Hemi Engine Rebuild

Rebuilding an Early Chrysler Hemi is usually a straight forward, relatively simple operation as there is a complete range of rebuild parts available these days.

The Engine Block

Firstly, dis-assemble the engine into it's appropriate sub-assemblies like heads, crank, external accessories, etc).

Think about a labelling system for the parts you have dis-assembled so you know what goes where when re-assembling.

The engine block should be completely stripped, steam cleaned, hot tanked, de-burred, measured and then machined.

Unless the cylinders look like "new"... it will be necessary to have the block re-bored, also check the top deck for trueness, although the inbuilt stiffness of the bottom end usually keeps the main bearing tunnels good and straight.

The block castings are usually in good shape but you will need to grind where the casting halves meet and inside the lifter gallery and the crank area to aid in oil drainage.

Look closely within the water passages as often casting debris forms between the cylinder wall and the outside wall of the block and will cause over heating problems later if it is not cured now.

Remember to clean all of the oil passages.

Camshaft

Camshafts used and new are available.

Hemi parts suppliers do offer new camshaft blanks for owners to have their own custom grind to suit their particular application.

A good street camshaft will yield around 280 - 290 degrees total duration.

Bearings

Main and Rod Bearings

Main bearings in a range of sizes are now available these days whether you require a set from standard to .030 undersized.

Unfortunately there is no compatibility of Main bearings between the three Chrysler HEMI engines.

Rod bearings to suit your particular application are also available.

Cylinder Heads

Valve Guides & Valve Seats

The heads will need basic reconditioning, by being cleaned, acid dipped and bead blasted prior to machining.

The ports are already large, needing only casting flash removal to relieve around the bulky valve guide bosses to pickup the breathing flow in an unblown engine.

You may wish to open the ports by grinding but do not grind in the area where the valve seat is located.

Valve guides are to be replaced and hardened seats should be installed and the seats given a multi-angle cut prior to final surfacing.

Piston Choice

Forged or Cast?

Piston choice is going to vary, according to personal preferences in the set up of the engine and your particular application for the engine.

Unless the engine is to be kept under the six grand maximum, the smart move is to use a set of tried and true forged pistons.

Fortunately, pistons both cast and forged are available from a variety of manufacturers, Ross, Arias and Venolia, just to name a few.

Cast pistons should be used for street naturally aspirated and mild supercharged engines.

If additional horsepower is planned in a hemi rebuild consider using forged pistons as a must.

Connecting Rods

Stock or Alloy?

Stock connecting rods are strong enough for street applications.

They should be given a magnaflux job, the rod beams ground and the entire rod bead blasted with heavy duty rod bolts fitted.

New piston pin bushes and a re-machine of the rod tunnels with the big end re-sized and the small end re-bushed will bring these units back into serviceable condition.

Competition or supercharged or hard running engines will need specialist connecting rods, like Child and Alberts or Venolia alloy rods.

Forged aluminium connecting rods should be left for race applications rather than to be used for street use.

Rocker Arms, Rocker Shafts, Valves, Valve Springs and Pushrods

Rocker arms and shafts are durable units and the stock set up is able to be used.

The stock rocker arms should be magnafluxed so that you can determine whether there are cracks and the bores should be inspected for damage.

With hard chromed rockershafts, good rocker bores and adequate oiling the standard rockers will work well.

Aluminium rocker sets that have been re-manufactured are also available.

Stock valve springs are OK and should be used with a low lift camshaft.

Stainless steel valves should be used and special oversize valves are available and high performance valve springs are preferred with lumpier camshafts.

Stock pushrods are also OK to be used with hydraulic lifters but when using adjustable pushrods these can only be used with solid or roller lifters.

Custom length pushrods are available from various manufacturers.

Crankshaft

Check the crankshaft for wear and as good security measure get the item magnafluxed.

You may find that the crankshaft will need to be ground.

I believe grinding a worn crankshaft isn't a good idea, as the wheel will cut through the hard skin on the journals and expose the softer steel underneath.

If you give this new surface a hammering the metal will wear rapidly and a ridge will form and may lead to a main bearing disaster.

If a good crankshaft is hard to locate (especially a 392 crankshaft) then find a machine shop that will tuftride the journals again or have the journals hard chromed, depending on your budget.

Remember to tap the rear flange holes to 1/2-20 to eliminate the need to use nuts on the flywheel bolts.

Used Stroker crankshafts are often found and are still available but the used ones that I have located in the past have often found to be cracked and unserviceable.

They have taken a "horsepower pounding" in a previous life.

For more information regarding Hemi Rebuilds don't forget to purchase Tex Smith's "The Complete Chrysler Hemi Engine Manual" available now from Graffiti Publications.

We acknowledge that some of the information we have used is from an article in "Street Machine Magazine Performance Series" including details contained within "The Beginning - Hemi Newsletters", "Bob Bailey's Hemi Headlines" and the "USA Early Hemi - Poly Newsletters".