# John Deere 670, 3-cyl Diesel



## GreenFlyer

Hello. I have a John Deere 670, 3-cyl Diesel. Along with a cpl other mowers, I am using it to mow about 30 acres of grass. It has a 60" deck. Last week it turned over 1,400 hours. This Fall I would like to tear down the engine, 18hp, and rebuild with a few more horsepower. I have a tech manual for the 670, but I need to get a CTM for the complete engine tear down and re-build. Any suggestions about how to get a about 5-7 more horsepower out of this engine would be much appreciated. Thank you. :usa:


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## irwin

I think you're asking for trouble unless you live above 5000 feet, but there's room for a small turbo in there...

You could also drop an engine for the 770 in there, it uses the same frame, sheet metal, transmission, radiator etc... The 770 is listed at 23 or 24 hp, depending where you look up the specs. Heck' an engine from a 790 or the 3005 might just bolt up too, you'd be looking at 27 to 30 hp, depending on the year of the 790..

I had the 770 for a couple years, great bullet proof little tractor, and like I said, it's basically the same tractor except the engine and tires.


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## Mickey

This is a Yanmar engine in this series JD's. At 1400 hrs, it is barely broken in. Not sure what you think you will accomplish with a complete tear down. Without going the turbo charger route you are pretty much limited to cam change and increase fuel delivery. As Irwin mentioned you could also go with an engine swap from a sim sized model.

What is the displacement of this engine and is HP rating engine or pto rating? Son's JD455 with Yanmar engine is ~ 900cc and is rated for something like 23HP. I'm sure that is engine rating and not pto or drawbar rating.


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## GreenFlyer

Mickey, the engine is 18.5 hp, w/pto @ 16 hp. The displacement is 879 cm3. I run this tractor weekly, 4 to 5.5 hours at a time. Steady, at 2,750 rpm, for mowing grass. It has a 60" deck. I run it in 5th(1H), or 6th(2H), gear, depending on the height and condition of the grass, and/or how bumpy the ride is. My only complaint about this great mower is not having a hydrostatic transmission, with 'cruise' control. Sometimes the rpm will drop about 100-200 when in thick grass, which means I have to either slow down, or raise the deck. This is accompanied by black smoke out of the exhaust. I would like to put a 59 or 60 in. snow blower in front of it this winter. It is 4WD with the mid-pto. I would like to get another 5 to 7 hp out of this engine. The overall size of the tractor is about twice the size of a 455, but with about 5 less hp. I will look into a 770 engine, but I will still see if I can squeeze some more hp out of the engine I already have. Thanks for your help/input. :usa:


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## Mickey

Looking at the eng spec for your 670 and a 455, they appear to be the same basic engine. You need to do some checking to see what difference there are that gives the 455 another ~5hp (advertised).

TractorData.com John Deere 670 tractor engine information

TractorData.com John Deere 455 tractor engine information

See the rated engine speed is ~500 rpm higher than on your 670.


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## harddock

I had a 650, When it was time to trade I was told I would have to get at least a 955 to match what a 770 could do. I can't imagine the 455 being more powerful than a 670. I went with the 770 and it has worked fine for 15+ years.


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## isisaugusta

I have a 670 that has been run too slow just got it A FEW WEEKS AGO AND THE GUY SAUD 1500 WWAS FINE TODAY RUNNING AT 2000 PULLING A MIDDLE BUSTER IT SUDDENLY WILL NOT RUN IN GEAR///WHAT DO I NEED TO DO


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## isisaugusta

Please help if you have answer


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## irwin

isisaugusta said:


> I have a 670 that has been run too slow just got it A FEW WEEKS AGO AND THE GUY SAUD 1500 WWAS FINE TODAY RUNNING AT 2000 PULLING A MIDDLE BUSTER IT SUDDENLY WILL NOT RUN IN GEAR///WHAT DO I NEED TO DO


Hey there.. The safety switches on this and the 770 are the same.. my guess would be the seat safety switch, or another safety device got moved, or is no longer working properly.. lift the seat up and check that seat switch make sure it's in the right position. Check the pto switch position, you might have hit it. You can use the pto but you'll need to set the seat switch in the up position (I think it's the up position?) .. I got rid of my 770 several years ago so I can't remember if there are more.

Not sure what you means by "run too slow"? it's okay to run at 1500 rpm. 2000 rpm is just fine also.

Also just to be sure do you mean the engine stalls when put in gear? (that sounds like a safety switch) or does it not move (like a slipping clutch? )


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