Bent Push Rods-John Deere M

[ndgregor]

Hi,

I am in process of a John Deere M restoration. I recently removed the crankshaft to have it cut down for new bearings. I have just reassembled the engine and went to run it for the first time last night. I was having a tough time getting it to fire, and noticed it was backfiring through the air cleaner. I adjusted distributor timing until it did finally fire, and rotated the distributor body until it began to run more smoothly.

I then noticed as I looked up that one of the valves was not functioning, and I immediately turned the engine off. Upon further inspection, both intake pushrods were bent.

When installing the crankshaft, I made sure that the timing mark aligned with the camshaft. I followed the instructions for installing the oil pump for correct timing, although I did it without the tool in the service manual. I also installed the distributor per the service manual.

Before trying to start it, I rotated the crankshaft with the hand crank and all the valves appeared to be operating correctly and it appeared to turn smoothly.

Any idea why intake push rods would bend and the valve would be stuck open? What should I be looking for before installing new push rods?

Thanks

 

[Stimw]

Did you replace the pistons or make sure they were in the right direction? If they are notched pistons they have to be in right to clear the valves.
Were the valves adjusted properly?
Did the valves operate freely or did they stick bending the push rods?

 

[jeff9366]

Using starting fluid in abundance can bend push rods.

 

[Ken]

While rebuilding did you remove the oil pump. its gear position determines the setting for points . assuming it is correct
remove spark plug and slowly turn until feeling pressure on front cylinder. Then continue turning until the TDC position not start adjust with feeler gauge for .012 in and when tappets is adjusted with nuts tight turn the engine 1/2 turn. for #2 cyl and adjust the tappets.
You can straighten the pushrods by tapping on a smooth surface.

going back to the distributor make sure the slot in oil pump shaft and dist. shaft are aligned. and #1 again at start pos. loosen bolts to retain dist. adjust CCW to take up slack and adjust points for .018 to.022 in slowly turn engine until points just start to open distributor body the voltage wire terminal should be away from engine or oil filter.
install the cover plate rotor and cap.
crank the engine over and watch the tappets there should be no restriction to open and closing of valves.

I usually crank full choke one complete pull of crank then turn on switch keeping thumb outside crank handle
give a quick upwards pull engine should run 1/2 throttle.

ken

 

[Jerry/MT]

Several reasons for bent push rods.

I've seen bent push rods on engines that had sat for years and the valve guides were so gummed up that the push rod bent when the engine was turned over with the starter. Flathead Ford N series were notorious for sticking valves but not necessarily for bending them. I found a couple on my OHV TO-30 when I rebuilt the head. On an "interference engine" if the valve timing is incorrect the piston can strike the valve and bend it.