So, if you had to replace your engine.....

   / So, if you had to replace your engine..... #1  

Frank Sorbello

Gold Member
Joined
Jul 12, 2011
Messages
362
Tractor
Power Trac PT-422
I think I am going to replace the 22hp Robin in my recently purchased PT-422. My question to you, is if you had to replace the engine on your PT-422 or 425 -what would you replace it with? and why?

I am leaning toward the 28hp efi Robin or maybe a Kohler.
 
   / So, if you had to replace your engine..... #2  
For simplicity - EFI Robin. It will fit and it will start in cold weather. It's dimensionally identical to your existing engine, except for being a little bit taller. The Robin V-twin seems to be the dimensionally smallest engine in it's horsepower class. My 2004 425 was designed around the Robin. Most other 25hp engines won't fit without substantial modification.
 
   / So, if you had to replace your engine..... #3  
For simplicity - EFI Robin.

++1.

There are two individuals on this board who have put the 28hp EFI engine in their PT422.

KMA: http://www.tractorbynet.com/forums/power-trac/202389-pt422-engine-swap-completed-pics.html
Vacuous One: http://www.tractorbynet.com/forums/...engine-shaking-sputtering-10.html#post2170245

It isn't as overpowered as it sounds: the 28HP is the same engine as the 25 HP engine except for the carburator is replaced with the EFI throttle body. The difference is that the 28 HP is quoted for a higher engine rpm then the 25 HP. Terry from powe rtrac has confirms that the PT422 pumps would work with a 25 HP engine.

One suggestion: if you have the square exhaust manifold that power trac cursed some of us with, then throw it away and find a stock robin exhaust manifold that can be adapted to your installation. The Power Trac exhaust manifold is really bad, and tends to restrict flow and trap heat in the engine compartment.

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It is too bad that Power Trac didn't set up their engine compartments to accept vertical v-twin engines. The vertical engines seem to sell for about $500 less then horizontal versions, possibly because of economy of scale. It seems that just about every lawn tractor or zero turn mower out there uses vertical engines. Some of those mowers are cheaper then just a horizontal engine.

I am thinking vertical engine with a clutch/pulley attached, and a vee belt or poly belt connecting to a vertical stack-up of hydraulic pumps. I think it would fit better, give better access in the engine compartment, and give you a clutch to make engine starting easier.

JJ, can the hydraulic pumps be oriented vertically?

Of course, trying to retrofit such an arrangement would require replacing all of the hydraulic hoses and fittings, since their existing lengths would be wrong.
 
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   / So, if you had to replace your engine..... #4  
years ago when I worked in commercial refrigeration I worked on over the road units that had small 2 and 3 cylinder diesel engines with a footprint roughly the same size as the 25hp robin Subaru engine, I regret that I do not have the specifications on these small diesel engines would have made a nice transplant engine, aside from that I would definitely go for the EFI engines with a factory exhaust system
 
   / So, if you had to replace your engine..... #5  
Just rememeber that whatever engine you put in it, it has to turn at 3600 RPM (at or near the original) to get the same flow in your hydraulics.
 
   / So, if you had to replace your engine..... #6  
Dear Washita,

Interesting idea. The Carrier Transicolds go up to 48HP, 150Ftlb of torque. But I doubt that they spin at 3600 RPM.

All the best,

Peter



years ago when I worked in commercial refrigeration I worked on over the road units that had small 2 and 3 cylinder diesel engines with a footprint roughly the same size as the 25hp robin Subaru engine, I regret that I do not have the specifications on these small diesel engines would have made a nice transplant engine, aside from that I would definitely go for the EFI engines with a factory exhaust system
 
   / So, if you had to replace your engine..... #7  
Tim_in_CT

JJ, can the hydraulic pumps be oriented vertically?

Yes.

Most vertical engines are way less expensive.

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   / So, if you had to replace your engine..... #8  
One thought on a vertical arrangement: you will probably raise your center of gravity. If you are on the flats, it may not make much difference, but any slope usage will be impacted.

All the best,

Peter
 
 
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