crankshaft deflection
crankshaft deflection
(OP)
I would like to get a handle on how much crankshaft rotational deflection occurs in engine operation .
I have heard that deflection could be in the order of 1 degree, say if number 1 cylinder has just fired and the resulting torque twists or winds up the crank to the flywheel end . I imagine there would be both positive and negative deflections.
Could anyone enlighten me to the actual measurments experienced in engines.
Thankyou
I have heard that deflection could be in the order of 1 degree, say if number 1 cylinder has just fired and the resulting torque twists or winds up the crank to the flywheel end . I imagine there would be both positive and negative deflections.
Could anyone enlighten me to the actual measurments experienced in engines.
Thankyou
A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare





RE: crankshaft deflection
RE: crankshaft deflection
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: crankshaft deflection
Shorter cranks are stiffer and tend to twist less.
For a I6 engine for cars I have experience of twist angles (end to end) of up to 1.5/2 deg, when rotating at high speed (7500/8000 rpm) with no engine load (driven by the dyno).
Twist is worse in this case because the 3rd order inertia torque (critical for a 6 cylinder) is not counteracted by firing torque.
RE: crankshaft deflection
RE: crankshaft deflection
RE: crankshaft deflection
RE: crankshaft deflection
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: crankshaft deflection
As with everything on this forum, it depends on the application. Top fuel engines see 15-20 degrees under power, enough that it has to be accounted for when you grind camshafts.
R1100S
Presumably the cam stays in time with the front cylinders as the drive for the cam is at the front of the engine .So do you have to retard the cam grind progressivly as you head towards the back cylinders?
Malbeare
A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare
RE: crankshaft deflection
RE: crankshaft deflection
Rod
RE: crankshaft deflection
Norm
RE: crankshaft deflection
RE: crankshaft deflection
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: crankshaft deflection
Top Fuel dragsters run reasonably low static compression as they run high boost and high nitromethane levels.
This leaves plenty of room for a lot of piston to valve clearance.
Another concern is that at the valve spring pressures they run, the camshafts also "wind up" a bit, so I guess they would need to correct for both.
The crank would be torque and load dependant, while the cam will be rpm dependant, so the relationship will keep changing according to several independent factors.
Maybe someone will come up with individual cylinder crank position sensors to control spark and to control individual lobe "V tech". Just kidding, this is reasonably big budget, but is not F1 we are talking about.
Regards
eng-tips, by professional engineers for professional engineers
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RE: crankshaft deflection
Ken
RE: crankshaft deflection
Rod
RE: crankshaft deflection
Maybe in the turbo era there was room to move the cam around.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.