Quote Originally Posted by Tim Kurcz View Post
Rods and crank will be weak links. Kiekhaefer did a great job of optimizing these engines: Nothing is beefier than needed. Should the rods make it, double duty on the crank journals will likely take them the crank out quickly.

Even so, it's a very cool project.
Actually the rods and bearing have a good bit of margin. In modified motors these parts are spun to much higher speeds than a stock motor. When you realize that stress and loads are a speed squared function, where a 20% increase in speed is a 44% increase in stress and loads, then the stock rods and bearings are actually pretty robust. In addition the big end forces peak at bottom dead center, and these are actually lower with a piston pushing the other way, so big end forces are higher, but they aren't twice as high. If big end bearing forces were a problem you could always go to titanium rods.

At some point you're going to have to get rid of the stock rod bolts and get something just a bit longer so that the area on the cap is a bit bigger in the area between the head of the rod bolt and the bearing area. That's a nasty stress concentration area and that's a failure location for sure.

Also think about making mods or getting rid of the stock crank. You need more area to hold onto the slave rod and I fear that there just isn't enough room to fit in what you need to do with thin area between the counterweights.