Rebuilding your 2 smoke engine

I have been fiddling with these engines for about three years now. The one thing they have in common is there is nothing but there looks that is common. I have a spare cylinder that I spent a few hours porting, yea I got a little carried away. So I next needed a lower end assembly to run it on, so I ordered one from Revolution. It arrived looking good, I was stoked and started to assemble the motor, and to my surprise the piston was about 1/4 of an inch from the top at TDC and hit the crank at the bottom! Now what the heck. I went home and got a new piston and cylinder I ordered from Kings a year ago, took it to the shop and lo and behold, it works. I set the pistons next to each other and what do you think, the wrist pins are in a different location on each, yes the one I needed had a lower pin location. I knew the crank for the 48cc was different but I never heard anything about the 55 and up. Also there is a two piece flywheel and a one piece, with and without balancing holes. One crank with 202Z bearings and one with 203's. I like the heads with the larger fins, but the one I have is not relieved for the larger piston, but it was on a 70! but I tried to install it on this 70 and the piston was hitting, so I used the head with the smaller fins and the relief. These engines need all the cooling they can get, they need a lot larger cooling fins, but this will have to do. I just wanted to let everyone know that you need to keep and eye out if you start ordering parts to do a rebuild, maybe you should just order all of them. Oh well you might as well get them all put together. Oh it is probably easier to just order a new kit. Have fun Dave
PS: I will let you know how the port engine runs. I can get my thumb down the intake. That's a compression release in the head.

Wow, that's a lot of differences! What's the difference between the 203 and the 202Z bearings?

The 6203 bearings are larger all around, and will not work in the 6202 engine. Also if you order the 6202 bearing it has to have the Z, it is a custom size. One of the engines that GruBe was going to sell had a steel sleeve and the larger bearings. It would have been nice to see how long that one would last. Have fun, Dave
PS: One other thing I forgot, there are two bolt patterns for the cylinder, & head I got a 65cc from Dax and none of my other engine top ends will interchange. I know the 48 is small but I thought the 65 would be the same as the 70. If you get a head or a Cyl for the 6mm bolts you can just drill them out to 8mm, or use the 8mm on a 6mm stud, no matter. I did mine.

Bikeguy Joe said:

Wow, that's a lot of differences! What's the difference between the 203 and the 202Z bearings?

Click to expand...

Thanks!
Yeah, I know the dax 70cc and 65cc are slightly different, just haven't explored all of it yet.