequency vibration can be more easily damped by the engine mounts, than vibration at lower frequency.

Torsional vibration just like primary and secondary vibration has a natural frequency. Torsional vibration only acts along the crank and is driven by the torque from the power stroke and torque taken to drive the other cylinders on exhaust, induction and compression strokes.

cyclic torque happens along the crank twice / rev. It winds thecrank up and then it springs back, it overshoots and springs back. Ifthat spring back is just as the next wind up takes place it's additiveand is either at or close to the natural frequency of the crank intorsion. It's only resisted by the spring rate of the main journalsin torsion and the inertia of each crank web. It's nothing at all todo with the whole mass of the engine. At the natural frequency thevibration can grow big enough to snap the crank. On old 3 bearingengines the lack of main journals gave a low natural frequency andcranks would snap at low speed, this limited engine speeds. The useof 5 main bearings on 4 cylinder engines (and 7 bearings on 6'sinstead of 4) made the crank much more rigid in torsion and moved thenatural frequency to a much higher speed. But harmonics at 1/2 or 1/3the frequency of the natural frequency can still build up largevibrations. The harmonic damper's inertia + spring and damping due tothe rubber bond is tuned to damp these vibrations. Even camshafts can suffer from torsional vibration. It means that at some engine speeds the valves at the far end of the cam on a long camshaft (eg 6 or a weak 4) may not be timed correctly as the cam winds up and springs back. Dr. Lanchester devised a torsional loading device to keep cam torsion constant and thus avoid vibration effects. It also removes the cyclic loading on the cam drive caused by torsional loading.

The mathematical technique used to calculate torsional vibration is Guyan Reduction. Section f your starter for 10.

you want a proper course and a tutor then sign up for this.http://www.isvr.soton.ac.uk/COURSES/MSCSVS/Moduledetails/FEVA.htmYou will need a good degree (2.2 hons B.Sc. used to be M.Sc. entryrequirement) with a decent maths content - Mech eng, Elect eng, Civileng, Physics or Maths. But I would just build a 3d model, set up the analysis conditions and let a FEM program do all the hard stuff.

-- Peter Hill Spamtrap reply domain as per NNTP-Posting-Host in header Can of worms - what every fisherman wants. Can of worms - what every PC owner gets!

What Peter said. The front end of the crank can twist several degrees out compared with the flywheel end. Eespecially on the transition from compression to ignition on the front cylinder, when the front of the crank can go from lagging behind the flywheel end, to being several degrees in front of the flywheel, in the space of under quarter of a turn. This sudden acceleration is enough to cause belts to slip, more so with modern multi-v belts, than ye olde v-belts, as the old v-belts had bit more give.

I would scan the books, but I'm currently sitting in a hotel room, and will be attending a course for the next couple of days on the quality* diagnostic kit we've had at work for the past year.

moray

*by quality, they really mean the heap of s*** that we've only ever managed to get to work on one vehicle reliably!

Thanks for all the replies.Some were a bit technical.

Ivor