Every grower in this part of Saskatchewan has had the year where the straw will not die. A wet August, a heavy canola crop, a few cloudy days in a row, and suddenly the machine that threshed beautifully last fall is plugging the shoe and throwing grain over the back.
The settings that worked in a dry year are the wrong settings now. Here is how to work through it without chasing your tail.
Change one thing at a time
This is the part most people know and almost nobody does at two in the morning with rain coming. If you change concave clearance, fan speed and rotor speed all at once and the sample improves, you have learned nothing you can repeat tomorrow in a different field.
Pick the variable most likely to be the problem, move it, run a hundred yards, and look. Then the next one.
Start with ground speed, not the machine
Tough straw is a feeding problem before it is a threshing problem. A combine set perfectly and fed too fast will plug; the same machine fed at a rate it can handle will often clean up with no setting change at all.
Before touching anything inside the machine, slow down by a quarter and see what happens. If the problem goes away, you have found your answer, and the question becomes whether a different header or a bigger machine pays for itself in acres per day.
Concave clearance: tighter is not always better
The instinct in tough conditions is to close the concave to get more threshing. Sometimes that works. Often it makes things worse, because you are now grinding damp straw into pieces small enough to go through the sieves, and the shoe cannot keep up with the load.
If your sample is clean but you are losing grain over the back, the problem is usually separation or shoe capacity, not threshing. Opening up slightly and letting the straw stay in longer pieces can cut shoe loading more than any sieve adjustment.
Your operator's manual has a starting point for each crop and it is worth being honest about whether you are actually near it or working from a setting that has drifted over three seasons.
Rotor speed and the damp straw trap
Higher rotor speed threshes harder and also chops straw harder. In damp canola that often shows up as a cleaner tank but a shoe that is overwhelmed with chaff.
Watch the tailings. Heavy tailings with whole heads means you need more threshing. Heavy tailings with broken-up material and no unthreshed heads means you are already threshing enough and the problem is elsewhere.
Fan speed is the setting people under-use
Most operators are more conservative with fan speed than they need to be, because blowing grain out the back once makes a lasting impression. In tough straw the air is doing more work than usual, and the setting that was right in a dry crop is often not enough.
The method: raise the fan until you see light grain going over, then back off slightly. You cannot find the edge without going past it once, so find it in a headland pass rather than in the middle of your best field.
Sieve openings follow the fan, not the other way round
Opening sieves without more air just moves chaff into the tank. Air first, then sieves to match.
What to check before deciding the machine is wrong
- Concave wear. A concave that has done a lot of acres threshes differently than a new one at the same clearance setting
- Rasp bars, for rounded edges
- Sieve condition, and whether anything is bent or partly plugged from last season
- Chaffer and sieve actually moving to the setting shown on the monitor, which is worth verifying by eye once a year
- Air leaks in the cleaning shoe, which quietly cost you capacity
When it is not the settings
Sometimes the honest answer is that the crop is not ready and the machine is doing its best with material that needs another day. Tough straw late in the evening is a different crop than the same field at two in the afternoon, and there is a point where waiting beats fiddling.
The other honest answer is capacity. If you are regularly fighting the shoe in average conditions, the machine may simply be smaller than the acres it is being asked to cover.
Need a hand?
Our service teams in Paradise Hill, Lloydminster and North Battleford work through this every fall, and a phone call in August is a great deal cheaper than a plugged machine in September.
Book a service appointment or browse our combine inventory.
