Why the Chain Diagram Matters When You Are Standing in a Hay Barn at 6 AM

You pulled the cover off the 335 and every roller chain looks the same. Gray grease, same pitch, same link count. The baler won't pick up, the knotter is slipping, or the chopper drum won't turn. That is when you need a reference that actually matches your machine and not just some generic diagram someone photocopied from a 1998 Parts Manual with the wrong part numbers in the margin. I spent a Tuesday afternoon on a farm outside Mitchell, South Dakota, trying to reassemble the pickup drive on a 1992 335 after the main crankshaft bearing seized. The dealer tech had told me to just replace the chain and keep going. He was right, but he did not hand me a diagram. I ended up routing three different sprockets back together by feel, guessing which tensioner spring went where. Took four hours. The next baler season I went straight to the manual and did it in twenty minutes. The John Deere 335 and 435 are sister machines from the same generation. Same frame. Same driveline architecture. The 435 just has a larger capacity chamber and a few extra hydraulic circuits for the kicker arm. Their chains run identical paths, which means one good diagram covers both if you know how to read it.

Deere 335 John Deere 435 Baler Chain Diagram

The drivetrain splits into three separate chains, each doing a different job. Mix them up and the baler either binds or throws hay everywhere. The first is the pickup drive chain. It runs from the main driveline input through a gearbox reduction to the two pickup wheels. On the 335 this is a single-row roller chain, usually a #420 or #520 depending on the year. The 435 uses the same size but often has an additional idler sprocket near the rear frame rail to take up slack from the wider header path. You can find the exact spec stamped on the chain guard in small white lettering that flakes off after three harvests. If you are standing there squinting and can not read it, measure the pitch with a caliper. Half-inch pitch is #520. Three-eigh inch is #420. Do not guess. The second chain is the plow wrapper. This is the one that causes the most headaches because it lives inside the chamber and gets buried under straw and dust. It connects the main shaft to the plow bar that pushes the bundle forward. When this chain stretches even a quarter inch past its original length, the plow will skip on the tie point and you get a loose knot or no knot at all. I have seen guys replace the chain and still have bad knots because they did not check the plow bar clearance first. The spec is usually 0.015 to 0.030 inch of total stretch measured over a twenty chain pitch length. Anything more and it is time for a new one regardless of how good it looks. The third chain is the knotter drive. This is the smallest but the most precision-sensitive. It runs from the main camshaft to the knotter assembly that wraps twine around the bundle. The timing here is everything. If the knotter sprocket is one tooth off from where it should be, the knife will cut the twine before the knot is tied and your bales will unravel in the wagon. I learned this the hard way on a 435 in '09. The previous operator had installed a replacement knotter shaft from a different year. Same diameter, same spline count, completely wrong timing. The baler ran fine until the first high-moisture day when the twine expanded and the knot slipped. Took me six hours to figure out because the diagram showed the correct timing and the part I had did not match it. There is also a thrower chain on some models, running from the plow bar to the conveyor slats that lift the bundle up into the chamber. This one is easy to miss because it is hidden behind the side panel. The chain tensioner on this one uses a spring-loaded idler that goes bad if you never lubricate it. Once that idler seizes, the chain snaps and you lose a day of cutting.

How to Actually Use the Diagram in the Field

Print the diagram. Put it in a plastic sleeve. Tape it to the inside of the engine cover where you can see it without taking anything apart. I keep one on every baler I work on and it has saved me more hours than I can count. When you are removing a chain, take a photo first. Not for the internet. For yourself, three weeks from now when you are standing in the same spot wondering which way the tensioner spring should be hooked. Your future self will thank you. Label every bracket and spring location with masking tape and a marker before you remove anything. I use a system where I write the chain number and the sequence on each bracket. Chain 1 - pickup, Chain 2 - plow, Chain 3 - knotter. Simple but it prevents exactly the kind of confusion I described above. Check the sprocket teeth while the cover is off. Worn sprockets will destroy a new chain in two harvests. The teeth should be symmetrical and pointed, not hooked or shark-finned. If they are even slightly deformed, replace the sprocket along with the chain. A new chain on old sprockets is a false economy that costs you more in downtime than the price of the sprocket ever will.

The Problem Nobody Warns You About

The diagrams in the manual show the chains in their ideal, factory-new positions. Real machines accumulate slack, wear, and modifications that the diagram does not account for. The 435 in particular has a reputation for the knotter chain riding off the sprocket when the chamber gets too full and the hay backs up against the plow bar. The solution is not to tighten the chain further, which makes the problem worse. It is to install a chain guide roller on the top run, about six inches from the sprocket. These are available through the parts dealer, usually listed as a knotter chain stabilizer or guide assembly. Without it, you will be adjusting the chain every three days during a heavy crop year. Another thing the diagram does not show: the lubrication path. The pickup chain is sealed in a gearbox housing and does not need external lube. The plow and knotter chains do. But the grease zerks on those two are in different locations depending on whether your baler was built before or after the 1996 mid-life update. If you are greasing the wrong zerks, you are wasting time and potentially damaging the seals. Check your serial number against the update schedule in the manual before you start turning the grease gun. The biggest gap in every chain diagram I have ever seen is the timing marks. The knotter shaft should have a timing dot on the sprocket that aligns with a corresponding mark on the shaft collar. If yours is missing, you can make one with a center punch and a hammer. Take two minutes to do this and you will never again have to guess whether the knotter is one tooth off. I made that mark on my 335 after the '09 incident and it has been worth more than the baler itself.

Where to Find a Reliable Diagram

The official John Deere parts manual for the 335 and 435 is available through the dealer parts department. You will need your serial number because the diagrams change slightly between the 1988 initial run and the final production year. The diagram you need is in the "Drivetrain" section, usually labeled as Figure 3 or 4 depending on the manual version. If the dealer cannot produce it, the service manual has the same information in a more diagram-friendly format. It is available as a PDF download from several agricultural documentation sites for a small fee, usually less than the cost of one failed chain that you installed backward. There are also third-party diagrams floating around on farming forums. Some are accurate. Some are from the wrong machine entirely. I once followed a diagram from a forum that turned out to be for a 242 baler, not a 335. The chain routings looked similar enough that I almost ordered the wrong parts. Always cross-check the sprocket positions against your actual machine before ordering anything. A five-minute verification saves a two-day parts delay.

What to Do When the Diagram Does Not Match Your Machine

It happens. Especially on machines that have been through multiple owners and partial rebuilds. The 435 in particular sees a lot of aftermarket modifications to the knotter assembly, usually involving longer shafts or different sprocket ratios to accommodate various twine types. When the diagram does not match, the only reliable approach is to trace the chain path yourself. Start from the power source, which is the main driveline input shaft, and follow the chain to each component in order. The pickup chain always comes first because it connects directly to the input gearbox. The plow chain comes second because it is driven from the main shaft downstream of the pickup reduction. The knotter chain is last because it branches off the main shaft through a timing gear. If you have modified components or replaced parts from different years, document everything. Not for the manual. For the next person who has to work on this baler, which might be you next season. Write the dates and part numbers on a tag and hang it from the chain guard. Five seconds now prevents an hour of confusion later. The chain diagram is a starting point, not the final authority. Your machine is the final authority. Trust what you see more than what you read, and always verify before you commit to a repair.