In the past we have always...
In the past we have always heard warnings about over carbureting; however, Scott Main points out that with today's better heads and hotter engine combinations, builders sometimes go too small.
11. Don't Check The Clearance
Jud Massingill, School of Automotive Machinists
"Not checking clearances in an engine is probably the quickest way to disaster. The moving parts of the engine are designed to work with the correct operating clearance, and it has to be right for the application. This means knowing the appropriate target clearance for the part and its use, and then measuring it and correcting it as necessary. For an engine build to be successful, the machining has to be right, and the parts need to be at the required specification, and then that needs to be verified by measurement. Starting an engine without sufficient coil bind clearance, piston-to-valve clearance, or improper clearances in the bearings and reciprocating assembly is a quick way to disaster."
"Not checking clearances in an engine is probably the quickest way to disaster."
12. Build It Filthy
Scott Main, MPG Heads
"Cleanliness is a big one. I often see people putting together stuff that is just filthy, and I can't believe it works, and a lot of times it doesn't. The mistake here is not washing anything. A guy might buy a cam, take it out of the box, and throw it into the motor. A block from the machine shop might look clean so it's easy to figure it must be clean, so they put it up on the stand and start throwing oil at everything and begin putting the rings and bearings in. It really needs to be hand cleaned-clean solvent, brushed, clear water rinse with hot water, blown dry, and so on. One of the jobs of the bearings is to absorb grit and protect the crank. If you start it up and they are already loaded up, it's all done in the first hundred miles."
This small-block Chevy shows...
This small-block Chevy shows a fatal assembly error, with numbers three and five pistons in the wrong hole. The valve notch orientation must correspond to the heads' layout or catastrophic failure can result.
13. Too Small A Carb
Scott Main, MPG Heads
"When it comes to carburetors there was always the warning not to over carburete, but now I see people making the opposite mistake of choosing too small of a carburetor. We have these good intakes, and it seems like you can put a pretty big carburetor on them and they work well. Instead, you see something like a 600-cfm carb on a 440 Chrysler engine [he laughs]. This is especially true with good heads. If you put on a trick set of heads you really need to up the carburetor size because it is breathing and it's running out of carburetor too quick. Guys tend to over-cam and under-carb."
"When it comes to carburetors there was always the warning not to over carburete, but now I see people making the opposite mistake..."-Scott Main