Frank Acampora
Supreme Mariner
- Joined
- Jan 19, 2007
- Messages
- 12,004
This one is for Spinkick:
It is really rather easy to replace a piston in these engines. Even though you have a 1998 Force and I have not yet done one, the block is the same as earlier Force engines and replacement will be the same.
The .020 stamped on the top of your piston indicates it is .020 oversized. If the cylinder has not been scored, then buy a replacement the same size. If it is scored, then you have no choice but to disassemble the engine and have it rebored to the next larger size.
I prefer Wiseco because they are forged pistons. The stock and Sierra replacements (in older Forces) are cast. Forging produces a superior piston, stronger and able to resist damage better. Many people will state that Wiseco pistons are "junk" and will refuse to use them. Personally, I have had good luck with them. However, the reason I recommend them is because they are way easier to install on the rod with no special tools. Cost? around 150 complete--piston, rings, wrist pin, and bearing kit.
Usually when a piston melts, the rod and bearings are not affected. However, with the Wiseco pistons, because the wrist pin is included, you must buy a special bearing kit for the small end. It only costs about 15 bucks though.
Now, any melted aluminum throw off that passes into the exhaust will just pass out the snout and not harm anything. Just check to see that some pieces have not melted to the port webs so they could possibly work their way back into the cylinder. No need to remove the exhaust chamber cover.
If the engine shows any evidence of aluminum throw off in the bypass ports, then you MUST remove the bypass cover and clean the whole area of any metal there.
As I said before, the head gasket is re-usable as long as it is not damaged and it is actually preferable to re-use it if possible: A new head gasket will compress the first time the engine is run long enough to heat and expand the aluminum. After the first run, the head bolts MUST be re-torqued. Since the old head gasket is already compressed, generally you will not need to re-torque the head bolts after test running.
To replace the piston, you remove the head, then remove the carb and manifold servicing that cylinder. Remove the rod big end capscrews and push the piston out the back with the rod attached to it. Do not lose any of the 16 roller bearings. Press out the wrist pin to remove the rod. Take note of the orientation of the rod--there are special grooves in it-- and reassemble in the same direction. The end cap only goes on one way also so be certain you put it on correctly after you install the piston and big end bearings. Also be certain the ground flats on the rod are perfectly matched. If correct, you should be able to run a pencil point or scratch awl, or small screwdriver over the crack without feeling it catch or jump. Do not tighten the big end capscrews until alignment is perfect. Take your time with this step: Good enough is not good enough. It must be perfect.
Since stock gaskets are glued they will be destroyed (in most instances) when you disassemble parts. SO: you will most likely need a carb gasket, manifold gasket, and a couple of bypass gaskets. If you are cheap like me, you will buy a 4 buck roll of 1/32 grey gasket paper from Pep Boy's and make your own. Child's hole punch makes the correct sized bolt holes and scissors does the rest with a little bit of time invested. You will need to remove the reed Vee blocks to replace the gaskets. Be certain to use threadlocker on the screws. It is also a good idea to check the reed screws for tightness at this time. If you find any loose ones, remove the screws one at a time and use threadlock compound on them. Beats having the engine eat a screw or reed.
To prevent melting another piston, find out why that carb went lean. Clean both carbs, set the float levels and set the idle needles. Put a cheap 3 buck plastic fuel filter between the fuel pump and the carbs. Sometimes when a diaphragm starts to go bad it will shed disintegrated pieces into the fuel. They will clog the carb, it will go lean, and the piston(s) associated with that carb will melt. The filter I use is Purolator F50153 available at Pep Boy's and probably most other auto stores. It costs around 7 bucks but you can back-flush it to clean it, you can see its condition, and it has a fine screen instead of a paper element. It also has a 90 degree fitting on one end so it generally fits nicely below the bottom carb on the 4 cylinder engines.
Since you have never replaced a piston before, figure on a whole weekend, but you will probably be able to do it in one day. Takes me a couple of hours taking my time. I could probably do it in an hour if pressed.
Tools needed: 3/8, 7/16, and 1/2 inch sockets. Torque wrench capable of 225 inch pounds, 1/4 inch drive 12 point 1/4 inch socket (Sears Lowes etc.), couple of open end hand wrenches, and a couple of screwdrivers.
Head bolts are torqued to 225 inch pounds and rod big end 12 point capscrews are torqued to 190 inch pounds UNLESS Mercury has changed the specs--Get a manual.
It is really rather easy to replace a piston in these engines. Even though you have a 1998 Force and I have not yet done one, the block is the same as earlier Force engines and replacement will be the same.
The .020 stamped on the top of your piston indicates it is .020 oversized. If the cylinder has not been scored, then buy a replacement the same size. If it is scored, then you have no choice but to disassemble the engine and have it rebored to the next larger size.
I prefer Wiseco because they are forged pistons. The stock and Sierra replacements (in older Forces) are cast. Forging produces a superior piston, stronger and able to resist damage better. Many people will state that Wiseco pistons are "junk" and will refuse to use them. Personally, I have had good luck with them. However, the reason I recommend them is because they are way easier to install on the rod with no special tools. Cost? around 150 complete--piston, rings, wrist pin, and bearing kit.
Usually when a piston melts, the rod and bearings are not affected. However, with the Wiseco pistons, because the wrist pin is included, you must buy a special bearing kit for the small end. It only costs about 15 bucks though.
Now, any melted aluminum throw off that passes into the exhaust will just pass out the snout and not harm anything. Just check to see that some pieces have not melted to the port webs so they could possibly work their way back into the cylinder. No need to remove the exhaust chamber cover.
If the engine shows any evidence of aluminum throw off in the bypass ports, then you MUST remove the bypass cover and clean the whole area of any metal there.
As I said before, the head gasket is re-usable as long as it is not damaged and it is actually preferable to re-use it if possible: A new head gasket will compress the first time the engine is run long enough to heat and expand the aluminum. After the first run, the head bolts MUST be re-torqued. Since the old head gasket is already compressed, generally you will not need to re-torque the head bolts after test running.
To replace the piston, you remove the head, then remove the carb and manifold servicing that cylinder. Remove the rod big end capscrews and push the piston out the back with the rod attached to it. Do not lose any of the 16 roller bearings. Press out the wrist pin to remove the rod. Take note of the orientation of the rod--there are special grooves in it-- and reassemble in the same direction. The end cap only goes on one way also so be certain you put it on correctly after you install the piston and big end bearings. Also be certain the ground flats on the rod are perfectly matched. If correct, you should be able to run a pencil point or scratch awl, or small screwdriver over the crack without feeling it catch or jump. Do not tighten the big end capscrews until alignment is perfect. Take your time with this step: Good enough is not good enough. It must be perfect.
Since stock gaskets are glued they will be destroyed (in most instances) when you disassemble parts. SO: you will most likely need a carb gasket, manifold gasket, and a couple of bypass gaskets. If you are cheap like me, you will buy a 4 buck roll of 1/32 grey gasket paper from Pep Boy's and make your own. Child's hole punch makes the correct sized bolt holes and scissors does the rest with a little bit of time invested. You will need to remove the reed Vee blocks to replace the gaskets. Be certain to use threadlocker on the screws. It is also a good idea to check the reed screws for tightness at this time. If you find any loose ones, remove the screws one at a time and use threadlock compound on them. Beats having the engine eat a screw or reed.
To prevent melting another piston, find out why that carb went lean. Clean both carbs, set the float levels and set the idle needles. Put a cheap 3 buck plastic fuel filter between the fuel pump and the carbs. Sometimes when a diaphragm starts to go bad it will shed disintegrated pieces into the fuel. They will clog the carb, it will go lean, and the piston(s) associated with that carb will melt. The filter I use is Purolator F50153 available at Pep Boy's and probably most other auto stores. It costs around 7 bucks but you can back-flush it to clean it, you can see its condition, and it has a fine screen instead of a paper element. It also has a 90 degree fitting on one end so it generally fits nicely below the bottom carb on the 4 cylinder engines.
Since you have never replaced a piston before, figure on a whole weekend, but you will probably be able to do it in one day. Takes me a couple of hours taking my time. I could probably do it in an hour if pressed.
Tools needed: 3/8, 7/16, and 1/2 inch sockets. Torque wrench capable of 225 inch pounds, 1/4 inch drive 12 point 1/4 inch socket (Sears Lowes etc.), couple of open end hand wrenches, and a couple of screwdrivers.
Head bolts are torqued to 225 inch pounds and rod big end 12 point capscrews are torqued to 190 inch pounds UNLESS Mercury has changed the specs--Get a manual.