70 D stalls cranking engine

Dan in Ohio

Well-known Member
Location
Mid-Ohio
My 1956 70D will stall the cranking engine immediately when compression is applied. Cranking engine is a strong runner, seems like something is stuck when returning the
decompression lever. Cranking engine will motor the diesel fine under decompression.
 
what if you had fluid in the cylinder that just pushed back and forth thru the valve while decompressed. Try pulling the tractor(while decompressed) if you can get enough rpm you may blow any fluid out, then you might be able to start it with the pony motor. CAUTION do not compress while pulling, if the idea does not work you may damage your engine. i would also make sure you have good gas in the pony and the rpms are set correctly for max no load. O ya if decide to pull it hang a can or rag on the muffler to deflect any fluid like antifreeze or black sootie water from raining down on you, don't ask how i know that.
 
bill,

Have you had this same problem ? Tractor has set since last fall but noticed this problem some before that but could always get it to start. Pony runs strong always . Just tried starting again and let it motor the diesel a couple minutes (decompressed), you would think that would clear any liquid from the cylinders. Still stalls the pony.
 
Dan.....in my experience that is a sign of a strong Diesel engine and a weak pony engine. If the Diesel engine has been rebuilt and has .045 or .090 oversized pistons, new rings and good valves the compression is at 16:1 or greater. I would check the compression on the pony engine cylinders and make sure the timing on the pony ignition is where it should be. Pony might just be short on power.
 

Starting engine is running on two cylinders due to ignition problems or broken connecting rods . Occasionally bent push rods .
 
I would chime in with buickanddeere. I worked on a 70 at the John Deere shop here, it soulded good and would start the diesel engine but when I checked compression on it there was 0 on 2 cylinders. When I tore it down it had one broken piston and one broked rod. as I say it sounded pretty good
 
Yeah I have to agree with the rest, it might not be hitting on all four. Check the spark and such. On two or three it still idles and revs fine, but falls flat on it's face under compression

Brandon
 
Dan....compression should be 120 psi in each cylinder. If a cylinder is marginally low (80-100 psi) it is usually a sign of worn rings and valves, if compression is less than 80 but not zero it is most probably bent or broken pushrods or sometimes a bent connecting rod. If the compression is zero you have a broken rod, piston, etc. If all the cylinders have good compression then make sure all four cylinders are firing. If not could be one bad coil, bad condenser, fouled plugs or bad plug wires. As mentioned below they sound "strong" even if they are running on less than 4 cylinders.If your 70 diesel has the original pony engine, they used the swizel stick pushrods that bend easily or break. The later pony engines had different lifters, pushrods and rocker arms. An indication that the early pushrods were problematic.
 
(quoted from post at 12:18:21 04/21/18) Dan....compression should be 120 psi in each cylinder. If a cylinder is marginally low (80-100 psi) it is usually a sign of worn rings and valves, if compression is less than 80 but not zero it is most probably bent or broken pushrods or sometimes a bent connecting rod. If the compression is zero you have a broken rod, piston, etc. If all the cylinders have good compression then make sure all four cylinders are firing. If not could be one bad coil, bad condenser, fouled plugs or bad plug wires. As mentioned below they sound "strong" even if they are running on less than 4 cylinders.If your 70 diesel has the original pony engine, they used the swizel stick pushrods that bend easily or break. The later pony engines had different lifters, pushrods and rocker arms. An indication that the early pushrods were problematic.

The wrong spark plugs will lower the compression and reduce starting engine power. If the plug doesn't extend to bottom of the head's threads. Compression and power is being lost.
 

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