Balanced and Blueprinted AMC 401
There aren’t as many engine shops around as there was when I was growing up. Ready-to-go crate engines and large-scale engine remanufacturers with computerized plants have lowered the buy-in price of a new or remanufactured engine, making the process of rebuilding your existing engine actually more expensive than just purchasing new equipment. As the aftermarket engine business evolved, a number of machine shops died out. The ones who stuck around … stuck around for a reason.
Thankfully, there will always be a need for quality machine shops. If you’re working with a discontinued engine or one that the aftermarket does not support, then an engine shop is your only option. If you have some nostalgic or “matching numbers” reason to keep your original engine, then an engine shop is your only option. If you want a balanced and blueprinted engine, then an engine shop is your only option. And if you want an AMC 401 built by the man who helped AMC redesign their heads in 1969, then Valley Head Service is your only option.
When the 360ci engine in a $200 ’79 Jeep Cherokee Chief blew up, I had already dumped $3,000 into it and wasn’t about to let my new beloved Cherokee go just over a motor. After searching Craigslist for a cheap replacement, I came to the realization that I wanted to put something in that would last and not have to go through this same process a year later. I could’ve retrofitted a used Tahoe LS engine into it for cheap and not had to worry about reliability, but it felt like that would be sort of lame and copping out—especially when these Cherokees were available with the venerable AMC 401ci V-8. The “right” thing to do was to find a 401 block and build a “perfect” engine for my Cherokee. Upon finding a 401 core, tearing it down at a friend’s shop, and confirming that machining would be a necessity, I took it to Valley Head Service (VHS) in Northridge, California, unaware of who I had just chosen to rebuild my engine. I picked Valley Head Service because the shop had done an excellent job on an aluminum 4.0L head of mine about seven years ago, and I believe in repeat performances. Only later did I learn that I had landed at the same shop that AMC had gone to for help designing the famous dogleg heads that were introduced in 1970.
What I ended up with was not just a better-than-new engine that would sip a little less fuel, make a little more power, and be just as reliable as a stock AMC 401; I also came away from this job knowing a lot more about engines and with four new friends from VHS who took the time to teach me a few pages from a history book that could (should) be written about Valley Head’s work over the years.
This month, VHS spent time machining the 401 block and balancing the internal parts so that we can later assemble the engine before putting it on a dyno and seeing how much power it made. While it’s not “necessary” to balance and blueprint an engine in order to rebuild it, paying money for a possibly lopsided engine sounds about as silly as wearing two different shoes. A basically stock engine that has been balanced and blueprinted will benefit from increased efficiency and longevity, and that will pay off in time, money, and power in the long run.
Why a 401?
It’s easy to tell if it’s a real AMC 401 block when you’re engine shopping. The original 401s have raised casting on the side of the block that labels them as such (though some replacement 401s did not).
Why a 401 block over a 360 or 304? Though they have the same architecture, the AMC 401 came with a high nickel content block, a forged steel crankshaft, forged connecting rods, and larger 2.248-inch rod journal bearings. Hot rodders loved them because they were not compression sensitive and they held together under extreme force. Not only that, but they would out-power the small-blocks that Chevy, Dodge, and Ford offered at the time (though some argue it’s not a fair comparison because AMC never had a “big-block”).
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Now that the machining is done to the block and the parts have been cleaned, collected, and balanced, we’ll be assembling a balanced and blueprinted AMC 401 in mostly stock form. Our small list of aftermarket parts consists of an Edelbrock aluminum intake, a COMP Cams camshaft and timing chain, stock-sized SI Valves, some KB Pistons, and ARP rod bolts.