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Crankshaft Damper Question

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77_MG_Midget

77_MG_Midget

Jedi Trainee
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Just to satisfy some curiousity... Does anyone know, why doesn't the 1500 motor have a crankshaft damper, just a pulley? Wouldn't it be better to have a damper? What about a damper from a 1275 motor, would this possibly fit a 1500?
 
The 1500 is a Triumph engine while the 1275 is a BMC A-series. I don't think the pulleys can be swapped. I'm not sure why the Triumph/1500 didn't use a damper.
 
According to some research I did previously, a GT6 (rubber) damper is a direct fit. However, along with a fairly recent thread, the determination was that the 1500 had a resonance above the normal frequencies of operation (perhaps 5500 RPM or higher). While I feel that a fluid damper would be most desireable, they are expensive and I would have to figure out a way to make it fit. Lightening the rotating mass is the next best way to increase the resonance, and it's generally less expensive (alloy flywheel: $400). Lightened pistons, rods, and crank can also help, but that starts to add up. The easiest way is by lightening the flywheel.
 
Ok, I've built a few motors in my day... mainly chevy's, but I've never heard of "resonance". Can anyone explain this? Thanks!
 
Every piece of equipment that rotates has a natural harmonic to it. As the equipment becomes more and more complex so does the harmonic. They kinda add up like resistances in a circuit to give the machine its natural or resident harmonic. This frequency can be near the operating frequency of the equipment or so far out that the equipment never gets excited. Natural harmonics can be pretty detrimental to equipment if they are close to the operating frequency. This is the resonance they are talking about. This "vibration" that sets in is self sustaining as long as the equipment "engine" is rotating at that frequency. It would be like striking a tuning fork at just the right repitition to keep it vibrating. It can damage shafts, gearboxes, couplings, foundations, etc of industrial equipment and to counteract it we install dampers that basically change the characteristics of the rotating equipment thereby changing is natural frequency. Of course the best way to counteract it is through engineering and design but sometimes exceptions sneek through the cracks. If the 1500 engine has a natural harmonic at 5500rpm I would recommend not operating it very long in that region. There would be an upper limit for rpm that would also bring it out of it's resonance state. I have a 1500 engine as well but don't have the guts to tach it up that high. The engineers that designed that engine probably decided it was something they could live with since it is outside the normal operating range of the engine.
JC
 
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