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Another 401 build and discussion thread....

17K views 183 replies 22 participants last post by  CSP 
#1 ·
Since I don't want to derail-highjack someone else's build thread I'm going to start my own.

1) My 401 spun a bearing and is done....

2) This will be my first individual build...

3) I'm new to AMC and their idiosyncrasies...IE oil pressure and drain back issues I've read about

4) Call me stubborn, but I'm not gonna take, what I feel could be, the easy route and drop a SBC into it.

The CJ (see profile for specs) is going to remain primarily an occasional daily driver that I want to be reliable and capable of moderate off road use.

The PO did the 304-401 swap and the 401 appears to be all OE. Based on the block (3198951) and head (3216090) appears to be of the '73-'74 vintage....which goes with the build tag on the valve covers (606Z21), which I'm told translates to June 21, 1973... Z denotes 401.

That being said, my research for similar builds had led me come up with this "preliminary" spec sheet:

Providing the bore just needs a hone, new .std pistons. I'm undecided on brand, thinking cast will do......I want to keep the comp around 9:1 (8.5:1 is stock I believe)

Re-use stock forged rods if possible.

I'm assuming the crank will need to be turned .010, will deck the block as needed, and hope to balance the rotating assembly.

Heads will be rebuilt...port matched

Edelbrock Performer Intake (EDL-3731)

Unsure on carb just yet...Holley TA 670...?

And for the most important, most debated piece...the cam. As of right now I'm leaning towards a Comp Cams XE256H kit from Summit, mainly because it comes with lifters, valve seals, timing and roller kit ect.....

MSD HEI with 6AL

....and of course all new bearings - seals - hoses and gaskets.

I'm sure I'm forgetting a few things, but that's basically it.

 
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#108 ·
Holley 670 TA arrived today. I opted to save a few $$ and bought a refurb from Holley Perf on eBay.





Seller holleyperformance has a rating of 99.8% with 13703 items sold so I figured it was worth a shot. Saved nearly $200 off Summits price for same PN

From the listing:

"This is an official Holley Performance Factory Refurbished Carburetor listing.

Factory Refurbished carbs are NOT old worn-out carbs that have been rebuilt. They are carbs that were returned under warranty. When these carbs are returned, we check them out and most of the time there is nothing wrong with them. Generally, they were simply adjusted out of working range by the installer.

Since these carbs may show signs of a previous installation, our policy is not to sell them as new. Rather than scrapping them, we are making them directly available to the public. Not only does this help us control the costs of our new carbs, it allows you to get a great deal on a like-new carburetor!

Factory Refurbished carbs have undergone a thorough inspection. Any damaged parts that would effect performance have been replaced and the carbs are solvent cleaned before being wet-flow-tested on Holley's state-of-the-art flow benches allowing them to be recalibrated to new carb specs. Factory Refurbished carbs may have scratches, blemishes, and other visual flaws from previous installation."
 
#112 ·
cw05 said:
What oil pan are you going to use? I like the larger capacity of the Milodon one that Bulltear and others sell but don't love the crazy price! I also wonder how durable it will be on the trail without a skid plate. Any other options out there besides the stock AMC?
For now I'll just be using the stock pan, but adding 6qts of oil...per just about everybody on The AMC Forum. A deep pan is on the short list though an long with Bulltears serpentine kit.
 
#115 ·
I have to ask you man, why would those guys run an additional quart of oil in a stock pan? Nearly everyone else in the performance world runs a deeper pan with the standard quantity of oil to keep it from becoming a chocolate milkshake from the crankshaft. Who wants a bunch of air-entrained oil being pumped to their bearings?

Just curious as to their reasoning.


Shawn
 
#117 ·
I'm curious, too, Shawn.

I always thought the reason for a deeper pan was to hold more oil, so the engine never sucks it dry under high RPMs. :dunno:

Matt
If the pan is getting pumped dry, oil drain-back is the issue, not the amount of oil. If it isn't getting back to the pan, it's either filled up to the top of the valve covers and/or flying around the crankshaft like a horizontal, chocolate tornado getting whipped full of air.

It needs to be sitting in the pan, away from the crank where it can cool and expel any air that it picked up on the way down. Air makes a poor hydrodynamic wedge in the bearings and it has a habit of compressing in hydraulic lifters.

Again, just curious as to their thinking :tea:

Shawn
 
#118 ·
IIRC, the OE pan is the same pan that was used on the police packaged Javelins, with a slight difference with the baffle? AMC apparently was putting 6qts of oil in those from the factory. Just about everybody over there, with some really built motors, runs 6qts in their 401s with stock pans. I'll try to copy/paste some posts later today.
 
#120 ·
I've read thru some of the AMC forum threads, and I'm not sure about the 6-qt theory. I suspect the police cars used the larger filter, therefore the manuals recommended 6. They also had an extra baffle to help with sloshing. The Jeep manuals say to use 5 qts with the shorter filter.

Here's a pic of the stock oil pan with 4 qts of oil. As you can see, the oil is right to the top of the baffle. If memory serves the crank weights are only about 3/8" from the baffle. So, 4 in the pan and 1 in the filter (and elsewhere) seems about right to me.

The 6-qt theory is just another case of shade-tree mechanics thinking they are smarter than the people who designed these engines, IMO.

Matt
 

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#123 ·
I won't say adding an extra quart is going to cause any damage (though there are valid points here), but I will say we have seen more power on the dyno with less oil. I don't see the point in putting more than is called for. I have a 7 quart pan on my Jeep, and I actually only run 6.
 
#125 ·
Honestly, I cant but help thinking about how/why/when I spun that bearing,

The thing ran great when I first got it. Then I changed the oil, per specs with 5qts of oil and 3 weeks later BAMN. I truely dont believe the PO sold it to me with a known issue, he didnt mention using 6qts of of..nor did I ask, it couldve been a number of things, but I just keep wondering...had I researched this earlier and spent an extra $5 then would it have saved me the $5K Im spending now?

Who knows, maybe Im over analyzing everything. I do have a deep pan on the short list along with the BT serp kit but I need to spring for a Borgeson steering shaft first. Going to be working some OT this week, just going to depend on the final cost at the machine shop.

At this point I just want it up and running, get the wheels aligned, take the top off and enjoy this AZ weather.
 
#126 ·
Was summoned to shop today....

While the block looks good:



Small cracks were discoverd in both heads....in the same spot:





Both are roughly the same size and according to the shop definately repairable. I opted to have them repaired for a few $$ in lieu of dropping about $$$$ for a new set. Shop owner assured me it would'nt be an issue with my build and that its a repair they've done hundreds of times.

On a good note my Hella headlights (ordered 2/17) should be on the doorstep when I get home from work tonight.
 
#131 ·
I dont necessarily think its a design flaw per se, as much as the motor just severely over heated. From what Ive read on the AMC forum, if the heads do crack it tends to be around the lower bolt lands and pretty much ruins the head.

They arent very deep at all..... As far as repairing, I was told they would drill and tap in cast iron studs along the entire crack.
 
#134 ·
never seen or heard about cracks in that spot mostly at the exhaust port were they are flat buy the head bolts
 
#137 ·
rod caps make sure they spot face were the nuts go to give a flat surface for the nuts to seat against
 
#138 ·
10-4.... and my caps had to be reamed slightly to get them to seat flush on the rods without forcing them over the rod bolts. I guess the ARP bolts are just a tad too fat.

And, I thought the piston pins were going to be pressed but but they will be floating.
 
#140 ·
they bushing the rod end with the brass bushings
 
#141 ·
Getting closer.....

Ready for paint:



4P on a Friday wasn't the best time to drop in, they were swamped.... But progress is being made. Should be painted and on the stand next week....however Ill be out of town the entire following week. So may be a full 2 weeks more till I can pick it up...

 
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