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 Crankshaft dampner - a functional descriptionJump to page : 1 Now viewing page 1 [25 messages per page] | View previous thread :: View next thread |
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BigRabbitMan |
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Expert   Location: Cottage Grove, OR | The following is a copy of a posting made on the Yahoo group site by Louis Cruise. Hello Greg,I'm not sure I understand "do best". Balance (actually UN-balance) of engines is quite complex. Depends on V-angle, firing order, firing pressure, rod length, stroke, piston weight, rod weight, counter balance weight on the crankshaft, A/C on and off, altenator variable load, even the number of vanes in the water pump, among others, and whether they result in 1st, 2nd, 3rd order and higher unbalance. Over the years a two piece disc on the front of the crankshaft (the thing that the pulley bolts to) that is held together by a rubber bond between the two pieces, has been the most useful of lots of different designs. The two pieces actually move as vibrations occur in the crankshaft, thus dampening of those forces. Inline six cylinders are the "most" balanced, V-8s are pretty bad, but inline four cylinders are terrible. Modern 4s have countershafts. Ever ride a single cylinder motorcycle ? They are called Thumpers for a reason - UN-balance. Ever see how much a flat four airplane engine shakes during cranking and shutdown ? In all my years in "engines" I have only known one guy that could really do the necessary calculations - John Hawley Brooks, RIP. I get all criss crossed with LaPlace transforms every time. Draw back is that the magnitude of the different forces occur at different RPMs, so the typicl rubber type was "tuned" to handle 1st order, and sometimes more, vibration around the most severe unbalance and common driving RPM. Like most things, it is a compromise, and really only tuned for a single RPM. But over time, the rubber bond sometimes breaks, the rubber gets hard and its stiffness changes, and this compromise dampening diminishes. Results - more crankshaft wear in bearings, rod bearing wear, piston pin wear, piston vibration, flywheel bolts loosening, crankshaft pulley vibration, which often causes squealing or pitching belts. In the worst case the rubber bond fails completely resulting in lots of pulley vibration and sometimes the bolt holding the pulley on to its keyed crank snout comes loose and everything comes apart. Remember our 5 groove crankshaft pulley is mounted to a damper that has a 35 year old rubber bond holding two pieces of rotating steel together. About 20 years ago, some old hot rodders came up with Plan B - the Fluid Damper. It is a sealed design that is filled with silicone "gel" and a free rotating inertia ring that absorbs vibration at all speeds/frequencies. It is not speed sensitive. They are SFI Certified for far more RPM than any of our FMCs will ever turn. Fluiddamper is the company that had the original patents(?), and have made a zillion of them. Now many are also made "off-shore" with varying degrees of quality. The price of the genuine Fluidamper for a Chrysler 440 has remained at $400 for some time, which is just more than I wanted to spend. I just happened upon the "SALE" at PAW last night, and did not hesitate to order one for update to my FMC #120. I have had one on my Turbocharged SBC El Camino for many years, one on my early Hemi powered 56 Ford truck (still to be finished), and one on my SBC powered Front Engine Dragster. Harry Day FMC #400 solved his belt squealing problems with one. I also think very favorably of the fluid type damper (read exact copy) offered at 440Source. I was going to buy theirs, but this great price at PAW came up. You can also get brand new rubber style dampers for $60-$100. Many a fine quality. Time is everythings and everybodies enemy. Next time you look at your "belts" take a look at the damper. 35 years is a long time for a squirming piece of rubber between two vibrating steel rings. One final "tip". The big bolt at the end of the crankshaft right in the middle of your bottom pulley is NOT there to turn your engine over with some long bar on a socket. It's only purpose is to keep the damper from falling off the crankshaft. Do NOT use it to turn the engine. It will strip-break- loosen in all kinds of failures. Press on, Lou #120. | ||
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| BigRabbitMan |
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Expert Location: Cottage Grove, OR | A further discussion of the harmonic balancer by Lou, # 120. I have also posted the pictures he is discussing. ******* Some time ago I talked about the harmonic balancer and how they get old and the rubber bond starts to fail and the rubber gets hard and cracks. A failing harmonic balancer can cause excessive belt wear, belt squeal, pitched belts, front seal leak, water pump seal and bearing failure, altenator bearing failure, and crankshaft breakage. Pictures are of a Chrysler RB harmonic balance for a steel crank with about 70,000 miles and 30+ years as a motorhome engine. What does yours look like ? Please feel free to put these pics and any info on any Web site and share them with any FMCers. My FMC has a fluid type harmonic balancer, which do not age like the rubber ones do. Vibrate On . . . to Nebraska. Lou #120 | ||
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