Tiger Cub engine repower Kawasaki FD731V

Discussion in 'Mechanic and Repair' started by awbryant45, Jun 25, 2014.

  1. awbryant45

    awbryant45 LawnSite Member
    Messages: 4

    Hello Lawnsite!

    Excellent forum!

    First time poster here.

    Has anyone converted or repowered a Scag Tiger Cub or Tiger Cat from air cooled to water cooled?

    Current Mower:
    2004 SCAG Tiger Cub, 19hp Kawasaki FH601, 48" deck, the Kawasaki blew a rod bearing at approx. 1,400 hours.

    I decided to be cheap and bought a FD731V-BS07 26hp water cooled engine from Surplus Center for $979 for the complete engine with muffler. Shipping was $180 FedEx residential. Small Engine Warehouse sells what I think is the same engine that has been "converted" to work on a Tiger Cub for $1,400 plus shipping.

    Just curious if anyone else has made this or a similiar conversion, and was looking for some advice before starting this project to keep from making too many mistakes.

    Thanks for your help in advance,


  2. Bob MacGregor

    Bob MacGregor LawnSite Member
    Messages: 221

    Your bad engine is a FH601V-????
  3. awbryant45

    awbryant45 LawnSite Member
    Messages: 4

    Bad engine is FH601V-FS21-S. Update - I think the FD731V-BS07 is going to mount to the SCAG frame without modification. In other words, the pre-drilled holes on the mower frame line-up with the holes on the FD731V. The output shafts are the same diameter and seem to be the same length (not completely sure on this yet, though), b/c I have not mounted the replacement engine on the mower. Reason being is that the new engine FD731V's mounting holes have not been tapped. They have been drilled, but not tapped. Why would an engine ship without being tapped?

    Will update more once I get the holes tapped for mounting bolts. The old engine, the FH601V-FS21, used a nut and bolt to secure the engine to the mower frame and the new engine, the FD731V, will have a bolt that just screws into the engine block.

    I really hope I can get this set-up to work...
  4. Bob MacGregor

    Bob MacGregor LawnSite Member
    Messages: 221

    It is normal that the bolt holes are not threaded, as either SAE or Metric bolts can be used depending what country the engine is shipped to. Use a taper tap then a bottoming tap to cut the threads and use some cutting fluid that is OK on aluminum, you don't want to screw up a new engine. The bolt length is also critical, too long will break the block when tightened, too short will strip the block and fall out.
    but most of all make sure that the crankshaft dimensions are the same as your old engine. You should also consider an engine temp gauge which your machine is not wired for, but can easily be done.
  5. awbryant45

    awbryant45 LawnSite Member
    Messages: 4

    Thanks for the reply, Bob.

    Update - The pre-drilled holes in the new engine FD731V case are 11/32 diameter. I used a drill bit to determine the diameter (my tape measure was only good for 1/16th). 11/32 happens to be the drill size of a 10mm tap. I'm using WD-40 as cutting fluid, and a 10mm x 1.50 tap ( a course thread instead of fine thread on the aluminum). I will mount the engine this weekend and see if the pump pulley and electric clutch mount up ok. If yes, then I still need to see if muffler will work (may need some mods), and I will need to adapt the new engine wiring harness to the Tiger Cub's harness. Will keep updating. All this to save ~$350. I wish had just ordered the already converted FD731V from Small Engine Warehouse.
  6. Bob MacGregor

    Bob MacGregor LawnSite Member
    Messages: 221

    The engine mounting bolt holes in the machine may be 5/16", so check them.
  7. awbryant45

    awbryant45 LawnSite Member
    Messages: 4

    Bob, you are correct, the mounting bolts were 5/16, and needed to be drilled a bit larger to accept the new 10mm mounting bolts. Engine is mounted, and running fine. Following are the modifications needed if using an FD731v-bs07 to repower a SCAG Tiger Cub:

    1. Tap the engine mounting holes.
    2. Enlarge the mounting holes on the SCAG frame to accept the new 10mm bolts.
    3. Cut off the heat shield on the muffler, and remove "snorkel" on the muffler.
    4. Negative ground from battery has to be mounted under the engine (using a mounting bolt from the engine).
    5. Made an additional ground cable to go from the battery to the wiring harness grounds and then bolted both to an open hole in the frame near the engine.
    6. Used three male wiring connectors to plug into the new engine's harness connector (from old engine connector to new engine connector). Would really like to find a way to make this more secure.
    7. The engine guard fits with the muffler, but in order to use my leaf bagging attachment, I will need to drill mounting holes that allow the engine guard to stick out another 1-2" more than stock to clear the carb.
    8. No radiator screen was included - will have to make one or order one off ebay for $40.
    9. The PTO and hydraulic drive belts work fine.
    10. The choke and engine speed controls mounted up fine.
    11. Fuel inlet is on opposite side of engine as compared to the old engine, but enough fuel hose is included that this was not an issue.

    That's it for the needed modifications. I was able to cut some grass today. My cost for the conversion was $979 engine, $180 shipping, $10bolts, $40 radiator screen = $1,209 for a 26hp, liquid cooled Kawasaki. The exact replacement, a FH601V, if you can find one is $1,600 + shipping. There was the option of a 27hp Briggs for around $750 (Northern Tool) +tax +shipping + plus a muffler ~$1,000. For an additional $200, I think the Kawasaki is a better deal.

    I don't do much mechanic repair work other than my own light maintenance and it took me about 10 hours to make the conversion.

    This engine is a LOT quieter than my old 19hp, and it really makes the cub move.


  8. Bob MacGregor

    Bob MacGregor LawnSite Member
    Messages: 221

    Sounds great!!
    There should be a non critical bolt somewhere on the engine to connect the ground cable lug onto, I don't recommend leaving it under the engine.
    My Cub originally had a 26 HP Briggs ELS that although was still running but with low compression in the L/H cylinder due to stuck rings, I replaced it at 472 hours with a 30 HP Briggs Professional Turf Series engine. This was almost a direct swap. The new engine has the Cyclonic Air Filtration system that appears to be doing the job. I also use a collection system most of the time and recently replaced the fan and bearings in the blower. When I was researching repower options, I really wanted a Kawasaki FX730V which is what is on my Hustler X-ONE, but the cost of the engine and needed parts was 2 1/2 times the Briggs, so I went with the Briggs. I'm happy with the Briggs, I like the increase in power and have noticed a reduction in fuel consumption. It now has about 120 hours on it and at 100 hours I swapped it over to full synthetic engine oil which is acceptable per the manual.
    Take care and enjoy the new engine!!!

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