bearings.

King AM-series main bearings for AMC V8's are half groove bearings: grooved on the upper bearing shell, and smooth on the lower bearing shell. They have locating tabs on the uppers and the lowers. The thrust bearing faces are nicely finished rather than the splotchy mess seen on many competing bearings.

King AM-series rod bearings for AMC V8's are of course smooth on both the upper and lower halves. Both halves are interchangeable and feature locking tabs and cut outs for the oil squirter holes.

I'm not reading from a catalog on this. I built my latest 360 with these bearings.

Trader wrote: Main bearings, I have been using King silicon/aluminum of late. Rod bearings: see this post: http://theamcforum.com/forum/401-rod-bearing-alternative_topic99248_page1.html?KW=pontiac Have not had any issues with 2 engines, mine has 8000 miles or more since posting. Still 5W30 and good oil pressure. Nice to be able to set all rod clearances within 0.0005" on just a re-polish of the crankshaft.

I just bought a set of Clevite bearings for my 401 and didn't use them. The number 3 bearing  top and bottom halves are both identical unlike the original. They also don't have the aligning tabs anymore. I call Clevite and was told they did that to save a step in production and the aligning tabs are not necessary. I figured that if AMC could have saved money in a safe way they would have done it first so I installed a set of Sealed Power bearings. They are made in Mexico but at least they look identical to the original bearings.

Several types of bearings.

1. Microbabbit. Simply a steel bearing shell with a thick layer of Babbitt (lead-tin alloy) plated to it. Babbitt is the best bearing material there is except for being unable to handle high loads and being so soft that is scratches, deforms, and wears out easily. An overloaded Babbitt bearing will fatigue, crack, and fail. AMC phased out Microbabbitt bearings in the 1960's. As of 1966, the 199 and 232 were the only AMC engines still using Micobabbit bearings and only on the main bearings. V8's stopped using Microbabbit bearings long before that.

2. Tri-metal. A steel bearing shell plated in a thick layer of Copper alloy which is then overplated with a VERY thin layer of Babbitt. The load handing capabilities and fatigue resistance of Babbitt increases significantly if the Babbitt layer is kept thin. Tri-metal bearings have the highest load capacity and fatigue resistance of any bearing. The trouble is, the thin Babbitt layer wears through easily. Just a few seconds without oil will completely wipe out the Babbitt. 100,000 miles of easy driving is usually all it takes too. Once worn through, the journal will ride on the copper underlayer which is not a very good bearing material. Bearing temperatures increase and the bearing will start to dig into the journal. AMC switched to tri-metal bearings in the 1960's, with six cylinder engines being the last to adopt them. As of 1972, all AMC engines used tri-metal bearings throughout.

3. Bi-metal. Same as a Microbabbit bearing but replace the Babbitt with an Aluminum-Silicon alloy. Bi-metal bearings fit in between Microbabbit and tri-metal for load capacity and fatigue resistance but beat either type for service life. The bearing surface is Aluminum, which is much harder than Babbitt, so it lasts longer. It tends to polish the crankshaft, too, making bi-metal bearings significantly more forgiving of a rough crankshaft finish that would normally rub out a Babbitt bearing. They can operate with poor lubrication or at higher temperatures for longer than a tri-metal bearing can. The downside of bi-metal bearings is they hate dirt and grit. That's not normally a problem on a properly cared for "modern" (post 1950's) engine. AMC switched to bi-metal bearings in the mid-1970's, with all AMC engines using bi-metal bearings throughout by 1977. Most other manufacturers switched to bi-metal bearings around that same time. They are the modern standard.

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Clevite 77 is a tri-metal bearing. Great for high loads, not so great for imperfect machine work or long service life. Every AMC I've torn apart that had original tri-metal bearings was worn into the copper underayer before 100,000 miles.

King makes all kinds of bearings, but the only bearings in their catalog for AMC V8's is their AM-series bi-metal bearing. Great for long service life and are very forgiving, but may not be up to the task for engines with exceptionally high bearing loads. However, they are more than up to the task for a stock to mild engine. I've torn apart AMC engines with their original bi-metal bearings at nearly 200,000 miles that still met OE clearance. King bearings are high quality and are made in Israel. King's head engineer, Dr. Kopeliovitch, is the leading engine bearing expert in the industry, and much of what I have posted here is information that I learned from him. I suggest reading some of his technical papers if you find bearing technology interesting. Though King doesn't catalog any other bearing for AMC engines, they might be able to match up something if you call them.

There are many other manufacturers of both bi-metal and tri-metal bearings out there. King and Clevite are not the end to all.

Edited by FSJunkie - May/22/2020 at 3:08am