OK, decision time: 28 or 35

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...