WTB 4ac or 3a builder

[Devin]

I'm looking for a 3a or preferably 4a to rebuild. My current 3a is going to kick it soon. If it's in Colorado I can come pull it. Doesn't need to be running.

[Petros]

after having rebuilt several 3a engines, and just rebuilt a 4a, the 4a engine is a much better place to start. the block has more stiffening ribs and the walls are thicker, so it is stronger. The 4a head has larger ports on the 3a, even though intake and exhasut manifold ports are the same size, and all of the external "hard points" are identical. Between the two, the crankshafts are identical and completely interchangeable, but the 4a connecting rod is stronger and heavier (but geometrically identical).

Stock the 3a has 62 hp, and the 4ac has 90 hp, yet it only has about 100 cc more capacity, both have the same compression ratio, the same carb, same intake and exhaust manifolds, same stroke length. So the difference in power output must be in the head porting, perhaps the camshaft profile and the carb jetting. A few more tweaks to the 4ac will get it to 100 hp and still maintain reliability, which would be nearly impossible to accomplish with the 3ac and if you could, the reliability of the 3ac will go way down.

[Devin]

That's good to know Petros, thanks. It would be nice to have some more power to keep those hazard lights off on the passes.
The problem is any motor from a local salvage yard is $199 plus $75 core. It's hard to find one nor sold as a running motor.

[Petros]

search craig's list for used engines cheap. they show up regularly. someone on this list recently scored a freashly rebuilt 4ac for only $100 on craig's list, it was a great find.