Sickle Mower - knife gap

Yesterday I went through and adjusted the knife gap using a feeler gauge and shims to about 0.010". I couldn't remember what I was told the gap should be - senior moment! :)

Can anybody tell me what it should be?

I am having a lot of trouble with it jamming so that the internal slip clutch slips, and last night within about 10 minutes of finishing a field, I broke the pitman. I have a spare, but it was late and I just wasn't up to replacing it and finishing after a long day.

This morning, I'll replace the pitman, then recheck the gaps, and try to figure out why it is so sensitive to jams before finishing what I started yesterday and starting on the last 2 acre field of my first cutting.

It's interesting...I can tell by the sound when I engage the pto if it's going to run smooth or jam. It it's a loose,rattling sound, it will work. If it's a softer sound with less rattle, it will jam.

I noticed yesterday that if it sounds like a jam, if I throttle up a little, then throttle way back down, and back up again, the sound changes - there's not quite a click, but there's some subtle sound or feel that tells me something changed - and that often takes care of whatever is going on and it works OK. The fields I mow are small, and most have irrigation risers so there's lots of stop-and-start. Most folks wouldn't mess with it, but it's a hobby and a help for friends who buy the hay for their horses. The mower is old, and I can't really justify putting a lot of money into it, but am hesitant to replace it with a pig-in-a-poke.

I'd appreciate any help with the gap, and any ideas on what might be the root of the problem.

Thanks!
Chuck, WA

Knife-ledger plate contact seems good. I gapped at 0.010" with a feeler gauge by running the gauge in at the back of the section where there was a gap and sliding forward till there was resistance when I pulled it out at the front (tip) of the section.

Sections are all new - mostly last summer and a few the summer before - and I only hay about 3 acres, three or four cuttings, so there shouldn't be a lot of wear on sections. In fact, looking at them, there's little wear.

Guards are all tight.

The problem is worse in late afternoon, so could be at least in part due to a little dampness, but our climate here is very dry, though this time of the spring, could be a little more moisture in the air and coming up from the ground as it cools in late afternoon.

I've installed a new pitman and checked knife-ledger gap and found a few a little tight and a few a little loose, and will adjust a little before trying again.

Any other thoughts are welcome.

Thanks!
Chuck, WA

The gap between the sections and the top of the rock guard to far apart. take a hammer and lightly hit them