Peter Cobbold Posted April 14, 2014 Report Share Posted April 14, 2014 Andy, It looks similar to the Rattler and the URL says pendulum damper. But Shacktune dont seem to have web site. Peter Quote Link to post Share on other sites
john.r.davies Posted August 8, 2014 Author Report Share Posted August 8, 2014 Further short article, same source as originally, this time about viscoelastic crank dampers: https://www.highpowermedia.com/blog/3918/visco-elastic%20dampers But no help in it on HOW to tune such a damper, if one were available, for the Triumph Six. John Quote Link to post Share on other sites
Ashley James Posted August 9, 2014 Report Share Posted August 9, 2014 You might find R-R's approach to six cylinder torsional vibration problems interesting and you may also be relieved that Triumph didn't do anything as complex and expensive. http://www.kda132.com/pdfs/technical/engine/Dampers-Springs-Drives-Camshafts-1.pdf Quote Link to post Share on other sites
Peter Cobbold Posted August 9, 2014 Report Share Posted August 9, 2014 You might find R-R's approach to six cylinder torsional vibration problems interesting and you may also be relieved that Triumph didn't do anything as complex and expensive. http://www.kda132.com/pdfs/technical/engine/Dampers-Springs-Drives-Camshafts-1.pdf Ashley, Fascinating reading. That third order 5136 rpm vibration, and half that near 2500rpm, will I think also be critical for the TR 6-cylinder engines. Its the amplitude that will change with tuning. The Bentley crank is much longer, and that will increase the risks of running at 3rd order rpm. The complexity of the friction damper is daunting. But this is interesting: ( page 2) " the damper is unusual in that it is untuned and will handle crankshaft vibrations across the entire rpm range". All others I've come across need expensive tuning to take out only the one or two worst vibrations. Perhaps this is the way to go? Peter Quote Link to post Share on other sites
Ashley James Posted August 9, 2014 Report Share Posted August 9, 2014 I don't know enough about it Peter but obviously the critical speeds and the intensity of the period depend on the crank, lots of BMW ones have been stiff enough without one as was the Aston DB2-3, although they now fit them with a newer crank design. I can't think the viscous ones need tuning, but the weight might be critical. Later Bristol 2 litre engines had one and also the 4 litre Jaguar engine as succeeded the XK and this has been used on other engines. US accessory manufacturers offer them as an upgrade to engines fitted with rubber bonded ones, so they might be a good place to look. Generally speaking the first period is very obvious if the damper is not working and the second because the crank has broken. This was why when BMW Turbo charged their formula 1 engine they chose the four cylinder and not the six. They knew it would break if revved any harder. Healey 3000s are being fitted with tougher cranks and better dampers and some of the fastest rev to 7000 now, although I believe DB2-3s rev even harder. Still Morris designed the old Healey engine and I'd guess their engineers would be astonished at how much power it can make and how strong it is. Quote Link to post Share on other sites
DaveR Posted August 9, 2014 Report Share Posted August 9, 2014 Hello all, This input may not be relevant but here goes. The 2.5 litre engine has a larger damper than the 2.0 Litre (Six Cylinder). As you would guess it's important not to mix them up. The 2.5 Litre damper is larger than the pulley. Where as on the 2.0 Litre the damper is about the same size as the pulley. To accommodate the larger damper the timing pointer was moved up. As this is welded on the timing chain cover, without work, the 2.0 litre cover will not fit with the 2.5 litre pulley. I believe the 1.6 Litre is about the same size as the 2 Litre damper. It's a long time since I worked on the 1.6 engine! Cheers Dave Quote Link to post Share on other sites
Peter Cobbold Posted August 9, 2014 Report Share Posted August 9, 2014 Hello all, This input may not be relevant but here goes. The 2.5 litre engine has a larger damper than the 2.0 Litre (Six Cylinder). As you would guess it's important not to mix them up. The 2.5 Litre damper is larger than the pulley. Where as on the 2.0 Litre the damper is about the same size as the pulley. To accommodate the larger damper the timing pointer was moved up. As this is welded on the timing chain cover, without work, the 2.0 litre cover will not fit with the 2.5 litre pulley. I believe the 1.6 Litre is about the same size as the 2 Litre damper. It's a long time since I worked on the 1.6 engine! Cheers Dave Dave, I suppose the longer stroke of the 2.5 puts more twist into the crank. Hence the bigger damper. You dont happen to know if its the outer ring thats bigger diameter on the 2.5, or is the rubber ring larger diameter too? Tuning for lots more torque - as I'm doing - will twist the crank even more. I've read that belt drive to a blower can help dampen crank vibration - so. more in hope than knowledge, I'll press on. cheers Peter Quote Link to post Share on other sites
john.r.davies Posted August 9, 2014 Author Report Share Posted August 9, 2014 That article was sooooooo Roll-Royce! I loved the caption to one illustration, "The feet of these main bearing caps are in no condition to complete further service." Goes with the RR mantra, that a Rolls never breaks down, they "refuse to continue". John Quote Link to post Share on other sites
jean Posted August 9, 2014 Report Share Posted August 9, 2014 The workshop that overhauled the engine on my TR3 fitted an MGB pulley/damper, they fit it to all the 4 cyl TR engines with narrow belt .On my car the fan has been removed and no problem in more than 10 years, but I do not race the car Quote Link to post Share on other sites
Red 6 Posted August 18, 2014 Report Share Posted August 18, 2014 I wonder if this thread is causing sleepless nights for TR6 owners. All this talk of the need for damping and snapped crankshafts will have some worrying about what might happen when driving along in OD 4th along a motorway at just above the legal speed limit: Will It snap the crank after all my rev- o -meter is at 3k rpm. I have never seen or heard of a snapped crank on a road going 6. I have heard of and seen plenty of front pulleys where the rubber has given out and the 2 sections have separated and then of course the evil one where the outer ring slips, just a little but enough. The real question is what to replace a worn out one with, I would just re fit a standard one, after checking it too was not a duffer, or perhaps spend £oodles on a blingy one! Quote Link to post Share on other sites
Andy Moltu Posted August 18, 2014 Report Share Posted August 18, 2014 The 4 cylinder TRs have a reputation for breaking cranks - although a great heavy flywheel may play a role in that, particularly if not well balanced. The 6's tend not to be crank breakers, perhaps because they have a damper. Race use may well result in far higher revs and vibrations. Quote Link to post Share on other sites
Peter Cobbold Posted August 18, 2014 Report Share Posted August 18, 2014 what might happen when driving along in OD 4th along a motorway at just above the legal speed limit: Will It snap the crank after all my rev- o -meter is at 3k rpm. Nothing to worry about. The damper damps torsional vibrations - actaul twisting of the crank - caused largely by the downforce of gas on the pistons in the power stroke. But at a constant 75 mph/3000rpm the engine is at cruise, its throttled well back. Its making about 20-30hp, while at full throttle it would make around 100. So the torsional forces are well down. Its not going to snap !! Peter Quote Link to post Share on other sites
john.r.davies Posted August 18, 2014 Author Report Share Posted August 18, 2014 Peter, Knowing your background, I hesiate to correct you, but surely a damper does does not moderate excessive force, but rather change the harmonics of the system? If the natural frequency of the crank were to coincide with the frequency of impulses, it could be stressed to distruction even in a "throttled back" situation. In the way that a voice can (allegedly) break a wine glass if sung at the right harmonic frequency, but not if the glass is held in the hand, whose skin and bone damps the glass's vibration. John Quote Link to post Share on other sites
Motorsport Mickey Posted August 19, 2014 Report Share Posted August 19, 2014 Andy, The 4 cylinder cars have a damper also, blooming great lump of metal with a long nose. They also normally have a machining fault inherent on the crank where the bearing surface has not been undercut, and it's this area where the crank often snaps. When a crank is prepared for racing that bearing surface is machined with an undercut and that seems to help prevent crank breakage which isn't prevalent amongst racing 4 cylinders using revs up to 7000. The fact that the crank is also balanced along with all the attendant mechanical gubbins which is spinning around may also coincidentally help reduce frequencies and stresses upon the crank. Even on a purely roadgoing car having the engine balanced makes it a much nicer drive and well worth doing. Mick Richards Quote Link to post Share on other sites
Peter Cobbold Posted August 19, 2014 Report Share Posted August 19, 2014 John I'm out of my comfort zone on this. The way I see it is the damper absorbes vibration as heat in the rubber annulus.That R-R friction damper clearly works by absorbing energy. That absorbed energy would otherwise build up stroke by stroke, reflecting back along the crank from one stroke to the next and excite the vibration 'modes'. So absorbing the twist-energy on the nose prevents a build-up of twist at the crank's critical, aka natural, frequency. So more throttle>more twist> more vibration>more failure risk. At cruise its not going to twist much at all, the causal forces are too small to be of concern. In your glass analogy the singer isn't singing loud enough, despite hitting the correct pitch. However, tuning for more torque or rpm, and lightening bits, eg flywheel, and the damper may simply not be able to absorbe enough twist from the extra-powerful strokes, or not do it fast enough. And the crank assembly critical frequency has changed: flywheel lighter. etc The damper will have been tuned for the standard engine's torque/rpm and the most critical frequency. It is an esoteric field - textbooks are skimpy, tuning books gloss over the issue. Peter Quote Link to post Share on other sites
Peter Cobbold Posted August 19, 2014 Report Share Posted August 19, 2014 Healey 3000s are being fitted with tougher cranks and better dampers and some of the fastest rev to 7000 now, The Healey dampers have been designed by ISVR Southampton Univ. They have the highly specialised laser kit tp measure the crank twisting and then to design a damper to take it out, and test it. A colleague from Liverpool Univ in the '70s, now an eminent engineer, pioneered the technique way back then: http://www.isvr50.soton.ac.uk/interviews/slides/Neil-Halliwell-6.jpg http://www.isvr50.soton.ac.uk/interviews/Neil-Halliwell-interview.htm Thats the approach that's needed to design replacement TR dampers. TRR sponsor a student project, supply a working engine ?? Peter Quote Link to post Share on other sites
Andy Brady Posted August 22, 2014 Report Share Posted August 22, 2014 Thats the approach that's needed to design replacement TR dampers. TRR sponsor a student project, supply a working engine ?? Peter Enough with your radical thoughts! Next thing you know you'll be pointing out that all our existing dampers are pretty much shot and need replacing. Hmmmm, many thousands of cars needing a new damper across the world… £$€£$€£$€£$€£$€£$€£$€!!!!!!! Quote Link to post Share on other sites
Ashley James Posted August 23, 2014 Report Share Posted August 23, 2014 (edited) R-R dampers rarely work as they should and their cranks are whippy, so at 62 mph on the motorway, you can make the crank actually roar, but on other cars you might just detect a vibration period at a certain speed if you're lucky. But it's unlikely to be as obvious as the one on the four cylinder TR engine. Edited August 23, 2014 by Ashley James Quote Link to post Share on other sites
Stanpartmanpartwolf Posted September 12, 2014 Report Share Posted September 12, 2014 ATI damper fitted in 1998 to 6-pot (good on 4-pot, but not vital) End of problem. PM if interested. Quote Link to post Share on other sites
alan atkinson Posted September 14, 2014 Report Share Posted September 14, 2014 Enough with your radical thoughts! Next thing you know you'll be pointing out that all our existing dampers are pretty much shot and need replacing. Hmmmm, many thousands of cars needing a new damper across the world… £$€£$€£$€£$€£$€£$€£$€!!!!!!! To drag a conversation from the bar into here - that's the sort of thing I'd actually join to contribute towards... Quote Link to post Share on other sites
GT6M Posted September 17, 2014 Report Share Posted September 17, 2014 Just found this intresting thread, but whats not been discussed is the number of bearings. a 4 bearing crank will have less torsional frquency as a 7 bearing one. but a 7 bearing one will be supported moer ridgedly, thus making torsional torsional modes higher so if all are thinking aboot dampers for the TR six, then ye gotta look at the number of bearings too. M Quote Link to post Share on other sites
RobH Posted September 17, 2014 Report Share Posted September 17, 2014 M - since by definition torsional modes are in the rotation plane of the crank, the number of main bearings should have no influence since the crank is free to rotate within them. The crank isn't bending, its being twisted from end to end. The frequencies will depend only on the stiffness of the crank, and a longer 6 cylinder crank will have lower torsional frequencies than a four-pot one unless its c.s.a is beefed up to compensate. Rob Quote Link to post Share on other sites
GT6M Posted September 17, 2014 Report Share Posted September 17, 2014 Rob, im quoteing frae an article that LJK Setright did for car magazine years ago he said that for high speed work, a 4 bearing crank was prefferable to a 7 bearing one. and that the T6 crank had the ..right number of bearings.. M Quote Link to post Share on other sites
RobH Posted September 17, 2014 Report Share Posted September 17, 2014 I guess there could have been a number of reasons why LJK said that - did he elaborate? One reason may be that to incorporate seven main bearings, a crankshaft would have to be longer than a four bearing one, and hence potentially whippier and weaker. Rob Quote Link to post Share on other sites
GT6M Posted September 17, 2014 Report Share Posted September 17, 2014 Cant recall exactly, but it sticks in me mind that a 4 was better than a 7 looking ont interweb for the article, but as yet,no luck but it was in a Car article in late 70,s i think M Quote Link to post Share on other sites
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