Every kid learns early on that you can't put a square peg in a round hole, and that early learning carries on right up until that kid learns about tools. Yeah, give me a milling machine and a lathe, and I'll make it fit like a glove. With a little problem-solving thought and the right approach, quite a range of compatibility issues can be overcome. One such problem can be encountered with the small-block Chevy engine. These engines are famous for the compatibility of parts over a production run spanning decades. One area where this compatibility doesn't hold true in a major way is in blocks and cranks before and after the production change to a one-piece rear main seal.
The one-piece seal assembly uses a redesigned crank and is sealed by a full-circle oil seal mounted to a seal retainer. This running change all but eliminated rear seal leakage, and is indeed an improvement over the older conventional two-piece design. Where the opportunity presents itself, my own preference is to go with the improved later setup. However, many performance cranks are only offered in the early style, which presents the old square peg problem when you want to use such a piece in a late-model block. Fortunately, by applying some design thought and manufacturing talent, this problem has been overcome through the use of special-built adapters. These adapters are not new, but some designs work better than others.
We recently ran into just this problem in one of our small-block Chevy builds. We went with the late-model truck block because they are abundantly available with four-bolt mains, and feature thrust-plate cam retention. The compatibility issue came to play when we found a sweet deal on a really nice Lunati lightweight forged stroker crank. This particular crank was the early style, designed for the standard early block. We knew that Enginequest made an adapter to marry these two incompatible components, but also heard of leakage trouble with some adapter installations. The Enginequest adapters are CNC-machined from billet aluminum, and are a staple of the tough production-rebuilder marketplace. The Enginequest part seemed like the best solution for our small-block build, but we had no previous experience with this particular product. The simple and sensible alignment procedure, and the fact that the part bolted on with no issues, gave us confidence that it would do the job, while bone-dry running on the dyno during break-in confirmed the value. This product works.
Our 350 Chevrolet small-block is a nice late-model four-bolt main truck block. These blocks are designed for the superior late-style one-piece rear main seal. The problem is, our trick Lunati crank is the older two-piece seal type, which won't work with this block style.
The solution for our problem is a billet seal adapter from Enginequest. The adapter comes with all the required hardware for installation, allowing an early-style crank to fit in a late block.
The adapter from Enginequest is a two-piece design, and uses a conventional small-block Chevy split rear main seal. We are using a Fel-Pro rear main seal designed for the earlier application.
The seal isn't the only difference between the later one-piece rear seal blocks and the earlier two piece seal setup—the oil pan is also different at the rear cut-out. Enginequest has two seal conversion kits, number RSH349 to take the earlier pan, and number RSH350, which is shaped to take the later pan normally used with the factory one-piece seal block.
The seal retainer makes up the rear mounting flange surface of the pan rail, and provides the rearmost two fastener provisions. The Enginequest seal retainer uses two special studs in these locations.
For a leak-free installation, the rear seal has to be perfectly co-centric with the seal. A simple fixture, Enginequest alignment tool number AT350, mounts in the rear main cap to index the installation of the seal adapter.
The rear main cap is installed over the alignment tool, and is torqued into place. The rear portion of the alignment tool is sized to fit the bore of the seal adapter, ensuring it is perfectly centered with the crank.
We went through a quick mock-up installation to make sure everything will go together as it should, and then put a thin film of silicone sealer on the mating surface of the block where the adapter will mount. This will prevent any oil seepage once the conversion is completed.
The adapter is mounted to the block, but the attachment bolts are just seated, not torqued. This will let the adapter float to center itself on the alignment tool as the upper half of the adapter is bolted in place.
With the seal adapter clamped on the alignment tool, the assembly is perfectly centered with the main. The seal adapter can be rotated slightly to level it to the pan rail at the left and right, and then locked into place by tightening the
If just the right amount of silicone sealer is used on the mounting flange, a slight ooze of excess sealant will squeeze out all around the adapter. Clean the excess sealant at the parting line where the adapter halves come together.
Now a standard early Chevy rear main seal can be installed as normal in preparation for crank installation. Make sure to lubricate the sealing lip surface, and that the lip of the seal faces inward toward the crankcase as shown.
The finished installation proved to be bone dry on our small-block, not spilling a drop of oil when we ran this engine on the dyno. This product works!