JohnD Posted January 25, 2018 Share Posted January 25, 2018 Once again, I'm asking for help from the Faculty of Sideways! And I'm asking as a genuine student! I retired a while ago, and since then I've gone back to college, where I'm now studying for a degree in Motorsport Engineering. I need a research project and chose to investigate the crank damper pulleys that Triumph fitted to all the six-cylinder engines it made. The crank damper was needed to suppress 'torsional', twisting vibration in the long crankshafts, and has a rubber layer between the inner hub and outer ring. They were suspect even in the day, when they were new. Kas Kastner described in his Handbooks his technique to ensure that the outer hadn't shifted, which would make the timing marks on them completely false. Worse, a faulty damper could lead to crankshaft failure! Today, none of those dampers are less than forty years old, and many show the rubber to have deteriorated. How many still work as timing indicators, let alone to suppress crank vibration? My study has two parts: In the workshop, I'm building an engine rig with sensors on the pulley and flywheel to detect vibration, and I'm asking Triumpheroes about their experiences with the dampers. Please help me by completeing the short survey questionanire I've put up on Survey Monkey? Go to https://www.surveymonkey.co.uk/r/GPTCDSG There are only five questions and it will take you less than two minutes! Thank you! John PS I'm posting this on several websites, to catch as many people as I can but no need to complete it more than once! Link to comment Share on other sites More sharing options...
Nick Jones Posted January 25, 2018 Share Posted January 25, 2018 Interesting. But I think you needed to make more effort to separate out the 2 and 2.5 as the 2.5 is reputed to be much more liable to torsion vibration related failures. For example - I've seen a busted crank (still have the short part) - from a 2.5, but I ticked the box for Vitesse/GT6 because that's where the majority of my experience is (and only allowed 1 selection. Broken 2L cranks are very rare. I've also seen 2 or 3 busted small crank 1300 cranks (no damper at all) and at least two of those were at least partly due to poor quality regrinds with poor fillett radii. You should maybe make contact with James Shackford and Andy Thompson. James made a batch of "Shackler" (based on the "Rattler") mechanical dampers and Andy has been "testing" one in his racing 2.5PI. I've a feeling Andy may also have a broken crank - though it had had a long hard life before it met the Shackler! I may have a few scruffy looking relics of dampers knocking about if you want some to test (would very interesting to see how consistent they are) and I think you can buy new again now - though goodness knows whether they are worth having and they seem to list the same part for 2L and 2.5, which is not very promising. Nick Link to comment Share on other sites More sharing options...
PeterC Posted January 25, 2018 Share Posted January 25, 2018 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 Link to comment Share on other sites More sharing options...
oldtuckunder Posted January 25, 2018 Share Posted January 25, 2018 6 hours ago, JohnD said: There are only five questions and it will take you less than two minutes! Done, worked, easy. Link to comment Share on other sites More sharing options...
oldtuckunder Posted January 25, 2018 Share Posted January 25, 2018 6 minutes ago, PeterC said: I think the first harmonic resonance on 6 pot cranks is at 5000rpm.....................well above my comfort zone. Blink and you miss it on the way up :-) Interesting comment though, in racing terms 5K is a blip, but 5K at a sustained high speed cruise? Makes you really want to know when crank failures occur, it may not be very high rpm's but maybe lower sustained for a longer period at a critical rpm point. NB. I have zero knowledge of such a thing, it just made me wonder. Alan Link to comment Share on other sites More sharing options...
Nick Jones Posted January 25, 2018 Share Posted January 25, 2018 The resonance that dismantles 2.5s is reputed to be about 6,500. 2L will be higher. Nick Link to comment Share on other sites More sharing options...
JohnD Posted January 26, 2018 Author Share Posted January 26, 2018 This is something I will be tackling, but Holtzer Analysis hat identifies the resonance zones is not for the faint hearted! John Link to comment Share on other sites More sharing options...
PeterC Posted January 26, 2018 Share Posted January 26, 2018 I wonder if lightening the f'wheel adds inertia stresses to the rubber insert ,eg when blipping the throttle, that the damper was not designed to embrace? Peter Link to comment Share on other sites More sharing options...
Chris W Posted January 28, 2018 Share Posted January 28, 2018 On 25/01/2018 at 11:46 PM, Nick Jones said: The resonance that dismantles 2.5s is reputed to be about 6,500. 2L will be higher. Nick That's interesting. My rev counter goes red at 5500 so why would Triumph have bothered with an harmonic damper to combat resonance 1000 revs above this? Link to comment Share on other sites More sharing options...
JohnD Posted January 28, 2018 Author Share Posted January 28, 2018 (edited) I think that the factor that "dismantles" 2.5 is more the mean piston speed than torsional vibration, although the two are allied. Unless special parts are used, production engines are at risk if the MPS goes above 20m/s. This "rule-of-thumb" figure is a surrogate for the actual peak speed, and the acceleration on the pistons through a stroke, but calculating that isn't trivial! Estimates say that a standard TR6 piston and gudgeon pin weighs 346grams on the bench and 1G of 'acceleration', but at 6K would 'weigh' 881.7 Kilograms - nearly a ton! Comparing the 2L and 2.5l versions. The piston velocity of the two engines 2L, 76mm stroke RPM Mean speed in mm/sec Mean speed in meters/sec 6000 15200 15.2 7000 17700 17.7 7500 19000 19.0 2.5L, 95mm stroke 6000 19000 19.0 6500 20840 20.84 John Edited January 28, 2018 by JohnD Link to comment Share on other sites More sharing options...
Scooter Posted January 28, 2018 Share Posted January 28, 2018 I'm more bothered with balance than balancers. I've chucked a set of 2.5 rods on a scale and found a surprisingly large variation. No sign of any grinding other than flash removal so 'as is' into the engine at the factory BL Quality control had gone out the door after the TR5 years. 15g, do the math! Link to comment Share on other sites More sharing options...
PeterC Posted January 28, 2018 Share Posted January 28, 2018 @ John, About 1 ton of force at peak cylinder pressure pushing the piston down on the power stroke. But little pressure or force to deal with in the other three phases. However peak combustion force will be at round 3500 rpm at peak torque, and will drop with VE as rpm rise. So I'd go with cranks suffering at 6500 rpm from inertia loading than torsional loading from combustion pressure. Which indicates the damper wont have much effect I think. Peter Link to comment Share on other sites More sharing options...
JohnD Posted January 28, 2018 Author Share Posted January 28, 2018 Have to ask, then why did Triumph fit them? They didn't to any four cylinder engines, and Sir John Black was notoriously keen to save fractions of a penny on production. Unless the engineering design dept. said they were essential, surely he would have vetoed them? Would those Standard-Triumph engineers have insisted on an unnecessary item on a production engine that would have been expected to spend its life at less than 6K? John Link to comment Share on other sites More sharing options...
oldtuckunder Posted January 28, 2018 Share Posted January 28, 2018 A quick google also reveals that 6 cyl BMW engines also suffer from the same problem http://www.vacmotorsports.com/ati-crankshaft-dampers-vac-motorsports.html and that most? engines these days are fitted with them? http://www.dieselarmy.com/engine-tech/engine/how-it-works-viscous-dampers-a-k-a-harmonic-balancers/ Link to comment Share on other sites More sharing options...
Nick Jones Posted January 28, 2018 Share Posted January 28, 2018 3 hours ago, Scooter said: I'm more bothered with balance than balancers. I've chucked a set of 2.5 rods on a scale and found a surprisingly large variation. No sign of any grinding other than flash removal so 'as is' into the engine at the factory BL Quality control had gone out the door after the TR5 years. 15g, do the math! In my experience, if they are a true set, all coming from the same factory-assembled engine, the weight match will be pretty good. Problems may arise once the engine has been through a rebuild or two in your "average" reconditioning shop and parts mixed and matched. This might be interesting http://www.eng-tips.com/viewthread.cfm?qid=427266 and this http://www.epi-eng.com/piston_engine_technology/crankshaft_torsional_absorbers.htm Nick Link to comment Share on other sites More sharing options...
oldtuckunder Posted January 28, 2018 Share Posted January 28, 2018 9 hours ago, Scooter said: I've chucked a set of 2.5 rods on a scale and found a surprisingly large variation. Put a micrometer/vernier across the width of the BE journal and see what you get also Link to comment Share on other sites More sharing options...
JohnD Posted January 31, 2018 Author Share Posted January 31, 2018 This is for PeterC - I've posted this survey on the US sites, and one responder told me that they could not use their damper pulley,as their TR6 was supercharged. The torque to drive tge 'charger was too much for the damper pulley, so they have resorted to a solid pulley, with no ill effects, they claim. Could this be beacue a 'charged engine is niot taken high enough for torsion vibration to be a problem? http://www.triumphexp.com/phorum/read.php?2,1509485,1509485 JOhn Link to comment Share on other sites More sharing options...
PeterC Posted January 31, 2018 Share Posted January 31, 2018 Thanks John, a blower could take up to 10 to 20hp depending upon boost, so, yes, I agree the rubber insert would soon fail. The Moss kit used a solid pulley. My DIY pulley uses the crank nose, replacing the fan boss. I read somewhere that the blower belt drive does a good job of taking out the torsional vibrations. But no numbers given as far as I can recall- Peter Quote . Link to comment Share on other sites More sharing options...
JohnD Posted February 1, 2018 Author Share Posted February 1, 2018 Of course! Rubber, just attached top the crank in a different way, using its viscosity to remove vibration energy! Doh! But I'm not going to even try to model that. Thnaks, Peter. John Link to comment Share on other sites More sharing options...
oldtuckunder Posted February 1, 2018 Share Posted February 1, 2018 Hi John Just something else to throw in the mix re 6 crank dampers, not sure when Triumph started fitting them, but I know the 1600 vitesse and MK1 vitesse and GT6 2ltr did have them. They also had a massive metal fan wizzing around bolted to the front of the crank. That's going to make one hell of a difference to the crank, were they ever balanced?, do crank failures occur on cars fitted with crank fans or those without? also the TR6 have one hell of a big boss fan extension on the front of the crank. Just some idle thoughts Alan Link to comment Share on other sites More sharing options...
JohnD Posted February 1, 2018 Author Share Posted February 1, 2018 Thanks, Alan! I'm grateful, as always to the Faculty of Sideways U. for thinking on my behalf! Please continue the seminar, as it makes me think to reply to points you make. I've read about TR4s needing a damper if they ran fanless, I presume with an electric one. They had an odd four bladed fan that was like a St. Andrew's cross, diagonal, with unequal spacing between the blades, a long extension boss on the pulley to put it right behind the radiator, and no damper. But the 6-fan was bolted to the central hub of the pulley, and the fan blades were light, should have been in good balance as the bolts had semicicrular slotted washers to balance it, or not, of course if your DPO hadn't bothered. And an out of balance fan would deteriorate primary crankshaft balance, causing a couple about the crank nose, not make torsional vibration worse. You will recall that it's the repeated impulses from the power stoke as each journal that twist the crank causing the torsional vibration, and meanwhile, the outer ring of the pulley would still have been free to move on the rubber and absorb the vibrations. (see https://www.canleyclassics.com/triumph-gt6-mkiii-fan ) So I can't think that a fan would contribute much to torsional vibration, and that for sixes the fan doesn't matter. That it is said to do so for TR4's is beyond me. John Link to comment Share on other sites More sharing options...
PeterC Posted February 1, 2018 Share Posted February 1, 2018 (edited) Firing order 1342. - one bang every 180 deg equally spaced in time The blades are 80 then 100 deg apart approx. I wonder if that fan was doing a job damping? Perhaps when cyl 2 then1 fired it helped damping to have the fan blades closer together ? Was the fan position tied to the crank position with a keyway and asymmetric bolts in the hub? If so that could be a clue to there being more to the fan than blowing air. Peter Edited February 1, 2018 by PeterC Link to comment Share on other sites More sharing options...
SDerbyshire Posted February 1, 2018 Share Posted February 1, 2018 Interesting topic ;-) steve Link to comment Share on other sites More sharing options...
DeTRacted Posted February 1, 2018 Share Posted February 1, 2018 This quote from the Revington website re the 4 pot engine: Q: If I fit a plastic fan to the original fan extension or remove the fan and extension altogether, would I be risking crankshaft breakage or damage due to changing the dampening effect of the original fan/extension arrangement? A: Irrespective of whether you use a wobbly aluminium fan or a wobbly plastic fan, the effect is the same. It helps (just) to cool the engine and that is all. In our opinion the amount of damping it offers is negligible. Dampers have been in use since the 20's where necessary. If Triumph (one of the largest sports car manufacturers in the world at the time) thought is was necessary they would have fitted one. We have been building TR2-4A engines with no fan and no extension for 25 years with NO broken crank related failures. As a result we are quite happy that an engine in good shape, from standard up to all bar the highest revving competition engines should not suffer ill effect by having the fan substituted for a later TR6 plastic type or having it and the extension removed altogether. If you do remove the fan altogether we recommend using a properly designed washer and bolt arrangement to hold the pulley to the crankshaft. Link to comment Share on other sites More sharing options...
roulli Posted February 1, 2018 Share Posted February 1, 2018 Hi, I've responded to John's survey a few days ago, claiming that I haven't seen any broken 6cyl. crank so far, but recalled only later that about 5 years ago I was at a traditional local engine part shop (I think they even used to rebuild engines a few decades back)... The owner told me he used to have big Triumph sedans, as a new car. He did like them a lot, they were fast back then, but on on 2 cars he had a broken crank. He used the cars for business trips, which means possibly long traveling at high revs into Germany in the 70ies (no speed limitation, no traffic jams...) I don't know, whether he was talking about 2l or 2,5l engines though. However, above story supports two facts: Triumph 6 cylinder cranks may fail with a new damper, or a new damper is no guarantee against crank failure. The 6.cyl is not made for running constantly at higher revs. On the other hand, blueprinted 2,7l TR6s with 230hp red-line between 7500 and 8000 rpm with OE cranks. (as stated by long term Triumph-Competition racer) But in a race revs vary a lot... So the culprit could be the word "constantly" . A local Triumph 10CR hero, with a quick 1500 Herald estate, told me he tries always to vary the revs when driving on long highway journeys, in order to "statistically" keep the crank possibly out of a resonance situation. I try to follow this advice, but nowadays, with all that traffic, it's anyway difficult not to do so... Patrick Link to comment Share on other sites More sharing options...
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