Hello, I have an IH McCormick pull behind sickle mower. For the most part a good machine. I do have an issue lately though, of breaking pitman boards. I had to order new pitman straps, plunger lever and spring. When assmebling, the spring that goes into pitman end then into the plunger is so tight when trying to close the plunger I've had to use a tie down strap to pull and eventually snap into place. It lasted one row before the pitman board broke. I had to order a new spring and board, the other parts I found in the grass. Does anyone have suggestions on why the spring is so tight that there's no spring left when trying to tighten? I believe the straps are correct as the holes match up with the old ones. The plunger is the same as well. Any help would be appreciated.
DanielW
Well-known Member
- Location
- Haliburton, Ontario
I have a 32 (and two C28's, which are the mounted version of the same mower and use the same pitman), and they are a little more finicky than most other sickle mowers about their adjustments and parts. Are you sure you have the correct jaws and fork on there? Every manufacturer had slightly different jaws and forks, and if you have the wrong one on there the latch position will be a little too close to the pitman and compress the spring too much. I had the same problem with the second of my 28's when I bought it due to the wrong jaws being on there. If I remember right, when I looked into it the jaws and fork were from a Massey, not an IH. It should be very tight to pry down and snap in place, but certainly not so tight that you have to use a ratchet strap. Usually a hammer handle used as a lever over the main casting will snap it in place.
Regarding breaking the pitman: How easily does your knife slide by hand? Are the guards all levelled up with the ledgers all in-line? And how sharp is your knife? A dull knife can cut thick grass and legumes just fine, but when you get into thin, stringy grass, it will put far too much stress on the pitman. Perhaps most importantly, is your sickle registered correctly? This is probably the most overlooked adjustment on sickle mowers. If the register is out, it will cut poorly and put loads of stress on the pitman.
Also: Are you sure it has the correct knife in it - with the correct knife head? Just like the straps and fork: All manufacturers used slightly different knives. They'd seem to interchange, but the ball location was slightly different on each manufacturers' knife. If it has the wrong knife head, the ball won't be in-line with the pitman connection point on the pulley. That alone puts a lot of stress on the pitman. But there's another concern: The base casting on the IH mowers doesn't have any allowance for the ball location to be slightly too far forward or backwards. So if it's slightly off (due to, say, the wrong knife head), the bolts that fasten the jaws to the pitman will rub the casting when it's dropped to cutting height and cause the pitman to break. Look under the main casting above where the jaws travel back and forth - See if you see any witness of the bolts hitting the underside of the casting. The correct knife head is MA999 - look for that (or the IH logo) cast onto the top of the knife head
How much slop is in the bearing on the pulley-end of the pitman. They were a pretty hateful bearing that would often get sloppy. When they get sloppy, you have less effective knife stroke and it plugs a little easier, putting more stress on the knife and pitman. I had a new bearing mount plate plasma-cut for my pitman. It uses a standard three-bolt flange bearing, and I had it cut out of 140 ksi yield steel, to be much stronger than the original (the originals all developed metal fatigue over time and broke - especially if it was used with the knife out-of-line).
Attached is a sketch showing the pitman dimensions of the 28 and 32 mowers. Might be worth checking to ensure your spring hole depth is correct, I'd suggest posting some pictures of your knife head, jaws, and pitman (and the mower in general) and we can probably help you out more.
Regarding breaking the pitman: How easily does your knife slide by hand? Are the guards all levelled up with the ledgers all in-line? And how sharp is your knife? A dull knife can cut thick grass and legumes just fine, but when you get into thin, stringy grass, it will put far too much stress on the pitman. Perhaps most importantly, is your sickle registered correctly? This is probably the most overlooked adjustment on sickle mowers. If the register is out, it will cut poorly and put loads of stress on the pitman.
Also: Are you sure it has the correct knife in it - with the correct knife head? Just like the straps and fork: All manufacturers used slightly different knives. They'd seem to interchange, but the ball location was slightly different on each manufacturers' knife. If it has the wrong knife head, the ball won't be in-line with the pitman connection point on the pulley. That alone puts a lot of stress on the pitman. But there's another concern: The base casting on the IH mowers doesn't have any allowance for the ball location to be slightly too far forward or backwards. So if it's slightly off (due to, say, the wrong knife head), the bolts that fasten the jaws to the pitman will rub the casting when it's dropped to cutting height and cause the pitman to break. Look under the main casting above where the jaws travel back and forth - See if you see any witness of the bolts hitting the underside of the casting. The correct knife head is MA999 - look for that (or the IH logo) cast onto the top of the knife head
How much slop is in the bearing on the pulley-end of the pitman. They were a pretty hateful bearing that would often get sloppy. When they get sloppy, you have less effective knife stroke and it plugs a little easier, putting more stress on the knife and pitman. I had a new bearing mount plate plasma-cut for my pitman. It uses a standard three-bolt flange bearing, and I had it cut out of 140 ksi yield steel, to be much stronger than the original (the originals all developed metal fatigue over time and broke - especially if it was used with the knife out-of-line).
Attached is a sketch showing the pitman dimensions of the 28 and 32 mowers. Might be worth checking to ensure your spring hole depth is correct, I'd suggest posting some pictures of your knife head, jaws, and pitman (and the mower in general) and we can probably help you out more.
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Hello, and thank you for the reply. Many great tips. Regarding the knife portion, yes it does slide easily back and forth. I bought the sickle knife piece from an IH dealer. You mentioned is the sickle registered correctly. I'm not sure what that means. An explanation would be appreciated. As far as the knife head, I'll have to check to see if it is an IH-McCormick. The unit ran fine for a couple of years with out any issues. But I'll double check stock number MA999. My Hobby Farm is located about an hour from where I live. Thanks for the drawing. I've included a picture of that assembly. I measured the hole with from you drawing which is 1 5/16". That checks out. When I was at the CaseIH dealer, I ordered another pitman. When they looked it up they ordered the correct one. I had to order another spring, as mine went flying in the grass. I should go look for it, as the new one is $44. Wow! I'll check the slop on the bearing. As I mentioned, it had been running great. I know I have a few knives that should be replaced. I'll work on that as well. I'll check the depth of the spring hole in the pitman. I'm picking it up tomorrow.
Attachments
DanielW
Well-known Member
- Location
- Haliburton, Ontario
The register refers to making sure the stroke of the knife enters the guards equally both directions. On many pitman mowers, the stroke of the pitman is the same as the guard pitch (3" on most mowers), so it's a case of making sure the sections are centred in the guard at the of each stroke. I think (but could be wrong), that those IH mowers have a slightly longer stroke than the guard/section pitch, to ensure it cuts positively. So it's a case of making sure the tip of the sections goes slightly past centre at either end of the stroke.
Adjusting the register on those IH mowers is a bit of a pain: The head-end casting threads further onto or off of the large (about 2" diameter) connecting bar. But to thread it on/off, you have to disconnect the trip arm, knife, and then either spin the whole bar with the casting, or remove the bar to spin the casting. Lots of folks compensated by making a 'custom' pitman that's slightly longer or shorter to correct the register accordingly. Which works fine, except that when you go to replace with a standard pitman, your register will be out.
Take a look at this video: It shows checking the register (in that video, the knife is registered a little too far to the right).
Adjusting the register on those IH mowers is a bit of a pain: The head-end casting threads further onto or off of the large (about 2" diameter) connecting bar. But to thread it on/off, you have to disconnect the trip arm, knife, and then either spin the whole bar with the casting, or remove the bar to spin the casting. Lots of folks compensated by making a 'custom' pitman that's slightly longer or shorter to correct the register accordingly. Which works fine, except that when you go to replace with a standard pitman, your register will be out.
Take a look at this video: It shows checking the register (in that video, the knife is registered a little too far to the right).
DanielW
Well-known Member
- Location
- Haliburton, Ontario
Here's an excerpt from the IH manual on adjusting the register. Ultimately it comes down to the outer casting (what they call the 'Shoe Hinge - D') being threaded onto the bar 'I'. You thread it further on/off to adjust the register. Which sounds a lot easier than it is. You want to make sure everything else is right before adjusting (pitman length, lead, knife head, etc.) because it would be a pain to adjust the register, then find out that it was out because something else was awry and have to adjust it back. The 'lead' refers to the far end/tip of the bar being slightly further ahead (1" or so) than the inner end, to compensate for the load/pull when it's being pushed through the crop. When these mowers get a older and their linkages get a little sloppy, they tend to develop negative lead. This causes all the crop to be forced into one side of the guards and it won't cut as well. Adjusting the lead has a small effect on the register.
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DanielW
Well-known Member
- Location
- Haliburton, Ontario
In addition to above: One old trick for making an old pitman a little more resistant to shocks is to wrap it in hockey tape. I do this for pitmans I make out of maple: Maple is uber-strong, but also brittle and prone to cracking when it dries out. The hockey tape helps it handle the shocks it gets on our rough/bumpy ground a little better. Here in Canada, you're never very far from a roll of hockey tape. But I suppose duct tape would probably do just as well...
DanielW
Well-known Member
- Location
- Haliburton, Ontario
It should rest against the pitman jaws. It's been a few years since I had both a newer knife and newer jaws on any of mine: Perhaps it being so tight on yours is just a case of everything being so new/tight.
The geometry of the fork is such that when it's clamped down all the way and resting on the jaws, the spring is pushing 'over centre' and working to keep the latch down and in-place. But it only has to be lifted a small amount before the spring's gone 'over-centre' the other way and working to push it open.
Thus: If it isn't latched down all the way, it will probably not be 'over centre' correctly and may spring up during cutting. Which could be part of your problem. This is inherent to the IH/McCormick design- carrying over from the days of the McCormick horse mowers. The 'idea' is that if the knife encounters an obstruction too tough to cut through, the jaws will be forced open enough to push the latch open and unlatch, saving the knife from damage (and only causing damage to the pitman, which is cheaply/easily made and replaced). I can't say that I've ever seen it actually work too successfully, but that's the theory.
DanielW
Well-known Member
- Location
- Haliburton, Ontario
Sounds good. I see where the confusion came from in my fist post. Yes, the latch should rest on the pitman. When I said in my first post that 'the fork will be too close to the pitman if the jaws are wrong', I meant that the socket of the pitman will be too close to the end of the pitman - i.e. the mount holes on the jaws are closer to the socket - compressing the spring too much even in its open position.
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