Ask The Mechanic

Sensitive Twine Baler

image by Steve Thompson

I have a 570 New Holland twine baler. It seemed to be losing its twine on one side out of the twine disc whenever I tried making the twine tighter on the bale. I tightened the twine disc adjustment so that it would hold the twine tighter, but now the baler will not tie on that side at all. It seems to be breaking the twine between the billhook and twine disc. Do you think I need a new billhook or twine arm to fix the problem?

STEVE: More than likely, you have overtightened the twine disc pressure adjustment, which is easy to do. When a twine baler is experiencing “twine disc pullout,” the adjusting cap screw should only be adjusted a quarter of a turn at a time. This adjustment is sensitive because when the billhook comes around to make the knot, it must pull the twine out of the twine disc in order to complete the knot. If the disc is too tight to slip in the twine disc, the rotating billhook will break the twine. If the disc is not holding the twine tightly enough to hold the twine during bale formation, the twine will pull out of the disc. Back off of the twine disc adjustment nut until it will hold the twine tightly enough to form the bale yet loosely enough to slip through the disc when the billhook grabs it. Make adjustments in a quarter turn at a time until your baler gets happy. A hay baler just likes to occasionally show you who is boss out there in the field.

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I know this is not technically a nut-and-bolt question like you usually answer, but I have always wondered where the noise comes from in an internal combustion engine. I thought all the fuel during the power stroke would have been burned up during the power stroke, and the “bang” would be encapsulated in the cylinder since both valves are closed during the power stroke. If I am right, where does all the noise come from out my truck’s exhaust manifold and out the exhaust pipe?

STEVE: I’ll agree that this is a different kind of question but still a good one. Let’s see if we can make some noise here. When the explosion begins just before the piston reaches top dead center (TDC), it has minimal force at that time. Gaining power as it goes over TDC, the explosive force on the piston increases and reaches maximum force on its journey down on the power stroke. Just like a bomb going off, the explosion begins slowly, gains power, reaches maximum power and then slowly tails off. Near the very bottom of the power stroke, the pressure has drastically dropped, but there is still enough pressure in the cylinder when the exhaust valve opens to help evacuate the cylinder. This initial exhaust before the full exhaust stroke is called “blowdown.” That “blowdown” pressure you hear is the last puff of explosion you hear coming out of the engine. The “blowdown” on an 8-cylinder gas engine happens every 90 degrees, making for a smooth sound out the exhaust. To check at what degree an engine fires on most engines, divide 720 by the number of cylinders of the engine. Keep in mind that a 4-stroke cycle engine must rotate 720 degrees (two complete rotations) to make a cycle of intake, compression, power and exhaust.

Is it possible to check for a leaking hydraulic cylinder by checking the cylinder with air?

STEVE: Yes. As a matter of fact, that is an excellent way to check a cylinder. If it does not leak air, then it surely will not leak hydraulic oil.

Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email


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