Pony Mag

Not as far as I know. Differences in mounting, impulse coupling if fitted, and firing pattern of odd vs even probably rules it out completely.

Definitely not. The inline mag fires twice 90 degrees apart, then skips 270 degrees. While the opposed mag fires evenly every 180 degrees. You can spot the difference by looking at the cap. Most have 2 extra nubs where the wires would be if it were a 4 cylinder magneto. 2 wires on adjacent nubs is an inline mag, 2 opposite is an opposed mag. It MAY be possible to reconfigure one into the other, but likely not worth the trouble.

[attachment=53281]IMG_0161.JPG[/attachment]

[quote="Layne"]Definitely not. The inline mag fires twice 90 degrees apart, then skips 270 degrees. While the opposed mag fires evenly every 180 degrees. You can spot the difference by looking at the cap. Most have 2 extra nubs where the wires would be if it were a 4 cylinder magneto. 2 wires on adjacent nubs is an inline mag, 2 opposite is an opposed mag. It MAY be possible to reconfigure one into the other, but likely not worth the trouble.

[/quote]

Ever since I read this it has confused me. At first I thought it might be an April Fools post but it was posted on the 2nd. I cannot understand why the inline engines would fire 90 degree apart and then 270. Looking at the manuals that I have with inline (D8 14A, 944 and 950) and opposed (D4 6U, D6 4R/5R and No 12 Grader) the crankshafts in all are set up so that both pistons reach top dead center at the same time therefore one cylinder fires each rotation or 180 degrees apart. This is confirmed by looking at the magnetos for each which although they have different assembly part numbers they are visually similar and functionally identical and even share some of the same parts.

Am I missing something here or do some later inline pony's fire differently?

[quote="PhilC"]Ever since I read this it has confused me. At first I thought it might be an April Fools post but it was posted on the 2nd. I cannot understand why the inline engines would fire 90 degree apart and then 270. Looking at the manuals that I have with inline (D8 14A, 944 and 950) and opposed (D4 6U, D6 4R/5R and No 12 Grader) the crankshafts in all are set up so that both pistons reach top dead center at the same time therefore one cylinder fires each rotation or 180 degrees apart. This is confirmed by looking at the magnetos for each which although they have different assembly part numbers they are visually similar and functionally identical and even share some of the same parts.

Am I missing something here or do some later inline pony's fire differently?[/quote]

Yes, they do! Like an John Deere 2 cyl.
My thought: on the smaller tractors that rope start it is easier to pull over two compression strokes. But with the lever they have two in quick succession. I suppose that firing pattern was used because it made for easier starting. You do have to get used to finding the spot where the #1 fires because the impulse will also trip on rotation when there isn't a TDC.

I thought Cat made both styles of inline crank. Both throws on same side and 180 degrees apart?

On the large vertical pony motors, by far the most common are odd fire. The 14 & 15a must be along about the time there was a swap to even fire ponies on the big verticals. By the time the 47/48a D7 came out, CAT had swapped back to odd fire. I suppose the crankshaft must have been expensive to make or problematic in some other way.

I always heard the odd fire design was originally half of an already existing 4 cylinder. I also heard that was the case for some of John Deere's early vertical cylinder tractors (M, 40, 420, 430 etc), but don't know what 4 cylinder engine that could have been at the time because there were no production 4 cylinder tractors for another few years until around 1960.

Half of a 4 cylinder design so the crank has two throws opposite each other. A vertical 2 cylinder 4 cycle engine with that crank cannot be made to even fire....when one piston is at TDC the other will be at BDC. It will fire at 0 & 180 then rotate 540 degrees before #1 fires again.........The missing two additional cylinders of the original 4 cylinder would have fired at 360 and 540 degrees of rotation.

On any 4 cycle, horizontally opposed two cylinder, the crankshaft with opposite throws results in an even fire engine since both pistons reach TDC at the same time, one is on compression stroke transitioning to power stroke while the other is on exhaust stroke transitioning to intake stroke.....firing on 0/720, 360, 720(0), 360, 720.................

The small buzz bomb side mounted vertical cylinder ponies for the D320(D311) D330 and D333 were also even fire very high rpm designs with a counterweighted design crankshaft.

I had the thought that having a center main bearing might be the reason for the opposed throw crankshaft design. It's easy to have one with the opposed throw crankshaft but difficult with both throws on the same side....... but none of the pony motors have a center main, so that wasn't it. In fact a lot of 4 cylinder engines of that time had 3 mains instead of the 5 main design we see today. So if you lop off the extra two crankshaft throws and the extra two cylinders, extra camshaft lobes and anything else you don't need just behind the center main bearing of one of those old designs, you pretty much have the common 2 cylinder vertical engines of the day.

Sorry, I wasn't aware there were even firing inline Cat ponies when I posted that.

It's always the same compromises when you try to design a 2 cylinder inline... Opposing the crank throws balances the engine, but it requires odd firing which gives you uneven power delivery, and the frankly unpleasant sound we've all come to associate with the color green. Putting the throws together evens out the power and the sound, but then the mass of the pistons is far off balance. Maybe not much of an issue with engines this size, but the old prairie sodbuster type tractors with horizontal pistons would rock back and forth substantially (as would John Deeres if they had gone this route). I'm not sure who made the last 2 cylinder 4 stroke inline (probably a japanese motorcycle?), but I'd be surprised if any are still made today. 1 or 3 cylinders makes a much better engine.