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  1. #1
    Silver Member
    Join Date
    Jul 2011
    Posts
    173
    Tractor
    Steiner 430

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

    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.

  2. #2
    Platinum Member
    Join Date
    Jan 2005
    Posts
    629
    Location
    SW Virginia
    Tractor
    PT425

    Default Re: So, if you had to replace your engine.....

    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.

  3. #3
    Platinum Member tmarks11's Avatar
    Join Date
    May 2005
    Posts
    635
    Location
    Port Orchard, WA
    Tractor
    2005 Power Trac 422

    Default Re: So, if you had to replace your engine.....

    Quote Originally Posted by Gravy View Post
    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/p...eted-pics.html
    Vacuous One: http://www.tractorbynet.com/forums/p...ml#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.

    --------

    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.
    Last edited by tmarks11; 03-16-2013 at 07:28 AM.
    -----------------------------------------------------
    Now in Port Orchard, WA
    2005 PT-422
    4n1 bucket, minihoe, auger, 48" mower, land pride aerator, tow adaptor, forklift, crane, Herd GT77 spreader, LMB, 60" blade, M1 abrams turret.
    PT422 (6/23/05) photo page

  4. #4
    Silver Member
    Join Date
    Feb 2009
    Posts
    224
    Location
    south western michigan
    Tractor
    pt 425, JI Case, Gravely Comm.10A

    Default Re: So, if you had to replace your engine.....

    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

  5. #5
    Epic Contributor MossRoad's Avatar
    Join Date
    Aug 2001
    Posts
    22,849
    Location
    South Bend, Indiana (near)
    Tractor
    Power Trac PT425 2001 Model Year

    Default Re: So, if you had to replace your engine.....

    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.
    MossRoad

    Click On My Little Tractor
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  6. #6
    Veteran Member
    Join Date
    Mar 2007
    Posts
    1,131
    Location
    Bay Area, CA
    Tractor
    Power Trac PT1445

    Default Re: So, if you had to replace your engine.....

    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



    Quote Originally Posted by washita View Post
    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

  7. #7
    Super Star Member J_J's Avatar
    Join Date
    Sep 2003
    Posts
    16,446
    Location
    JACKSONVILLE, FL
    Tractor
    Power-Trac 1445, KUBOTA B-9200HST

    Default Re: So, if you had to replace your engine.....

    Tim_in_CT

    JJ, can the hydraulic pumps be oriented vertically?

    Yes.

    Most vertical engines are way less expensive.

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    J.J.

    When I works, I works hard. When I sits and thinks, I goes to sleep.

    Git er done.

  8. #8
    Veteran Member
    Join Date
    Mar 2007
    Posts
    1,131
    Location
    Bay Area, CA
    Tractor
    Power Trac PT1445

    Default Re: So, if you had to replace your engine.....

    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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