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post #1 of (permalink) Old 04-30-2000, 06:59 PM
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401 rebuild questions

my 85 cj-7 has a 76 401, th400 in it, and i am about to get it rebuilt, and i would like the performance of a pre-smog motor. it will be an everyday driver, any suggestions on how to build it? can anyone tell me if the 401 debuted in 1971 and if so, what were the specs for the motor that year? thanks for any help you can give me.

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post #2 of (permalink) Old 04-30-2000, 08:39 PM
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Re: 401 rebuild questions

'71 was the first year for the 401. The only specs for that year that I could find was 330 hp. No figure for what rpm that hp came in at and no torque figures. Last year for 401's in AMC cars was '74. '74 specs were 235 hp @ 4600 rpm for single exhaust and 315 @ 3100 rpm for dual exhaust. Jeep used the 401 in FSJ's from '74-'78. Those specd out at 215 hp @ 4400 and 320 lbs torque @ 2800. The Jeep figures were all net, while the '71 car figures were still gross. The Jeep data indicates that the compression was 8.35:1. I would suspect that the early 401 car and police motors had somewhere around 10:1. I had a '76 Waggie w/401 that I had rebuilt and it was an impressive motor. I had the Edelbrock Performer intake and carb and Comp Cams HE-262 cam. If I were to do it again, I'd try to get the compression up to 8.5-8.7:1 to still be able to run 87 octane gas, (either by pistons, if available or milling the heads some), use the Edelbrock Performer intake, Edelbrock Q-Jet carb, and either the Edelbrock Performer cam or some other mfgr's, (Crane or Comp Cams Extreme 4x4), cam that was one notch below the Comp Cams HE-262 that I had previously. I like a very smooth idle and high vacuum to produce great low-mid range power. Good luck.

'66 Jeepster Commando w/Buick 252/4.1L V-6
'70 Wagoneer w/Buick 350 V-8
'76 Wagoneer w/AMC 401 V-8 (sold)

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post #3 of (permalink) Old 04-30-2000, 08:51 PM
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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.

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