I just acquired a '94 300EX. The top end was removed but I have the parts. A previous owner swapped the head and had an adjuster come loose, jambed between the cam and casting and broke out the casting. It's not in a critcal area and can be tigged up.

A couple questions to get me started. It came with the bottom end from the engine the head came from. It's a high compression pop-up piston. Can anyone identify it with these numbers off the crown. 4574P2. It also has 0.50mm so I'm assuming it's a .5mm overbore. The piston in the quads engine is brand new. The cylinder has either been bored or at least freshly honed. It's marked with HM3 and 1N. Does that identify the bore or anything? It is a flat top. I'd like to use the popup piston if it's not smaller than what's already in the quad. I will be micing it later but was hoping for some quick info since I don't have it at my house until next week.

Anyone have an electronic service manual?

 

the piston you have marked 4574p2 is a wiseco 11.1 piston with a 74.5mm bore. the standard bore is a 74mm bore. you'll gain 3ccs of displacement of that bad boy. if you have the cylinder from the parts motor you could use it.

 

I miced the existing cylinder and Wiseco and, believe it or not, the clearance is .002. Just what it's supposed to be. The bore is brand new with maybe 5 minutes on it, so no honing is needed. I checked the end gap on the rings and it's good to go too. What are the chances of that?!!!