Join Date: Sep 1999
Location: Vancouver, Washingon
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Re: 401 rebuild questions
According to my Perfect Circle engine parts catalog, the AMC 401 was produced from 71 - 76. Seems the 401 was offered with Police performance parts. I figuring from the information in this catalog the 401 does not have an adjustable valve train. Seems the Police performance 401 did have adjustable valve trains. I guess what I'm leading up to, is to get long lasting performance from the 401 special attention needs to be given to the push rod lengths. The Perfect Circle catalog offers push rod lengths ranging from 7.696" to 7.996". There is even a two piece cut to length push rod that can range from 7.420" - 8.420".
When surfacing the heads, or decking the block, the push rods are going to need to be adjusted for length. Very often when 401 heads have a valve grind or new valve seats installed the push rods are going to need to be adjusted for length.
If your CJ7 needs to be emission tested I recommend boring the block and going with new pistons. I know this adds considerable cost to an engine rebuild. Just a re-ring engine will work fine usually for 20,000 miles, sometimes more. I would think an average daily driver CJ7 would see 20,000 miles is just a couple years. The emission test could reveal a problem with the rings and piston clearances, so don't chance a re-ring engine to meet emission standards for more than a couple years.
According to my Federal-Mogul master piston catalog, the 71 401 piston was a dish piston of .170" deep, the 72 - 76 401 piston was a dish piston of .325" deep. My personal opinion would be to use the 72 - 76 dish piston for a compression ratio of about 8.5 : 1. I feel it would be OK to use 87 octane unleaded gas with 8.5 : 1 compression ratio. I would also think the 72 - 76 piston would be a few less dollars.
The end results of an engine rebuild depends on the budget you have. It goes without saying, if you can do most of work yourself, you will save hundreds of dollars. It also goes without saying, shop around, prices for parts and machine shop fees will vary! The AMC 401 is not the least expensive engine to get engine parts for.