Do I have to have an adapter for my occ sprocket?

Some people say that the sprocket will not fit without an adapter, but mine bolted right on. If your bike is the single speed OCC stingray than most likely it should fit. Some kits have different sprockets meaning the mounting holes are located further or closer to the center. With mine, I put the sprocket on, marked the 5 holes, drilled into the hub and bolted it directly on, with a thin piece of rubber (old innertube) in between so the spokes will not wear and possibly snap. Is the engine kit 2 stroke? You will need a engine mount adapter and different exhaust for the bike, I got mine from Barry on ebay, but you could modify or make one yourself. Here is a picture of my bike, I don't have a close up picture of the sprocket, but just to give you an idea what your bike could look like when complete.

These OCC stingrays can be a pain to build, but I think it is worth it in the end because they are just so unique. I think the wheel is a 36 spoke but I am not sure, I would have to count them. If it where me, I would try drilling the holes on the sprocket one size bigger with a drillbit, and then see if the bolts would go in then. If that doesn't work maybe you could try drilling 5 evenly spaced holes closer to the center that would line up with the hub then bolt it to the hub. If you do that, try not to drill too close to the spokes because they could break. I first built my bike in 2005 with a 48cc kit and the 1 gallon tank came with the kit. But in August 2008, I upgraded to a 66cc engine, and the tank in that kit was only 1/2 gallon, so I kept the old one on. I painted the tank, it was originally black. You might be able to find a motorcycle tank on ebay or a tank like mine to use instead of the kit tank. The sprocket from my first kit fit, I just drilled into hub and bolted it to the hub. The sprocket in the second kit did not fit because the holes were further from the center and if I remember correctly, they did not line up just like you are saying that yours doesn't, so I kept the first sprocket on it. Here is a picture of the bike when it was first completed in 2005, and some others with the most recent paint job on the tank. Towards the bottom of the gas tank I hand painted my initials but you can't really see it in the pictures.

My first OCC, the stock sprocket w/rag mount worked fine. however getting the bolts to line up took some effort but did not require drilling. You may need to open up the center hole in the sprocket with a dremel.
MAKE SURE that the sprocket is true(measuring from the axel), before mounting the wheel on the bike.
That will save you a lot of headaches with the chain tensioner.

I used an adapter from Pirate Cycles on my OCC and I never tried installing the sprocket without it. The sprocket adapter is worth it for the benefit of driving the hub of the wheel itself and not the spokes in my opinion. Either way the OCC is a cool looking project.

where did you install the chain tensioner? it seems like my break is in the way whats the best way to run the chain?

I have seen the tensioner run upside down, pushing chain below the brakes

The brake arm can be bent up slightly(remove it, do not bend it on the bike) I've done several and haven't had a problem.
I fabed a 90 Deg. bracket and installed the kit tensioner wheel on it. The bracket pivots on the bolt that supports the muffler. Have had no problems with it 900+ Mi.