Hello all, I just joined up to seek some advice on my current motorcycle project. Let me give a little background before getting to the questions so you will know where I'm going with this. Recently I bought a Sachs MadAss 50cc with a bad engine. Some of you may be familiar with these. It's sort of a mini-motorcycle powered by a version of the CRF50 motor, similiar to a pitbike but designed by Sachs and much higher quality than your typical Chinese toy. The obvious thing to do would be buy one of the Lifan-type bigbore motors that are available in 140-160cc for well under a thousand dollars. But where's the challenge in that? Instead I am swapping in a two-stroke dirt bike engine. For one I have always wanted a two stroker. I've been into street bikes and have never had anything to do with a two stroke, but they just look like fun. So I went to a local motorcycle junk yard and scouted around for something that I could make fit. I was hoping for something in the 125 to 200cc range, but the most promising lead was a 1980 Honda CR80R. They had a complete bike which simplified things, it is aircooled which was a must for the sake of simplicity, and it's a Honda which may simplify things by keeping it in the family. I've pulled the engines out of both machines and here's what they look like next to each other (sorry I can't post pictures directly): http://www.flickr.com/photos/22974775@N05/5747434307/ Obviously I will be modifying the engine brackets but it looks doo-able. This should be an interesting bike once it's all done with. The 140cc engines people frequently put in these only make about 15 hp or so and the CR80R is supposed to make 16.5 hp...with two more gears. With the 50cc engine the thing only weighed 212 pounds dry and the CR80 engine is about 9 pounds lighter even including the expansion chamber. So anyway, the CR80 engine was reported to have no compression. I have the top end off and the piston skirt has come apart. The cylinder is scored and there must be debris in the crankcase. I was hoping to avoid getting into the bottom end but it looks like I will have to. What concerns me most is the lower connecting rod bearing. There is quite a bit of slop in it. Apparently the crankshaft would normally be replaced in this situation? Parts availability doesn't seem to be very good with this old engine. I could probably find one but this is supposed to be a cheap project. Looking at the parts diagram on BikeBandit it appears the crank pin is a separate piece and only $15. Why can't you replace only the crank pin and bearing? I plan on replacing all of the seals and such. Are the main bearings typically replaced in a case like this or only if they are clearly bad? What about the crankshaft drive gear? I have the clutch cover off and there is what I would consider excessive slop between the crank gear and clutch basket gear. There is visible wear marks on the crankshaft drive gear. I know my way around engines and have had motorcycle engines apart before but have never split a case. I've been researching this and have been surprised by the amount of special tools that seem to be required. Flywheel puller, crank puller, crank pusher, etc. Maybe I can borrow some of this if I can find a dirt bike guy, and there seem to be some tricks to getting around using the special tools, but this seems to be a lot more involved than I had first thought. I've got many more issues and more will probably develop as I get further into it but this is probably enough for today. Thanks for any help!