Allis Chalmers 620 reliability?

Hi Allen,
The original Onan engine is very expensive to rebuild if it needs it.  Many repower with a Honda.  The steering boxes can get loose and sloppy over time - Adjustment can be done to help, but haven't tried on mine yet.  The rear PTO can be very troublesome if it has it.  Most of the trouble was electrical in nature for the machine as a whole.  Your starter might not be the problem, but rather a wiring or safety switch issue.  When they are working right, they are a nice and comfortable tractor to operate.


Edited by DSeries4 - 30 Jun 2015 at 10:08pm

How to wreck an Onan 2cyl opposed:
Failure to screw down the oil dipstick cap.

The opposed pistons go in and out in unison. There are large pressure pulses inside the crank case. They even use this pressure to run fuel pumps in some models. With the oil dipstick cap not seated, dirty air is sucked in thru the dipstick tube,contaminates the engine oil. At the same time, engine oil is pumped out of the engine thru the crankcase breather system, into the intake manifold or air cleaner. So contaminated engine oil and also loss of oil pressure do to low level. If your Onan suddenly starts smoking, check the seating/screw down of the oil check dipstick. And its gasket. Lucky for us, the Onan in the 620 has the large 3.75 qt. oil capacity. The P218 Onan used in the John Deere's can loose their 1.75 quarts of oil in a hurry. This smoking can be intermittent, as an accumulated slug of oil passes into the intake stream.

For the starter solenoid to activate the electricity must pass the neutral safety switch at hydrostat controls, front PTO switch and rear PTO switch. I don't think there was a seat switch, nor a neutral switch for the 3 speed range selector transmission. Can someone confirm?

mostly the pto switches and connections.                 some of those p 216 18 20 will not even pump fuel with a bad or loose dipstick learned that on a customers welder that came for some electrical things had tape covering the dipstick hole would not make pulse until the dipstick was replaced

BrianC wrote: How to wreck an Onan 2cyl opposed: Failure to screw down the oil dipstick cap. The opposed pistons go in and out in unison. There are large pressure pulses inside the crank case. They even use this pressure to run fuel pumps in some models. With the oil dipstick cap not seated, dirty air is sucked in thru the dipstick tube,contaminates the engine oil. At the same time, engine oil is pumped out of the engine thru the crankcase breather system, into the intake manifold or air cleaner. So contaminated engine oil and also loss of oil pressure do to low level. If your Onan suddenly starts smoking, check the seating/screw down of the oil check dipstick. And its gasket. Lucky for us, the Onan in the 620 has the large 3.75 qt. oil capacity. The P218 Onan used in the John Deere's can loose their 1.75 quarts of oil in a hurry. This smoking can be intermittent, as an accumulated slug of oil passes into the intake stream. For the starter solenoid to activate the electricity must pass the neutral safety switch at hydrostat controls, front PTO switch and rear PTO switch. I don't think there was a seat switch, nor a neutral switch for the 3 speed range selector transmission. Can someone confirm? The is no seat switch or neutral switch for the transmission.

Merle,
Being the steering box is "down under" so to speak, the adjuster faces the driveshaft, so I would imagine that you have to remove the wrap around cooler at the back of the engine to get access to the steering box, or drop the belly pan access panel and see if you can get in there from there. You can't get to it removing the center inspection panel in front of the dash cause' its to far forward. Another thing that I have found with the steering, is before I tore down the Tractor to restore, the steering seemed to be real loose in it. Well, come to find out, once I got down to the steering box, the bolts in the steering box were loose also! Another thing you might want to check out while your in there. One of those steering box bolts face upward and is on the inside of the frame rail support brackets. You can just get a 3/4 open end wrench in there to tighten the bolt if need be. Here's a pic of the box and its position. Without the engine in it, and cooler stuff, you can see it. I installed new bolts n' lock washers in the steering box to make sure they don't get loose again.  HTH
Steve

Can't say that I blame ya Merle for not wanting to pull the engine out again! LMAO!! They are not easy to remove!