Rebuilding an early Hemi engine

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by: Jon
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An "Early Hemi" engine being machined at the start of the rebuilding process.

The early Hemi engine is being rediscovered by enthusiasts all over the country. For some, nothing can match the class and power of an early Hemi under their hood.

However, before tackling an early Hemi engine rebuild, several factors must be considered. The high cost of Hemi rebuilds, and the difficulty in acquiring parts, plays a significant role for most rebuilders.


[edit] Cost and parts availability

It will cost 2 to 4 times as much to rebuild an early Hemi than it will your average engine. This difference in price has been the cause of many a Hemi just sitting in the corner of a garage somewhere instead of rumbling down the street in all its glory. However, it is very rare to find an early Hemi in a wrecking yard that can be rebuilt.

Depending on the size and location of the motor, expect to pay anywhere from $300 to $1500 for an engine to rebuild.

After price, the second item you need to be concerned about when rebuilding a Hemi is parts availability. Stock rebuild parts are widely available. However, performance parts for some of the less popular Hemis can be a real challenge to find. Especially the DeSotos -- performance parts for these motors are virtually non-existent. Some factory equipment was supplied way back when, but it's very difficult to come by, and quite expensive. For example, a DeSoto factory dual quad manifold with carburetors and linkage intact could fetch $2000 or more. Limited performance equipment is available for the Dodge Hemi, but far more parts are available for the Chrysler 331-392 series than any other. The good news is that as these engines are being rediscovered and as they become more popular, manufacturers are beginning to re-introduce performance parts they stopped making 20 or 30 years ago. Newer companies are providing parts and services for the early Hemi enthusiast, and more are sure to follow.

The Chrysler early Hemi had a cast iron block. Thin wall casting techniques had not come into practice in the early 50's, so these motors were quite heavy for their size. All were produced with 2 bolt main caps, and forged crankshaft and connecting rods. Most engines came with cast aluminum pistons and hydraulic valve lifters, with the exception of some of the high-performance versions, which left the factory with forged pistons and solid lifters. These motors can be identified by four bumps in the valve covers between the spark plugs.

[edit] Parts interchangeability

Each Chrysler division (Chrysler, Dodge, DeSoto, and Plymouth) produced their own version of the Hemi. Only a few specific parts will interchange, including the following:

  • All '51-'53 Chrysler front covers will fit all DeSoto engines.
  • All '56-'58 Chrysler front covers will fit all Dodge engines.
  • Dodge high block connecting rods may be used in the DeSoto high blocks despite wider side clearance, but DeSoto rods must be narrowed slightly for use in Dodge engines. The lengths are close enough to be compatible: Dodge 6.618", DeSoto 6.625".
  • Distributors, oil pumps, and bellhousing/starter mounting flange plates will interchange, except for the extended block versions. Keep in mind that these flanges vary in thickness depending on the transmission used.
  • Valve stem diameter is the same in all engines and length is very close, so the larger diameter valves from the bigger engines can be used to improve the breathing of the smaller motors.

Within divisions some parts will also interchange. Although some low block and high block cylinder heads will interchange, care must be taken when considering certain combinations. For example, 392 heads are wider than earlier low block (332-354) heads, allowing the earlier intake manifolds to be used on stock 392’s, However, when using early (low block) manifolds and heads on a 392 block, spacers must be used because the higher deck height of the 392 will align the intake manifold mating surfaces too far apart. Conversely, 392 heads won't work on a low block (331 or 354) Hemi unless a log manifold is used, because the lower deck height of the 331-354 combined with the longer intake runners in the 392 heads will align the intake manifold mating surfaces too close together to use a standard manifold.

There are also dowel pin diameter considerations to deal with as well as mismatched coolant passages in the lower corners with some head/block configurations. As an example, ‘56 low block (354) heads will not easily fit on a ‘54 or earlier low block (331) for these very reasons.

DeSoto and Dodge heads interchange between high and low blocks without any major difficulty. The differences between the low and high deck heads are combustion chamber, valve, and port sizes. With the DeSoto and Dodge the intake manifold must be matched to the block being used. A low deck manifold is required for a low deck block, and a high deck manifold is required for a high deck block. A cast aluminum 4BBL manifold for the low deck DeSoto has recently been released, and a high deck manifold will follow. Offenhauser has recently re-released a 4BBL manifold for the low deck Dodge.

  • Hemi heads will fit poly blocks of the same family, but will not fit "A" series poly motors.
  • Chrysler 331 Hemi heads can be used on the 301 and 331 Polys, and 354 Hemi heads can be used on 354 Polys.
  • No camshafts will interchange between low and high blocks of any engine family because of differing lifter bore angles. The incorrect cam can be installed, but the engine will run badly.

The low deck Dodge early Hemi (241 and 270 CI) will accept a later small block distributor with no modifications. This may also be true of the other Dodges.

331 cid 1951 Hemi bellhousing detail

[edit] Transmission choices

The '51-'53 Chrysler 331's (and some of the '54s) had an extended bellhousing cast into the back of the block, which limits transmission choices. Some outfits have reintroduced adapter kits which allow the GM 4-speed to be bolted to these blocks. These adapters are a welcome addition to the parts bin for many enthusiasts. For years, these extended blocks were considered useless (except for spare internal parts) and many of the blocks were trashed by shortsighted hot rodders. DeSoto, Dodge and Plymouth never produced Hemis or Polys with the extended bellhousing.

In '54, Chrysler fell in line with its other divisions and introduced a more conventional bellhousing design, making the installation of modern GM and Chrysler automatic transmissions much easier. However, adapters are still required; they're available from several sources, but be prepared to pay between $300-$400 for a good one.

[edit] Cylinder heads

Hemi cylinder heads were cast iron, as were the intake and exhaust manifolds. 2 bbl. and 4 bbl. versions were available while the high performance line usually had a dual 4 bbl. low rise manifold equipped with early Carter WCFB carbs.

[edit] Hemi parts suppliers

[edit] Resources

[edit] Related Crankshaft Coalition Wiki articles

[edit] External links

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