Junkyarddog,
To try to answer your questions on standard guides, etc.
Bronze guides are not original in any American manufactured engine. That includes today's aluminum-headed engines. They use iron.
Bronze guides are made for race engines, in general. Race engines are "custom" engines, so all the pieces must be "fit". With the advent of BIG cams in street engines, bronze has gained popularity over the last few years. As a result, it would be difficult for the manufacturer to supply specific sized guides for each application. So, they make "universal" length, and cut-to-fit.
Also, most shops use a "standard" size for installing guides. Those are .502" in OD. We ream the hole to .500", allowing .002" interference, so the guide won't move.
Once the guide is installed, it must be clearanced. Again, guides are made to fit multiple applications, so the ID is "unfinished". The machinist is responsible for setting the stem-to-guide clearance, and each application may be different from another. This is done either by reaming or honing the ID to size. Reamers are quicker and cheaper. Honing is more labor-intensive and the tool more costly. A hone will maintain "round" and "straight" better than a reamer. The hot lick is to ream to "close", then hone to size.
There are bronze guides made with the seal provision you speak of. They're made to fit aftermarket heads, such as Dart, World, Edelbrock, etc. They use an "odd" size OD (.562"). For the most part, only high-end race shops install these guides. The price of the special guide is more than the cost of machining the universal guide to accept the seal. The seals required by the "Brodx" guide are rather expensive, as well. The Viton seal used by most of us these days, is half the price of the former.
Any clearer?
Jim
|