It’s been a long-awaited endeavor, but the time has finally arrived. We can start assembly of the 416 small-block Mopar we are affectionately calling LA Thumper. Supply chain issues have made parts acquisition tedious at best, but the pieces are finally arriving. One of the main pieces of the puzzle that is on the bench and ready to slide into place is the SCAT rotating assembly.

A few months ago, we had an in-depth discussion with SCAT’s Tom Leib about parts selection, and you can read that article in its entirety by clicking here. Suffice to say, Tom’s recommended parts are ready to go in the block. Installing these hunks of steel and aluminum requires some preparation and proper installation techniques. Sliding the rotating assembly into place brings us to the point where any overlooked detail can cause catastrophic issues later. That means care must be taken during installation to achieve the proper clearances and gaps.

By paying attention to details, many of the reasons for early engine failure can be avoided. All that is required is patience and a few measurement tools that will help make your life a lot easier.

We had our bearing clearances checked at the machine shop with proper mics, but wondered how close we could get with Plastigauge. The main journal diameters were mic’d showing us main clearances of 0.0024-, 0.0023-, 0.0024-, 0.0025-, and 0.0021-inch. Well within spec for use with our 10w-40 Torco Oil.

LA Thumper Is Getting Cranky

The first step of our actual engine assembly is installing the crankshaft. We are not covering machine work, because that should be completed before you get to this point. However, we will show you how to make sure the machine work does bring required measurements into spec. That means making sure aspects like ring gaps and proper bearing clearances are in place. We’ll also talk about a few basics that you should understand as well.

Since we mentioned bearing clearances, let’s start there. An accepted rule is to have a bearing clearance of 0.001-inch between the bearing and crankshaft journal for every 1-inch of journal thickness. LA Thumper has a journal diameter of 2.5 inches, which means we need .0025-inch of clearance. The rod journals are 2.125 inches, so we will be shooting for a bearing clearance of .0021-inch.

Connecting The Beams

When it comes to pistons and rod assemblies, you can have one of two connections: a floating wrist pin or a press-fit pin. The rotating assembly we are using features SCAT’s Pro I-beam rods and ICON forged pistons with floating wrist pins. With a press-fit pin, care needs to be taken when installing the wrist pin. We have seen many shops break a piston or two while pressing the pin into place.

“In the case of the small-block Mopar you are building, the Pro I-beam is a great choice,” says Tom Leib of SCAT. “This rod features floating wrist pins, a reinforced big end, and the beam itself is machined to remove any stress risers from the casting. The benefit to having a machined or polished beam is that you remove the source of potential stress fractures, reducing the risk a crack will develop. If you were building an engine to go racing or adding forced induction or nitrous, then an H-beam would be the better choice.”

With the crankshaft in place, tighten the main caps to roughly 10 to 20 ft-lbs of torque. Next, tap the rear of the crankshaft forward with a soft mallet to align the bearing thrust surfaces. Now, torque only the main cap with the thrust bearing to spec. Mount a magnetic base and a dial indicator to the engine. Gently pry the crankshaft forward and zero the gauge. The crankshaft should now move with very little effort and the dial indicator will read the clearance when the crankshaft is moved toward the rear of the engine. We needed between .002- and .007-inch. We have .004 and are good to go.

With a floating pin, rod and piston assembly is an easy DIY affair we can do at home without relying on a press or a machine shop. However, there are a few things to consider when assembling the pistons and rods. Those considerations revolve around orientation. For starters, with a traditional V8 engine, piston orientation in the cylinder must have the valve recesses at the top of the pistons. As far as the connecting rods, crankshaft design needs to be considered.

When installing the rings, they must go on the pistons a certain way. For starters, each ring must go in the correct piston groove. If the ring has a dot or laser mark, install that side up. Unmarked rings with an inner bevel are installed bevel side up. Rings without a dot or inner bevel can be installed either side up. There are two opinions when it comes to installing the rings. One says to use a ring installer and expand the rings to go over the pistons while the other is to gently feed them around the piston and into the groove.

Most crankshafts feature a large radius on each side of the rod journal. The big end of the connecting rod features a larger chamfer (machined angle) on one side. The side with the larger chamfer must be installed facing the crankshaft’s journal radius fillet. With the floating pins we are using, the orientation was arranged and the spiral locks were put into place.

All Lubed And Ready

Now that it is time for assembly, there are a myriad of opinions available about what assembly lube you should use. Some say a quality motor oil is sufficient while others claim a thick oil additive is a great assembly lube. Technically, both “liquids” can produce good results. We are not sure how long the engine might be sitting until it is ultimately installed. That is why we decided to use a dedicated assembly lube from Torco. While it might just be our thought process, we wondered if the “oil” could eventually drain off of the parts over time? If it does, when we finally fire up the engine, the protective coating could probably be in the oil pan before the first turn of the crankshaft.

Oiled up

When selecting an oil pump, do you have an idea about what you really need? Will a stock pump be sufficient? Do you need a high-pressure pump or will a high-volume pump be the best option? Stock (OE replacement) oil pumps are typically sufficient for use in most stock applications. But start building higher than O.E. power numbers, and some are not up to the task. When building an engine to deliver increased horsepower, increased engine RPM, or whether the stock bearing clearances have been altered to be more compatible with a thicker – or thinner – viscosity oil, choosing the correct oil pump is crucial.

The Pro I-beam rods get torqued into place with lubed-up ARP fasteners. ARP recommends a certain “stretch” of the rod bolt be achieved. However, not many enthusiasts have a stretch gauge to use. After some research, we found ARP wants .0060- to .0065-inch stretch which they equate to a torque of 50 ft-lbs.

According to Mike Osterhaus of Melling, “pump selection is dependent on the engine’s assembly specification, additional oiling demands, and intended usage of the engine. High-volume pumps are normally recommended for engines with loose bearing clearances, oil coolers, and remote filters. High-pressure pumps are designed for engines that will spend time at high RPM levels. A high-pressure pump simply means the bypass will open at a higher setting. Using too much pump, and/or too heavy an oil, can cause very high pressures or very-high oil temperatures. This is because the bypass circuit is only able to handle a given amount of oil. This forces an additional volume of oil through the engine clearances, causing this increased pressure and temperature.”

Basically, the application in which the pump will be used always dictates the hardware needs. Engine RPM will increase the pump speed, which can lead to pump cavitation. OE pumps are not typically designed for engine speeds beyond the OE red line. As such, engines modified to turn higher RPM need to be equipped with pumps capable of that RPM. The planned revs for LA Thumper are not expected to exceed 6,000.

Once the rotating assembly was fully installed, It is time to check the side clearances between the connecting rods – or is it? Factory spec for a 340 Mopar is .006- to .014-inch. However, it has become trusted that rod clearance is not a huge concern. You can read more about that by clicking here. But, in case you were wondering, we have .020-inch.

While this build could theoretically be content with a standard volume pump, we plan to run a 10w-40 oil and we just feel better with an HV pump. That is why a Melling HV-72 pump was selected. High-volume oil pumps typically flow about 15- to 20-percent-more oil than a comparable stock pump.

With the rotating assembly safely nestled into position, the Melling pump is primed and mounted.

Retaining the oil for our Melling pump will be a Milodon oil pan (P/N: 31590). Milodon considers this a road race oil pan. It has an 8-quart capacity but hangs no lower than an O.E. pan. The Milodon pan has sump kickouts that increase oil capacity while still offering ample ground clearance. We also plan to incorporate a Milodon windage tray and you can read more about these parts by checking out this article.

The Build Goes On

This is just the beginning of our assembly process. We’ll be covering many aspects of the process in various articles to help you guys. Check back often for updates and to see what’s going on with LA Thumper, our small-block Mopar.