H oil pump

[Mike(NEOhio)]

Has anyone here had one apart and reassembled. The top drive gear doesn't want to go back on. It's a press fit with a woodruff key. Been apart for a long time and when I first had the tractor I made a new shaft for it due to some wear I didn't like. It fit perfectly. Shaft measures .624 dia. but the gear ID is .616. That's a lot of interference. I'm thinking it was originally a shrink fit but that still seems like a lot. Nothing else to retain the gear, only the press. The old shaft is still laying around and it's also .624.

 

[dan_41jdh]

Mike, I have never disassembled a pump so I don’t know what the dimensions should be. However, something is very wrong with the dimensions of your parts. Using a good rule of thumb for a press fit of 0.0015 inches of interference per inch of diameter means the gear’s bore should be around 0.623. There is absolutely no way that a 0.616 bore will press on to a 0.624 shaft. And even if it was intended to be a shrink fit (which is doubtful), there would have to be around a 2000 degree Fahrenheit temperature difference between the gear and shaft to allow those parts to assemble, based on a thermal expansion coefficient of 0.00065 in/in/100 degree F. Because your old shaft is the same diameter as your replacement, it sounds like you have a bad top drive gear.

 

[Mike(NEOhio)]

Mike, I have never disassembled a pump so I don’t know what the dimensions should be. However, something is very wrong with the dimensions of your parts. Using a good rule of thumb for a press fit of 0.0015 inches of interference per inch of diameter means the gear’s bore should be around 0.623. There is absolutely no way that a 0.616 bore will press on to a 0.624 shaft. And even if it was intended to be a shrink fit (which is doubtful), there would have to be around a 2000 degree Fahrenheit temperature difference between the gear and shaft to allow those parts to assemble, based on a thermal expansion coefficient of 0.00065 in/in/100 degree F. Because your old shaft is the same diameter as your replacement, it sounds like you have a bad top drive gear.

I do recall it was very hard to get off. I'd expect it to be very tight since there is no pin or set screw to resist the axial thrust and only half the length of the bore is 5/8. The rest is counter-drilled from the bottom. But that seems excessive. I have to do some machining on the governor shaft so I'll cut down the diameter then but recheck my measurements. Been out of the shop a while and a bit out of practice.

 

[J.Wondergem]

Mike, this is a stupid question
, But is it posable that you picked up the wrong gear?

 

[Mike(NEOhio)]

Mike, this is a stupid question
, But is it posable that you picked up the wrong gear?

Only one, hard to miss.,

 

[Mike(NEOhio)]

Issue solved. On closer inspection after cleaning up the old shaft on a wire wheel the last inch at the top end of the shaft is .619. Still pretty tight but doable. The shaft also shows some shearing on either side of the keyseat.

 

[dan_41jdh]

Issue solved. On closer inspection after cleaning up the old shaft on a wire wheel the last inch at the top end of the shaft is .619. Still pretty tight but doable. The shaft also shows some shearing on either side of the keyseat.

So it sounds like Deere used 5/8" cold-rolled round (which typically is just a little under nominal) for the shaft and then machined the end(s) down to 0.616 for an interference fit with the gear(s). But 0.003 is a LOT of interference, definitely more than a press fit needs. That's even more than a shrink fit would typically need as there would have to be about a 750 degree temperature difference between the 0.616 gear and the 0.619 shaft to let the gear slip on.... However, the keyway notch interrupts the continuous wrap of the gear onto the shaft, so it's possible that when being pressed on, the keyway opens somewhat, thus effectively increasing the bore diameter and permitting the gear bore to expand sufficiently to be pressed on. Thanks for the follow up.

 

[Mike(NEOhio)]

That's exactly what I made the new shaft from. Back when I tore the tractor apart I just went ahead and made the new shaft and never noticed the smaller end. My guess is they made the tight fit to counteract the axial thrust from the helical gears. I could never understand why the bearings are so tight on the governor and fanshaft. I had the fanshaft off my A and needed the bearing separator, hammer and some torch to get it free.