spark plug hole partly covered from new pistons 1940A

[tugboattim]

I just need more than than one person to tell me this will work. I bored my early gas only A out .125 and found used aluminum pistons that are a little longer than the iron ones I took out. the dealer said they were out of an early A but they were noticably longer. Someone from this site assured it would work but would I still use the same number spark plugs ie colder or hotter all ideas will be pondered thanks in advance
 

[Dodgeit]

The aluminum aftermarket pistons usually have a chamfered edge on the piston crown. This chamfer should line up with the spark plug hole and allow clearance for the spark plug. Use Autolite 3116 plugs. after installing roll the engine over by hand to double check that there is not a problem.
 

[Mike M]

In addition to the below info. If you do have the champher or notches lined up and thet still block the holes I'd be tempted to grind some material away to make it open.

I had a late B with one piston upside down that partially blocked the hole and previous owner told me that he has had it blow out valve cover gaskets before from a crankcase explosions and never could find the problem. I can only assume this was it ? I flipped it around and sold it and never heard anymore after that.
 

[Mike N Mo]

I have had the same problem on an early "A". I used a die grinder to deepen the existing spark plug notch. After grinding use a flap bit to smooth everything up. Be carefull NOT to leave any sharp edges, as a sharp edge will cause detonation. Mike
 

[wilamayb]

There should be no reason to do any grinding to any piston so long as you have the correct pistons for your tractor and it still has the original crankshaft. If someone has installed a later A crankshaft which has a longer stroke it may be a problem.
 

[buickanddeere]

Machine as required but leave enough support for the top ring.
 

[alvan]

I have a 45 a that I put a set of 125 over pistons in that were a inch taller. They are notch from the factory and they work fine they cover the spark plug hole by half use 3117 plugs and runs great.
 

[John 37A]

I used .125 late A pistons in my 37. Spark plug holes half covered, no machining, and it runs great. Autolite 3116. Just make sure you turn it over for clearance before attempting to start. If its hand start, you'll want the petcocks open to roll it over.