oversize piston on front cylinder, standard on rear?

[charles d cannon jr]

While attempting to successfully break in my rebuilt Shadow's motor, I seized the front piston, probably due to a combination of improper timing and lean mixture. When I inspected the cylinder wall it showed some scoring. My machinist doesn't think it is capable of being honed out so I am probably going to need to go to the first or possibly even second oversize piston. My question is this-- is it heretical or poor engineering to consider an oversize piston on one cylinder and not on the other? I understand that in theory that there may be some minor difference in weight of the pistons and that may be objectionable from a balance standpoint. It also may give the next person who opens the motor some pause when he eventually figures out there are two different sized pistons. Regardless, I am very interested in opinions, doctrine, or "I did it" experience. My options are new liner for front with new standard piston, or overbored liner for front with new oversize piston. ( My liners were new, oversized externally, and the liners were fitted properly in ovebored muffs. The new liners only had about 400miles use.) Thanks, Charles Cannon

 

[clevtrev]

While attempting to successfully break in my rebuilt Shadow's motor, I seized the front piston, probably due to a combination of improper timing and lean mixture. When I inspected the cylinder wall it showed some scoring. My machinist doesn't think it is capable of being honed out so I am probably going to need to go to the first or possibly even second oversize piston. My question is this-- is it heretical or poor engineering to consider an oversize piston on one cylinder and not on the other? I understand that in theory that there may be some minor difference in weight of the pistons and that may be objectionable from a balance standpoint. It also may give the next person who opens the motor some pause when he eventually figures out there are two different sized pistons. Regardless, I am very interested in opinions, doctrine, or "I did it" experience. My options are new liner for front with new standard piston, or overbored liner for front with new oversize piston. ( My liners were new, oversized externally, and the liners were fitted properly in ovebored muffs. The new liners only had about 400miles use.) Thanks, Charles Cannon

Change the muffs over and put the oversize as number one.

 

[charles d cannon jr]

Thanks for your rapid and concise reply, which may be too concise for my fatigued brain and my elementary knowledge base! Is this because the rear cylinder is the "leading cylinder" and the small difference in size of the bore and the piston weight is not that significant as relates to the second or front cylinder? Further comments awaited with interest. Thanks again, Charles Cannon

 

[ksbundy]

On V8 Caterpillar engines they supply different size pistons for replacement. They are all the same weight so that engine balence is not affected when only some of the cylinders are bored. Get the new piston the same weight as the old one
Rgds ken.

 

[johnmead]

Last month I took a 3 cylinder Mercury outboard engine apart for a rebuild. One of the piston/cylinders was oversize. The engine had run well that way for 10 years.
The engine is a 2-stroke and the cylinder head is part of the block
John Mead