4" Is Out!

My research has been slowed down considerably but has not been stopped. I believe that I have established that the 4" stroke is not feasible for phase 1 of project #001. I still have not read anything about the reliability of the engine but I have seen plenty on the difficulty of assembling such an engine in a stock block. Some very knowledgeable and experienced builders said, I think verbatim, you are fool if you try to build a 4" stroke engine in a stock block.

First, there is A LOT of grinding of numerous places on the block so that the crank and rods won't hit anything. This entails assembling the bottom end, finding where there is interference, disassembling the engine, grinding (but not too much!), cleaning the block, reassembling, finding that you didn't grind enough, and repeating the process only to start all over again with the next place of interference.

Second, the block holds the cam too close to the crank with a 4" stroke and requires the use of a smaller diameter camshaft. This is referred to as a "reduced base circle" camshaft. This also means that the lobes can't be too high or they will hit the connecting rods. I'm not sure if I will be running a camshaft with high enough lift for that to be an issue. It is looking like I will be using a high lift short duration camshaft for low end torque so interference may be an issue. Since I don't know just how far I want to open the valves, I don't know how much total lift I will need but some of the guys were having to run higher ration rocker arms to get the lift they needed. With the higher ratio the valve springs can push harder on the camshaft (more leverage) and in some cases cause the reduced base circle camshafts to flex. I don't know exactly how this ended up being bad for the engines. The two bad things I can think of right off the bat are breaking the camshaft from flexing it and the flexing giving inconsistent opening and closing of the valves.

Third, as mentioned before, special "clearanced" connecting rods had to be used. There was even discussion of using crankshafts with smaller rod journals to bring the outer circumference of the crankshaft down. Clearanced rods don't seem like a big deal to me but reducing bearing surface is not in line with the kind of reliability I am after.

I don't think any one of those things alone or in concert are way beyond my capability but they sound like A LOT of work and definitely not the engine to start out with.

There was a simple (and expensive, for me) solution. Buy an after market block with a raised camshaft location and a taller deck height that was designed to accommodate a 4" stroke. This makes sense to me! There are some other headaches that come along with this solution but none that get in the way like the PRICE. I looks like these block sell for $1,000-$2,000.

So there's an end to that. There was a discussion of using a 3.82" (I think that dimension is correct, I know it is close) stroke but, at the moment, I'm inclined to go with the 3.75" stroke. I'm guessing that there is greater parts availability for it and I know I can get decent rod/stroke ratios. I guess that is the next thing to check on.

Builder