OK, decision time: 28 or 35

KMA · Jul 19, 2015

tmarks11 said:
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 433434 View 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 on 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. That being said, I didn't actually look at measures, etc...

Marks481 · Jul 19, 2015

KMA said:
Maybe the rear-facing side of the cover could be removed so that it would rotate right over it when opened?

That might be a good approach. It looks like the radiator makes up most of that extra 4" that would be required. If so, that would be easier than welding 1/4" plate extension onto the back of the tub.

The version of the Kawasaki 791D that mounts in a Toro has a stub shaft on the flywheel side. So you could mount the engine backwards, with the muffler hanging out the back (which seems to be a better place for it than hanging over the hydraulic pumps in the middle of the tub). The radiator could be mounted at the front (or middle) of the tub, drawing air into the tub from behind the drivers seat. Establishing a natural air flow like that would help cool the whole engine compartment better. This might require some innovative reworking of the gas tank to allow a path for airflow to the radiator.

The Toro part numbers for the stub shaft I came up with was 110-6249 and 112-2335 (both required). Not sure this is specifically for the Kawasaki.
Toro Z580 parts

joshlee · Jul 19, 2015

Oh really? I didn't know that. Is there a special reason why?

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

stray · Jul 19, 2015

I just bought another pt. A 428 fi. First time I used it; it got hot and would not run. I assume it was vapor locked. It didn't surprise me. I just went and got the old 422 and finished the job. These engines don't like cold and they don't like it hot. So I have to fix the design problems with an oil tank heater $150. Then I will add a blower to force air in to the tub for hot weather. That is just the way it is. And I was not surprised when this happened. I just have to do the design work Power Trac should include if their engine does these things.
I will eventually put an engine in my 422 but I probably won稚 be a robin engine. Moss seems to have good luck with his engine starting in cold and not quitting when hot. Isn稚 it a Kohler.

PS I realy still like my Power tracs. and i am happy with the 428. just need to do these things to get it right. it's fixable.

marrt · Jul 20, 2015

Well, it isn't looking to promising for the 35. The 35 uses (I think) an SAE B engine mount configuration. This has a pilot flange of 5.75". My old 25 has a pilot flange of 6.43". This is probably some type of metric standard. It's a lot easier to take metal off than put it on. I may call PT and see if they have a motor mount that will work. However, it's now looking like the 28 will be the easiest fix.

Interestingly, my shaft is 1 7/16. Further, it doesn't use a lovejoy connection. It uses some type of geared arrangement connected by a sleeve. Pretty neat set up.

joshlee · Jul 20, 2015

So, how long do these wheel motors usually last on these PTs? Just curious.

marrt said:
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

woodlandfarms · Jul 20, 2015

joshlee said:
So, how long do these wheel motors usually last on these PTs? Just curious.

Like any part on any machine, 3 weeks or 30 years. JJ will probably know, but I bet the life expectancy is around 3000 to 5000 hours. But there are so many variables.

Marks481 · Jul 20, 2015

marrt said:
My old 25 has a pilot flange of 6.43".

OK, my google-fu is weak; I cannot find an engine flange size that corresponds to 6.43" (or 163 mm). Closest I can see is 160 mm (6.30").

More important question: what is the flange dimensions for the hydraulic pump. Assuming that is standard size, you should be able to buy pump-engine mount that will fits between the engine and the pump. That would free you up to buy the engine you really need (35 hp) vs settling for an engine that fits the current mount.

You probably can find the replacement mount for less than $100).

joshlee · Jul 21, 2015

Thanks. Thats what I sort of figured. As far as the life of the Subaru EH72 goes, hopefully it will last a good while after installing the fan and Subaru header/muffler.

MuncyBob · Jul 21, 2015

Is your side fan pushing or pulling air?

marrt · Jul 21, 2015

Here's a pic of the bolt circle and pilot flange for the 25:

I spoke yesterday with someone who knows a lot about these tractors and he suggested I stick with the stock carburated 25. Apparently, Subaru changed the carburetor and made other changes over the years to the engine. Since I already have the side mount muffler, I'm now leaning toward this option.

ponytug · Jul 21, 2015

Perhaps I am misreading the plan, but I count 143, no 163.5?, and 196mm bolt patterns. That's 5.63", (6.437"?), and 7.72", but with only the inner and outer prethreaded. No idea what it cross references to, but that would seem like it would give you a lot of freedom to make an adapter plate.

All the best,

Peter

joshlee · Jul 21, 2015

This fan is blowing air inside the engine compartment, so its pulling air which isn't as effective for this model, but to turn it around and push air through the engine compartment would have taken way more time to design than what I wanted to do. Here are some cool faqs on these cooling fans. Its interesting knowing the difference between the "S" type blade and the "Flat " type. Since I live in a different climate than Kent does ( that designed this cooling system for the PT), the White Rodgers Snap Disc he used didn't work well for mine, so I used a White Rodgers Snap disc that is adjustable from 140 to 180 degrees. It works really well.

Farmall140 said:
Is your side fan pushing or pulling air?

https://www.a1electric.com/spal/faninfo.htm

Marks481 · Jul 21, 2015

marrt said:
Here's a pic of the bolt circle and pilot flange for the 25:

Where did you find the diagram? The one on the Robin site is low resolution and impossible to read.

The diagram of the 35 shows that it also accommodates 3 different flange sizes. Are you sure one of them doesn't match the pump mount you are using on the 25?

Moorrr Powerrr!!!

MossRoad · Jul 21, 2015

joshlee said:
Oh really? I didn't know that. Is there a special reason why?

Couple reasons. First, airflow over and around the engine is diminished at lower throttle which can lead to overheating. Second, hydraulic braking and response is best with full engine power.

MossRoad · Jul 21, 2015

woodlandfarms said:
Like any part on any machine, 3 weeks or 30 years. JJ will probably know, but I bet the life expectancy is around 3000 to 5000 hours. But there are so many variables.

I have heard many times over the years that as a guideline to expect around 2000 hours before a teardown and rebuild for the average twin cylinder air cooled lawn tractor type engines. Of course, this is completely unpredictable. Too many variables, like load on the tractor, hours of operation in dirty or dusty environments, operator error or operator babying the machine, oils, lubricants, air cleaners, and even the mood of the guy that put it together at the factory that day or made the parts, etc... just too hard to guess. :confused3:

Gravy · Jul 21, 2015

Quick replies to a couple of questions and comments:

According to my research before I bought the EH90, the mechanical weaknesses of the early Generac version are supposed to have been fixed in the newer versions. There's not a lot of data online, so I'm accepting some risk.

The exhaust manifold was made for a Generac GTH990 which was the predecessor to the Robin EH90/99. Mine came from an ebay vendor. I don't have the listing handy.

The bolt circle and pilot flange are different from the EH72, but it's a simple modification with a lathe and a drill. The coupler is a Bowex M42. My EH72 and EH90 both have 1-7/16" crankshafts.

It was a surprisingly simple conversion. I had to drill new holes in the bottom of the tub for the mounting bolts and shorten the spacers a good bit. I had to modify the pump adapter to fit the new pilot/bolt circle. That was it as far as modifications to the basic platform. The existing cables worked with a little rerouting. The wiring harness plugged in. I disabled the oil pressure interlock because it extended the cranking time more than I thought necessary.

So far, I am very pleased with the conversion. The engine is no longer the limiting performance factor. Unlike the EH72, there have been no vapor locking problems, so I suspect the cooling air flow is more than adequate. The EH90 starts way better in cold weather. Sadly, the fuel consumption has not improved noticeably. It may have even worsened a bit, but if so, it's a trade-off I'm willing to accept.

MossRoad · Jul 21, 2015

Gravy said:
......... I disabled the oil pressure interlock because it extended the cranking time more than I thought necessary .........

I'm interested in your comments about disabling the oil pressure interlock and cranking time...

I take it the unit has to build up oil pressure before it allows the spark?

Wonder if this is a feature on the other Robin engines? It would be an interesting experiment in cold weather starting to put that function on a switch and see if it makes any difference. Just throwing that out there.

Marks481 · Jul 21, 2015

Gravy said:
...I bought the EH90...So far, I am very pleased with the conversion....so I suspect the cooling air flow is more than adequate. The EH90 starts way better in cold weather.

wow, I had forgot all about you making the conversion.

A quick look at your thread:

http://www.tractorbynet.com/forums/power-trac/326704-well-now-ive-gone-done-2.html

...shows me that you STILL OWE US more PICS!!!

marrt:
I think this is your new engine, it even has your name on it:

Subaru Robin Engine EH900DS0010 Heavy Duty Air Cleaner(Donaldson) Electric start, pulse fuel pump, 1 7/16 crankshaft, 20 amp charging

...of course the water cooled Kawasaki DFI engine is almost the same price... decision...decisions...