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JohnD

Triumph Crank Damper Pulley Survey

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Ah ha, you're speaking of JC & Guy with the 1500 estate.  We followed them for quite a bit of the last part of the last 10CR.  It goes very well.......

I've broken a 1300 small crank crank.  Between #1 BE and the front main.  That used to get revved to Smiths - it just never gave up, until it did, 20k hard miles after it was built. No other damage though.

This one I didn't break but discovered in an engine I bought. 

P1050943s.jpg

broke from a badly machined fillet radius by the looks of it

P1050942s.jpg

was an "ES" stamped factory replacement engine with crank ground -0.010

Actually it came free with another 2.5 I bought, described as unknown.  The other one was meant to be "good".  To be fair it did run and even gave good oil pressure when cold (I ran it on the garage floor, there is a vid somewhere) but having gone to the trouble of fitting it to the car it had very low oil pressure once hot and made rather scary noises.  Turned out to have non-matching main bearing caps and shims made from a coke can to make them "work".  Not my best shopping day that.  The block was good on this one though.

Nick

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Peter,

Those TR4 fan bolt holes are in line with the fanblades, so only two positions it will fit on the hub, and they all look the same, so no less.

How does the firing order affect any damping the fan might provide?  The drag from all four blades is constant, whatever the angle at whihc an firing impulse arrives.

And interesting stories from roulli and Nock - I'm taking notes, I promise.

John

Edited by JohnD

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John, I was thinking that the blades offer an elastic element to the crank nose, the crank torsional vibrations being 'buffered' by the drag. Transiently the drag wont be constant. A bit like the fluid filled torsional vibration dampers. But I take your point, the angles should not matter.

Peter

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This arrived in the post today, hot from ‘a friend in america’

a new, balanced and timing-marked Crank Damper !

once its fitted i’ll donate my old ‘slipped a bit’ damper to the ‘John’s Experimental Labs’......

steve

71E2E183-C876-44AA-9D28-51DA77E0BBE9.jpeg

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That pic reminds me......

While the 2.5 damper design means that the damping material also has to transmit torque from the  crank to the pulley (and thus on to water pump, alternator PAS pump etc), on the 2L ones the pulley is part of the centre and the outer ring is just a dumb weight.  Suspect the 2L ones last better......

Nick

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37 minutes ago, Nick Jones said:

That pic reminds me......

While the 2.5 damper design means that the damping material also has to transmit torque from the  crank to the pulley (and thus on to water pump, alternator PAS pump etc), on the 2L ones the pulley is part of the centre and the outer ring is just a dumb weight.  Suspect the 2L ones last better......

Nick

I suspect the 2.5 arrangement is using the load from the alternator/water pump as damping?

my old pulley looks quite ‘tired’ but then it is 44 years old :-)

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49 minutes ago, Nick Jones said:

That pic reminds me......

While the 2.5 damper design means that the damping material also has to transmit torque from the  crank to the pulley (and thus on to water pump, alternator PAS pump etc), on the 2L ones the pulley is part of the centre and the outer ring is just a dumb weight.  Suspect the 2L ones last better......

Nick

Yes looking at that you realise that there is a lot more weight outside of the rubber on the 2.5 pulley than there is on the 2ltr, so even without the load of the water pump and alternator (and alternators can exert quite a lot of load with a low battery) there is a lot more torque being applied to the 2.5 rubber ring.

Makes one wonder when/if they discovered that the 2.5 needed a different weight on the damper, given that the 2L came first. Also wonder if some people may have put a 2.5 crank in and kept the 2L damper without realising the possible consequences.

The rubber in my now 50 year old 2L pulley looks surprisingly good.

Alan

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15 hours ago, Nick Jones said:

That pic reminds me......

While the 2.5 damper design means that the damping material also has to transmit torque from the  crank to the pulley (and thus on to water pump, alternator PAS pump etc), on the 2L ones the pulley is part of the centre and the outer ring is just a dumb weight.  Suspect the 2L ones last better......

Nick

I've learnt from elsewhere, thanks to this project, that people who have run a supercharger off the pulley have had to go with solid pulleys, they say without ill-effect.  The drag (?torque) of the 'charger' rips the damper apart.     A 'charger' won't affect the vibrations, or only by putting more impulses through the journals, but maybe a supercharged T6 doesn't need to go up the dangerous revs?

One for Peter C, of https://supertrarged.wordpress.com/ fame.

John

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2 hours ago, JohnD said:

I've learnt from elsewhere, thanks to this project, that people who have run a supercharger off the pulley have had to go with solid pulleys, they say without ill-effect.  The drag (?torque) of the 'charger' rips the damper apart.     A 'charger' won't affect the vibrations, or only by putting more impulses through the journals, but maybe a supercharged T6 doesn't need to go up the dangerous revs?

One for Peter C, of https://supertrarged.wordpress.com/ fame.

John

John, 

Indeed I hardly ever go over 4000 rpm or so, drive the torque like a diesel.  The blower has two three lobed solid ali rotors about 8 inches long, 3 diameter . So it will offer considerable resistance to the belt tension fluctations induced by the crank, more  than water pump or alternator. So the belt's elastcity could perhaps act as tv crank damper . The boost will increase the torsional amplitude of the crank, but as I keep to low rpm  the crtical frequencies exciting the crank should be avoided. And when the blower is delivering boost of say 9psi the resistsnce seen by the belt will be greater as the belt will be under greater tension.

IIRC the mass of the flywheel/clutch affects the amplitude of the vibrations, or maybe the critical frequencies ? Does a lighter flywheel help to eliminate the vibrations ? or make them worse?

Peter

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Well, as you know, the natural frequency of a spring and mass is

Fn = (1/2Pi) x SQR(k/m)

where k=spring stiffness and m=mass

So the larger the mass the lower the frequency, and vice versa, but this is a very complex spring!  With masses all over it!

I've got some other work to do before I can get down to the crank calculations!

JOhn

 

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On 25/01/2018 at 3:15 PM, PeterC said:

John,

You deserve a degree just for tacking the question......waterfall plots etc.  Am looking forward to seeing the finished project on here!

I think the first  harmonic resonance on 6 pot cranks is at 5000rpm.....................well above my comfort zone.

Peter

And also the first harmonic is the biggest, all other things being equal...

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Update from me, my TR6’s damper os off!

ive posted more details in ‘another place’ but suffice to say an easy job this afternoon to remove the damper.

the timing marks from my new damper courtesy of Tom do not lign up with the old ones, but i wont know for sure whether the old damper had slipped untill i install and do a tdc measurement.

so, soon i’ll be able to donate a ‘well used’ damper for John to experiment on !

 

steve

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Sunny again today so took a few hours off to fit the new damper, no need for a diaper change as it all went smoothley !

the new damper fitted like a glove, i thought it might need tapping on but it slid on beautifully.

back in with the steering rack, cross tube, radiator and the car fired up just as before, which of course it should as i hadnt changed anything!

next i’ll check the new damper’s timing marks against true tdc, and set up the 123tune+ correctly.

’whilst down there’ i fitted new bushes, poly, to the arb...... which turns out to be 7/8” so back to Moss for the correct set.....nice run in the Alpina

once all is settled i’m thinking a rolling road setup for the 123tune+ to get the best out of it, And get some numbers :-)

steve

 

76377CD1-16BE-4C16-BF59-E7BF054B2A3E.jpeg

55761434-E03C-4350-AB35-642F29A16478.jpeg

37EA40EA-95E4-497D-AE4F-182A5538A132.jpeg

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Steve,

your new damper appears to be plain metal, I can't see any rubber.

Who's actually manufactured the new damper?

Patrick

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Just spent 30 mins checking tdc, and the timing marks line up perfectly!

car is now basically ready for a rolling road session and then perhaps a trackday or two :-)

ive done trackdays on motorbikes, and with Prosche, but never in an old sports car

Brands Hatch is nearish and i know the track well, so might look for something there in the spring

steve

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Here's one for you John

What is reported as being a Triumph Spitfire pulley but from picture incorporates a harmonic rubber, and I though the 4 cylinders never used them?

ebay item 222855898630

Alan

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I'll ask him if he's sure.   The hub on that has a much smaller diameter in relation to the outer than 6-cyl ones.

J

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