Trash Or Treasure

How To Determine Whether Your Small-Block Chevy is a Builder or a Boat Anchor

By Tommy Lee Byrd   –   Photography by the Author

If you’ve been around old cars for very long, you’ve experienced the pressure and anxiety of buying a used engine. It’s always a gamble, whether it’s a freshly plucked junkyard engine or an abandoned build that someone claims is “ready to assemble.” Occasionally, you’ll get lucky, but there are plenty of duds and so-called “Corvette engines” out there, so beware.

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002 Early small blocks like the 265 283 and early 327
Upon first inspection, we spotted the medium-sized harmonic balancer. Early small-blocks, like the 265, 283, and early 327, had a very small balancer, while the trusty 305 had a much larger balancer; this one falls in the middle, which is a good sign. There are a few exceptions to the balancer size, such as the large balancers used on the legendary Corvette 327s from the mid ’60s. Also note that 400s had a specific counterbalanced design due to being externally balanced.

Our intention with this article is to give you some clues for quick inspections when you’re under the gun, and some tips for further investigation when you have time to run the numbers.

003 300hp and higher engines from 1969 72
Another immediate clue to this engine’s identification are the later Camel Hump heads with accessory holes. Without even looking up the numbers, we know these heads are desirable based on the fact that they were used on 300hp and higher engines from 1969-72.

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In the case of our subject engine, we picked it up in a package deal with a ratty late-’70s Nova. No information was provided with the car or engine, so we took a chance because the price was right, and we needed to get the deal wrapped up quickly. Upon arrival, we were pleased at first glance because the engine has a set of small Camel Hump heads (also called Double Hump) with accessory holes. These heads were used on performance engines (300 hp and up) and were used on iconic engines like the DZ302 and LT-1 from 1969 through the early ’70s, so that was an instant win.

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004 casting number on the back of the block
The first place we typically look is the casting number on the back of the block. There are dozens of numbers used from 1955 through the ’90s, but there are a few standouts that indicate a performance engine. Common casting numbers for performance engines include 3970010, but ours reads 3956618, another great number to put in your memory bank. This means the engine could be a ’69 DZ302, a ’68-69 327, or a ’69 model 350.

The easiest way to determine early (large) Camel Hump and late (small) Camel Hump is the accessory holes and thick bosses cast into the front of the head. The bottom line is that the cylinder heads gave us confidence in our purchase the moment we saw the engine. Even if the rest of it was trash, the heads were worth the price of admission.

After we got the engine home, we were able to give it a more thorough inspection, and we found some good things and some unfortunate things, which likely led to the engine’s removal and disassembly.

005 small pad on the front of the engine
The next place to look is the small pad on the front of the engine (passenger side). This area is hard to see if the alternator is in place, but ours was stripped down, giving us easy access. There is a series of numbers and letters stamped into the pad, and the most important is the “suffix,” meaning the last two or three letters.

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To identify this engine, we used a combination of block casting numbers, block suffix code, block casting date code, head casting numbers and date codes, crankshaft casting numbers, and intake manifold casting numbers. It can be confusing because certain casting numbers were used on multiple engines, and the same can be said for suffix codes, but we used the process of elimination to narrow down the exact configuration of our mystery small-block purchase. This engine could’ve been a 267ci boat anchor, or a super-rare beast from the muscle car era, so let’s dig into the process of identifying this crusty small-block Chevy and find its history.

006 our engine has the suffix code of HN
As we zoom in a little closer, our engine has the suffix code of “HN.” Once again, this gives us multiple options. HN designates a ’65 327/375 hp, ’68 327/250 hp, or a ’69 350/300 hp. An important note regarding these stampings: Any stamping with the prefix CE indicates a replacement block.
007 inspect the rotating assembly and decode the crankshaft to determine
Our next move was to inspect the rotating assembly and decode the crankshaft to determine whether it was a 3.25-inch stroke (327) or 3.48-inch stroke (350). The first observation is the use of two-bolt main caps. While some Chevy guys only believe in four-bolt mains, these two-bolt blocks were plenty strong.
008 look at the crankshaft shows a casting number of 3932442
A closer look at the crankshaft shows a casting number of 3932442. Here we go again with multiple answers, as this was a very common cast-iron large journal crankshaft used from 1968-82 in everything from 267s to 350s. The bottom line is that it’s a 3.48-inch stroke, helping us to determine that our engine is a 350.
009 date code confirms it as it reads B209
Now that we know this engine is a 350, it helps us narrow down the exact configuration, as noted from the casting numbers and suffix code. It is a ’69 350/300 hp, a pretty desirable piece. The date code confirms it, as it reads “B209,” designating a block casting date of February (B), 20th (20), 1969 (9).
010 cylinder head casting number and casting date code is visible with the valve cover off
The cylinder head casting number and casting date code is visible with the valve cover off. The 3927186 casting number, often referred to as “186,” could have 1.94/1.50-inch valves or 2.02/1.60-inch valves, but we’re betting on the smaller combo, as this engine was 300 hp. The date code “B189” means February 18, 1969.
011 On the other cylinder head it features the same 3927186 casting number
On the other cylinder head it features the same 3927186 casting number but features a different casting date. This one reads “A239,” designating a casting date of January 23, 1969. If we look back at the stampings on the front pad of the block, it will give us the build date (no year). Ours reads 0310, meaning March 10.
012 cast iron four barrel intake manifold with a semi modern Holley carburetor
Our engine came with a pile of parts, including a cast-iron four-barrel intake manifold with a semi-modern Holley carburetor (with an adapter). This isn’t something we’d likely use on a high-performance engine, but a factory four-barrel intake is usually worth hanging onto.
013 The intake manifold casting number is 3927184
The intake manifold casting number is 3927184, which designates a ’69 350 cast-iron intake for a Quadrajet carburetor, used on 250-, 300-, and 350hp engines. This intake is a perfect match for the engine, a rare find because the heavy iron intakes were typically swapped for aftermarket aluminum intakes somewhere during an engine’s journey.
014 cast iron water pump with GM casting numbers
The pile of parts included a cast-iron water pump with GM casting numbers. Again, we would probably toss this aside in favor of a modern replacement, but it never hurts to check those numbers.
015 casting number of 3953892
With a casting number of 3953892, and a date code of E200, we’re looking at an original-style water pump but likely a replacement due to the date code discrepancy. One of the most desirable water pump casting numbers is 3953692, which was the code used on DZ302 engines.
016 rocker arm studs beginning to pull out of their bosses
Since this engine seems to be mostly original, it doesn’t look like it’s been someone’s hot rod project. There is a chance a larger camshaft was installed, as we noticed some issues, like the rocker arm studs beginning to pull out of their bosses. These press-fit studs often pull out when a more aggressive camshaft is used or there is excessive wear.
017 186 Camel Hump heads
Despite the pulled studs, these 186 Camel Hump heads are worth saving. We can send them to the local machine shop and have them drilled and tapped for screw-in studs and milled for guideplates.
018 1969 gm 350
What’s the verdict? This gamble turned out to be a ’69 350/300 hp that looks like a budget-friendly rebuild project. We could keep it original and sell it to someone needing a numbers-correct engine for a restored muscle car or give it a few updates and put it in literally any project car needing a stout small-block.
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