We see this all the time, especially with SBC, and even brand new engines going cheap, like the Goodwrench crate engines.

Here might be one reason. The production shops buy the rebuild parts a lot cheaper than you can across the counter. Another factor is that maybe the ones you are seeing at those prices are not using top name brand bearings, rings, pistons, etc., as you would in your own rebuild.

Rebuilt engines are dicey, even from top name rebuilders. At our Marina, we refuse to install any rebuilt engine, regardless of who did it, and we won't even rebuild them ourselves. First reason is that 10-20 % of all rebuilt engines fail, right out of the box. That isn't a number I made up, I worked for a large retail chain and we tracked those numbers, and they are factual. Second reason is, the rebuilder generally will not pay the labor the 2nd time, but will only give you a replacement engine. Customers usually can't accept paying the labor twice, so guess who eats that one?

Finally, the term "rebuilt" can mean anything from a rering/ rebearing job to a "remanufacturing" of the engine, wherein every component is either rebuilt or replaced within that engine. Depending on the skill level of the technician who put your engine together, you can also either get a good one or not.

I am like you, I enjoy rebuilding my own engines, and trust myself to try to do the work correctly. But I always hold my breath for the first few hours until I am sure I don't hear that scary "knock, knock, knock" coming from the block. You also have to get a machine shop you can trust, and check all the parts you get back. They screw up too.

Don