Probably as common to break the crankshaft itself. That could take out the valves and mag or one piston, the valves and the mag, but I guess you would have figured that one out already.
Time to pull the sparkplug and put something in it to feel if the piston is going in and out. If it is, then take mag cap off and watch the rotation etc.
Breaking a magneto shaft is pretty common. There are mags and parts for them available. Look at this sticky parts supplier listing. http://www.acmoc.org/ACMOC_BB/showthread.php?t=492
If there's serious trouble in the engine, your cheapest repair may be an electric starter IF you have the hole for one or don't mind making it yourself. Look at OldMagnet's page on starter conversions.
http://img400.imageshack.us/gal.php?g=header4oq.jpg
This one for parts sources
http://www.acmoc.org/ACMOC_BB/showthread.php?t=844
ccjersey,wow,I had no idea there were so many parts suppliers for this old of equipment. Thanks for all the names and addresses,I will definatley be checking with most of them.I have been fortunate to have a friend who is giving me a used pony for parts but I am not familiar with the engine numbers to be sure it will cross over as the numbers are different than mine.My D4 has the number N1 2A3929 on the head.The free pony has the number2H3053 on the head and the number4F8395 on the block.I could not see the block number on my pony.Do you know what numbers would be a match or are the ponys all the same,sorry for all the questions but I have never had to work on anything this big or old before but I think I can do most of it myself if I can find the right parts. Thanks again.
Don Alves 😊
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