mean piston speed and reliability?

R

Riss

New member
Is calculating the mean piston speed a good gauge on the reliability of a motor?
What would the thresholds be on a motorcycle?
Saw this page:

all_redline_rpm_vs_reliability

so if we (vols/c50/m50) ran at 5500 rpms in 5th (think thats 'round 85-90mph and 70% of redline) the mean piston speed is only at 2691 ft/min. which puts it at well under the 3500 ft/min threshold for good reliability. meaning we can cruise those speeds all day w/o stressing the motor?

just curious :)
 
No, it is not a gauge at all of the reliability of a motorcycle. Nor does lower RPM necessarily mean more longevity out of the motor.

A low RPM mill with a high reciprocating mass could put more stress on the bottom end than a high RPM motor with a low reciprocating mass. The overall design of the motor is far more important than RPM. For example, my high-revving Intruder 800 went 135,000 miles, while I have yet to find anyone with a lower-revving Intruder 1400 that has gotten over 80,000 miles out of one. Nor can I find anyone who has ever gotten more than 40,000 out of a super-low revving shovelhead before it needed a rebuild, while the higher-revving Harley Twin Cam 88 is easily good for 125,000+.
 
the only thing it DOES speak to is potential reliability of wrist pins and connecting rods, assuming you know their weight and can then calculate the force on the parts (F=m*a)

it's quite easy to get high rpm motors to have low piston speeds, since one factor is rpm and the other is stroke - a longer stroke creates higher peak piston speeds.
 
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