1973 Yamaha RD350 Crankshaft Replacement

| 4/10/2015 2:33:00 PM

Tags: Yamaha, How-To,

New RD350 crankshaft installed in case with original crankshaft at left.

It’s funny – and not always in a “ha ha” way – how often simple projects go off course, taking unexpected and typically expensive detours. In our How-To in the March/April 2015 issue, we walked through the process of pressure testing a 2-stroke engine, the object being to suss out engine leaks that can cause a 2-stroke to suck air, resulting in a lean mixture and poor performance. Boy, did we find leaks in our subject 1973 Yamaha RD350. Aided by Yamaha RD350 and 2-stroke expert Brad Obidowski of HVCcycle in Lincoln, Nebraska, we found intake and head gasket leaks, the former likely causing an extremely lean condition in the right cylinder, resulting in the piston starting to burn away.

Where it all began: The right piston on our 1973 Yamaha RD350 was burning up thanks to an intake leak.

That discovery meant we were in for a top-end overhaul, but all things considered, on a 2-stroke like the RD350 that’s a fairly simple and not hugely expensive proposition. New pistons with rings are $180 from HVC, with gaskets and other miscellaneous bits adding another $100. Throw in cylinder reconditioning and it’s about a $350-$400 project.

6/11/2015 7:44:54 AM

Goes toward explaining why so many of these bikes got scrapped when the problems surfaced. I paid $400 for my used RD350 back in the day.