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John Deere Tractors Discussion Forum

830 adjustable cam timing

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Plant Doc

12-02-2012 15:16:30

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What was John Deere's reasoning for the adjustable cam timing on the 830? Why not an adjustable cam on the 730 also? The cam on my 830 is almost fully advanced. The tractor starts well and runs well, but it doesn't do well as a puller. Is there a formula for setting the cam timing on a 830? When side by side with my 730 the 830 isn't what I think it should be, it does a little more work but burns a lot more fuel to do it.

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12-04-2012 09:39:00

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 Re: 830 adjustable cam timing in reply to Plant Doc, 12-02-2012 15:16:30  
Oh gosh! I remember that chart! What a goofy sense of logic. So, they read the torque as hydraulic pressure at the pto speed of 540, then they kept cranking up the pressure, and lugging down the engine and read the max pressure with the engine barely continuing to stay alive. So even if was making more pressure, it was doing it in fewer turns over time, hence could even be less horsepower, and quite possibly is. Which is why you always have to pick a standard speed to rate it at, and the manufacturers agreed, or rather the Univ. of Nebraska test lab recommended after the government decided to regulate the outrageous claims of tractor manufacturers, the standard pto of 540, and the engine speed that it takes to develop 540 rev/minute. A quick check on torque curves is to crank the pressure wheel in to get a 10% reduction in pto speed, and then see if you gained 10% on the pressure meter. If you didn't get 10%, you didn't "gain" at all.

This was not the first time I've seen a dyno operator not understand what the gauges were telling him.

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12-04-2012 11:17:12

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 Re: 830 adjustable cam timing in reply to F-I-T, 12-04-2012 09:39:00  
A couple of those 80 series must have had a lazy governor setup. Of note the stock 435 with the 2-53 made "46HP" straight through from 1200 to 2400rpm. Flat torque "curve" was great for running up through the gears on a highway tractor but felt like a dog on hills. The irony being the two stroke was always at peak torque and was considered gutless. And the fourstroke that falls on it's face as it loses torque approaching redline is considered the powerhouse?

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12-03-2012 07:30:41

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 Re: 830 adjustable cam timing in reply to Plant Doc, 12-02-2012 15:16:30  
For what reason it"s important. I have a picture of dyno results around somewhere. It was amazing the power difference of three "identical" tractors.

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12-03-2012 08:38:12

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 Re: 830 adjustable cam timing in reply to buickanddeere, 12-03-2012 07:30:41  
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Nothing beats having access to a dyno. My plan in the next three weeks is to get the 70D out and run it at different fuel levels showing how little you gain out of a 2 cylinder diesel when you set it to stock, and then you "turn it up". I've done that before. I need to rig up a graduated cylinder with a tap so I could derive the fuel consumption rate versus horsepower at various fuel delivery levels and plot the hp/gallons per hour.

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12-03-2012 18:10:55

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 Re: 830 adjustable cam timing in reply to F-I-T, 12-03-2012 08:38:12  
Well on my R it gained 10hp by turning up the fuel. Starting with 48 hp, thats about 20%. On 2 different belt pulley dynos. Turning up the RPM from 1050 to 1400 gave it another five horse. Zero other changes.

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12-04-2012 05:40:15

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 Re: 830 adjustable cam timing in reply to gtx1967jewison, 12-03-2012 18:10:55  
Increasing rpms's 133% to gain 107% more power if a slim rate of return. Past 1000rpm the volumetric efficiency will drop fast.

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12-03-2012 16:50:58

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 Re: 830 adjustable cam timing in reply to F-I-T, 12-03-2012 08:38:12  
This link may work ?


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12-03-2012 04:33:20

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 Re: 830 adjustable cam timing in reply to Plant Doc, 12-02-2012 15:16:30  
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I re-read that procedure carefully, and the condensed version of CHECKING the timing is this:

Remove the valve cover, place a dial indicator on the #1 exhaust valve. Rotate engine in the running direction until #1 exhaust is shown to be closed. Reset dial indicator to "0". Back engine up 1/8 turn, and rotate forward until #1 TDC lines up. At this point, #1 exhaust should have traveled .044". If not, THEN you have to remove the timimng cover, drain the coolant, lift the pony motor all to remoe the timing cover behind the flywheel in order to adjust the eccentric on the timing gear. Adjust eccentric to achieve .044" lift, and re-rotate to check.

After this, if you moved anything, you need to recheck and reset the injection timing, referencing the #1 INJ mark.

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12-02-2012 21:22:52

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 Re: 830 adjustable cam timing in reply to Plant Doc, 12-02-2012 15:16:30  
Its kinda hard to reverse engineer something and then say "why did they do that" when more modern methods have been invented. The 80-830 line is an overgown r that got its start from a d. The first diesels were running as early as 1935 and I would guess the adjustable timing was to #1 make sure things were spot on #2 be able to make changes during the Expermentation process #3 to make allowances for wear #4 to make sure the service shops sent the tractors back to the farmer or field just like all the others #5 to be able to tolorate some production inaccuracies remember this was in the 30's and 40's and the r's through 830's used exactly the same parts w/ very few alterations

As a side note John deere never changed the timing on the injection pumps and the spec is the same for all 2 cylinder diesels. also racers have been playing with cam timing since before the 70 diesels cam out.Paul

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12-02-2012 15:50:28

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 Re: 830 adjustable cam timing in reply to Plant Doc, 12-02-2012 15:16:30  
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I don't know why they made it adjustable, but there is a very specific procedure published in Field Service Bulletin, #234, November 1955, for the Model '80', but no otherws. It basically explains that you will balance the cam gear position so as to provide identical lift between #1 and #2 exhaust valves, but it is several paragraphs long. You might want to purchase the FSB CD-ROM from Duane Larson's estate, as there nearly 2,000 pages of interesting information. And since it is copyrighted, I can't print it for you here.

Here's a link to order a CD:


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