Click to Print

Technical Advices > Engine Preparation, Assembly Environment, Documentation and Testing

1.1 - Using the correct components.

As with any project, one of the most important steps is properly identifying the correct components that need to be incorporated. This process starts by carefully outlining the goals to be achieved. What the intended use of the engine is will guide you as to what may need to be done.

If a motor is for a street car, with a moderate increase in power, then you may choose to use some standard components. If you are building a motor for a "historically" correct restoration of a car, such as an Abarth 750, then you will have a different focus. On the other hand, if your intent is to build a motor for competition use then you will want to use a great many specialty parts, to insure both good power and reliability. This means buying the best possible parts available for the purpose that your budget will allow. As Scuderia Topolino deals principally in competition parts and services, most of what I discuss will have to do with developing competition engines.

It goes without saying that, if you are building an "all-out" competition motor, you have already spent some time developing the rest of the car. This means chassis preparation, gear ratio analysis, and brake development. All too many people start a race car project by building the motor first. I do not recommend this. My suggestion would be to build the car first and get it to handle correctly. This does not require a high horsepower motor and perhaps a standard motor could be used to do this development. This does not require a great deal of horsepower until the car is fairly well developed. Only then do you need a powerful motor to test the ultimate limits of vehicle development.

Once you have identified the components that you need, they should be assembled and laid out to make sure that everything that you need is there. Then each component must be double checked to make sure that it meets the dimensional and quality standards you have set. Do not simply assume that the part is "right", just because you bought it from a company that has a good reputation. Everyone makes mistakes, so make sure that your parts are made to specification before using them. Making the proper measurements means having your own measuring tools or at least having access to someone who can make the measurements for you.

1.2 - Preparation

Once you have assembled all of the parts and determined what you project is going to be, make a list of all of the operations that have to be performed in preparing all of the components that have to be assembled. For purposes of illustration, I will go through the steps involved in building an Autobianchi 1050 motor, assuming that everything has to be checked, measured, and renewed. Many of the steps will applicable to other engine combinations, including Fiat and Abarth 750, 817, 843, 847, 903, 965, and 982cc motors. For specialist Abarth "Bialbero" motors, those with double overhead camshaft installations, there are some other special considerations.

The list of operations below is simply an outline, and not particularly in any order. Some items marked with an "*", may be done during assembly. As I work through each particular area of the motor, in following chapters, I will expand on each of the subjects in the outline. It goes without saying, that you are going to start out with a block that does not have any obvious internal, or external, damage. The fact that it is well used, or rusty and dirty, is really inconsequential.

  1. Hot tank block and head. Not a chemical hot tank, as you do not wish to destroy installed cam bearings.
  2. Crack-test and pressure-check the engine block that you wish to use.
  3. Check block "squareness".
  4. Check block for main bearing and cam bore alignment and bore diameter size.*
  5. Check crankshaft for cracks and bearing size.
  6. Regrind main or rod bearing surfaces if required.
  7. Clean all crankshaft passages.
  8. Check camshaft for straightness.
  9. Modify front cam bearing for oil pump drive oiling.
  10. Check lifters for proper lifter surface curvature.
  11. Check lifter bores for damage and clearance.
  12. Check push rods for straightness.
  13. Check connecting rods for straightness.
  14. Check connecting rods for bore and pin size*
  15. Check pistons for proper bore and pin dimensions.
  16. Check piston/rod combination for proper deck height.*
  17. Check rockers and rocker shaft for proper alignment and clearance.
  18. Check valve guide/valve stem clearance.
  19. Install new valve guides if required.
  20. Check valve/seat for proper seal
  21. Calibrate valve springs
  22. Check valve installed height.
  23. Check valve spring for coil bind.
  24. Check valve spring seat and "over the nose" pressure.
  25. Check rocker arm geometry.
  26. Check for correct push rod length.
  27. Check center cam bearing alignment and oil feed orifice to cylinder head.
  28. Debur block inside and outside.
  29. Remove any excess block material not required.
  30. Bore/Hone cylinders for new pistons
  31. Align hone main bearing bores.
  32. Debur, port and surface finish all head surfaces.
  33. Surface block and cylinder head.
  34. Install new cam bearings if required, line bore and check clearance.
  35. Check camshaft for clearance with connecting rods.
  36. Check main and connecting rod bearing shell thickness.
  37. Debur any sharp edges on piston crown, check valve pocket size, depth and radial clearance.
  38. Check piston ring to ring groove clearance.
  39. Check piston ring end gap in bore.
  40. Check piston to valve clearance at 20-30 deg. BTDC and ATDC.
  41. Double check main and rod bearing clearance.
  42. Check crankshaft thrust clearance and replace bearing if required.
  43. Install pilot shaft bushing/bearing in crankshaft.
  44. Balance crankshaft, flywheel, pressure plate and front pulley/nut.
  45. Balance pistons/rods.
  46. Determine the cubic capacity of each of the cylinder head chambers and equalize.
  47. Determine the cubic capacity of each piston crown or depression and equalize
  48. Check clutch assembly clearances
  49. Make sure that all gaskets, seals and other items are available

1.3 - Motor Assembly and Environment.

After you have all of the components individually prepared, cleaned and inspected, you are ready to begin assembling the motor. If there is anything that is not ready, then you will not be able to finish the job. That is not the end of the world, but it will simply mean that you will have to stop at some point, and then continue later.

The room that you use for engine assembly should be clean. By this I mean that if you have access to a dust free environment, use it. It does not have to be a "cleanroom environment", but this area should absolutely not contain any machinery or abrasive materials. If there is reason to modify any component, then this should be done outside of the assembly room, and the part thoroughly cleaned before it is returned to the assembly room.

Assembling a motor is like a surgeon doing a major operation. There is a certain sequence and order to be maintained.

Make a running record of all specifics about the motor as it is being assembled. This includes numbering and dating the block and head used. This will assist you, later on, when the engine needs to be rebuilt again. As you then inspect the motor it will give you a better understanding of the things you find when you disassemble the motor. Your record keeping should include all clearances maintained and torque, and/or stretch, settings for all fasteners in the motor.

Remember that we are assembling a competition motor, which will be subject to severe stresses. These records will be vital to make sure the components still comply with the original component specification.

As an example, you will want to make a record of the overall length of each connecting rod bolt, and the location in the motor. As these bolts are designed to stretch up to 0.005-0.006 inch (0.1-0.12mm) when properly installed, you will want to make sure that they are within 0.0005 inch (0.0127mm) of their original length when removed. If they are not, then it is an indication that they have been stressed beyond their elastic limit and should be replaced.

1.4 - Post Assembly Test Procedure

Testing a motor is all about "comparison". Sure it would be nice to say that a motor develops 115 horsepower. The problem is, by what standard? Actually the finite number of horsepower is not nearly so important, as whether improvement is being made. Even "improvement" can have different meanings.

Therefore, what is important is to make sure that the same test procedure is used in all cases. Only then can you be sure that an improvement was made or not.

By preference, here is a list of performance testing options.

  1. Engine dynamometer with a temperature/humidity controlled environment.
  2. Chassis dynamometer
  3. A stop watch.

By far the best test procedure would be to test each engine build on the same engine dynamometer. Here you have control over as many testing parameters as possible. You will be able to asses a multitude of performance parameters, not the least being torqued and horsepower.

The problem is that 95% of amateur racers will not have such a device. However, I am sure that they would have access to a chassis dynamometer. The chassis dynamometer has the additional advantage of being able to test the entire driveline package. So if you are also looking at reducing parasitic losses in the power transmission system, it can be of help there as well.

Finally, find a track where you can test. An accurate stop watch should be able to tell you if you are turning better lap times or not. You may not fully understand the reason for the better lap times.

As you can see each successive testing option introduces more variable that have to be dealt with. On the engine dynamometer "driver" variables have no impact, as compared to track testing, but each will tell you different things.

Next you must develop a repeatable testing procedure. Here are some of the steps that I include in my procedure.

  1. Engine Run In
  2. Carburetion settings
  3. Power Runs

Engine Run In - To begin with each motor should be "run in" for a period of 20-25 minutes, in an RPM range from 2500-4000 RPM under light to moderate load with no more than 26 degrees total ignition advance. I recommend that this run-in procedure be conducted using a non-synthetic, petroleum based oil, with sufficient levels of zinc and phosphorus. This is vitally important to ensure that items such as camshafts and lifters are properly broken in. DO NOT run the engine at idle for extended periods of time. It goes without saying that you would monitor oil pressure, oil temperature and water temperature during this run-in period. See Section 3.2.2 Oils and Additives for more information on oils with the proper levels of zinc and phosphorus.

Even though I have carburetion settings as the next item, you should at least make sure that in the run-in RPM range the engine is running at an air-fuel ratio of around 12:1-13:1. If either too rich (less than 11:1) or too lean (more than 14.7:1) then this must be addressed BEFORE continuing with the run-in procedure. To rich a mixture may cause a decrease in cylinder lubrication and cause piston damage, and too lean may bring on pre-ignition or detonation.

Once this run in procedure is completed then the cylinder head should be retorqued, and the valve clearances re-set to the camshaft manufacturer’s specification.

Carburetion Settings - The most common carburetion will be either a single two barrel downdraft carburetor or, as used with the PBS 8P and TCR heads, a set of dual side draft carburetors. These could be manufactured by Solex, Del’Orto or Weber.

In the range of 2500-4000 RPM the engine will be running on either the "cross over" orifices or the main metering system. For the run-in procedure you need only concern yourself that each cylinder is operating in the correct air-fuel mixture range. In the next section I will go into more detail the carburetion tuning options for maximizing performance. For a complete discussion of carburetion settings, please refer to section 3.4.1 Carburetion and Fuel Injection.

Power Runs - Here is where we find out what the optimum settings are for horsepower (and of course torque). This will be a combination of a multitude of settings, including ignition, fuel, cam timing, valve settings and other variables. What is important is that you develop a methodology that can be repeated so that improvements can be noted.

You must make sure that certain basic parameters are properly adjusted before any power runs are attempted. These are:

Oil Change - If you wish to change to synthetic oil, then this would be a good time. Again, make sure it is oil with elevated levels of zinc and phosphorus (1200-2000 PPM).

Camshaft timing - Usually set during engine assembly (for chain driven camshafts this is usually 4 degrees advanced).

Ignition Timing - Use a total advance of 28 degrees as a starting point.

Fuel Pressure - Maximum pressure of 3-4 PSI, with adequate flow.

  1. Carburetion Testing - Optimizing carburetion settings for Idle, Cross-Over, Full Throttle and Acceleration.
  2. Venturi air flow optimization.
  3. Ignition timing variations.

Power runs may combine changes in any of the above elements to finalize what the best combination of settings may be. It is important to maintain good air-fuel ratio measurements during all of these power runs, as changes in ignition timing will affect carburetion settings and vice-versa.

For more detailed information on each of the elements involved in power runs, please consult applicable subject categories.

As before, recordkeeping is a vital element of the testing methodology. Without it you will not be able to cross-reference your findings and get the best benefit of your testing.


Specialist Services
Calendar and Race Reports