Combines things to look for when buying a JD 643 head

High tin _ low tin is just that. low tin has clip on ear savers (inner covers) that can easly be removed for down corn. They're bolted and taller on the high tin. Fenders on the low tin are down corn friendly but can loose occasional ears over the side. Down corn can hang up on high tin fenders. Deere sells 40 series replacement poly ponts and fenders that bolt on. High tin does not have oil bath drives like the low tin. Greatly improves drive chain life, but can leak if not sealed properly. look at the stalk rolls for wear. They should show a tight straight V between the rolls. Same with the snapping plates. Go for a lower price if these are worn, or a discount on replacements if buying from a Deere dealer. Gatherer chain idler on the high tin is a sealed bearing type while the low tin is greaseable, which is slightly better. Between seasons - remove the gatherer chains and flip them over (lH to RH and RH to lH) and move the gatherer drive sprocket lh to rh. set the chain inner link on the tooth that ran on the open link the previous season. This will equalise the wear and extend the chain life.

We retrofitted JD knife rolls to our two older low-tin 643 heads about 8 years ago. Within 3 years, the double bevel gear inside the gearbox had failed in 5 out of the 12 rows. We finally changed all the remaining gears in the off season to prevent further down time. The newer design double bevel gears have been trouble-free. Not sure what year JD changed the design -- maybe 10 years agoIJ So, if you want to run knife rolls, or you're looking at a head that's been converted to knife rolls, beware!

Check the gearboxes. Take the outer chains off and put a 1" wrench (I think 1") on the outer gear and spin the head and auger by hand. On a good head this is easier than you think and may give you a feel for any trouble spots. The biggest expense you could have would be row unit gear boxes. If I remember right they run about $700-$900 new. If you do find bad ones probably cheaper to buy an older 443 or something and scavenge the boxes off of it.

pbutler, I think you forgot the "1" in front of the new gearbox price