Mystery Pistons

[Al Peffley]

Hi All,

Lee Tietze ordered me two new pistons for my Yamato 250cc motor from Jim M. about two years ago, and he received two pistons that do not fit my over-standard-bore pro outboard motor. My question is: Is there a website that lists Yamato Pro motor parts by motor model/size and part number recorded in English?

These pistons have the numbers "41-1330" and "142" stamped inside of them, near the "Yamato" name stamp on the inside of the front skirt.

Al Peffley

[alky6]

My understanding is that Yamato has never produced oversized pistons. Only 1 size available for each engine. If your sleeves are oversized, you may have to look for after market pistons. There is a little room left with the 250 and 500 engines for oversize bores before one exceeds the displacement allowed. However this is not the case with the 4 cyl. 350 engine (stock is 348.8cc).

[Al Peffley]

Yamato Piston Differences

No, I do know that some oversize pistons were manufactured for Yamato dealers in the US (maybe by a second-source piston supplier to Yamato?), probably at the request of US racers in the late 1980's (Ric Montoya, Sid Bass, or Jim M. could confirm this as a myth, or fact.) I was told that the standard Yamato 250cc and 500cc pistons have different skirt and exhaust port relief machinework designs within the reed-port engine series ('87-93?). I know that Mike Schmidt said he re-machined two piston-port pistons for use on my reed-port Yamato. I don't know who manufactured the oversize replacement pistons for my 250cc motor (maybe Zak?)

I still would like a list of Yamato part numbers for the reed-port series of Pro Yamato motor power heads, by year and model type, if anyone has such a list. I have the exploded-view iso drawings of my 250cc motor, but I am missing the associated parts list numbers and specs for the drawing part reference numbers. I can't imagine a Yamato reed-port piston parts list would be very long -- they did not make that many motors...

Al