help with piston
help with piston
It is possible to replace the piston without disassembling the engine, however, it is not fun. It is much easier on 3 cylinder engines. You need to remove the carb and manifold for the affected piston and remove the big end rod cap through the reed opening. This requires a 1/4 inch 12 point socket with a 1/4 drive and a 6 inch extension bar. And you must fiddle the cap around some to get it out. Then you need to be sure you retrieve all roller bearings. The piston and rod can then be pushed out the cylinder after you remove the head. But, if it is the bottom cylinder, you must remove the "Support Plate" (the plate the hood sits on) and move it up, out of the way.
You do know that the wrist pin is pressed into the piston with two keepers--one on each side of the rod small end. It requires a special tool, and a press to remove the rod and re-install it in the new piston.
After you insert the new piston-rod assembly into the cylinder, THEN comes the fun part. Reinstall the rollers and cages and reinstall the rod cap. the cap bolts must be torqued to a specific value which can be different with a particular engine--But usually up around 225 INCH pounds. And, the cap must be very carfully aligned to the rod--put it on the wrong way or misaligned and you will destroy the rollers --and most likely the rod and crankpin too.
You must have patience; it is a long process, but it is still quicker than a complete disassembly.
You have not said why the piston went bad. If you have scored the cylinder, you must do a complete disassembly and rebore that cyl. To put a new piston into a scored cylinder leads to lower performance, shorter service life, and disappointing results.
Now, after all that, these instructions are for up to a 1990 engine. After that, I am not sure if merc changed the powerhead or big end bearings. But all the above parts need to be removed anyway if you do a complete disassembly, so it wouldn't hurt to look.
