Chrysler Air-Raid Siren Maintenance Manual

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The Chrysler 8 cylinder Industrial Engine, which provides the power for the Siren, has been designed and built to high quality standards. With a reasonable amount of care and proper maintenance attention, highly satisfactory and dependable performance is assured.

The following text is provided as a guide in performing such routine operations as can be handled by the Siren operator, as well as containing condensed maintenance information and specifications. In order to maintain the original high standard of performance of the Chrysler engine, only competent mechanics, having access to suitable tool equipment, should be assigned to perform any major repairs.

If the facilities of the user are not adequate, it is recommended that the service department of the nearest Chrysler Corporation dealer be consulted, or write to the Chrysler Corporation, Industrial Engine Division, 12200 East Jefferson Avenue, Detroit, Michigan.



To keep the engine at the highest point of efficiency, it should be frequently checked and, if necessary, tuned up.

The following points should receive attention:

  1. Spark plugs-clean electrodes and porcelains and adjust spark gap to .025 inch.

  2. Inspect and dress, if necessary, the breaker points in the distributor and adjust the gap to .018 inch.

  3. Check distributor cap and rotor for cracks or corrosion.

  4. Inspect condenser lead wire for damaged insulation.

  5. Check ignition timing. (Distributor points should start to open when number one piston is on top dead center, firing stroke.)

  6. Check valve tappet adjustment. (Hot engine-intake .010", exhaust .012". Cold engine-intake .012", exhaust .014".)

  7. Clean sediment bowl and screen on fuel pump and gasoline filter.

  8. Check ignition wires for damaged insulation, or loose connections.

  9. Test battery (reading should not be below 1.225).

  10. Check and adjust carburetor float level. (See carburetor instruction.)

  11. Check manifold heat control valve. Be sure valve operates freely.


The engine is of L-head, 8 cylinder, full length water cooled, 4 cycle type, having a 3-1/4" bore, 4-7/8" stroke and 323.5 piston displacement, developing 140 horsepower.


The pistons as used in the Siren engine are cam ground and of the four piston ring design.

Should it become necessary through normal wear to replace pistons, pins or rings, it is always advisable to check the cylinder bores for out-of-round and taper. If the check of the cylinder bores show that they are more than .002" out-of-round or tapered more than .0015" it is recommended they be reconditioned with special equipment and fitted to the following specifications.


Fitting Clearance                                                       .003"
(Check with .003" feeler stock '/z" wide.)

Piston Pins

Pin Size                                                                  51/64" x 2-3/4"

Clearance in Piston                                    Thumb Push Fit At 130 Temperature

In Connecting Rod            Bushing Thumb Push Fit At Normal Room Temperature

Piston Rings

Compression Rings (top)
Number Per Piston                                2
Width                                                   1/8"
Oil Control Rings (lower)
Number Per Piston                                2
Width                                                   5/32"
Gap Clearance                                .007" to .015"
Side Clearance in Groove
Compression (upper)                       .002" to .004"
Intermediate                                 .0015" to .0035"
Oil Control Rings                           .001" to .0025"


The camshaft is of "Hi-lift' design which gives greater power output at high speeds and better idling characteristics. It is chain driven and supported by six bearings.

All camshaft bearings, except the rear, are removable but seldom, if ever, have to be replaced. If the bearing clearance is excessive, new bearings may be pressed in place after the camshaft and camshaft bearings have been removed.

Replacement bearings are finished to close limits when manufactured and do not require reaming, scraping or burnishing.

Bearing clearance-No. 1 bearing         .001" to .003"
All others                                          .0015" to .0035"
End-Play                                          .002" to .006"


The crankshaft is of drop forged high carbon steel, statically and dynamically balanced, with eight counterweights and supported by five bearings of steel backed, babbitt, lined, replaceable, precision type.

Very close manufacturing tolerances, make it possible to replace bearing shells without scraping or fitting.

Bearing clearance desired   .001" to .002"
End-Play                           .003" to .007"
Thrust taken by                  Rear bearing


Connecting rods are drop forged from highest quality manganese forging steel with an "I" beam section or design to provide extra strength and light weight.

The upper, or piston pin bushing, is of bronze, with the lower bearing of babbitt, bonded to steel and Superfinished to provide a mirror smooth surface.

Connecting rod bearings are easily replaced by removing bearing caps and bearing shells. Replacement bearings require no reaming or fitting.

Lower Bearing

Bearing clearance               .001" to .003"
Side play at bearings          .006" to .011"

Upper Bushing

Material                              Bronze


With dome shaped heads, the intake and exhaust valves are manufactured from the finest of materials, having high resistance to corrosion, pitting or softening under high temperatures and are Superfinished to provide quieter operation and longer life.

The exhaust valve seat inserts are manufactured from a special hard metal capable of withstanding hard service and are replaceable where the occasion warrants.

The valve springs are of special spring steel, designed so that the heavy end of the spring is placed "up", thus taking the load off the tappets at the beginning of spring compression. When replacing, the closely spaced coils should be installed at the top, or in the recess of the cylinder block.

The valve guides, which insure the valves seating properly, are finished to precision limits and, with the valve stem Superfinished, a practically frictionless surface results.

The valve tappets, which ride the cams of the camshaft and give the valves the correct action, have self locking type screw without lock nuts and any adjustments to the tappets should be made with the engine running and at normal operating temperature.

Stem diameter                              .340" to .341"

Valve Guides

Guide diameter to ream after installing
     Inlet and exhaust                     .3425" to .3435"

Stem clearance in guide
     Inlet and exhaust                    .0015" to .0035"

Valve Seats

Angle                 45
Width               .058"

Valve Springs

Spring pressure, compressed to 1-21/32"              129 to 137 lbs.
Spring pressure, compressed to 2-1/32"                  52 to 58 lbs.

Valve Tappets

Clearance for valves (engine hot)
     Inlet               .008"
     Exhaust         .010"

Valve Timing

Valve tappet clearence to check timing
     Inlet               .011"
     Exhaust         .014"
Inlet opens          6 or .017" B. T. D. C.
closes   12 or .068" A. T. D. C.

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