I picked up a Polaris atv last year for some trail riding. It needed some work as do most 20 year old quads. This 250cc atv is a 2 stroke with a CVT (automatic) transmission. The thing ran great until a friend of mine buried it in the mud and rev'd the engine too high. 2 stroke motors are made to run at high rmps but this engine was made in 1990 and still had the original piston and crank bearings. The stock piston broke apart inside the cylinder and that was bad news. Well I decided to rebuild the entire motor myself since the repair cost would be well over $500. This would be the first time I've ever opened up an engine for repair. I've already come pretty far on the project but I plan to recite some of what I've done.
Here's a look at the shattered piston after removal. I've replaced the original piston with a Wiseco brand forged piston along with new crank bearings and seals. The new piston is much stronger and much better quality. The second pic is of the engine after rebuild.
The quad with some new decals, patiently awaiting its rebuild engine. 1194 is the perfect compound for gluing the cases (engine halfs) back together.
The bearings are located on both sides of the engine case. I had to pry the to halfs of the engine apart very carefully. The crankshaft runs through these bearings as it spins from the movement of the piston. The bearings were badly worn and contained fragments of the shattered piston. I had to push the first hearing out with a hammer and punch. After it was removed I washed the engine case in solvent. The other bearing was still attached to the crankshaft itself which you can see in the pictures below. In order to install the new bearing into the engine case I had to freeze the bearing in a freezer and heat the engine case with a heat gun. As metal warms it expands and as it cools it becomes smaller. The bearing then fell easily into the case and as it warmed it expanded into the engine case causing it to remain in place.
I had to use a bearing separator and puller to get the old bearing off the crankshaft. After it was removed I froze the crankshaft and warmed the bearing in order to place the bearing on. It's the same idea as listed above.
Heres a look at the crankshaft with the bearing installed. Next I put the crankshaft in a freezer again and headed the opposite case. I had to move quickly as i placed the 1194 gasket maker on each side of the engine case, placing the crankshaft in between and pushing the two sides together. Next I would install the new piston, rings, gaskets, and engine head.
