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Having to rebuild the top end on a 2-stroke engine is a fairly common process. Heat and friction are the biggest enemies of any mechanical device and the rotating assembly or more specifically the piston(s) on an engine is/are extremely susceptible to failure because of these forces. Under normal operating conditions this isn't an issue because the engine is designed to run at a specific temperature and a thin layer of oil separates the piston and cylinder wall. Having that said, many things can and do go wrong, resulting in a damaged pistons. Once this happens, your engine can face anything from a loss in power all the way to a catastrophic failure.
In my case, the engines in both of my Polaris jet skis needed a top end rebuild. The 750cc Fuji 2-stroke engines have a know list of problems that can lead to piston failure. Some of the common issues include, oil pump failure, damaged reed valves, cooling passage obstruction, fuel line corrosion, detonation, water intake, incorrect carburetor jetting and many others. The first time I had a piston failure on my jetski was because of a lousy engine design. The engine was designed with only a single fuel pickup that fed all three carburetors. When the engine was run at wide open throttle for extended periods of time, the fuel pump could not deliver enough fuel to third carburetor and caused it to run lean. A lean fuel mixture results in excess heat, and in my case, the extra heat burned a whole through the piston. In my second jet ski, a read valve broke, which cause it to run lean and also burn a whole through the piston.
Now I'm not going to provide a detailed instruction on how to access damage and rebuild the top end of an engine, but I will provide some insight on the process. (There are detailed instructions available on the internet as well as books to help guide you through the process.) A compression test is the first way to access whether or not the engine has any piston damage. If the compression reading of any of the cylinders is significantly lower than spec, it's time for a rebuild. (I had 0 compression in both cylinders, due to the holes in the pistons) At the very minimum, you will need a new piston and rings. Depending on how much damages was done, you may need, a rebore, new sleeve, new crank/rod, new cylinder head, new block or even a fully rebuilt engine. In my case, one piston was otherwise fine with the exception of the hole. The other piston however had overheated, and as a result it expanded and formed vertical seizures on the piston. The cylinders looked like they were in pretty decent shape with out any scarring, but the cylinder hone was somewhat deglazed.
Cylinders are generally cast iron, where as pistons are cast aluminum. Aluminum is much softer than iron and as a result pistons wear a lot quicker than the cylinders do. When rebuilding the top end of an engine, it is critical to check if the cylinder bores are still in spec (this is done with a cylinder bore guage). If the cylinder bores are out of spec you will either need to have them machined to accept a larger bore piston or have a new sleeve pressed in. Both of these options cost a lot of money, but aren't required if your cylinder bores are still within spec. In my case, I lucked out both times and didn't need the costly machine work. However I did want to have my cylinders honed for increased piston life. Cylinder honing scuffs up the cylinder wall and creates microscopic scratches within it. These scratches are used to hold oil for proper lubrication and help seat the rings.
My Experience With The Lisle 15000
After doing some research I came across a cylinder honing tool that impressed me. The Lisle 15000 Engine Cylinder Hone is a high quality American made tool that can be used with a standard ½" drill press. I own many automotive especially tools made by manufactures such as Lisle, Snap-On, Matco, and Mac and they have all exceeded my expectations. I learned a long time ago that buying harbor freight or other Chinese junk tools was actually wound up costing me more in the long run. The standard cylinder bore range for this tool is for bores between 3.000" - 4.125" inches. Additional racks can also be purchased to accommodate cylinder bores ranging from 2.750" - 10.125". In stock form this tool is perfect for small displacement engines and most car engines. (This tool should come in handy when I decide to rebuild the 454 Big Block Chevy motor in my Nova.) The model uses the typical 3 stone design, and is designed to work with five different interchangeable stone grits. The interchangeable stones available are 500 grit, 280 grit, 220 grit, 180 grit and 80 grit. Another nice feature was that this cylinder hone tool featured a real heavy duty universal joint where as many of the other models had a cheapo spring loaded mechanism.
I have lots of automotive experience and a bit of machine shop experience but I've never honed cylinders before. Having that said, I had a knowledgeable machinist friend assist me with the process. We set the drill speed to 1600rpm (according to my friend the desired speed is between 1200rpm - 1600rpm), inserted the tool into the chuck and mounted the jug/cylinder. We then applied 3 in 1 oil all over the cylinder lining and all over the tools stones. We wanted to create a cross-hatch pattern in the cylinder which is done by lowering and raising the drill while it's spinning. He started the drill and made 20 up/down monitions while I continually sprayed lubricant on the cylinder. We repeated this process a total of three times, once with the 280 grit, the 180 grit and finally the 80 grit. After we were finished we washed the cylinder jug with solvent cleaner and used the supplied brush to remove any particles followed by a soapy water bath. Afterwards I used compressed air to blow out any residue in the exhaust/intake ports and the water jacket then sprayed it with WD-40. What I was left with was a honed and cross hatched cylinder that looked like it was done professionally. I assembled the motor back together with a new stock sized piston and ran it on the starter for about 20 minutes to help seat the rings. Then I did a compression check which yielded 130 psi; which was in perfect spec. I took the jet ski out on the water the following day and let the motor break in for a bit. After a short break in period I was able to go wide open throttle and the engine performed phenomenally. When the piston melted in my second ski I repeated the same process all by myself and was blessed with the same results.
This is a high quality American made tool that is essential for rebuilding the top end on a 2 stroke engine. While I have yet to use it on other engines, I feel it should work the same way and yield the same results.