Alloy crankshaft pulley
Alloy crankshaft pulley
(OP)
Hi guys,
I don't know if i'm writing in the correct topic if not sorry...
I would like to ask if someone can resolve my question wich is
The crankshaft pulley has a specific material, weight and diameter given by the manufacturer...when we change it for a light weight ones and smaller diameter don't we put stress to the crankshaft and piston rod's bearings?
For an instance, when an engine run at 7000rpm the sympathetic vibration of the crankshaft must be absorbed from the flywheel and...the pulley.
If not why the manufacturers created the double mass pulley (like the flywheel)???
Thanks
p.s. sorry if my english are not so good...
I don't know if i'm writing in the correct topic if not sorry...
I would like to ask if someone can resolve my question wich is
The crankshaft pulley has a specific material, weight and diameter given by the manufacturer...when we change it for a light weight ones and smaller diameter don't we put stress to the crankshaft and piston rod's bearings?
For an instance, when an engine run at 7000rpm the sympathetic vibration of the crankshaft must be absorbed from the flywheel and...the pulley.
If not why the manufacturers created the double mass pulley (like the flywheel)???
Thanks
p.s. sorry if my english are not so good...





RE: Alloy crankshaft pulley
That is an acceptable risk for a racing engine, possibly.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Alloy crankshaft pulley
RE: Alloy crankshaft pulley
If it did, I'd expect a modified engine will need one too.
Generally speaking, some inline 4s get away without torsional dampers, but inline and V sixes and 8s do not.
Drag racers can get away running damperless because each race is so short, and time spent at any of the dangerous rpm (or any particular rpm) is brief, but I think other forms of racing require much greater duty cycles
RE: Alloy crankshaft pulley
All this information is on line or in "How To" books. Unless you are building a racing anomaly like a M20 Pobeda...(I'll bet no one even knows what that is...Hint---GAZ.)
Rod
RE: Alloy crankshaft pulley
Many engines will have a satisfactory durability AT THEIR ORIGINAL RED LINES if they don't have a TV damper. But of course for a race engine you don't care about the original red line. if you spend most of your time at an RPM that doesn't line up with a resonance then the harmonic damper won't be helping much anyway. (There is a small reduction in TV away from the resonance, but the levels seen are usually OK).
Also bear in mind that crank bending, as opposed to torsionals, is a perfectly good way of destroying engines, for instance the LT5 would eat itself without a crank bending damper.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Alloy crankshaft pulley
M20 Pobeda, good one haha!(i can't get a smilie...)
The reason i asked is that a guy i know told me that racing engine's (let's say for a hillclimb) don't need any damper and with the alloy pulley they are fine, with no wear in the cranks bearings.
Something that in my opinion can't happen...And that's why racing engines must be open after one or two race's for examination.
Torsional vibration rise as the crankshaft size rise right?
RE: Alloy crankshaft pulley
I am not sure all is optimum or even well Just because the main bearings bearings look OK after the first race.
I suspect the crank bearings may be among the last components to show the effects of prolonged operating at a torsional critical speed.
I guess Modern engines sometimes have dampers (or is it sometimes the flywheel?) with features that make them effective at taming lateral or bending crank (or whole engine?) vibration.
I believe Historically dampers were usually torsional dampers. I base that on SAE papers that introduced engines of the 50s and 60s (Chevy, AMC, and Pontiac V8, Corvair) including charts showing dampered and damperless crankshaft angular deflections at certain crank rpm, but with frequency many times operating rpm. Typically like this -
http
If a damperless engine is run at full power at an rpm where a torsional resonant frequency exists, the amplified angular twist/untwist/reverse twist motion will subject the crank to a million fatigue inducing overstress cycles in a few hours, and that leads to cracks and eventually breakage. That's bad enough.
How about the possibility of more insidious effects on valve train, especially overstressed valve springs, and ignition timing?