Yanmar RFM PTO rpm (YRM48)

[JCByrd24]

Anyone out there have a Yanmar YRM48 (or other size) rear finish mower and a manual for it, or do you know what PTO speed it is supposed to be run at. I've been running mine at 540rpm based on guidance from JD dealer I bought it from last year (with my 186d). For no other reason than curiosity today I calculated the blade tip speed and found that it looks like I want 1000RPM PTO. I don't really use it to mow the lawn so I haven't found that it doesn't cut properly. I have about an acre of old hay field that I mow with it around 4-5" once or twice a month, and it does that with decent results at 540rpm, but it could be better. To be clear it's basically grass now, only about 8" when I cut, and it's not really working the mower or tractor at all. Now that I think about it the mower doesn't really sound like a mower either, the airplane taking off sound when the blades engage, just the whirl of the belts and gears. Here's my math...my understanding is 18000-19000 fpm or just over 200 mph tip speed is "standard".

17" blade x pi = 53.4" = 4.45 ft circumference or ft per revolution
540 PTO rpm x 4.25 gear/belt ratio = 2295 blade RPM (I counted the ratio)
2295 rpm x 4.45 ft = 10213 fpm tip speed or 116 MPH

Now, 1000/540 = 1.85

10213 x 1.85 = 18913 fpm or 215 mph, which tells me this mower was designed to run at 1000 PTO rpm.

 

[Roonabeck]

That does seem a bit slow compared to my woods rdc54 at 16,200 fpm.

 

[JCByrd24]

Thanks for the reply, I agree it seems very slow. If the numbers didn't seem to indicate that 1000rpm PTO was PERFECT, I'd question it more. I had also noticed that the woods smaller sizes are about the slowest of today's mowers. The 60 and 72 over 18000+fpm. A user here has a manual and hopefully will be getting home from a trip today and look it up for me. I'll report back.

 

[YannyMan]

Give Gary Jamieson at Jamiesom Tractor a call. He'll know or be able to look it up.

 

[sacsr]

Read the manual I have for the YRM-48 and there is no mention of what rpm to run at all??

But just read my YRM 48A manual and it says 540 rpm.......

Gary will know.