R4 Piston help

Working on a stuck R4 motor [6G884WSP ], and I have found it appears to have Pistons different to the parts Book . Parts book shows 3 differnet pistons were available ,standard and two different altitude pistons and they would appear to be all flat Top . this engine has a dome type piston . I have never been into a D4 motor but My recollection is that they use a Dome type Piston . Any suggestions or thoughts from Someone ? have not removed them yet to measure . I have another block and it has flat pistons in it . Any advise appreciated . Happy New year to all everywhere . LJ

My wifes got some nice dome ones too. lol [ two cylinder starting motor lol] Burt Monroe in the movie Worlds Fastest Indian made his own pistons.pretty cool!

Sorry no pics!! lol

All diesel engines I ever saw had the combustion chamber in the piston head, never saw one that could have stood to have a domed piston. I suppose the R4 head and pistons are likely the big difference between the diesel engine and the spark ignition engine, so surely could have a combustion chamber cast into it and domed pistons specific for gasoline vs kerosene/tractor fuel?????

Perhaps yours was originally equipped or modified for propane/LP gas. That was a common modification on farm tractors of all types around here in the WWII and post war era since LP gas was very cheap and readily available during wartime rationing compared to gasoline.

Many of the engines were low compression designs, probably because of the need to burn tractor fuel instead of gasoline with better anti-knock characteristics, so when they were converted to propane with a very good anti-knock tendency, the compression ratio could be safely increased to gain more efficiency from the slow burning propane/LP gas. For example, some of the old 2 cylinder JD tractors had an aftermarket cast iron insert put in the head and secured by the spark plug to raise the compression. Not sure how well they hand started after the conversion, I believe all ours had electric start though. Seems like there may have been petcocks on the heads to open so that compression was reduced for hand starting as well as the normal draining of any liquid which may have accumulated in the cylinders.