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Assuming you could get the motor to unlock, it would require a complete overhaul in order to run properly again because either the crankshaft bearings or the camshaft bearings (or both) and possible the pistons themselves have welded themselves to the engine internals. Most likely a new crank, cam, pistons as well as having the block bored and resurfaced.....get the drift?
Often there are not any broken parts when an engine is ran low on oil.. The engine never really makes it to far out of oil before it welds the pistons to the side walls seizing the engine tight. Every now and then a rod will break because at hiway speed the engine went empty the piston seized but the crank and rod did not thus pulling it with such force to snap it in half then producing sometimes a hole in the engine block, hood, oil pan where ever it decides to go. And this is about it Crank not often cam not often. Hope this helps
If the cam stuck, you likely have ruined camshaft bearings causes by oil pressure issues. If you try to replace the camshaft, the replacement cam will likely seize up as well, or even break.
The only proper way to fix that is to get the engine out, remove the rear cam plug from the block and drive it forward out of the engine. Once it's out you can have a machine shop check the block for proper bore alignment and have new cam bearings installed. It's a lot of work. That's why most repair shops would rather replace the engine.
Even if you get the camshaft and bearings replaced, you still have to deal with why the first one seized.
If the engine runs dry of oil it will seize on the big eng journal, because the piston is still moving at speed the alloy roy will snap, you can just imagine the amount of damage caused inside the engine, i would suggest a new short block would be the cheapest way out of this now.
There are a few things you can try, but there are no guarantees. You will have to do some disassembling, but much of what you broke depends on what broke first.
Sometimes it is easier to buy a used engine out of a wreck and replace what you have as a unit. Or you can get a rebuilt engine either as a short-block or long-block and use your old parts to complete the engine.
On your seized engine you need to take off the oil-pan and visually inspect the bottom for shavings and pieces that used to be your engine. You need to get the Crankshaft and Camshaft rotating again. Its almost guaranteed that the timing chain or gear between the cam and crank will need to be disconnected so you can see if both are seized or only 1.
This is the part I was referring to about which item broke first. If the camshaft turns then you need to check the lifters for damage, as in not having a flat surface to strike the cam with. Always keep the lifters matched to the same hole they came out of. Even if a lifter needs replacing, continue inspecting the motor.
Now move the crank. If it does not move, back off the maincap bolts one by one until the crank turns. If the crank still does not turn you will need to remove the rod caps one by one until the crank turns. Keep each rod cap identified to where it came from and do not mix them. When the crank moves immediately after disconnecting a particular rod, that is the bad cylinder.
You can remove 1 piston and even hone 1 cylinder without rebuilding them all. Just ask a parts-counter person about plastic-gauge and gauge all the bearings you have. Buy corresponding parts if it is financially worth it to salvage your old motor. You can buy bearings of different sizes
to improve the tolerances if your Crankshaft is not scratched.
You need to get the engine turning before you can try any miracle additive like Lubeguard. I hope my solution helps you. You may want to fog the cylinders and remove your plugs before you try turning the motor. It will be much easier to turn without fighting compression.
If you are seizing the engine, the problem could be related to several things:
1st: If you are running lean, the engine will seize.
2st: If your engine timming is too advanced, it will also seize (plug fires too early).
3rd: If your piston to cylinder gap is too narrow it will overheat and seize (sometimes in just about 2 miles).
Any of these could be causing your problem, but there is one last advice I would like to tell you. Two stroke engines rely on fuel+oil mixture to lube the cylinder/piston parts. Most times I see someone seize and engine it happens after an uphill when the descent starts and the pilot cuts throttle resulting in overheating the engine. If you cut the throttle you also cut the oil (because it goes mixed with the gasoline) and that can cause the engine to seize.
My advice is to blip the throttle one in a while when on a descent.
Hope this helps and you wont get any more problems with your scooter :)
in adition to the above coment, which i must say is spot on, the posability of a used barel and piston if a new piston is not available could be worth considering, other things you may wish to check on that particular engine is camshaft seizure, in a uk bike it runs directly in the machined surface of the cylinder head, oil failure due to blocked oil filter has severe consequenses, located on the l/h side of the engine under a 22 or 24mm spaner head cap just below the gear change lever, this is a washable filter retained by a cap and spring, correct replacment is inperitive. are you located in UK? HOPE THIS HELPS YOU
You'll need to remove the motor, disassemble the engine, take the engine parts to a machine shop and have them check the heads, block, pistons and rods, crankshaft, camshaft and lifters. They should be able to give you a parts list of what you need to replace.
The piston seize destroys the piston, rings and cylinder wall. Bad enough, and repeated seizing, can get metal bits into the crank rod bearing and crank end bearings and seals. This is serious stuff. Sorry to be the bearer of bad news.
Seizing is caused by friction. Not enough lubrication means friction that creates heat. The heat builds and the piston and rings "weld" to the cylinder. A faulty cooling system can also cause heat. Any oil will break down and loose it's lubrication ability when the heat gets too high. A water pump malfunction or plugged coolant lines, leaking coolant hoses, plugged radiator and bad gaskets can create heat.
Other sources are > timing is off, air leak causing the fuel to be too lean, incorrect spark plug heat range, carbon buildup on piston and head causing detonation, motor oil used in gas instead of 2 stroke engine oil and over revs on the engine. I have probably left a few things out but these are the usual causes. Be aware that combinations of small problems can add up to a seize.
The engine needs to be rebuilt. Normally I would just rebuild the top end but since you have had multiple seizes the bottom end is probably contaminated. New crank bearings and seals should be installed. If the cylinder can't be bored then you will need a new cylinder. New piston and rings are also required. Bear in mind, you must find the cause or causes of the heat and fix those problems also. If you don't, the new piston will quickly seize up.