john.r.davies Posted April 1, 2014 Report Share Posted April 1, 2014 (edited) All Triumph sixes are fitted with a crankshaft damper, in the form of the pulley. These viscous dampers are, more than a little, mysterious and ill-understood. The online magazine RET (Race Engine Technology) Monitor has published a couple of short articles recently that may be of interest: https://www.highpowermedia.com/RET-Monitor/3850/damping-vibration https://www.highpowermedia.com/blog/3870/more%20on%20dampers John Edited April 1, 2014 by john.r.davies Quote Link to post Share on other sites
Peter Cobbold Posted April 1, 2014 Report Share Posted April 1, 2014 Yes.... difficult. We dont have data to hand that allows repro dampers to be re-manufactured, whether for road or racing. More info here, but the bottom line is, quote: Some aftermarket damper manufacturers and some engine builders have torsiograph equipment and can do torsion testing and can fine tune dampers for an engine for a fee. For true custom designs, BHJ, for one, has the ability to do both computer engine modeling & simulation and torsion testing on a dyno. Again, this isn't free, but what's that engine worth to you, even just a rebuild, especially if it breaks a crank http://www.bhjdynamics.com/index.php?main_page=page&id=4 Seems to me that remanufactured dampers need those torsiograph data. Ideal projects for NSF? But not trivial - need working engines on engine dyno and torsion measuring kit. Peter Quote Link to post Share on other sites
alan57 Posted April 1, 2014 Report Share Posted April 1, 2014 For high revving competition engines,the standard damper is inadequate - leading to everything up to and including a snapped crank!!! Quote Link to post Share on other sites
Richard71 Posted April 1, 2014 Report Share Posted April 1, 2014 Hi Alan, How high RPM are you taking your engine too, and what is your solution? Richard. Quote Link to post Share on other sites
john.r.davies Posted April 1, 2014 Author Report Share Posted April 1, 2014 (edited) Kastner used standard Triumph dampers. And he used to rev 'em a bit. He had a gandy idea to check that they hadn't delaminated. Drill a small hole in the depth of the V, right through the rubber into the central part. Then check by probing the hole with a wire. If the wire won't go all the way in, the rubber has let go. JOhn Edited April 1, 2014 by john.r.davies Quote Link to post Share on other sites
Peter Cobbold Posted April 1, 2014 Report Share Posted April 1, 2014 Kastner used standard Triumph dampers. And he used to rev 'em a bit. He had a gandy idea to check that they hadn't delaminated. Drill a small hole in the depth of the V, right through the rubber into the central part. Then check by probing the hole with a wire. If the wire won't go all the way in, the rubber has let go. JOhn So he fitted a fresh one when his test indicated. But we haven't any fresh dampers as far as I know. And what state will the rubber be in on new old stock dating back 40 years ? Peter Quote Link to post Share on other sites
Ragtag Posted April 1, 2014 Report Share Posted April 1, 2014 (edited) Is there any merit in looking to more modern engines for such parts? For example,SAAB 900/9000 engines have a similar 'rubber sandwich' crank pulley and can rev to 7500. I wonder how much machining it would take. There must be other examples. Edited April 1, 2014 by Ragtag Quote Link to post Share on other sites
Peter Cobbold Posted April 1, 2014 Report Share Posted April 1, 2014 (edited) Is there any merit in looking to more modern engines for such parts? For example,SAAB 900/9000 engines have a similar 'rubber sandwich' crank pulley and can rev to 7500. I wonder how much machining it would take. There must be other examples. Er, not sure about that, tending to think not. The review suggests the torsional vibration frequencies are much the same. What we dont know is the amplitude of the torques, and hence the force the damper needs to exert. So the outer mass and rubber annulus may not be the same as SAAB Quote: The good news is that the peaks in an engine without a damper are usually ALL THE SAME FREQUENCY unless the engine revs very high. This is normally the first mode frequency of 300-450 Hz as mentioned above. The second mode frequency of the crank is usually 1.5-1.8 time higher than the first mode and is usually high enough that is does not have peaks in the normal rev range.The exceptions to this are long engines (inline 6s and 8s) Its complicated..... Peter Edited April 2, 2014 by Peter Cobbold Quote Link to post Share on other sites
alan57 Posted April 2, 2014 Report Share Posted April 2, 2014 (edited) Kastner used standard Triumph dampers. And he used to rev 'em a bit. He had a gandy idea to check that they hadn't delaminated. Drill a small hole in the depth of the V, right through the rubber into the central part. Then check by probing the hole with a wire. If the wire won't go all the way in, the rubber has let go. JOhn And of course Kastner was changing major parts very regularly! Also Kastner's Competition Preparation Manual, referring to gearing, does state that the rev limit red line "in most cases this will be 6000". Higher rev limits were achieved on the 2litre Gt6 engine - shorter stroke(?) Edited April 2, 2014 by alan57 Quote Link to post Share on other sites
Andy Brady Posted April 3, 2014 Report Share Posted April 3, 2014 I've been told a Cadillac Northstar damper makes a good alternative. Just needs a light ream to fit. Failing that… http://www.rimmerbros.co.uk/Item--i-214479 Quote Link to post Share on other sites
john.r.davies Posted April 3, 2014 Author Report Share Posted April 3, 2014 The Northstar engine was a V6/8. Several available on US eBay, but would these suit a straight six engine? JOhn Quote Link to post Share on other sites
AlanT Posted April 3, 2014 Report Share Posted April 3, 2014 Perhaps a little theory on these may help understanding. Resonances arise when a system has two ways of storing energy. The crankshaft stores energy by virtue of being a rotating mass and also by being able to "wind-up" like a spring. At the resonant frequency energy swaps cyclically from the "spring kind" called Potential-Energy to the "rotating kind" call Kinetic-energy. Its the rotational equivalent of a weight jumping up and down on a spring. There are a few "special frequencies" at which this occurs without much loss of energy. So large twisting deflections can build up and damage the crank. The damper will have its own resonant frequency created by its mass and the stiffness of the rubber. But rubber isn't like a metal spring. Rubber is partly viscous, you could make a great damper with oil and a real spring just like a suspension. If you can tune the resonance of the damper to the same frequency as the crank resonance then the viscosity of the rubber will suck energy out and prevent damage from excess twisting. You will note that the mass of the damper is nowhere near as big as the crank. But it can still tune to the same frequency if the stiffness of the rubber is just right. The frequency is set by the ratio of stiffness to mass, more precisely the square-root of the ratio. Just think of Big Ben and a domestic Grand-father clock both marking off time with a pendulum which resonates at 1 second. So when the rubber goes old and hard the damper will go "off-tune". Does this matter? We are now asking questions that are easy to answer using maths and difficult to discuss in words. Put simply the nearer the damper mass matches the crank the easier it will be to get energy to flow into and be absorbed by the rubber even if its not tuned dead right. Think of it like this. A mouse dies on Big-Big. You loose a few seconds a week. Same dead mouse on a small clock and you loose five minutes. So can you use a damper from another vehicle. Probably. You just need to check the tuning! That'll be easy then. Quote Link to post Share on other sites
Peter Cobbold Posted April 3, 2014 Report Share Posted April 3, 2014 V6 crank is shorter than straight-6 so resonant frequencies will differ ( if I'm right) I refound this explanantory blog: http://deviantmethods.com/bigmoose/papers/damper2/torsional_vibration.htm quote: "The six-cylinder engine is the difficult one, with a major critical near 5000rpm, where the forces are high enough to render a good damper essential." and note the figure of a Summers torsiograph from a 6 cylinder : resonance at 2025rpm not at 2000 or 2100. Quote Link to post Share on other sites
Peter Cobbold Posted April 3, 2014 Report Share Posted April 3, 2014 (edited) The Sterling Rattler looks like it will work without need to supply expensive vibration measurements on a working engine. Might be worth looking into? http://vibrationfree.co.uk/our-services/motorsport/the-rattler-frequently-asked-questions/ http://vibrationfree.co.uk/our-services/motorsport/sterling-rattler/ http://vibrationfree.co.uk/our-services/motorsport/rattler/ quote: "The trouble is that the harmonic damper is inherently heavy, it is also specifically “tuned” to the rotating masses of the particular engine and it’s drivetrain. Any deviation from that, eg; lightening flywheels, clutches, engine swops etc, etc. will require a change to the inertia mass on the damper. This is hard maths and gets expensive. Alternatively, the “Rattler” works on a totally different principle. It is generic by design to specific engine types eg; V6, V8, 4cyl- inline, 6cyl- inline " Peter Edited April 3, 2014 by Peter Cobbold Quote Link to post Share on other sites
Bald Rick Posted April 3, 2014 Report Share Posted April 3, 2014 Try this for a layman's explanation of crank torsional vibration and dampers: http://www.deviantmethods.com/bigmoose/papers/damper2/torsional_vibration.htm Tony Quote Link to post Share on other sites
Peter Cobbold Posted April 3, 2014 Report Share Posted April 3, 2014 Try this for a layman's explanation of crank torsional vibration and dampers: http://www.deviantmethods.com/bigmoose/papers/damper2/torsional_vibration.htm Tony Tony, Snap!! Peter Quote Link to post Share on other sites
AlanT Posted April 3, 2014 Report Share Posted April 3, 2014 A old machinist trick is to absorb vibration when boring a deep hole by hanging big nuts over the boring bar. They rattle about but the work does not. This improves the surface finish. Make no mistake this absorbs energy and makes heat just like a rubber damper. Might work though. Quote Link to post Share on other sites
Andy Brady Posted April 3, 2014 Report Share Posted April 3, 2014 The Northstar engine was a V6/8. Several available on US eBay, but would these suit a straight six engine? JOhn Rick Patton uses one on his very impressive TR6. Quote Link to post Share on other sites
Paul Down Posted April 7, 2014 Report Share Posted April 7, 2014 While at a VSCC Trial at the weekend I happened to be speaking with James Baxter who some of you may be aware as he holds many hill climb records throughout the UK. Jame's main business apart from race tuition is the restoration of pre war cars and he happened to mention Viscous Dampers which he fits to numerous cars. He said that unlike the rubber coupled version the viscous type do not require tuning to the particular engine so are a much easier fitment. If anyone is interested I can forward his details. PS. I know nothing about these devices (4 cylinder lumps dont need them) and am just relaying the conversation as I thought it may be of interest to 6 and 8 pot owners. Quote Link to post Share on other sites
Peter Cobbold Posted April 7, 2014 Report Share Posted April 7, 2014 (edited) I'm not so sure 4 cylinder engines dont need a crankshaft damper - dont they have a reputation for snapping their cranks, and a "critical rpm" ? Baxter's Frazer-nash has a straight-6 Alvis engine, so TR6ers have an good lead here. Whats his companies name? Peter Edited April 7, 2014 by Peter Cobbold Quote Link to post Share on other sites
Paul Down Posted April 7, 2014 Report Share Posted April 7, 2014 (edited) Baxter now drives an ERA! Peter you have a PM Paul Edited April 7, 2014 by Paul Down Quote Link to post Share on other sites
Peter Cobbold Posted April 7, 2014 Report Share Posted April 7, 2014 Paul, ERA, top of my wish list. Six cylinders, 2 litres, 300bhp. The wonders of methanol and supercharging, when did we lose our way? See you at Loton ? Peter Quote Link to post Share on other sites
roy53 Posted April 8, 2014 Report Share Posted April 8, 2014 The Sterling Rattler looks like it will work without need to supply expensive vibration measurements on a working engine. Might be worth looking into? http://vibrationfree.co.uk/our-services/motorsport/the-rattler-frequently-asked-questions/ http://vibrationfree.co.uk/our-services/motorsport/sterling-rattler/ http://vibrationfree.co.uk/our-services/motorsport/rattler/ quote: "The trouble is that the harmonic damper is inherently heavy, it is also specifically “tuned” to the rotating masses of the particular engine and it’s drivetrain. Any deviation from that, eg; lightening flywheels, clutches, engine swops etc, etc. will require a change to the inertia mass on the damper. This is hard maths and gets expensive. Alternatively, the “Rattler” works on a totally different principle. It is generic by design to specific engine types eg; V6, V8, 4cyl- inline, 6cyl- inline " Peter Hello Peter what do you think re RATTLER verses viscous HARMONIC ones. ROY Quote Link to post Share on other sites
Peter Cobbold Posted April 8, 2014 Report Share Posted April 8, 2014 Hello Peter what do you think re RATTLER verses viscous HARMONIC ones. ROY Hi Roy, I'm uncertain now that Paul posted about Baxter using harmonics. From what I've read viscous harmonics need the engine vibrations measured - maybe VSCC customers are happy to pay him to do that. On balance ( p t p ) I think the rattler may be the better option, but there's not a lot of info to go on. I'd have liked to see some torsionmeter data on an actual fitment. Maybe there's more info on the USA site. I'm a complete amateur on this. But I do think it needs answering: our tired old rubber damper pulleys will soon start flying apart with age, or adding more vibration than they absorbe!! Peter Quote Link to post Share on other sites
Mk1PI Posted April 14, 2014 Report Share Posted April 14, 2014 (edited) http://triumphwestoz.blogspot.com.au/2011/10/shacktune-pendulum-damper-shackler.html I fitted this damper a few years back - I have nothing but praise for it. You can probably work out what style of damper it is - quality from James Shackford is impeccable. My mate fitted an ATI super damper about the same time - from Goodparts - he has just snapped his crank - bad luck I'd say - certainly not the Superdampers fault http://triumphwestoz.blogspot.com.au/2011/11/triumph-car-club-display-and-humphs.html Edited April 14, 2014 by Mk1PI Quote Link to post Share on other sites
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