Help! Engine difficult to turn



so I got my kings motor on my bike a week ago. everything seemed to be correct. I peddled it up to speed and then let out the clutch. The back wheel locked up and bent a few of my spokes and damaging the rim in the process. I took it back to the garage and tried to turn the engine with a wrench. It was very difficult to turn but I managed to get it around. It seems as though the compression of the engine was too much to get it all the way around.

I tore the engine down today to see if anything was binding. I checked the piston and the cylinder and there was no damage.

With the cylinder off, I turned the crank and the bottom assembly spinned freely. I put on the cylinder and the head (with the plug out) and it turned while making some compression. I then put on the spark plug and it seemed like it made too much compression. I dont know what to do.

How much compression do these 80cc engines make?

How difficult should it be to turn one of these engines by hand?

What can I do to make this engine turn smoothly?

Sorry to hear your problem....One thing you might want to check is your chain tension...If the chain is loose, it can jump off the engine pinion and jamb up thus locking the rear wheel....Happened to a customer of mine....Only reason I bring this up is because you mentioned that the engine would or could turn over fairly easily by hand until the plug was put back in and that upon tear down there was no visible damage (no piston hitting the cyl head etc...)....The compression on these engines is about 6.5 to one...well at least the ones from Dax are....not 100% sure what a King engine would be but I would guess fairly similar but in either event definit;y not super high.

the chain did jump the sprocket when I was test driving it. but the chain was not on when I tore ithe engine down and turned it by hand. Is it possible that the difficulty that I have turning the crank is simply just the compression of the engine?

Is there any way I could make sure it runs without mounting it to the bike?

thanks for all the help guys
if the chain jumped the sprocket on testing, then that was your problem! Tighten and align your chain and you will be fine...i just ran into a problem where my chain was binding because it was too loose and put an excessive load on my engine, causing it to not hit max rpm and powerband. Chain tension and alignment is everything on these setups

If you are trying to turn the engine by hand it would probably have a fair amount of perceived resistance because the sprocket is small and the teeth are sharp.....
If you tear it down again put a little 2-stroke oil on the cylinder to lube it hopefully it will be enough for you get to get it to run and brake it in. Good luck and pics would be fantastic.
How are you turning the engine over? If you are using the drive sprocket you are turning it over through the primary gears, and this is not to your advantage, I never figured the ratio out but it would give the impression of hard turning. My Kings engine needed a lot of carving on the sprocket teeth, too square. there is a page with the info on the correct shape. It is important to have the chain snug and in alignment. You can look at the bike photos and get a good idea of placement of the idler and chain rout. Have fun Dave

PS: If you can get a good hold on the engine you could start it with a power drill, on the end of the crank, left side. The engine turns opposite of wheel rotation. Starts easy, keep stop button close at hand.
This is normal for me, if I'm not going fast enough and I let the clutch out then the back wheel will just lock up, but usually will start as my new tyre is scraping the tarmac. Doesnt this happen to everybody? hmmm I better take a look
High compression is your friend, you got a good one. Put some light oil in the engine before you crank. Also, with fuel source off and carb drained, use a heat gun to heat the cylinder head until it is fully warmed up. A heated cylinder head is a tip that I used for new ABC ringless two stroke engines that are very hard to spin on a first start situation.