It would be a guess-estimate at best!  Having a ratio of 6.12:1 likely means it is a double reduction, seriously increasing the complexity.  In addition, by definition AGMA nameplate gear ratios may not be exact.

Some possible methods that might help.  As a rough guide use about 18 to 20 teeth on the input pinion and estimate the gear mesh.  So on a 1780 motor, mesh would be about (18 * 1780) / 60 = 534 Hz.  Do you have a peak in the spectrum around that frequency?

How about the ability to examine a spare machine in a warehouse, or a damaged machine where the internals may be accessible?

Thank you for the reply! This is a single reduction Marley cooling tower gear box. I have a peak of 10,200cpm and a running speed of 1,457. So I was think it has 7 teeth on the pinion gear. I am also seeing 2 and 3 times the 10,200 peaks. Mathematically this works but I am hoping to get the actual gearbox data so I wouldn't have to guess on the report.

Thank again

Seven teeth on the pinion would be very low, but not impossible.  If indeed that is the case I would suspect it is a spiral bevel.  Can you provide the best obtained out put speed when the input is 1457 RPM.  I have various ways to calculate the tooth combination; one involves using ratio and the other using speeds.  The two methods differ significantly in the method so I typically do both as a cross check.

This is a spiral bevel. Output speed appears to be about 210 rpm.

@Registered Member posted:

This is a spiral bevel. Output speed appears to be about 210 rpm.

Something wrong…1457/210 = 6.938 but up front you said the ratio is 6.12:1.  Verify the speeds, confirm this is a single reduction and see if you can get any info that would confirm seven teeth on the pinion.

Thanks for your help