mugen nos piston kits found

[Marty]

Went on a short notice pick today and this is what seller was not selling he had a ton of these piston kits. None of the kits were for sale but he did give me one. Does a187961187960187959187958anyone know what these are for?

[whitetail hunter]

not sure, it looks like a 4stroke piston.

[Daddio]

It may also be for a car. Not really sure. Definitely not a mugen 360 piston.

[barnett468]

That’s a bizarre piston.

1. I don’t remember ever seeing a flat top piston with no valve reliefs.

2. It is most likely an auto piston due to the offset piston pin. This is why they have “IN” on the top even though there are no valve reliefs. I don’t remember ever seeing a motorcycle piston with an offset piston pin.

3. My guess is that it is a std bore piston, because there is no oversize noted on the piston. I have never seen an oversized piston with no size markings on top.

4. Mugen made parts for Honda and Acura cars. The Honda Civic has an 1800 cc engine which has a std bore of 81 mm. You should measure it around 3/8” up from the bottom to see if it is 81 mm there. If so, the prob of the missing valve reliefs still remains. Perhaps the std Civic has no valve reliefs but then would Mugen make a totally stock piston?