Re: Water Pump for 91 Force 150
If you have not scored the cylinder, you can replace the piston without disassembling the engine. It's not easy but it is do-able. I have done it on four cylinder engines.
First remove the reed plate and using a 1/4 inch drive 12 point socket, (3/8 won't fit) remove the rod big end cap screws. push the piston and rod out after removing the head. The rollers will fall out so be careful and retrieve all of them from the block. Putting it back together is the difficut part. use a lot of grease to hold the rollers and cages. Put them in after pushing the rod onto the crankpin and roll them around it until you get all in. The rod cap is difficult to get in and you must fish it around some. Then insert the cap screws and check for rod cap alignment and torque down the cap screws. If you buy a WISECO piston, you don't need tools. It comes complete with rings, wrist pin, and circlips. You do need to buy their bearing kit for an extra 12 bucks. I've heard some people say bad things about WISECO pistons but I have never had any trouble with them, so you pays your money, and you takes your choice.
If the cylinder is scored, you need to rebore and this requires complete disassembly. You only need to do the one cylinder because aftermarket pistons are balanced to factory weight and even at an 030 overbore(max recommended by factory) the engine will not see any significant increase in displacement on that cylinder. If you have worked on auto engines, this will be a piece of cake for you.
If you need more than 030, there are sleeves available to re-line this engine but you need to find a marine machine shop to do it. it is not cheap -- probably 250 labor plus part.
