Rotoflex to swing spring conversion

[johny]

Think theres only one pulley design for all the Triumph sixes - rubber type as in Johns picture except it should be in one piece😊 

[Pete Lewis]

I found the moving outer damper ring on my 1600   way back in 2003ish when we bought the car 

you could turn the outer by hand to get the timing where ever you fancied  Ha ! 

fitted a second hand one to solve the problem 

 

Pete

 

[johny]

Mine feels alright but has the rubber gone hard and my crank is at risk of exploding?

[Ian Foster]

17 hours ago, JohnD said:

I can test your damper, tell you if it's working, even before it loses the timing!

Hi John

I might take you up on that next time I have cause to remove the radiator etc. At the moment I am concentrating more on getting the car ready to use this 'season'.

I did check my timing marks using a dial gauge last time the head was off and there are pretty accurate.

Ian

[Wagger]

5 hours ago, Wagger said:

That was very interesting John. My 2.5 TC engine has a pulley similar to the typr shown. According to the strobe, it was running retarded by 20 degrees. I ignored the marks, checked TDC via plug holes, set the Dizzy, then by ear when running, I;ll take a picture sometime and send yo you so that you can tell me which pulley I have. I suspected that PO's fitted the pulley without a key.

As a sequel to this, I have been turning the engine to adjust rockers etc by pulling on the fan blades. (With some plugs out). I am a little confused now as to whether or not I would notice any 'Spinning'. Is the rubber supposed to even out the loading on the pulley (water pump and alternator) or is it more complex? I believe that the rubber joints used on RWD cars cushion the drive impulses, therefore making all loading more even. (As do dual mass flywheels).

Those containing rubber are a pain and dispensing with them can cause vibration and transmission failure. Again, more sophisticated cars use metal springs instead. Motor cycles have used both options too.

 

[johny]

19 minutes ago, Wagger said:

As a sequel to this, I have been turning the engine to adjust rockers etc by pulling on the fan blades. (With some plugs out). I am a little confused now as to whether or not I would notice any 'Spinning'. Is the rubber supposed to even out the loading on the pulley (water pump and alternator) or is it more complex? I believe that the rubber joints used on RWD cars cushion the drive impulses, therefore making all loading more even. (As do dual mass flywheels).

Those containing rubber are a pain and dispensing with them can cause vibration and transmission failure. Again, more sophisticated cars use metal springs instead. Motor cycles have used both options too.

 

No this isnt to do with the drive the pulley supplies but damping vibrations in the crank itself which presumably if left uncontrolled could lead to its failure....

[Wagger]

So, what would happen if I installed an electric water circulating pump, removed the pulley and disconnected the existing water pump and alternator. If running, say, driving a generator at the clutch end, how does this damper affect the vibrations in a one piece crankshaft. I would understand this more thoroughly if there was a flywheel on each end of the crankshaft with shock absorbers. Symmetry, and all of that.

I've seen rubber dampers on big diesel generators that use 'Ganged' engines. Also know that straight Eights suffer all sorts of crank harmonics.

I am and Electrical Engineer, so understand harmonics and resonance in that field. I need a good Mechanical guy to explain this one. Like RF transmission it is, probably, another 'Black' art. Very interesting though.

[NonMember]

As an electrical engineer, your dealings with resonance and harmonics probably resulted in increased transmission gain at particular frequencies. It wouldn't normally break things...

So, as I understand it, in simplified terms... When no1 cylinder fires, it attempts to accelerate the crankshaft from the front end. At the back end, there's a big flywheel, which resists that acceleration. The result is a torsional force trying to "wind up" the crankshaft. Later in the cycle, this wind-up is released, and the front end falls fractionally behind. Normally, this effect is very small, but at the right RPM it hits the resonant frequency of the crank, and gets amplified. At a minimum, this is unpleasant. In extremis, it could result in stress fracturing of the crank, rather as the Tacoma Narrows Bridge incident. The damper on the pulley is tuned to suppress that resonance by absorbing some of the energy into the rubber.

[Wagger]

33 minutes ago, Wagger said:

So, what would happen if I installed an electric water circulating pump, removed the pulley and disconnected the existing water pump and alternator. If running, say, driving a generator at the clutch end, how does this damper affect the vibrations in a one piece crankshaft. I would understand this more thoroughly if there was a flywheel on each end of the crankshaft with shock absorbers. Symmetry, and all of that.

I've seen rubber dampers on big diesel generators that use 'Ganged' engines. Also know that straight Eights suffer all sorts of crank harmonics.

I am and Electrical Engineer, so understand harmonics and resonance in that field. I need a good Mechanical guy to explain this one. Like RF transmission it is, probably, another 'Black' art. Very interesting though.

Just readit up on Wiki, so, sort of, understand it now. Howev

 

1 minute ago, NonMember said:

As an electrical engineer, your dealings with resonance and harmonics probably resulted in increased transmission gain at particular frequencies. It wouldn't normally break things...

So, as I understand it, in simplified terms... When no1 cylinder fires, it attempts to accelerate the crankshaft from the front end. At the back end, there's a big flywheel, which resists that acceleration. The result is a torsional force trying to "wind up" the crankshaft. Later in the cycle, this wind-up is released, and the front end falls fractionally behind. Normally, this effect is very small, but at the right RPM it hits the resonant frequency of the crank, and gets amplified. At a minimum, this is unpleasant. In extremis, it could result in stress fracturing of the crank, rather as the Tacoma Narrows Bridge incident. The damper on the pulley is tuned to suppress that resonance by absorbing some of the energy into the rubber.

Thanks Rob. I have just read some of the theory on Wiki. Yours is a better summary. I would not expect a Mechanical Engineer to understand transmission line theory in one pass, so I won't try either. It does explain why some motorcycle engines take the drive off the centre of the crank. Resonance will still arrive at the centre though, maybe cancelling out at some frequencies. Bit like transmitters and repeaters spaced half a wavelength apart. (Another reception headache).

[JohnD]

Wagger, 

This is is about torsional vibration in the crankshaft, a twisting motion.    I wrote the dissertation for my degree on this subject and the paper runs to some 90 pages, but I wrote a  three-page summary that was published in TRaction which you might like to read.    I hope that it will help you understand the subject:

 

[Wagger]

Thanks JohnD. I have read about 50% of that I will return to it. There is clearly a wealth of invaluable knowledge on this forum. Very useful information.

The graphs remind me of my time working in an acousitc lab in my twenties observing the resonances of acoustic transducers used in hearing aids. Also when doing work on analogue mixers and multipliers.

I have recently returned to the maths in order to sort out poor reception on BBC radio 4 FM. All caused by being in line between two transmitters, with another at 120 degrees. It's a real b**ger. Move the antenna half a wavelength and all is well, until the air pressure changes.