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Discussion Starter #1
This is my 1st post. I have been lurking in the forums for years and acquired a lot of info from goggling. so its about time I got into the club!

Everyone claims that the motors are the same in a 425 and the 445 except, a carb on the 425 and EFI on the 445 with a gain of 2 HP. However, I looked at the operator's manual and it states in specifications that the 425 have 9.0 compression and the 445 has 10.3. So can someone explain to me what component(s) (cylinder heads, piston, or ect) offsets the compression difference between the two engines?

Also; what should a compression gauge show for good compression for the two engines?

Thank you in advance.
 

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Corndog Hater
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Unfortunately I don't have the answers, but before long someone will be along who does.....in the mean time welcome to GTT!


Sent from my iPhone using Tapatalk
 

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This is my 1st post. I have been lurking in the forums for years and acquired a lot of info from goggling. so its about time I got into the club!

Everyone claims that the motors are the same in a 425 and the 445 except, a carb on the 425 and EFI on the 445 with a gain of 2 HP. However, I looked at the operator's manual and it states in specifications that the 425 have 9.0 compression and the 445 has 10.3. So can someone explain to me what component(s) (cylinder heads, piston, or ect) offsets the compression difference between the two engines?

Also; what should a compression gauge show for good compression for the two engines?

Thank you in advance.
Welcome from West Virginia

:wgtt:

Can't say what difference inside the engine, but I will say the big difference between the carb of the 425 was the rear tires are smaller I believe 10" wide and the 445 has the 12" wide. I owned a 425 about 12 or so years ago, and daughter fil bought a 445 the same time . He still has the 445 but only puts maybe 5-20 hrs a year on it plowing snow. Still runs great has over 650 hrs , I never had a chance to mow with his 445 to see how it ran compared to my 425, both had 54 " decks. I had all intentions of buying the 445 ,but a friend I went to high school with was shop foreman and he talked me into buying the 425.

Good luck on finding your info , sure someone can help you.
 

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The only internal difference of the 2 engines are the pistons.The carburetor engine pistons are dished on top and the injected version the pistons are flat on top resulting in the higher compression ratio.I believe the higher compression pistons are NLA,also the FI version of the 620 was a Deere exclusive engine not offered in any other brand tractor.
 

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Can't speak for the 425 but in the 445 some of early model year engines came with a plastic cam gear that is known to fail in the 1000 hour range give or take.
 

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Discussion Starter #7
Thank you everyone for the welcome.

Thank you Junior. You just explained to me that if I go to Deere for new over sized pistons for a fresh engine, I won't see any performance increased with a bigger bore because of loss of compression. That also raises more questions of why Deere eliminated the performance pistons.

I'm still looking for compression numbers if anyone knows them.

BTW; I understood that both early 425 and 445 had plastic gears with the idea that they were quieter and became a failure.
 

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The 425 and 445 used the same engine along with some of the John Deere gators only difference with the gators were the heads, intake and crankshaft was tapered on a gator and not the L&G engines. Deere put plastic cams in all the early models which were later changed to the metal camshaft and most do fail around 1,000 hrs. I believe the only difference was the pistons the bore size was still the same. One thing to be cautious of is the water level when the water pump goes out it does not leak externally the weep hole is on the back side of the water pump which puts it directly into the oil (chocolate milk). I have owned a 445 and 425 I prefer the 445. I also have bought and fixed these tractors up to make a little extra cash on the side. I stand by this series, X400 series and now X700 series700 as I have or family has owned one of them. The tractors to me are the Cadillac of the L&G series. I also currently have a X485 listed for sale on here with rear pto and 3 point hitch.
 

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Discussion Starter #10
In a nutshell; I stripped the aluminum threads replacing the oil pressure sending unit. So as I was trying to repair that, I destroyed the block beyond repair. So I finally got another engine block. My plan is to simply swap all the parts from one engine to another with new; water pump, rings, push rods, valve springs, valve seals, governor gear, and a complete gasket kit. (Am I missing anything?) As I was looking and researching parts, I stumbled on the compression difference between the 425 and 445.

I first operated a 445 back in the 90's when my boss at the farm had one (now he has two). I remember it like yesterday when it was new and shinny and I was using it. The things that I struggled with this mower was; to put the thing in reverse, I had to lift my butt off the seat to get it to go backwards with the small nubby pedal. That caused the deck and or whole tractor to shut off.

I told my own father that I was gonna get a JD 445 with a 60" deck. Dad said "Any mower with a deck bigger than a 50" is no good. They don't mow right and 50" is all you need anyway". Well as Dad didn't know what he was talking about (at that time), he got on it and mowed with a smile on his face all day when I got it home! Then a couple weeks after that, my brother's mower went down, so he borrowed mine, and that made Dad frown for about 6 weeks. Then little brother quit working on his brand X mower and bought a 445. Then ole Dad got tired of it and he bought him self a fine 425 with a 60". Now that he has a 425 and looks at my 445, I surly believe that he wished he bought the 445. He is really looking at the 26X12-12 on mine!!!

Their are many stories around here that brag on these great mowers. Mostly how people use them as farm tractors more than lawn tractors.
 

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If your looking for a block check on Ebay or I may have contact information from two local guys who buy mostly nothing but JD lawn mowers who may have what you need. I would definitely check Ebay first as I have seen many of these tractors being parted out now sadly to say. Just let me know if you want the contacts I have and I will get them to you.
 

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First post other than the introduction. The 425 and the 445 both use a dished piston but the dish is smaller on the 445 hence the higher compression. You can't get the 445 piston from JD anymore so if you want the higher compression, you will need to find some used ones. Other than the carbureted vs. fuel injected, the engines are the same. The springs are different for the plastic geared cam vs. the full steel cam.

Hope this helps.
 

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Discussion Starter #13
Thank you everyone. In this case of what I done was a simple new engine block honed with new rings, push rods, valve seals, valve springs, water pump and of course a gasket kit. The engine had the cam gear replaced in the past already so, I was good their too.

However; someone can tell me what the Gauge compression should be.
 
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