1937 RD4 Pony Motor starting issues

With my very limited knowledge of magneto ignition systems I'm puzzled that the motor doesn't at least pop back through the intake or exhaust systems when there is fuel in the cylinders even if it is 180 degrees off. Just off the top of my head I'd replace the spark plugs. When they get fouled newer spark plugs never seem to fire afterwards.

May not be your problem but it is worth a try.

Check the switch. Is it hooked up and is it turned on. Is the mag grounding out. Do you have good spark when you take the plug out and turn the engine with the plug grounded? Just rambling on why no spark. Are the plugs new? Do you have solid wire core wires?
Chuck C

Is the engine spinning the pony in the direction of the arrow cast into the flywheel?

The other thing I wondered is if you have checked that the points in the mag are gapped properly and open before TDC. Recently had an old Kohler that started fine and would idle all day but was dying whenever the throttle was opened. I was at a loss but decided to close the points gap slightly and that fixed it. I never realized points gap was quite so important on a magneto ignition. The other thing is if the magneto rotor is timed properly with the armature shaft. Some have a gear drive between shaft and rotor that can be out of time.

Hi, Jake1991,
As the others has said i would also swap the plug leads on the magneto, it could be firing on the wrong cylinder this is a common mistake when you put them back together i have done it too.

Just my thoughts

Regards

Having spark and having good consistence spark are different. check connections to and from coil and conditioner. a bad coil will throw spark intermittently and so can a bad conditioner. I had a conditioner wire that had an indirect short inside the mag that gave me fits.

Hi Team,
depending upon which Brand magneto you have can require a different Points Gap to have the internal timing of the magneto correct--namely the edge gap which can make for a stronger spark if not correctly set on an Eisemann especially.
Eisemann points gap setting is 0.020" and for an American Bosch is 0.014"-0.018" meaning 0.016" is the ideal setting.

We have found here that people who claim to be magneto experts are adjusting Eisemann's to 0.014-0.016 as is used on other Eisemann models and Am Bosch and so perform poorly.
With the points gap set correct they usually perform well if not then the edge gap needs to be checked and set.

Another trap is using carbon core spark plug wires--magneto's must use copper or other metal core wires.
I also recommend reducing the spark plug gap down to around 0.014" until you sort this out.

As mentioned above there are internal timing marks on the distributor and armature gears that need to be aligned such as whether the mag is Clockwise or Anti-clockwise turning, these marks can be confused if not versed with these units.

The Grey Operation and Maintenance Instruction Book has most of this in it for both Brand Mags.
Form No:-10902 -03, the 03 is the change level telling how late a publication is--the higher this number the later the book with updates is.

My D4 Servicemen's Reference Book (SR😎 Form No :- 7490B--this time the B indicates the change level--and has the Eisemann workshop instruction for overhauling and adjusting/setting the Eisemann Mag's.

I do not have a D4400 SRB Engine Book but I would assume that a 4 1/4" Bore-4 Cylinder D4400 Engine SRB would have this too--the D4600 SRB I have here does.

Finally a magneto can spark a plug outside an engine, but under compression there may not be a strong enough spark generated to fire under compression pressures.

I would say you have more than ample compression pressure for a good starting engine--many are well below this at around 50psi or even less and run OK.

Hope this helps.
Cheers,
Eddie B.

Thank you to everyone who answered. This is all GREAT information. I am going to try and answer as many of the comments and questions as I can here.

First off, I do have a Eisemann Magneto, not an American Bosch. That was a typo on my part earlier due to thinking about a post I was reading.

The wires are copper core wires. They are older, but appear to be in good shape.

I am getting good, consistent spark on the plugs while outside of the engine. I do know that you can loose spark under conditions inside the cylinder, and that is part of what I am afraid of. Thank you for that Eddie B, as the people standing there earlier when I mentioned that looked at me like I was insane. lol

The plugs are new/have never been in the engine running. They are several years old, and have been used to try to start the engine a lot.... Does anyone know the correct plug to go in there? I noticed today that the original plugs I replaced were two different plugs.

I will set the point gap to .020. The manual that was loaned to me by a friend of a friend late this afternoon only had the American Bosch numbers in it apparently, and I set the gap to .016.

Plug leads were swapped during each and every test to make sure I was never 180 degrees off.

The timing of the magneto and the rotor is something that I may be concerned over. The book that was loaned to me, which is for newer machines, (serial 6U and 7U on up, and mine is a 4G,) talks about being able to see the gear inside the magneto with the cover and rotor off. This magneto does not have that. But where the rotor is when the points open and close does not seem to make sense with my knowledge of how a points ignition system works.

Mag cap brushes are like new.

Mag switch wire is disconnected off the top of the mag to eliminate that problem.

Points are very clean.

I have tried timing the mag with the motor at TDC compression stroke by looking at the piston and valve motion with the head off with the mag installed, and it doesn't run. Have tried timing it multiple different ways from threads, manuals, and knowledge.

Eddie, the SRB that you are referencing. Is that something that can be purchased somewhere? Or is that published somewhere here on this site? I have a reproduction of the Shop/Service books for the dozer and the motor, but no where in them does it mention any information for the pony motor, which I find very strange.

Thank you to all. I will be going at it again tommorow, and will check back for additional ideas and to update you. Thanks!

Eddie, is this the book you are talking about? Thank you

https://www.ebay.com/itm/CATERPILLAR-D4-D-4-D-4-4G-7J-2T-ST-6U-7U-Servicemens-Service-Manual-Cat/272938291766?_trkparms=aid%3D1110007%26algo%3DHOMESPLICE.DISC%26ao%3D1%26asc%3D20200220090753%26meid%3Dc90cd2c53d3b471983376407276dc05d%26pid%3D100009%26rk%3D1%26rkt%3D1%26sd%3D333101022980%26itm%3D272938291766%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3Ddefault%26brand%3DCAT&_trksid=p2047675.c100009.m1982