TECHNICAL TERMS OF THE CAMSHAFT, VALVE TRAIN AND TIMING,
AND HOW TO TIME YOUR CAM.

LIFT:
This can be cam lift or valve lift.  The latter being the cam lift multiplied by the rocker ratio. 

DURATION:
This is the number of the camshaft degrees that the valve is off its seat.

In these data sheets, Piper give you this figure as well as the timing figures.  To calculate the duration, add the timing numbers together and add 180. 

Example:  a cam with timing of 26/67 added, totals 90 plus 180, gives 270 degree duration. 

OVERLAP:
The number of degrees at the crankshaft, that the inlet and exhaust valves are open at the same time.

To calculate the overlap, add the opening number of the inlet cam to the closing number of the exhaust cam, ie the first and last numbers of the cam timing.  Using our same example of 23/67 inlet and 67/23 exhaust ( usually referred to as 23/67 - 67/23), add together the first and last numbers (23 and 23) and the total is the overlap.  In general terms the larger the number or the greater the overlap the hotter the cam.

CAM TIMING:
The position of the camshaft in relation to the crankshaft.

This is expressed as the number of degrees that full lift occurs after top dead centre (TDC)  In the case of the inlet and before TDC for the exhaust.  This figure is included in the Piper technical data, but to calculate this, take the duration figure and divide by 2.

Example:  With an inlet cam of 23/76, the duration is the addition of these two numbers, plus 180, equals 270.  Then divide by 2 resulting in 135.  Deduct the number of degrees before TDC that the valve has started to open, ie 23 degrees - the result is 112.  The valve is correctly timed with full lift 112 degrees after TDC.

VALVE TIMING:
The opening and closing position of the inlet and exhaust valves relative to the crankshaft.  As figures before and after TDC and BDC.

CAM CODING:
The Piper cam 'CODING' is designed to assist selection.  The number of the code indicates the duration period of the opening of the cam.

            255 Profiles            Improved road and suitable for towing

            270 Profiles            Fast road - lightly tuned engines

            285 Profiles            Fast road for modified engines

In most cases, the above profiles can be fitted without any machining.

            300 Profiles            Rally, hill climb and short circuit racing

            320 Profiles            Race, hotrod

            330 Profiles            Race

CAM KITS:
Wherever possible, a Piper cam kit should be used as this gives the advantage of buying all the necessary components correctly matched, and ensures compliance with the warranty conditions.

THE RULES OF SUCCESSFUL CAMSHAFT INSTALLATION:  

Research and experience has shown that most cams that wear out start to fail during the first few moments of operation.  Many cams are irreparably damaged, even before the engine is started, because the basic rules of camshaft installation and 'break in' have not been followed.

The cause for premature cam and follower failure is metal to metal contact between the follower and the lobe.  Should this contact occur due to lack of lubrication and excessive high pressure due to valve train interface shearing the oil film, then 'galling' will take place.  When this happens, metal is transferred from the follower to the cam lobe or vice versa in a process comparable to welding.  Microscopic high spots, which are present on all machined parts, become overheated due to friction and pressure and bond together, tearing sections loose from the follower or lobe.  These pieces of metal remain attached and create further local overheating during the following revolutions of the camshaft and lead to the ultimate failure of the affected components.  The following procedure should be used to ensure a long and trouble free life from the camshaft and associated components:

1.         New Piper cam followers must be used.

2.         Coat cam and followers generously with Piper cam lube.

3.         Check the entire valve train to ensure that no interference is occuring.

Spring Boxing:  Valve springs should show .030" clearance between the centre coils.

Valve to piston contact:  Valves should have a minimum of .060" clearance from the piston.

In the case of twin cam engines:  Possible 'valve to valve' contact should be checked.

4.         To ensure that Piper Camshafts reach the customer in the same condition that they leave the factory a special rust inhibitor coating is used.  This must be removed by washing in paraffin.  Do not remove the black phosphate coating from the cam lobes.  This is in aid to 'running in' cam and followers.  After washing, it is essential that the cam is liberally coated with Piper cam lube.

5.         It is essential that the customer checks that the cam being fitted is identical in every way (except for lobe profile) to the cam being replaced.

6.         Before starting all engines, prime the oil system by turning the oil pump manually, fill the carb or injection system with petrol, fill the radiator, ensure correct ignition timing.  The engine must start right away and not be subject to a long grind on the starter.

7.         Do not idle the engine during the first minute of operation: run at 2500 rpm or above.  In pushrod engines, 'oil throw' from the crank is the main lubrication for the cam followers.  Also contact stresses at the nose of the cam are very high at low speeds.  Engines may be run in the shop, on the road, or the track.  If adjustments need to be made during the first 20 minutes 'break in' period, shut the engine down.  DO NOT IDLE.