I have a 3 cyl JD diesel mower with a Yanmar motor. Engine (hence blade) speed seems a little low. There is no tachometer on this machine. So how would I go about measing the engine rpm at full throttle? I see there is a governor adjustment screw on the pump/throttle body, but I don't want to mess with it unless it needs some adjustment. There are no direct electrical signals coming off the crank or camshaft. Here's what I've considered:
My Dad had a gizmo that was some type of shaft rpm indicator (maybe for a lathe or drill press). Its just a huge worm gear reduction set. You push the bit into the shaft center and count the wheel turns per time interval. Not sure I want to put my fingers that close considering the tight space.
Clip a playing card onto a bracket and let it rub on the crank pulley with a notch filed into it. Record the noise with Windows Sound Recorder and analyze the wave file for dominant frequency.
Park the mower near my JD tractor with a 4 cylinder motor (which has an accurate tach) and see if they hook up into a Dopplar frequency tone. This probably isn't accurate because the 4 cyl firing frequency is not the same as the 3 cyl firing frequency. The 4 cyl with tach is accurate because when the rpm is set to 540 and my pto alternator is hooked up, I get a measured 60 Hz line frequency off my circuit analyzer (measures Watts, Hz. and Voltage).
Another deviation from #3 is to use the playing card trick on both motors and listening for when they both hook up.
Is there a tool I could buy or rent to give me this answer? It's for setting idle AND top speed rpms. Once it's done I won't need it again so buying a tachometer is a hard investment to justify.
Just wondering out loud today....
My Dad had a gizmo that was some type of shaft rpm indicator (maybe for a lathe or drill press). Its just a huge worm gear reduction set. You push the bit into the shaft center and count the wheel turns per time interval. Not sure I want to put my fingers that close considering the tight space.
Clip a playing card onto a bracket and let it rub on the crank pulley with a notch filed into it. Record the noise with Windows Sound Recorder and analyze the wave file for dominant frequency.
Park the mower near my JD tractor with a 4 cylinder motor (which has an accurate tach) and see if they hook up into a Dopplar frequency tone. This probably isn't accurate because the 4 cyl firing frequency is not the same as the 3 cyl firing frequency. The 4 cyl with tach is accurate because when the rpm is set to 540 and my pto alternator is hooked up, I get a measured 60 Hz line frequency off my circuit analyzer (measures Watts, Hz. and Voltage).
Another deviation from #3 is to use the playing card trick on both motors and listening for when they both hook up.
Is there a tool I could buy or rent to give me this answer? It's for setting idle AND top speed rpms. Once it's done I won't need it again so buying a tachometer is a hard investment to justify.
Just wondering out loud today....
