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J.D. 720 Poney engine

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Dave Wallace

07-10-2002 11:31:43

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Frank-in-Tallahassee. Thanks for your help Re J.D. 720 Poney engine V 4 I have cleaned
out the Carb which had a bit of cork pluging one of the passageways , Checked the oil
return passageways from the rockers they are clear, in fact its like a new engine in there
spotless. It took about three weeks to get a 6 volt battery (like Hens teeth here in
Scotland) It eventualy started,after a lot of churning and backfiring seemed to run ok but
was only doing about 1500 revs,Ileft it running for about 5 mins but there wasent enough
power to turn the main engine, I wonder if its firing in the correct order,can you tell me
the firing order and the cylinder layout, After running it blew oil out everywhere so its
probably a rebuild. Thanks Dave Wallace.

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Ralph

07-10-2002 20:45:51

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Re: J.D. 720 Poney engine in reply to Dave Wallace, 07-10-2002 11:31:43

I am a novice on the 2 cyl diesels, but one item I would watch closely is dilution of the crankcase oil with gasoline. It is tempting to leave the gas on and cut the ignition to the starting engine, but unless the oil pressure shutoff seals, it is inviting dilution. When I got my 820 I think the crankcase oil was 1/2 gasoline. As a result it slobbered oil out of the exhaust and killed the mosquitos over three townships in spite of compression test of 125 psi when I started it. An over filled crankcase has to be hard on the crankshaft @ 4500 - 5000 rpm.

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F-I-T

07-10-2002 15:13:31

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Re: J.D. 720 Poney engine in reply to Dave Wallace, 07-10-2002 11:31:43

Dave:

The firing order is very simple. The front two pistons rise together, and the back two pistons rise together. In other words, all of the pistons are on a common crank throw. The firing is such that the coil on the front side sparks both front plugs at the same time, on both compression as well as exhaust....pretty simple there, too. Same for the other pair of plugs. Might have to check the timing (there is no advance mechanism) and check the adjustment of the governor linkage. Maybe then it will rev out better. (Can you move the governor linkage by hand and force it to rev out ?) Mine idles pretty well, and revs out nice. Has good governor action,too. It should have more than enough power to spin that big engine, but if it�s blowing oil, it might need the oil seal behind the clutch as well as rings. That was the reason for tearing mine down. Watch the float level. I found that this affected the idle. I would say that you might still have something starving the load needle. Look for some more of that cork float!

Let me know if I can help with anything.

Frank-in-Tallahassee
70D // 855

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