Keep in mind we're dealing with metric threads. Metric threads are specified by it's major diameter x thread spacing. A typical spec would be 12x1.25 which means the OD is approx. 12mm and there is 1.25 mm from the top of one thread to the top of the next.
When you measure OD of the threads, they are going to come out an oddball number like 11.86 mm (you lose a little material when the threads are cut). For male threads, round your reading up to the next whole number, in my example 12 mm. For the pitch of the thread, a thread gage makes it quick and easy, but it's not absolutely necassary if you have a caliper or a good rule. Since metric thread pitches are specified by their spacing, measuring the distance from 1 crest to the next will tell you the pitch. It gets a little tricky on smaller sizes where the pitch may be .7, .75, or .8. But the crankshaft is probably going to be 12 mm so a pitch of 1.25 or 1.5 is typical. Measuring the distance between 10 crests then dividing by 10 will make things easier and less prone to error (there's little difference between 1.25 and 1.5 but a big difference between 12.5 and 15). If you don't have 10, use as many as you have then divide the result by how ever many you counted.
The bigger problem is determining what the female threads are. You can measure the ID to get the size, but you really have to use a thread gage to determine the pitch. An option would be pull to the flywheel off and see if you can put the weight on backwards. If the threads are a screwed up, it's likely only the first few threads are so the outside ones should be fine. If it fits correctly, then you'll know it's just buggered threads. If it's a common size, you might be able to find a tap locally. OTOH, if it's an oddball, try someone like
http://www.jlindustrial.com/ that serves metalworking industries.
Finally, if it turns out to be the incorrect thread, don't attempt to alter it. It's obviously close in size which means you can't safely re-tap it a different thread. You'll be removing way too much material for it to be safe. When it fails, it could ruin the threads on the crank and take out the cover $$$$$. :eek: It's not worth the risk. If you got it on Fleabay, contact the seller and get a refund because it's not what they said it was. Otherwise, either try to resell it or chalk it up to experience and purchase the correct one. One of the important lessons in life is: Cheap is Expensive!
Marc -