39 M stiff area in motor when cranking

This tractor has always had a stiff area when starting in one area.Has to have a good battery to crank a complete revolution. Mag. was set on #3 {4 o'clock] instead or #1 and this is how it ran when I got it.Am in process of restoring and have everything off from behind motor to back of tractor.[tank,steering & seat]. Today took all spark plugs out and jacked up rear wheel to match up #1 piston with mag click. Timing advanced 1" past second pully mark.Got mag set only to second mark, but when rolling tire around I still hit this real hard place . Same problem as when starting with battery. What could this resistance be? Trans. and rearend not causing this because with clutch in and cranking with battery ,it did the same. Tractor also has orgional mag. with cable switch and you can rock rotor quarter inch. Rotor does not fit slot in mag shaft. New one does same thing. slot not walowed out. Tried to give all info, sorry for so long. I do need help. Thanks, Buck

Sounds like some parts are not fitting where they are supposed to fit. Maybe somebody at some time replaced something that came off the wrong tractor.

If I understand correct, with the sparkplugs removed the engine still has a tight spot I wonder if the engine run good after started? If so the valves and valve train is probably okay and maybe the pistons. May want to check the main and rod bearings for wear. Wear pattern should show if a crankshaft or rod is bent or block bearing bore off. Also maybe a bent cam or other shaft bent that bind the front timming gears. Also do you mean the timming was one inch from mark and you changed it?

Did this ever run? Was it running when you bought it? Sounds potentially like something is bent. Crank, Cam, connecting rod or similar. Also, not quite sure I understand what you posted about the mag, but sounds like something is screwy on the timing gears as well.

If it actually runs if pull started and seems fine when running, It is a mystery. The only thing I can think of that might apply to the given content is dramatic carbon buildup in one cylinder such that its compression ratio is near 10:1. A bore sight tool (for looking into gun barrels) used in the cylinder after dark or in a dark building would show that if it was the case.
A broken ring in one cylinder scoring the cylinder, would be very short lived, make noise, and smoke like a fogger.
Broken pistons would be similar in quick death.
Is the tight spot once every crank revolution, or every other revolution (actual 360 on front pulley).
This tells us if it is a mechanical issue, or a compression issue. Jim

Bad spot in the ring gear?

If when cranking yes, but he stated it happens when turning the rear wheel with it in gear! Jim

Men, I don't think I gave you enough info. My Uncle bought this tractor in 1963 . It had been changed to propane in 1953, with pressure radiator and aparantly overhauled at this time . Does have flat pistons and I tried to check preasure in cylinders and my guage threads too small.Tractor has been runing well for years and never been overhauled again. A little smoke when starting and then clears,but does use a little oil.. I found out about the different timing when a year ago took all wire off to redo valve side cover.[Clean wire mesh inside and paint]. When putting wires back on the way book says , could not start tractor . Finally put #3 wire on dist. where #1 should be after looking at old picture, and motor ran just like it always did . Good. With so much trouble with leaking tank , I jerry riged to run off 5 gal tank on draw bar. On restoring tractor I decided to put back to gas because of propane diffficultys and not wanting grand kid hurt fooling with it. All that said , this is what burned all my wiring and amp guage and Alt. on super M last fall when I tried to jump it. It pulled too much juice. Now I'm tearing it apart as little as possible just to get in good shape and paint. Hope some of this helps you guys on this problem. I don't know how it ran good with that much play in rotor.... Thanks men. Buck

I changed timig back 1". It's right where mag. clicks now and I believe stiff area every conplete turn of wheel. There is another mark on pully about 2 " forward of right timing marks. Mayby timing for propane was different. Buck

I have a C that was stuck when I got it. After I broke it loose it would stick real hard in one area. I tore it all down and found that the rings were all froze up in the piston and the clinder wall had the usual taper after years of use, so when the piston got near the bottom the rings wouldn"t compress and I could barely turn it over. Maybe on yours one or two of the rings are stuck with corrosion or even some carbon(I know unlikely on a propane tractor). Just a thought.

The jumping tractor (SM would burn up its wiring only if it was accidently hooked up backwards. THe alternator is self limiting, and the battery will only put out so much. If it has not run for a year or more it could have stuck rings. If you do a compression check, and it seems to be in the 120 to 130 area on all cylinders, I suspect stuck rings.
Putting a two tablespoon shot of ATF into each cylinder can't hurt. Best of luck, Jim

Jim; Thanks for your come back. I will do this and see what happens. There are lots of [Know How] people on this forum and you and others have given me much good information. Thanks all. Hope to get this together some time this winter in the cooler weather so can get it fired up. Thanks again everyone. Buck

GREGK; I think you all have put me on the right track I agree about this and the tractor did set for many years before I got it. . Thanks. Buck

You said there was a stiff spot every turn of the WHEEL.

Even in 5th gear, the engine has to rotate several times to make the wheel go around once. That means the stiff spot you're feeling is in the TRANSMISSION, not the engine.

Unless you can crank the engine directly by hand from the front, you can't even confirm there is a "stiff spot" in the engine.

The starter will lug down and struggle to get the cylinders past compression, every 1/2 revolution. That's perfectly NORMAL, if the starter isn't in the best shape, or the battery cables need work.

Get out the hand crank and turn the engine over from the front before you panic and start tearing into the bottom end looking for bad bearings and bent rods.

MKIRSCH; I read what you say. Can't crank from front. Crank rod all froze up thru front end . Hard to change belt.Mayby I can get a wrench on pully to turn motor. Will see. A good thought. Thanks for your interest. Buck

Turning the rear wheel is OK if you look at a chalk mark placed on the front crank pulley when it gets stiff. You can see when it turns and count the number of turns of that pulley between stiff spots. You might need a helper, to watch, but not a difficult situation. Jim