GM 602 and 604 Crate Engines

Q: What is the recommended engine warm-up procedure?

Recommended Engine Warm Up Procedure
  • Check All Fluid Levels
  • Cover Radiator to assist the warming process
  • Start Engine and Maintain a Low RPM Level (under 1200) for 30 to 45 seconds making sure that oil pressure is over 40PSI
The low RPM period is to allow the lifters to pump up decreasing the chance of rocker arm misalignment
  • Raise RPM to 1300 to 1500 until water temperature gauge begins to move
  • Check for any fluid leaks
  • Once The Water Reaches 140 Raise The RPM And Oscillate It Between 1600 to 2000 RPM
  • Let the water raise to 215 to 220 degrees before removing the radiator shield----water should then lower to 180 to 190 or less
  • Continue running until oil temperature is a minimum of 150 degrees


You may have to repeat covering the radiator and climbing the water temp to achieve satisfactory oil temperature


When Outside Air Temperatures Are Below 70 Degrees A Torpedo Heater or Other Similar Device Will Be Advantageous To Your Success

Q: How do I bed down my engine for off-season?

First and foremost—if you are not storing your engine/car in a garage that is heated 100% of the time you need to get all the water out or install antifreeze in the system NOW.
Draining the block can be done through the drain plugs located at the bottom center of the block (just above the oil pan).

We recommend putting at least a gallon of antifreeze in anyway. **IMPORTANT: Antifreeze is NOT recommended to race with but insures against freeze failures and adds some rust inhibitors.

If your plan is to drain the system dry for the winter then do that after the fogging process **IMPORTANT: If you are going to do an antifreeze mix, do it BEFORE fogging.

Fogging Process
Disconnect the feed line to your fuel pump and run a hose from the pickup side of the pump into a fuel jug with quality gasoline (AV gas or 93 octane pump gas). It is also recommended to mix Marvel Mystery Oil into this gas or 2 stroke oil.
(Use the HIGH side of recommended amount by manufacturer.)

Place the fuel jug into a safe location away from headers.
Then warm the engine up to operating temperature.

After the engine is warm begin drizzling straight 30 wt. motor oil down the carburetor at a high idle (1300 to 1500).

Once the garage becomes filled with smoke increase the stream of oil, and choke the engine out with oil.

Next, take several oil soaked rags and stuff them into the ends of the headers.

If you want added security remove the rocker arms so all the valve springs will be relaxed.

If you used an oil-mixed gasoline for your fogging process and made sure the secondary side of the carburetor was also flowing fuel during fogging, then there is no need to do any further carburetor bedding—but some like to remove the carburetor drain and fill with WD-40.

When wakening the engine, remove the spark plugs and spin the engine over a time or two to release any excess oil; then prime the oil system, and reinstall the same plugs to initially fire the engine.
You will need to change the spark plugs after you warm it up and clear the winter oil away.

This process does not take long and will help to insure your engine will wake up the same way it went to bed!

Any questions? Feel free to call or e mail Brad TODAY!

Q: What should I know about the GM 604 Retrofit Bee-Hive Spring Kit?

The “new” GM upgrade keeper and retainer package may have some clearance issues when used with the old style rocker arm. The old style rocker arm was used on engines built prior to 2010 however could possibly be on any 604 due to replacement of warn or broken parts.

The “old style” rocker can be identified by its thrust washers beside the roller. New style rockers have a one piece roller that incorporates the alignment of the rocker without thrust washers. In all cases it is recommended to check for clearance between the rocker and retainer at full lift during installation.

Q: Proper Oil Level for GM 602/604

With the use of more expensive and exotic oils some racers have a false sense of security and do not check oil on a regular basis. This is a dangerous practice and it is stongly recommended to put the following procedure into your weekly maintenance schedule or pre-race prep.

  • Using the oil level inspection plug located on the left side of the 604 oil pan —make sure you can see that oil is near the hole.
  • Reasonably level the engine front to rear and side to side
  • Warm the engine to operating temperature
  • With the engine level, warmed up, and running at idle remove the oil level inspection plug and measure oil level.

We recommend the level to be 3/8 to 5/8 of an inch below the female threads of the inspection hole.


  • On tracks with extremely long straight-aways 1 additional quart may be needed to maintain a safe level.
  • Over filling under normal conditions will overheat the oil and cut power significantly
  • Engines with oil coolers MUST be checked running
  • The inspection plug for the 602 is on the right side of the pan and both 604 and 602 inspection plugs are higher than the centerline of the pans.
  • Do not confuse the inspection plug with the drain plug as they both have a 9/16 wrench head.

Q: New Engine Start-Up

The following is recommended by Race 1 for all new crate engines from GM

Special Note: The engine will not break in properly without a load on the crankshaft.
  • Avoid unnecessary run time.
  • If a dyno is not available go to the race track and run several ½ throttle laps until oil temperature is over 150 degrees and then run it as you would race it.
  1. Complete the Race-1 recommended new engine check list.
  2. Prime the oiling system with a pressure tank or a drill operated primer that installs in place of the distributor.
  3. It is highly recommended that one of the above mentioned are used for the initial prime.
  4. Spinning the engine over with the starter is NOT recommended and may cause early engine failure.
  5. We recommend priming the engine with Joe Gibbs BR30 or BR50 dependent on ambient temperature a 50/50 mixture is safe for all temperatures and preferred by Race 1>>> We also recommend a Wix racing oil filter.
  6. After the prime is complete —-starting the engine as soon as possible is recommended.
  7. Start the engine check for oil pressure immediately – check for any leaks immediately.
  8. Check that timing is near 32 degrees—–final timing adjustments should be made after the engine has reached operating temperature.
  9. Run the engine at varying rpms between 1500 and 2800 until water temp is over 180 (cover radiator to speed the warming time).

Q: New Engine Check List

All information below is a recommendation from Race-1 - not necessarily from GM

  • Remove rocker arms and lubricate roller (604)
  • Check torque on rocker studs (604)—-50 to 58 ft lbs
  • Check torque on head bolts —65 ft lbs (No specific order is necessary)
  • **special note** the 2 short bolts adjacent to the factory seal bolt should be checked at a reduced torque 60 to 61 ft lbs recommended
  • Reinstall rocker arms adjusting valves and locking the posilocks in the appropriate manner. (see 602/604 valve adjustment)
  • Check rear galley plugs above camshaft ¼” square
  • Check head plugs on the side of the heads in between ex. Ports 5/16 square
  • Mark desired timing lines on the balancer
  • Install oil pressure fitting
  • Grind the RF middle (long) timing cover bolt (604)
  • This is the long bolt on the fuel pump side and it will interfere with many water pump set ups—-remove the bolt and grind ½ of the head –reinstall
  • Check oil pan bolts and rear studs also rear seal housing fasteners
  • Turn the Breathers—shield should be towards the front of the engine.
  • If additional security and performance is desired the valve springs can be removed for testing and installed height can be checked
  • ***Check Intake Valve Date*** intake valves with a date code of 7-13; 8-13 and 10-13 are recalled by the manufacturer and are not recommended to be used in a 604 circle track engines ----- the date code is located on the tip end of the valve, the retainer must be removed to expose the date

Q: Broken Flywheel Bolts

We have seen several engines with broken flywheel bolts in recent years. The blame is immediately placed on the bolt, and that is partially correct. The actual cause in most cases is the length of the bolt and not the grade or quality. A common length bolt to be used is 1 ¼ inches in length and when used with a Bert flywheel and no shims will be too long. Even with a washer under the head of the bolt, in most cases this will be too long.

In ALL installations the bolt length should be verified to be correct.

  • 1) begin by measuring the depth of the hole and the thickness of the flywheel–add those two dimensions and subtract .100” (little less than 1/8”) and verify the total thread length from your calculation.
  • 2) Double Check:
    • Install the flywheel and torque the bolts to 65 ft. lbs.
    • Remove the bolts and inspect the first thread on the bolt.
    • If the bolt has a drag when being removed –chances are it is too long.
    • If the first thread is mushroomed chances are the bolt is too long.
    • A bolt that is too long by 1/16 to 1/8 of an inch will appear to be tight but in actuality is not, and will shear (break) because of constant side loading.

NOTE: Manufactures have many different tolerances and styles—the example given above is what we have found for a BERT flywheel used on a GM crate engine that is externally balanced (602–604). ALWAYS VERIFY YOUR PARTICULAR APPLICATION!!!!

Q: 604 Broken Spring Shims

The factory spring shims in the 604 that commonly break are actually called locating shims and serve multiple purposes.—-some racers refer to these as retainers which is an incorrect term. The retainer is at the top of the valve spring and is entirely a different subject. The locating shim commonly breaks for several reasons.

  • 1st Harmonics in the valve train (most commonly on cylinders 5&7)
  • 2nd a stamping burr on the bottom of the shim preventing shim float
  • 3rd uneven seating surface–most commonly caused by a previously broken shim
  • 4th weak valve spring pressure–which permits float, bounce and harmonics

There is what we are calling a “new style” locating shim coming in the latest orders from GM, they are a little bit thicker than the ones we have been using in the past—–not sure if this was produced by accident or possibly to help in the failure rate. These newer thicker shims have raised another concern with us at Race-1.

Since it is now permitted by most major sanctions to install as many aftermarket shims as needed to achieve the minimum installed height of 1.780”——if a competitor has set the minimum installed height at its absolute minimum with the older style (thin) locator and then during regular maintenance discovers a broken shim and replaces it with newer style (thick) the engine could possibly be found illegal.

Q: 602 and 604 Valve Adjustment

“Original” Recommended
604--602 Valve Adjustment

**Positioning of the valve for adjustment**
When the intake valve is closing—Adjust the Exhaust
When the exhaust valve just begins to open—Adjust the Intake
There are other methods but we have found this to work on all engines and leaves less room for mistakes.
**NOTE** If you follow the firing order you will only have to turn the crank ¼ turn between valves once you get #1 in position.

Roll the pushrod between your finger and thumb as if it were a cigar.

At the same time begin tightening the adjuster nut.

The INSTANT that you feel an increase in resistance to roll the push-rod—STOP—that is zero lash.

NOTE this does require a certain amount of “feel.”
By the time you finish your first set you will be a pro!

Next: tighten the adjuster nut ½ to ¾ turn more.

Next: tighten the set screw (Allen)

Next: with your hex key (Allen wrench) and your 5/8” wrench turn both into the stud another 1/16 to 1/8 turn.
This secures the set screw from backing out.

Q: 602 and 604 Timing

  • We recommend that both these engines be set at a TOTAL timing of 32 degrees. NOTE different amounts of timing may be beneficial due to different fuels, exhaust designs and carburetor choices. However, unless dyno testing is available or controlled race track testing we advise 32 to be the number.
  • For dirt late model applications we recommend that the advance curve be locked out.
  • The balancer is marked out in degrees and we highly recommend using the marks on the balancer and NOT a high tech timing light with dial up advance. (keep it simple). **NOTE** the small white paint mark that is near the “0″ groove in the balancer means NOTHING. The groove is 0 (TDC) and actual degrees are marked on the balancer.
  • Total timing is set with the engine hot and at an elevated rpm (even with a locked distributor). The timing actually will retard and this is due to timing chain stretch, be sure to increase rpm until the timing marks become steady.
  • **SPECIAL NOTE FOR MSD DISTRIBUTORS** After the timing is set, align the timing marks with the engine shut off, then remove the dist. cap and validate rotor phasing. The rotor should be pointing directly at either #1 or #6, if the rotor is pointing between terminals, then the pick up coil wires are reversed and must be corrected and the timing reset.

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