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Discussion Starter · #1 ·
I have a 425 with an engine that needs overhauled. Low compression in both cylinders, one side worse than the other by a good margin, smokes and blows oil out the breather. I looked at the price of parts both thru JD and at a Kawasaki small engine dealer. Not a huge difference between them, both being somewhat pricey. Since the tractor also has the "old" carb (along with the associated operating issues) on it I decided to look at a total replacement engine.

I looked up a FD620D at Small Engine Warehouse and found they have one, but state that it is NOT a direct replacement. Since the PTO end of the crank is not used on a 425, what are the differences in FD620's that make the current ones "not a bolt in replacement"?

I figure by the time I rebuild/replace everything on the old motor, I'd be closing in on the cost of a whole new motor. This way I could keep the old motor and work on it at my leisure (as funds are available) or sell it to offset some of the cost of the new motor.

Anyone else tried swapping in a "new" FD620 into their 425/445?
 

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Jay, I haven't done any work on an FD620 equipped JD yet, but did replace a w/p and cam on an FD620 Kawasaki Mule utility vehicle. One thing I remember well is that it had no internal governor. The transaxle (?) governor was linked to the engine. Another thing, the Mule used an electric fuel pump. I don't recall if the engine had provision for a mechanical one.
Hope you find something that will work. I think the Kawasakis are great engines, but repair parts are outrageously priced. Possibly all parts are shipped in from the motherland with lots of import duties, shipping, and taxes. I dunno.
You might consider a small block Chevy. Cheaper to rebuild too, if you ever had to! LOL

tommyhawk
 

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I remember seeing something about a difference in flywheels. The cooling fins or the ring gear are shaped differently, or something........? The 425 has the in-tank pump, so fuel shouldn't be a problem. It may have been on one of the engine supplier sites, just recall reading a somewhat lengthy article about the differences, etc. If it's an FD620, it should fit....

"Jim's Repair" has a bunch of info on Vanguard swaps, sorry, not interested, I prefer to stay all original.
 

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I've got pics of a 425 with a supercharged SB Chevy in it. Supposedly the deck and everything else works. On a little more reasonable side, I've often wondered about putting in one of the old Oldsmobile Quad 4 motors in one.
 

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Discussion Starter · #6 ·
Does anyone have a good copy of the engine wiring schematic for a 425? I downloaded the 4x5 tech manual from another site but whoever scanned it, scanned the wiring diagrams in while folded up. My tractor is an early model with the old style carb. It appears the engine wiring is different between the JD spec and regular Kawasaki engines.
 

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Discussion Starter · #7 ·
I decided to tear the engine in the tractor down for further analysis. If I can get by with rings and a valve job, I will replace the carb with a new, late model, one and not have to deal with the potential wiring "issues".
 

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Discussion Starter · #8 ·
I finally got time to tear the engine down last weekend. It was much simpler than I anticipated. The tractor is showing about 745 hours. Inside of the engine looks very clean, bores are not scratched and the pistons look new, no marks or scratches at all. After measuring the cylinders (all within spec); I pulled the rings off and put them in their respective cylinders to measure the end gaps. One side was good (less than .050") the other side was about 1/4"! I think I found the problem with oil usage and blow-by. Crank, rods and everything else all look good. I believe I can get by with a quick hone job and some rings and a gasket set. I may as well pop the valves out and clean them up and lap them. There is LOTS of carbon caked on the head/valves, but virtually none on the piston tops?? Also, the pistons have a pretty significant dish in the top. Not sure why, but I sort of expected them to at least be flat tops. No big deal, just an observation.
 

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Jay, check the side clearance on the rings. Mine were worn substantially and required one piston to be replaced. The piston had too much clearance, even with a new ring.

The book calls for .006 on the top ring and .005 for the second ring. The worn piston on mine measured .008 for the top ring, even with a new ring.

The spec does call for .050 gap. That sounds loose, but both my manuals show the same spec.
 

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I would think the dish shaped piston tops would significantly lower the compression ratio. I wonder how much more power the engine would have with flat tops. Probably would have to burn high octane.
 

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Discussion Starter · #11 ·
Fred, thanks for the heads up on the ring side gap. I will check when I get the new rings. My manual just says end gap should be "less than .050". I am used to seeing a max/min range for other engines I have worked on. I suppose Kaw figures the min clearance is not as important since the engine is water cooled? I know it's critical on air cooled engines.

Jim, flat tops would certainly raise compression and power, but even with 1 half dead cylinder, I never felt I was short on power. I bought this tractor used, I can't wait to run it with a completely healthy FD620.
 

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Jay, I agree, my mouth flew open when I saw that .050 end gap figure! I'm used to automotive figures that are roughly .004-.005 per inch of bore size. The last SB350 I built with aftermarket pistons called for .022 top ring gap. That's with a 4.030 bore! I remember measuring some stock engines at .016-.018 and never having problems.
 

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Discussion Starter · #13 ·
Finally finished up the ring job on my 425. It took longer than I had hoped but that was due to other projects getting in the way. The only 2 real set backs I encountered were: 1) A "ring set" is only for 1 cylinder, had to call the JD dealer to order a second “set”. Seems odd to tear an engine down that far then only replace rings in one cylinder? All measurements were well within specs with the new rings installed. 2) Broke off a bolt when torquing down the crankcase cover. Not sure what happened because it was real easy to get the threaded part out of the block. The M-8 bolt just snapped off clean with only about 15 ft/lb applied. Spec calls for 20 ft/ib. Finished reassembly and installed the new "late model" carb. The carb was truly a bolt-in replacement and hooked right up to the electrical connection used by the old vacuum/electric solenoid. Engine cranked right up and runs SMOOTH. I tinkered with the adjustments outlined in the tech manual but ended up back where it was, right out of the box. I did notice an odd exhaust odor similar to the one Fred mentioned in another thread. I had attributed it to the fresh high temperature paint I had sprayed the muffler with. I took this opportunity to also straighten up some of the spaghetti bowl of wires at the rear of the engine as well. I drove the tractor up and down the driveway a few times and then installed the mower deck and ran the PTO for a few minutes. Engine seemed to barely notice when I engaged the PTO. I even was able to engage the mower deck at ½ throttle. Couldn’t do that before. Overall this project was not that difficult and ended up costing less than 1/3 the price of a replacement engine. A big chunk ($296.00) was the new carb. Looking forward to cutting some grass, if this rain ever stops.
 

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Good job Jay! Hope it dries up soon, or we'll need to break out the STS combine! Western OR is looking at another week of drizzle stuff! ....but that's why we like it here, it's green, right?

I don't put too much fertilizer on my lawn, because it makes it too dark, I prefer it to match the 'Classic Green'....
 

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Discussion Starter · #15 ·
Mowed for 5 hours today. WOW, what a difference. Apparently this tractor has not been 100% since I have owned it. It operated like a totally different machine. I think the carb made as much of a difference as anything. Starts right up, hot or cold. Runs very smooth. I only used about 1/2 the fuel to mow what I mowed today compared to last year. After running 6 hours total, the oil is still like new clean.

I got to thinking about the cause of the ring failure. I wonder if the old carb repeatedly boiling gas down the intake after a hot shutdown washed the oil off the cylinder walls and then when restarting ate up the rings? Possibly augmented by the healthy dose of dust ingested due to the loose air filter.

Whatever the cause, it's a beast now.
 

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Fuel dilution and washing down of the cylinders is sure to cause excessive wear. That's one of the reasons some racers change oil so often. The fuel dilutes the oil bad enough to affect the lubricity.

A 'dust out' from an air intake leak can cause the rings to go almost immediately. I experienced the result of that on a local farmer's filbert sweeper a few years ago. He built a sweeper, I put together an older model SB 327 Chev for power. He hooked up hydraulic pumps & motors to both axles and the sweeper brushes, he used the original THM 400 trans to run a large squirrel cage fan on the back to blow the nuts from between the trees over into the next row. This thing looked like something from the "Mad Max" movie!

Somehow, the air filtration system failed, the fine dust took out the rings within an hour! I rerung it, he fabricated a very, VERY large Donaldson air filter and cleaned it every three or four hours. No more problems, it paid to run clean air in that old engine.
 

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In my search to find a new motor for my 210, I came across a like-new Kohler M16 Magnum which is the exact same thing as a K341. Same block, different shrouding and uses solid state ignition. It has the proper mounting tabs and muffler box mount like the JD's used specifically. Still waiting to hear from the guy selling it to see what size crank it has. Assuming it's a 1", would it be a simple job to drop this in my 210? I could swap the oil pan over from my K241 if the mount is an issue. Anyone put a Magnum in a 200 before?
 

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I am just wondering if it will fit snug into the frame with the way the frame is cut to fit the flywheel of the K241. The Magnums seem to stick out a little bit more and have more of a square appearance so I don't know if it would be much trouble trying to fit it snug in the engine bay.
 

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You might have to use the K-series shrouds to fit that engine into your 210, and you will want to use the ignition switch from an electronic ignition tractor instead of the original switch. You could use a normally-closed relay instead.
 
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