Ask The Mechanic

Shear Pin Snaps

(Progressive Farmer photo)

Q: I live in an unusual area in Texas where we use both wire and twine balers. I have two John Deere 348 balers, one is a wire and the other is a twine, and I’m having problems with both. When the baler metering wheel trips in the slot to tie, the shear pin in the flywheel snaps. They both snap the pin even though there is little hay going into the baler, so I know the pin is not shearing from overload. Sometimes they will bale five bales without shearing the pin, and sometimes they will bale 50 bales. But the problem seems to be getting worse. I have never broken a chain on either of the balers. What can be causing the same problem on both balers?

P[L1] D[0x0] M[300x250] OOP[F] ADUNIT[] T[]

A: Since the flywheel pin is shearing when the baler trips to tie, then more than likely the problem with both balers is that your swing frame (where the needles mount) is sneaking out of home position when the baler trips to tie. That then allows the plunger crank to hit the plunger stop. As long as the baler-tying system is not in tying stroke (before the baler arm trips to tie), the system is locked. However, when the system trips, the only thing holding the swing frame in place is the needle brake on the left side of the baler. And, since the spring on the plunger stop is pulling against the plunger stop arm behind the swing frame, the needles want to creep up if the brake is not tight enough. Screw in the nuts (usually a couple of turns each), put more pressure on the needle-brake pad springs, and that will fix your problem. Another note: If the flywheel pin shears after the bale is tied and the plunger is ending its tying stroke, then you will need to adjust your plunger stop linkage (turnbuckle) to exit the bale case a little quicker. However, loose chains can slow down the needle timing and not change the plunger timing since it is driven directly from the baler’s transmission. Your problem is a common problem with all brands of balers with a plunger stop. The swing frame (needle) brake does require occasional adjustment.

Steve’s Back & Forth:

Reader: I have a John Deere 2955 tractor that is hard to start. It turns over slowly, but when you jerk the steering wheel back and forth, it starts—unless it’s really cold. The tractor has multiple operators, and many of them do not know the “trick” to start the tractor. We have been through the alternator, starter, battery cables and batteries. I would like to know what I might be able to do to get the tractor to whiz over a little faster like it once did. I’m curious why shaking the steering wheel will allow it to start most of the time.


Steve: If your batteries are not of the proper cold-cranking amps suggested by your John Deere dealer, change them to JD specifications. Other than a load from something the fan belt is turning or an engine trying to seize, the other likely problem would be weak amp flow to the starter. Do this test in order to isolate the problem without any meters, test lights or battery testers: Take the positive post off one of the batteries and see how the tractor starts. See if it starts a little better or about the same. Then, replace the positive cable you removed and remove the other positive post. How does the tractor start now? If it starts better with one of the batteries than with both batteries hooked up, you probably have one bad battery. Now check the ground. Remove the ground cables one at a time, and see how the tractor starts. If both grounds are good, and all positive connections are good, the starter should whiz the engine. One interesting thing about a parallel system like you have on this tractor (using two 12-volt batteries that remain at 12 volts) is that the voltage in each battery is averaged to make the total volts. In other words, if one battery has 11 volts and the other battery has 12 volts, then you only have 11.5 potential volts. That’s why it is possible for a tractor to sometimes start better when the bad battery is disconnected. Don’t be fooled by a bad ground at the end of the negative battery cable. It can make a good battery look bad.

Reader: Wow! The one battery was bad and only had 10 volts when I checked it. I replaced that battery, and she starts fast. Now, what about the steering wheel jerking trick?

Steve: Like many technical tricks, the steering wheel jerk was invented by a farmer. Your tractor has what is called a closed center hydraulic system. This system holds a constant pressure at around 2,200 pounds per square inch. If there is no hydraulic demand, the hydraulic pump goes out of stroke. When your tractor has been resting for a while, the pressure slowly leaks off. When you begin to start the tractor, the hydraulic pump is now in full stroke, putting an extra load on the starter. The steering and brakes on your tractor have priority hydraulic oil for safety reasons. When you jerk the steering wheel back and forth, you are relieving some of the hydraulic pressure loading the starter.

(BAS)

P[L2] D[728x90] M[320x50] OOP[F] ADUNIT[] T[]
P[R1] D[300x250] M[300x250] OOP[F] ADUNIT[] T[]
P[R2] D[300x250] M[320x50] OOP[F] ADUNIT[] T[]
DIM[1x3] LBL[article-box] SEL[] IDX[] TMPL[standalone] T[]
P[R3] D[300x250] M[0x0] OOP[F] ADUNIT[] T[]