OK, decision time: 28 or 35

[marrt]

I called Terry and my engine is shot. Less than 500 hours.

So, go with a 28HP EFI (really, a 25HP at 3600 RPMs) or upgrade to a bad boy 35HP Robin? Frankly, I'm a little scared of the 35...BUT...I see a lot of advantages as well. I think this should be a fairly safe upgrade. I'll be installed a supplemental fan with any upgrade.

Thoughts?

Tom

 

[KMA]

Personally, I wouldn't put more HP in the PT425 tub. I don't think there are enough "band aid" fixes to address the inherent heat related issues. If I do it again, the next engine will be liquid cooled with the radiator mounted external to the tub. I went with the EH72FI. Good luck!

 

[Frank Sorbello]

Kevin, do ou know what liquid cooled engine you would go with? I have often thought of finding one that would fit.

Tom, Did Terry say how much bigger the 35hp would be size wise? and are both EFI? Good luck in what ever you choose to do.

Frank

 

[Gravy]

I vote 35. Mine is working well with no supplemental fans or bandaids. I haven't done any scientific temperature testing, but it hasn't vapor-locked like the EH72 did. I'm assuming that it stays cool enough because it's a 40hp design tuned down to 35hp instead of a 25hp design cranked up to 28. It also starts way better in cold weather.

 

[Marks481]

Liquid cooling would be nice, but I don't think you will be able to shoe-horn it in without welding up a 6" tub extension. I have toyed with that idea several times, and the dimensions don't seem to stack up.

If you look back in the archives here, there is of course scarg'se Kawasaki 29HP liquid cooled conversion. But that didn't come close to fitting... he ended up raising the height of the hood by about a foot and strapping a gas tank on the back.

http://www.tractorbynet.com/forums/power-trac/112869-2004-model-pt-422-modified.html

Maybe it is time to go play around with Solid Works...

 

[MossRoad]

If the footprint is the same and the shaft sizes are the same and you won't have to re-engineer a bunch of stuff, I'd go with the higher HP. The motor won't have to work as hard, but that just means you might push it more?

In all seriousness, when I look at any piece of equipment, car, truck, boat, tractor, lawnmower, whatever, I look for the size model I want, then get the largest HP engine that's available in that size frame.

 

[MossRoad]

Liquid cooling would be nice, but I don't think you will be able to shoe-horn it in without welding up a 6" tub extension. I have toyed with that idea several times, and the dimensions don't seem to stack up.

If you look back in the archives here, there is of course scarg'se Kawasaki 29HP liquid cooled conversion. But that didn't come close to fitting... he ended up raising the height of the hood by about a foot and strapping a gas tank on the back.

http://www.tractorbynet.com/forums/power-trac/112869-2004-model-pt-422-modified.html

Maybe it is time to go play around with Solid Works...

Yes, I believe your are correct. There just isn't enough room for a liquid cooling system in the existing tub. You have to either go UP or BACK.

 

[Frank Sorbello]

Is the footprint of the 35hp engine much larger than the 28hp?

 

[marrt]

Frank,

If I remember right, Gravy said the 35 is only about half an inch longer. I assume that doesn't include the debris shield. Apparently, the 35 has some type of rotating debris shield that keeps junk out of the fan. Grady also mentioned the engine was actually a bit narrower than the 25 which could help a lot with cooling.

I was leaning toward the 28 but, after the responses here, I may go for the 35. It's not much more expensive and it's not a Subaru (it's a re-badged Generac). Whatever I do, I'll try to document it with lots of pictures. I already have new wheel motors on the way and a suspension seat in the garage along with some new LED lights. So, might as well do everything at once.

Tom

 

[ponytug]

Not that I know diddly, but it seems like it worked well for gravy. Besides, it is your nickel, but if it is close, I'd go with the 35, for a slightly different reason. The Generacs have been designed and built to be in confined spaces, so it probably has an edge on dumping heat.

If you do, I would be interested to hear whether you end up using it at half throttle, or wide open. My bet would be that you can get the RPMs up, but that the fuel consumption isn't going to be much different than your current machine.

Sorry that you have to replace the engine. I hope that the next one treats you better.

All the best,

Peter

 

[Raw Dodge]

If the 35s a 992cc generac,I'd pass..those engines have a very spotty reliability history and parts are not easy to find and get quickly.Early versions threw rods thru the block often (red valve cover ) 30hp, the later version 32hp was supposed to fix all that but many of those too threw rods,the latest black shroud version i don't know about but that engine has large internals in a tiny crank case,which i believe is part of the problem...I'd avoid that engine altogether. .Supposedly they work well in a genset where they fire and immediately run to 3600 and stay there that's what they were designed for not a variable throttle engine. .much like the old 2 stroke Detroit diesels,they were one of 5 best stationary engines every made ,they'd run forever at a steady 1825rpm,but put one in an over the road truck and they wouldn't last nearly as long.

 

[Frank Sorbello]

Tom, In 2010 I bought a new Steiner 430 with a Generac 33hp air cooled engine. It had a lot of power compared to the Steiner 420 I just sold with a a 20 hp Onan. What I didn't like was the throttling of the Generac. The throttle almost always had to be wide open to do any type of work. I talked to the engineers at Steiner and they said it was because the Generac engine I had was made for powering generators, so it was always loud and used a quite bit more gas than my oman.

 

[Frank Sorbello]

EH90 and EH99 Big Block V-Twin Engines from Subaru Industrial Power Products

 

[MossRoad]

Since we're supposed to run our gas engine Power Tracs at full throttle anyway, would it really matter?

 

[Frank Sorbello]

With my Steiner and the attachment I had for laying wire it did matter. The throttle controlled the speed of the front PTO and I was tearing up lawns when I didn't need to.

 

[marrt]

Well, this is the problem with a lot of stuff these days. Kohler's are made in China and "ain't what the used to be." Kawasaki's had lots of problems a few years ago. Subaru's don't like the cold or the heat. Frankly, I don't see how it's even possible to get 40 HP out of a 120lb engine with ANY reliability. Pretty amazing really.

Anyway, I've narrowed the choice to a Subaru 28 or 35 due to ease of installation. The 28 is the same 25 I have now with fuel injection. So, it's not much of an upgrade. As Gravy mentions, the 35 is a detuned 40..or, at least is able to handle 40 HP. The cooling fins and fan probably have excess capacity in a 35 HP application. It may not be reliable. But we know for sure the 25 has lots of issues in this application. So, it doesn't seem like I'm increasing my risk much.

Gravy, any chance I can beg you for a picture of your muffler set up? This is the one area where I'm uncertain how to proceed.

 

[Raw Dodge]

Since we're supposed to run our gas engine Power Tracs at full throttle anyway, would it really matter?

Yes but it is still a different application, gensets don't typically bounce around,operate in wet pr dusty conditions ,operate on side hills,and the generator head is direct coupled and matched so that at maximum output the engine only.pulls back maybe 100 rpm below the governor setpoint.They hsve no throttle either it literally fires and goes to 3600,the only lower rpm operation will be by choking it too long to prevent it clearing out and revving out.And no matter how your supposed to operate it.i see so many people especially older men operating equipment at too low an rpm,either for noise ,trying to save fuel or whatever, but in most cases they end up causing more wear and damage to the hydraulics and engine by lugging them.This happens alot.

 

[Marks481]

I would like to see an adaption of a vertical liquid cooled engine, with the hydraulic pumps mounted vertically and driven off a drive belt with a clutch to make starting easier. I am betting it would be a more efficient use of the space in the engine compartment, and maybe allowing shoehorning in a liquid cooled engine.

Something like this Kawasaki 26:



OK, that might be a bit much to make that work. Back to the Kawasaki FD791D horizontal liquid cooled, DFI 26 HP engine. This would require an additional 4" in the tub over the existing Robin 25. At $2200, it isn't much more expensive that the air cooled twins.

Kawasaki Engine Model FD791D-S01 - On Sale At Tulsa Engine Warehouse



I think that cutting the back plate off the tub and welding a 4" extension would work. You could continue the natural slope up of that back section of the tub to avoid giving ground clearance problems. I think with a bit of thought this could be done elegantly. I think if I was re-engining that I would start playing around with solidworks to see if I could fit it all in.

You could also step up to the FD851D 31 hp engine, which I think has the same footprint, for $2450.

 

[MossRoad]

Its my understanding that the Kohler command pro engines are made in Wisconsin.

 

[KMA]

OK, that might be a bit much to make that work. Back to the Kawasaki FD791D horizontal liquid cooled, DFI 26 HP engine. This would require an additional 4" in the tub over the existing Robin 25. At $2200, it isn't much more expensive that the air cooled twins.

Kawasaki Engine Model FD791D-S01 - On Sale At Tulsa Engine Warehouse

View attachment 433434View attachment 433437

I think that cutting the back plate off the tub and welding a 4" extension would work. You could continue the natural slope up of that back section of the tub to avoid giving ground clearance problems. I think with a bit of thought this could be done elegantly. I think if I was re-engining that I would start playing around with solidworks to see if I could fit it all in.

This was the engine I was looking at a while back. I didn't spend much time on it, but do you think the radiator connections could be extended such that it could be mounted out the back of the tub (with a protective shroud)? Maybe the rear-facing side of the cover could be removed so that it would rotate right over it when opened? I was thinking the bulk of the existing tub could be left as-is and the only major fab would be the shroud (and maybe some cutting of the rear tub section). That being said, I didn't actually look at measurements, etc...