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jfischer · Feb 15, 2016

Josh, why don't you start a new message with "Diesel for 425" and see if you get any answers to some that work with them all the time. I looked at that engine, and think it is too wide, and seems the length on the Subaru is short also. They kind of have you by the short ones here as to what will fit in there.

joshlee said:
Has anyone ever checked out one of these Kohler Diesel engines? I didn't take any measurements or anything, but I'm always looking for what to swap the Subaru out with when its at the end of its life. Are the Hydro pumps in the PT 425 designed to work well while turning at a lower RPM?
Kohler Engines: KD625-2: Kohler Diesel Air-Cooled: Product Detail: Engines

Marks481 · Feb 17, 2016

joshlee said:
Are the Hydro pumps in the PT 425 designed to work well while turning at a lower RPM?

No

You put an 1800 rpm engine in there, and the hydraulic pump will only be putting out 50% ( or slightly more) of the current flow rate (depending on where the governor is set on the current engine, it is either 3300 or 3600 rpm, IIRC).. If you are using a brush hog, snowblower, or lawn mower, that just won't cut it. Not to mention you will be moving real slow.

You want an 1800 rpm engine, then you either need to do an indirect (belt) drive to get the pumps back to speed, or buy new pumps... which will cost you as much as the new engine.

joshlee · Feb 17, 2016

Yeah, I see. It just wouldn't be worth it. Right now I'm looking at these Hatz engines that do run up at 3600 rpms.091E

tmarks11 said:
No

You put an 1800 rpm engine in there, and the hydraulic pump will only be putting out 50% ( or slightly more) of the current flow rate (depending on where the governor is set on the current engine, it is either 3300 or 3600 rpm, IIRC).. If you are using a brush hog, snowblower, or lawn mower, that just won't cut it. Not to mention you will be moving real slow.

You want an 1800 rpm engine, then you either need to do an indirect (belt) drive to get the pumps back to speed, or buy new pumps... which will cost you as much as the new engine.

MossRoad · Feb 17, 2016

Something else to consider... if you have a PT425 and intend to drop in a 22hp engine, you may notice a difference if you intend to power a 60" mower. When I was considering a PT back in 2001, Terry at Power Trac highly recommended NOT using a 60" mower on the 22hp unit. He said 48" would be the max. He also said you'd notice a considerable difference with broom, tiller, brush cutter, etc.... between the 22 and 25 hp units.

I'd like to see the torque curves on that diesel and the robbin and kohler 25hp motors.

Marks481 · Feb 18, 2016

MossRoad said:
He also said you'd notice a considerable difference with broom, tiller, brush cutter, etc.... between the 22 and 25 hp units.

yes, when I am brush cutting with my PT-422, I have the choice... cut brush or drive fast. Not both. I would like a few extra hp, if anyone has some to spare?