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1984 650 scut
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Discussion Starter · #1 ·
I have early 80s JD 650 that is leaking fuel into crankcase (oil). Starts and runs good, moderate blow by. Where is good place to start? Injector pump seal? Injector leak? How big of a job to replace pump seal? All suggestions appreciated.. thanks
 

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How many hours on it?
 

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1984 650 scut
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Discussion Starter · #3 ·
How many hours on it?
800 on broken hourmeter. Probably 1500. Moderate blow by. Starts in one cyl for 5 seconds then other chimes in and runs good. Plenty power for mowing no smoke unless overloaded then little black smoke. Temperature under 50 gotta use thermostart in first startup of the day. Could injector be problem?
 

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Trying to remember... I was working as a "factory trained technician" (i.e. going home every day smelling like diesel and motor oil) at the local JD dealership in the 1980's. I don't believe that I ever worked on anything that small, but on the larger ones the fuel pump is driven by the camshaft, IIRC (no guarantees, I'm old after all). When the diaphragm in the fuel pump gets a hole in it from wear & tear, the fuel leaks right into the crankcase. That's the first thing to pull off and rebuild (kits should be available from your local dealer). The injector pump can wear enough to let fuel into the timing housing as well, but that is less likely and much more expensive to fix since it requires a specialized shop to rebuild. Hope that helps. IIDRC (If I Don't Remember Correctly) I am sure I will be corrected shortly.
 
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1984 650 scut
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Discussion Starter · #5 ·
Little tractors like mine don’t even have lift pumps. Fuel is gravity fed to filter then to injector pump. I just changed filter(old filter cracked and filthy) but can’t see how that would let oil into crankcase. Could be injector with poor spray pattern. I’ll get them pop tested. Thanks so much. I’m 83 next week too!
 

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Sounds like you've got a plan. And you've got a good decade more life experience on me as well. Good luck & I hope that it's something cheap and easy!
 

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one of the small gear drives HAS a fuel pump mounted on the side of the injection pump.
I've not seen this before but found it a few weeks ago for another member.

His may have been a 750 or 950...I don't remember

Have a good look at yours.......injection pump was on right side.
Fuel pump was about centered on Inj. pump towards the bottom.
Small round unit with No primer lever.
 

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These little 2 cylinder yanmars do not have a lift pump that could leak into the crank case. They are gravity feed.

You are on the right track to have the injectors pop and leak tested. The next thing to look at doing is a compression test. A possibility is you have an injector leaking, the extra fuel is washing one of your cylinders down which causes ring wear. Thus you run on one strong cylinder till the weak cylinder warms up, also causing blow by.
 

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Discussion Starter · #9 ·
These little 2 cylinder yanmars do not have a lift pump that could leak into the crank case. They are gravity feed.

You are on the right track to have the injectors pop and leak tested. The next thing to look at doing is a compression test. A possibility is you have an injector leaking, the extra fuel is washing one of your cylinders down which causes ring wear. Thus you run on one strong cylinder till the weak cylinder warms up, also causing blow by.
You’re reading my mind! Thanks so much. Gonna do exactly as you suggest and will report results.
 

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Hoye tractor carries parts for the grey market yanmars. The yanmar YM2000 is close to the deere 650 with some part compatibility. So for parts that aren’t available from deere they may be available and a better price from hoye.

They also sell a injector puller that will save you a lot of frustration.
 

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Discussion Starter · #11 ·
Hoye tractor carries parts for the grey market yanmars. The yanmar YM2000 is close to the deere 650 with some part compatibility. So for parts that aren’t available from deere they may be available and a better price from hoye.

They also sell a injector puller that will save you a lot of frustration.
I saw a demonstration on u tube where mechanic used compression of engine to loosen stuck injectors on little two cyl yanmar such as mine. He loosened up the hold down bracket a few turns of nuts then turned engine over and injector came right out. Wonder if this was done with starter or a crank type bar? Sure looks simple. I’m thinking about replacing injectors. Your thoughts?
 

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Give it a shot to see if you can get them to pop out with the starter. If it doesn’t work then see about the puller.

Just make sure it is very clean around the injector, you don’t want anything falling into the cylinder while it’s turning over.
 

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Discussion Starter · #13 ·
Give it a shot to see if you can get them to pop out with the starter. If it doesn’t work then see about the puller.

Just make sure it is very clean around the injector, you don’t want anything falling into the cylinder while it’s turning over.
I’ll pressure wash injector area. One injector is clean as a pin, the other dirty as if it is leaking fuel. I’m gonna replace both. Thanks again for your input.
 

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I’ll pressure wash injector area. One injector is clean as a pin, the other dirty as if it is leaking fuel. I’m gonna replace both. Thanks again for your input.
Seems to me the manual recommended changing the injectors out at about 1000 hours. Sure wish I had kept the manual.
I had just a touch over 1600 hours on our 650 when I traded it, original injectors.
 

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Discussion Starter · #16 ·
I’m preparing to remove injectors in my John deere 650. Seems like simple slide hammer pullers can be bought for 25-30 bucks online. I need to know what is thread size of the nut on very top of injector ( return fuel fitting) I intend to purchase puller and screw it into this opening but need size. Any help appreciated. I know, I could remove this fuel return fitting and might have to if no one has done this before. Thanks to all
 
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