How To Assess A Used Engine Block And Step-By-Step Machining Process

Project Tiger's Eye - L&R Machines 350With Project Tiger’s Eye well underway, the next step for Rod Authority’s traditional custom project was to track down a motor. To honor a main tenant of our project we sourced a used block that would need to be torn down and given second life, in a matched effort, alongside our frame-off 1950 Chevrolet Fleetline.

IMG_8439Running down our list of contacts, classifieds, and local yards, we tracked down leads for a potential donor motor. Eventually, we honed in on a 350ci small-block Chevy being sold at a yard in nearby Ontario, California.

With a potential motor in our possession, it was imperative that the next step was addressed without delay–assessing whether the 350ci was useable, and if so, re-machining it to give us a restored foundation to build upon.

We reached out to the techs at L&R Engines located in Santa Fe Springs, California to help us get the job done. Derek Ranney, second generation owner and operator of the family-owned business, gave us a closeup view of his facility’s testing and machining processes. In the interview below, Derek sheds some light on those processes and offers insight on some questions that you might have when in the market for sourcing a used motor.IMG_8510

Giving Our Block Second Life–Q&A With Derek Ranney Of L&R

Rod Authority: Can you describe the hot tank process?

Derek Ranney: “Hot tanking’s biggest role is to clean the block enough so that we’re able to clearly magnaflux it. We have the old fashioned jet tanks where the block’s placed on a carousel wheel. As the row of jets sprays cleaner, the block is rotated.”IMG_8410

Eddie preps our 350ci on their carousel-style hot tank. To help aid the hot tank process he sprays degreaser on the block.

RA: Have EPA regulations affected the hot tank process?

Ranney: “What we use now works, but 15 years ago we were using caustic soda, or sodium hydroxide, and that stuff worked awesome. Nowadays, with the EPA, we use a bio-degradable chemical–it takes a little while longer and isn’t as potent, but it works. A lot of people have gone to different methods for cleaning blocks because of the regulations though.”

RA: What are the most common examples of block wear that you see coming into your shop?

Usually when a block is damaged it’s been overheated and abused. Sometimes it’s just a lack of maintenance–it’s run on low oil for example. I’ve even seen cylinder wear from running a motor without an air cleaner. –Derek Ranney, L&R Engines

Derek: “Usually when a block is damaged it’s been overheated and abused. Sometimes it’s just a lack of maintenance–it’s run on low oil for example. I’ve even seen cylinder wear from running a motor without an air cleaner. The 350ci Chevy is a pretty solid block. They do tend to crack in the valley, sometimes, but other than that their alright.”

RA: What is your opinion on the quality of a block in relation to casting numbers, why are some more desirable than others?

Derek: “See, GM casted their blocks here in the United States up until the 80s. Then they moved their production outside of the country. Their castings got weaker, thinner, and materials just weren’t as quality as before, and that sucks, but you know…the early blocks are casted stronger and to answer your question–in my experience, while earlier blocks are stronger, when it comes to the newer ones that come in; we check them really close.”

IMG_8490RA: What examples of block damage are repairable and in which cases are you better off sourcing another block?

Derek: “If it’s got a cracked cylinder we can always sleeve it, or bore it to the next size. Cylinders are usually repairable other than a completely catastrophic blow up where you’ve got holes through cylinder walls. In that case, I’ll tell a customer that it’s not worth trying to repair it–the money they’re going to put into it, they’d practically be buying another block.

When it comes to the line bore on the block–sometimes the crank spins the main bearing so bad where we can’t line bore it because it’s way out of spec–that would be a block that I toss to the side.

Depending on where the crack is on a block is also a factor. If it’s a one-inch crack I can repair it. If it’s a 10 to 12-inch crack I say throw it away and start over.”IMG_8552

Here, Eddie took a cracked block from storage and magnafluxed it to show us how the magnetized powder reveals compromised surfaces.

RA: What is the method for repairing cracks in blocks?

Derek: “We do it a couple of different ways.  We have what we call a cold weld–it’s a pinning process. If the crack’s two inches long we’ll drill a quarter-inch hole–we use a tapered tap and then screw in tapered metal plugs that lock in. We’re essentially drilling out the crack and filling it by lacing the plugs–that’s the old school way of doing it.

We also do a lot of vintage blocks, blocks that you can’t find anywhere so sometimes we’ll hot weld them. That’s the process of welding cast iron. We put the block in an oven, bring it up to temperature, weld it, and let it cool at a slow rate.”

stitching in progress

An example of cold welding, or cold stitching courtesy of:

RA: Aside from magnafluxing are there any other tests that you utilize to assess the usability of a block?

Derek: “Yeah, we can also pressure test blocks. Just like you do with bicycle inner tubes, we put air pressure into the block and use a mixture of soap and water to tell us where any compromised surfaces are by checking for bubbling.

On a normal basis, we don’t pressure test blocks, we usually just magnaflux unless the customer requests it and we’re looking for a particular problem. If they tell me they’ve got water in the oil, or vice versa, we magnaflux it, and if I still can’t find anything then we’ve got to go a step further and look a little deeper.”IMG_8809

Left: The steel powder is poured into this rubber container with a shaker-style cap. It provides a steady and controlled means to distribute the powder when checking the block section by section. Right: The steel powder used in the magnaflux process.

RA: Can you expand on the magnaflux process?

Derek: “Magnafluxing, or magnetic particle inspection, is a process where we check any kind of iron or steel. We use a big magnet and put it against the block’s surface. If there’s a crack in the block you’ve got that separation of metal. When you put a magnet on the block, that separation from the crack will create a magnetic field. With the magnet attached, a steel powder is then sprayed all over the block. The powder is then drawn to a crack’s magnetic field, filling it, and exposing it to the naked eye.”

RA: Once a block is deemed usable, what is the step-by-step process when you machine it?

Derek: “I’m sure every shop has their own way, but the way we do it here is I usually bore and hone the cylinders first. I do this because I want to make sure that if we’re going .030-inch over that the cylinders are cleaned up before any other machining process is done. After the bore and hone we go to the line hone, then to the decking of the block. The decking is the last thing because I don’t want to risk scratching it up from the shavings of the other processes.”IMG_8900

RA: Are there any tips or things to look out for when shopping around for a block at the junkyard or through online listings?

Derek: “You know, I look for things that have been hot. Usually, if a motor’s been overheated you can see indications of discoloring on the block or head, or whatever you’re looking for. But that’s the only thing you can do. You don’t know what that motor’s been through all its life, or if it’s been abused, overheated, or run on low oil. The rust that appears on decks or inside cylinders can either be from a blown gasket, crack, or the block simply sitting out in the open. There’s no way to truly know until you take it into a machine shop for proper assessment.”IMG_8472

Cleaning, Assessing, And Machining Our 350ci Small-Block Chevy

Below is a walkthrough of the steps that were taken during the assessment and machining process of our motor. Rod Authority was in the dark as far as the true state of the block before taking it into L&R. Aside from hooking up the starter, having the seller turn the motor for us, and tearing the 350ci down to a bare-block for closer inspection, we knew that getting it to a machine shop was the only way to see if we’d made a smart purchase. Part of the excitement, and anxiety was getting our motor over to L&R to see if it was even useable. Special thanks to:

  • Hot Tank, Magnaflux, and Block Prep – Eddie
  • Bore & Hone – David
  • Line Hone – Henry
  • Deck – Phillipe
  • Final Prep, Holes & Plugs – Andre

Eddie was in charge of all the hot tank runs, block testing, and prep for subsequent machining stations. Hauling our block over to their hot tank room, Eddie hoisted our block into their carousel-style tank. Degreaser was sprayed on the block to aid the cleaning process which lasted 15-20 minutes.IMG_8458

After the initial hot tanking, Eddie used an air gun to completely dry the block, making sure to drive out all the moisture from every oil and water passage. He used a combination of large and small diameter wire-brushes to clean off loose material from the block’s surface.


The next step was what we’d been waiting for–the magnaflux. Eddie prepped by removing remaining gasket material from the mating surfaces. By doing this it ensured that the steel powder was always contacting iron, giving the tech an accurate read when inspecting for cracks.IMG_8554

Each block needs to be signed off by Eddie after the magnaflux process. Here you see the mag certification, who conducted the test, the owner of the block, and the type of block all written in bold so that subsequent stations have a reference.

While the entire block was coated, key areas such as the block’s mains, valley, and decks, were closely inspected. With our finger’s crossed, Eddie gave our block the OK–there were no cracks and this 350ci was definitely useable.

IMG_8677After magnafluxing the block, our 350ci was moved over to David’s bore and hone station. Even though we bored our 350ci a total of .030-inch over, David only bored out .020-inch during the boring process. The remaining .010-inch was achieved during the final hone.

To properly inspect for a consistent diameter, David used a dial bore gauge to measure the top, middle, and bottom of each cylinder after boring, and again following honing.IMG_8598

During the honing process, David attached a deck plate that was torqued to the same specification as cylinder heads. This simulates the tension and effectively, block distortion, that is applied to the cylinders when heads are installed. He then honed each cylinder using the honing load meter as a guide. According to Sunnen, L&R’s hone machine supplier, “Load meters indicate high and low spots allowing the operator to adjust their stroke as required for optimum cycle time.”

IMG_8683After the honing process Henry took over and brought our block over to his line hone station to re-align our main bearing bores. We wanted to achieve a bore of 2.640/2.641-inches. As an aside, we’ve seen questions pop up around hot rod and custom forums concerning whether or not this is an accurate measurement when line honing main bores for a 350 ci. Here’s a simple equation that we ran to double check proper fitment.

IMG_8697The standard diameter of a 350ci’s crankshaft main journal is 2.4484/2.4493-inches. Oil clearance should account for .0005/.0029-inch. The wall thickness of our main bearings is .095-inch. These specs were confirmed by a diagram provided by our main bearing supplier.

By adding the diameter of a crankshaft’s main journal, oil clearance, and main bearing wall thickness (don’t forget to add wall thickness twice), you can see why a main bore size of 2.640/2.641-inches is the magic number.IMG_8685

After the line hone station Eddie transported our block back to the hot tank in order to clean the debris and oil that had accumulated from the last two processes. Once cleaned, Eddie wheeled our block over to Phillipe’s deck station.

After removing the cylinder head retainers, Phillipe mounted our block and got an initial assessment of the deck surface using a dual-axis level. The initial pass cut our deck down by .0.20-inches. According to Phillipe, “This initial pass acts the same way that a guide coat does during the painting process–it reveals your high and low spots and gives you a better idea of the deck surface’s state.”IMG_8755

The second and third pass each took off .030-inches for a total removal of .080-inch from the height of our decks. At the end of the decking process Phillipe pointed out that the minor bit of erosion that was evident around the water passages was due to electrolysis, or charged water that sits and slowly eats away at the surface. This is usually the result of an inaccurate water/anti-freeze mix.

With only minor signs of electrolysis after removing .080-inch from our deck height we were more than obliged to play it safe and rely on head gaskets and silicone sealer to do the rest of the work as far as ensuring a proper seal.


After another 20 minute run in the hot tank, Eddie dried the block so that he could apply a fresh coat of high-temp engine paint. Pure synthetic colloidal graphite, or dry film lubricant, was applied to the valley, timing area, and mains. Dry film lubricant provides a high-temp protective layer for these surfaces and also lubricates them allowing for optimum oil circulation.

With our block looking much better than it had when we first rolled it into L&R it was time to head over to the last station where we met Andre. Andre was responsible for putting the finishing touches on the freshly machined block. This covered everything from installing the freeze plugs and head retainers, to the cam bearings and camshaft backing plate.IMG_8877

By chamfering the bolt holes, Andre is essentially taking down the top thread. When a cylinder head is torqued, it pulls the threads up. By taking down the top thread it prevents the thread from damaging the head gasket.

One of the first things Andre did was tap, or chase the thread, of the cylinder-bolt holes. “The main purpose of this is to clean the threads of any debris or build up,” Andre explained. With all the holes tapped, Andre chamfered the holes. It’s a small detail, but like any process that occurs during machining, serves a practical role. “When you bolt a head down, it pulls the threads of the hole upwards. With this, you risk them tearing into the gasket. Taking the highest thread down prevents this,” Andre explained.IMG_8925

Andre stakes the oil gallery plugs to secure them in place. You can see the previous stake marks from before our machining process at L&R Engines.

After cleaning out the lifter holes using a rotary tool and sand paper, Andre took break-parts cleaner and an air gun to clear the rest of the debris.

From initial assessment to plugging the last hole, the machining process was completed just shy of a full work day. The important thing to learn is that the machinist is your friend–if you’re in the market for a used block the machine shop is a necessary and responsible step that you need to take in order to ensure that you’re building your engine upon a sturdy foundation. Whether you’re a backyard builder, or an avid performance enthusiast–assessing your block and reconditioning it back to tip-top shape is more than a worthwhile investment.

Be sure to check out the entire machining process and a behind the scenes look at L&R Engines in the gallery below.

About the author

Andrew Almazan

Andrew Almazan is a graduate of CSULB with a degree in English and a passion for traditional kustoms and hot rods. His first exposure to out of this world vehicles was through the prevalent low rider, baja bug, and kustom culture of LA county.
Read My Articles

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