Nothing ruins a hay day faster than a square baler that trips, cycles and spits out a bale with the twine lying loose on top of it. The hay is down, the weather is coming, and the knotter — a mechanism designed in the 1800s and barely changed since — has decided today is the day.
The good news is that knotters fail in a small number of recognizable ways, and the failed knot itself tells you which one. This guide walks through how a knotter actually ties, how to read the symptom, the adjustment ladder in the order experienced baler mechanics work it, and the twine and feeding problems that masquerade as knotter faults. The mechanical detail here is drawn from decades of accumulated troubleshooting on HayTalk, cross-checked against manufacturer service literature.
How a knotter actually ties a bale
You cannot troubleshoot a knotter you don't understand, and the single most useful thing to learn is the twine numbering system. New Holland labels the three lengths of twine involved in every tie, and the same logic applies to any Deering-pattern knotter:
- #1 twine — the twine already lying on top of the bale, its end held in the twine disc from the previous knot.
- #2 twine — the twine the needle brings up the front of the bale during the tie cycle.
- #3 twine — the twine on the back side of the needle, which becomes the #1 twine of the next bale.
The cycle goes like this: the bale-length measuring wheel trips the knotter clutch, the needles sweep up and lay #2 twine into the twine disc alongside the #1 twine already held there. The twine disc — which turns exactly a quarter turn per knot — grips both. The billhook rotates, wrapping both strands around itself. The twine finger (some brands call it the tucker finger) lifts the twine into position for the billhook. The knife arm swings, its knife cuts the twine free of the twine holder, and the billhook's tongue strips the loop off the beak. Then the bale moves back and that is what pulls the knot tight. As one grower summarized after working through the theory: "the twine disc turns a 1/4 turn per knot."
Two knotter designs exist. The Deering pattern is used by New Holland, John Deere and most others. The McCormick pattern was used by International Harvester, which eventually abandoned it. The tell is the knot itself: "McCormick knots have a loop in them, Deering knots don't."
Why this matters for diagnosis: if #1 twine pulls out of the twine disc before the tie, the billhook still makes a knot — but only on the #2 twine. You get a knot on one strand, a loose end on the other, and a bale that falls apart. That single failure mode explains a large share of "my baler isn't tying" calls.
Diagnose by what the failed knot looks like
Walk back and pick up the twine off the failed bale before you touch a wrench. What it looks like narrows the cause dramatically.
| What you find | Most likely cause | Where to start |
|---|---|---|
| Knot tied on one strand only; other end loose | #1 twine pulled out of the twine disc before the tie | Twine-holder tension; twine disc wear |
| Both knotters failing on the same bale | Something common to both — usually the twine fingers | Twine-finger return spring and finger condition |
| One side ties perfectly, other side misses | Wear or adjustment on that knotter only | Compare billhook beak, knife and knife-arm roller side to side |
| Knot present but tails look chewed or ragged | Dull or nicked twine knife; poor knife-arm travel | Sharpen or replace the knife; check arm clearance |
| Knot forms then hangs on the billhook | Burred billhook beak, or knife cutting too early | Dress the beak; check knife timing |
| Twine unthreaded from the needle, still on the bale | Twine ball upside down, no tension at the twine box, or a missed twine guide | Rethread the baler from the box forward |
| Knotter trips but will not reset for the next bale | Clutch dog, trip linkage or measuring-wheel problem | Trip mechanism, not the knotter itself |
| Random misses that come and go | Stuck hay dogs, loose bales, or a flat-spotted cam follower | Hay dogs, bale density, twine-finger cam |
The left-versus-right distinction is genuinely useful, and worth remembering: misses on the left knotter tend to be more straightforward to chase because you are not fighting hay pushing the twine out of position the way you are on the right.
See it happen: the hand-turn flywheel test
Guessing at knotter faults is expensive. Watching one is free. Every experienced baler mechanic recommends the same procedure, and it is the single highest-value thing in this article.
- Bale until the chamber has hay in it and the bale is nearly complete, then stop.
- Shut off the PTO and shut off the tractor.
- Manually raise the trip arm so the clutch dog releases and the knotter is ready to cycle.
- Have a helper turn the flywheel by hand, in the direction it normally runs. You may both need to turn it until the plunger starts moving forward.
- Watch the whole tie cycle in slow motion: needles up, twine into the disc, twine finger lifting, billhook rotating, knife arm sweeping, knot stripping off the beak.
The point is that a knotter running at operating speed is a blur. As one mechanic noted, it is useless to try to watch the knotters at the speed they normally run. Hand-turning it is how you actually see which step fails — and that turns an all-afternoon guessing session into a ten-minute diagnosis. Have hay in the chamber when you do it, because an empty chamber does not reproduce real conditions.
Twine-holder tension: start here
If the twine is slipping out of the twine holder, the knot never gets a second strand to tie to. This is the most common single cause of missed knots on a mechanically sound baler, and it is also the easiest to fix.
"Twine holder tension. I'd say tighten the tension bolt down a quarter turn. Twine is slipping out of the holders. The New Holland service manuals show that."
— bjr, on HayTalk
Work in small increments — a quarter turn, then bale and check. Too much twine-holder tension is its own failure mode: the billhook cannot strip the knot off the beak and the twine breaks or the knot hangs. The correct setting is the lightest tension that reliably holds the twine through the cycle.
Related and often confused with it is twine disc timing: where the twine disc sits relative to the twine holder when tying begins. If the disc is out of time, #2 twine can slip off the billhook even with perfect holder tension. Service manuals give a specific dimension for your model — check yours rather than eyeballing it. If you do not have the manual for your baler, buy one. It pays for itself the first afternoon.
Twine fingers and the return spring
The twine fingers (also called tucker fingers) are the half-moon-shaped plates below the knotter. Their job is to pick the twine up from the needles and carry it into position for the billhook. If they don't do that, no amount of billhook work will help.
"When both sides do not tie the first place to look is the twine finger return spring. The twine fingers are the half moon shaped plates below the knotter. They should be pointing forward."
— mike10, on HayTalk
That "both sides at once" rule is one of the fastest shortcuts in knotter diagnosis. Two independent knotters rarely wear out on the same bale. When both quit together, look for what they share — and the twine fingers, their lever and their return spring are top of that list.
Movement alone is not enough, though. Check the fingers themselves for wear:
"Don't just check for movement of twine fingers, but make sure the 'hook' on the end of the one that isn't tying isn't worn compared to the side that's working for you."
— 8350HiTech, on HayTalk
Side-to-side comparison is the most underrated diagnostic tool on a two-string baler. You have a working control sample bolted to the same frame — use it. Compare the finger hook, the billhook beak, the knife edge and the cam follower against the side that ties correctly.
While you are in there, check the roller on the twine-finger lever where it rides the twine-finger cam. Flat spots on that roller change the finger's travel just enough to cause intermittent misses that will otherwise drive you around the bend.
Billhook, knife arm and dull knives
If tension and fingers check out and one side still misses, the problem is usually wear on that knotter's business end.
- Billhook beak and tongue. A burr, a groove or a rounded beak keeps the knot from stripping off cleanly. Compare it to the good side. A light dressing with a fine file fixes a burr; a worn beak needs a new billhook.
- Billhook cam spring. Too loose and the tongue does not grip; too tight and it will not release. Adjust in small increments — a quarter turn at a time is the usual guidance.
- Twine knife. A dull knife tears rather than cuts. If your knots look like "a really ragged cut," sharpen or replace it before chasing anything else. Ragged tails also drag hay into the knotter, which compounds the problem.
- Knife arm and its roller. The knife-arm roller can seize and develop flat spots, which changes arm travel and timing. On older knife arms the roller is not replaceable on its own — you buy the arm. If you suspect the arm, swapping arms side to side is a decisive test: if the fault follows the arm, you found it.
None of these parts are individually expensive. What costs money is replacing all of them because you never isolated which one was actually at fault.
Twine problems that look like knotter problems
Before you tear into the knotter stack, rule out the twine path. A surprising share of "the knotter is broken" calls end here.
"If the ball of twine is installed upside down ... the twine will come out of the needles. If there is no twine tension at the twine box it can also happen. If when threading the baler you miss the twine guide below the needles it will also happen."
— mike10, on HayTalk
The field check for this is beautifully simple: if you see loops forming in the twine between the twine box and the needles, the ball is in upside down. The twine is coming off the ball with a twist that unwinds instead of feeding, and it will eventually walk right out of the needle eye. Note that the paper wrapper on a ball can itself be printed upside down, so "I followed the arrow" is not proof — watch for the loops instead.
Also worth checking:
- Twine box tension. Not enough and the twine feeds slack; too much and the needles fight it or break twine.
- Every twine guide. Rethread from the box forward and confirm the twine passes through the guide below the needles. Skipping one guide is a classic.
- Twine spec. Use the knot rating and length-per-pound your baler's manual calls for. Cheap or wrong-spec twine causes misses that look mechanical. Sisal and poly behave differently through the same knotter — if you switched types and the misses started, that is your suspect.
- Twine age. Sisal that has sat in a damp shed for years loses strength and gets fuzzy, and fuzz packs the twine disc.
Hay dogs, bale density and needle timing
Three more things sit outside the knotter but cause knotter symptoms.
Hay dogs. These are the spring-loaded pawls in the bale chamber that keep the charge from pushing back between plunger strokes. When they stick or lose a spring, the hay in the chamber moves when it shouldn't, and the twine ends up in the wrong place at the wrong moment. The advice comes up over and over: be sure your hay dogs are not stuck and do not have broken springs. Malfunctioning hay dogs cause genuinely strange, intermittent tying faults on otherwise healthy balers.
Bale density. A loose bale does not put enough tension on the twine for the knot to pull up tight when the bale moves back. If your knots are technically forming but pulling apart, tighten the bale tension before you touch the knotter. Soft bales also travel in the chamber, which upsets twine positioning.
Needle timing and penetration. Needles that come up early, late or short do not present the twine to the disc correctly. Needle-to-plunger timing is also the adjustment that protects your needles from being destroyed by the plunger, so it is worth verifying whenever you have the knotter shields open. Confirm the needle safety latch works while you are there.
When it is wear, not adjustment
There comes a point where you are adjusting around wear instead of fixing it. Signs you are past that line: end play in the knotter stack, a billhook that will not hold a dressed edge, knotter frames with elongated bolt holes, or a baler that ties fine for 300 bales then starts missing as things heat up and loosen.
Rebuilt knotter assemblies are available for most common balers, and on a machine you plan to keep, a rebuilt stack is often cheaper than a season of missed bales and re-baling. If you are shopping for a replacement baler instead, our small square baler buying guide covers the models worth stepping up to, real used price ranges, and a pre-purchase inspection that puts the knotters first — because this article is exactly what you are trying to avoid buying.
One more piece of practical advice: fix knotters in the off-season. Every hour spent in a warm shop in February is worth five in a hayfield in June with rain on the radar.
One less thing to tie
Every producer who has spent an afternoon on a knotter has had the same thought at least once: there is a bale format that does not use knots at all. Round balers wrapped in net eliminate the entire tying mechanism — no billhooks, no twine discs, no needles — and wrap a bale in about two seconds instead of twenty or thirty twine revolutions.
That is not an argument to abandon small squares; the horse and small-livestock market pays for them, and they stack in a barn in a way rounds never will. But it is a real reason many operations run a small square baler for the premium market and a round baler for the tonnage. If you are weighing that, net wrap vs twine compares the two systems on speed, weather resistance and storage loss, and round vs rectangular bales covers the format decision. On the round side, the equivalent troubleshooting guides are baler won't stop wrapping and net wrap tearing when baling.
Frequently asked questions
Why is my square baler not tying knots?
The most common cause is twine slipping out of the twine holder because holder tension is too light, which leaves a knot on one strand and a loose end on the other. Tighten the tension bolt about a quarter turn and retest. If both knotters fail together, check the twine-finger return spring instead.
Why is only one side of my baler tying?
One-sided misses almost always mean wear or adjustment on that knotter alone. Compare it directly against the working side: look at the billhook beak for burrs or rounding, the twine knife for a dull edge, the twine-finger hook for wear, and the knife-arm roller for flat spots or seizing.
How do I know if the twine ball is installed upside down?
Watch the twine between the twine box and the needles. If you see loops forming there, the ball is upside down and the twine will eventually pull out of the needle eye. Do not rely on the printed wrapper — wrappers are sometimes applied upside down on the ball itself.
How can I safely watch my baler tie?
Bale until the chamber is nearly full, then shut off the PTO and the tractor. Raise the trip arm by hand to release the clutch dog, and have a helper turn the flywheel slowly in its normal direction while you watch the cycle. Never put hands or tools into a knotter that can move.
What causes ragged or chewed-looking knots?
A dull or nicked twine knife tears the twine instead of cutting it, leaving frayed tails. Check knife sharpness first, then knife-arm travel and clearance past the billhook. Ragged tails also drag hay into the knotter, so a dull knife tends to create additional problems over time.
The bottom line
Knotters look mysterious and behave predictably. Read the failed twine first: one strand tied means holder tension, both sides down means twine fingers, one side only means wear on that side, and loops before the needles mean the twine ball is upside down. Then shut everything off, trip the knotter by hand, and turn the flywheel slowly until you actually see which step fails. Adjust in quarter turns, compare left to right, and do the real work in the off-season — not with the hay on the ground.
Running a round baler too? XES Netting makes heavy-duty bale net wrap — no knots, no needles, a tight bale in about two seconds. Find your roll size with the baler size checker. Shop net wrap →
Sources: Knotter operating theory and adjustment sequence cross-checked against New Holland and John Deere square baler operator and service literature (accessed July 31, 2026). Field troubleshooting detail and grower quotes from HayTalk.com discussion threads, linked above. Always follow the specific adjustment dimensions in the service manual for your baler model.
Image: "John Deere 338 square baler" by Daniel X. O'Neil, licensed CC BY 2.0, via Wikimedia Commons.
