Re: 85Hp Force piston replacement
The original wrist pin must be pressed out of the rod small end. There is a special tool for this which slides in between the wrist pin keeper and the rod. It provides clearance so that the needles don't bend or don't dent the keepers. This is not so critical during removal but during re-assembly, if the tool is not used (assuming the Sierra piston re-uses the original keepers) the needles will be jammed tight between the keepers and will not roll on the wrist pin but rather slide over it. If the Sierra piston does not have a circlip groove on each side of the wrist pin hole (just inside the surface of the piston), then you are meant to re-use the original keepers.
The original wrist pin is a press fit in the piston and in the keepers. Because of manufacturing tolerances, some are a close loose fit in the piston and some are and easy press fit. Some of the wrist pins are an easy press fit in the keepers and some are a tight fit. A 6 ton press is the minimum required to dis-assemble and re-assemble. I bought the special tool years ago when I first started to mess with these engines. Right now it is in a very safe place in my basement--So safe, that I can't find it to give you a number. But it was something like .028 on the removal end and .032 on the installation end.
Because of this, I recommend and use WISECO pistons which come with a new wrist pin, new rings, and circlips to hold in the wrist pins. You must buy a new small end bearing kit for another 15 bucks. They are just so much easier to assemble.
You won't drop the bolts on the big end of the rod, but you might drop some of the 16 rollers. Depending on the position of the engine, they will all be retrievable. There are just not that many places for them to go.
If the engine is vertical, the piston is horizontal and the rollers will fall onto the crank cheeks or under it. They can't go anywhere -too big to get into the bearing-- so you will be able to scoop them out with a bent piece of wire. If the engine is horizontal with the piston vertical, they will fall into the piston with the possibility of a few falling into the bypass passage. Once you take out the piston, these can be retrieved through the ports or remove the bypass cover. As long as you get 16 back, you have them all. DO NOT use a magnet to retrieve rollers. Hardened steel rollers are very easy to magnetize and they will then capture small normal wear particles leading to the eventual failure of the bearings.
