Bottom End Basics

July 28th, 2010

Installing a Crank and Rods the JMC Way

Text and Photos by Matt Emery

We have all heard that engine builders are a breed apart. They’re guys who lock themselves away in “clean rooms” with a multitude of parts and tools and wear lab coats; they build the mysterious apparatus known as the internal combustion engine.

Don’t get us wrong, when it comes to an ultra high performance engine, the type that has over 12:1 compression, is capable of spinning at eight-grand all day long while producing 800-plus-hp, a certain amount of black magic is required, especially when it comes to the crank and related bottom end pieces. The stresses placed on the bottom end are considerable, even for a stock engine that has only seen basic performance upgrades, such as a carb, cam and exhaust. We can’t even imagine what goes into an F1 engine that spins at 20,000 rpm, but for the rest of us, those whose cars are equipped with the ubiquitous 350-ci Chevy small-block, things are a bit simpler.

But what is really down there, and how is it really put together? In order to get a better look at what it takes, we traveled to JMC Performance in Placentia, California, where owner Jon Carren was in the process of rebuilding a 350 Chevy engine. Carren, who was the bottom end guy on Dennis Taylor’s Alcohol Funny Car “Way Cool,” has taken ASE courses, which mainly dealt with late models, but is a true hot rodder at heart and has been since he was a mere 15 years of age.

Even for a stock engine, tolerances are tight. A mere 0.002-inch clearance is all that gaps the crank journal and the bearing-laden cap, so care must be taken when assembling the engine. There’s a reason that clean rooms are used, as needless to say, any wayward chunk of dirt will cause severe problems.

The process begins with the machining of the block and crank. The block is line bored or honed to ensure that all of the holes line up and are the same size. This is, of course, done with the bearing caps on and torqued to specs. The line boring is usually done after the crank is turned and the resulting specs on the crank are used in the boring. That means that when the caps are removed, they must be replaced exactly as they were removed from the block. The bearings to be used must also be the correct size. Normally, as in the case of most stock engines, there are well established sizes and specs. This makes gathering the required parts and machining the block and crank a relatively standard job.

Though this is a job that you at home could do, it’s also something that’s as much art as science, so having a pro do the job may be the best bet. That being said, let’s watch and learn as Carren installs the bottom end on this Chevy.

Sources

JMC Performance

713 Monroe Way

Placentia, CA 92870

714.323.2913

jmcperformance.com

BEP Performance Center

1171 N. Kramer Pl.

Anaheim, CA 92806

714.666.1663

bepperformance.com

Clevite

clevite.com

Yes we know it’s painted blue, but trust us when we say it’s a 350 Chevy block. The block has been line bored and prepped for the install to come.

The crank has been balanced and the journals turned to match the specs of the bored block by the crew at BEP Performance Center in Anaheim, CA. All that's needed is assembly.

Due to its being line bored with the caps in place, the caps must be reinstalled in exactly the same way as they are removed. That means their position and orientation cannot be mixed up! This is imperative to the operation of the engine, so don't say we didn't warn you.

To better maintain their position, Carren removes the crank caps in sequence and lays them aside so that they go back onto the block just as they were removed.

There are things to be aware of when dealing with the main bearings. First, there is a notch that fits into a slot in the block that corresponds with a tab in the bearing. Theoretically, this makes it impossible to install them incorrectly.

Bearings are designed with a top and bottom; in other words, one of the pair goes into the block, while the other goes into the caps. The bearings are put into the block dry.

The seal needs to be aligned properly or it will leak. In this particular type of seal, the large lip goes to the outside.

The crank is carefully placed into the block.

To determine the proper spacing between the crank journal and the cap, Plastigage is used.

A strip of the Plastigage is carefully placed on the journal.

The cap is installed and torqued to 65 ft-lbs.

The Plastigage will squash down due to the force applied by the cap. The resulting width is measured with the supplied gauge. For a standard 350 Chevy engine, 0.002-inch of clearance is recommended. Be sure to wipe off the residue before moving on to the next step, though.

With the clearance deemed good, a coating of assembly lube is placed onto the bearing surface.

Once the caps are on, the hardware is torqued to 65 ft-lbs. The caps should be torqued in a rotating pattern starting in the middle of the block and working out to the sides.

The crank is spun by hand to ensure that it rotates freely and doesn't bind.

With the crank in place, it's on to installing the pistons and rods. The first step is to install the rings onto the piston. Though some sets of rings don't have them, with these rings there is a dot punched on one side. This indicates that these rings need to be placed dot side up on the piston.

It's easier to start with the lower rings first and work your way to the top.

The wrist pin needs to be pre-lubed. The lube is placed on one side of the rod end, then the end is slipped over and more lube is applied. Sliding the end back and forth, as well as using fingers to rotate the pin, ensures that a good coating of lube is applied.

There are many different types of ring compressors out there, but they are the only way to get the piston into the cylinder.

It may take a few taps to get the ring-laden piston into the bore, but notice that Carren is using the rubber handle of his mallet to do the job. Never use anything hard, or especially metal, that could damage the tops of the piston. Also, be aware that the rod end bolts are sticking out, so diligence is needed to avoid damage to the crank journals. There are rubber covers available that slide over the ends of the bolts, and it’s a good idea to use them.

Assembly lube is placed onto the rod cap prior to assembly.

Anti-seize is applied to the nuts before they are installed.

The rod end caps are torqued to 45 ft-lbs.

Installing a lower end isn't rocket science. With a little patience and the correct tools, this is one job that you can do in the sanctity of your own garage, but know that Carren will be happy to do it for you.

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