Technical Advice -> Camshaft Installation
The Rules of Successful Camshaft Installation
Important note: When installing camshafts (especially those with limited spacing between cam lobes), it is the fitter's responsibility to check to see that none of the followers foul any part of neighbouring cam lobes and camshaft core. If any followers do foul neighbouring cam lobes or the camshaft core, you must stop installation and report this to Piper.
Research indicates 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 break-in have not been followed.
The cause of premature cam and tappet failure is metal to metal contact between the tappet and cam lobe. Should this contact occur due to lack of proper lubrication or excessively high pressure due to valve train interference shearing the oil film, then ‘galling’ will take place. When this happens, metal is transferred from the tappet to the cam 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 tappet or lobe. These pieces of metal remain attached and create further local overheating during the following revolutions of the camshaft and lead to ultimate failure of the affected components. Listed below are steps to ensure 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 entire valve train for interference before starting engine, i.e. valve to piston contact, for twin cam engines, valve to valve possible contact and spring boxing. Valve springs should show .030” clearance between centre coils. Valve should have minimum .060” clearance from piston/block. Engines that utilise hydraulic tappets should have at least one inlet and one exhaust tappet temporarily replaced with mechanical item set with zero clearance. This will allow accurate figures to be obtained from the above checks. Once the checks have been done make sure the original hydraulic items are refitted.
4. Do not remove black phosphate coating from cam lobes. This coating helps the bedding-in procedure by aiding oil retention on the surface of the cam lobe.
5. To ensure that your Piper camshaft reaches you in the same condition that it left the factory it has been coated with a transparent rust inhibitor that must be removed before fitting. Wash off in a suitable solvent e.g. paraffin. After washing, it is essential that your camshaft be liberally coated with cam lube.
6. It is ESSENTIAL that you ensure that the cam you are fitting is IDENTICAL IN EVERY WAY (apart from the lobe forms) to the cam you remove. Failure to check may invalidate you warranty.
7. Before starting all engines, prime the oil system by turning the oil pump manually. Fill carburettor with petrol, fill radiator, and ensure correct ignition
timing. Engine must start right away and not be subjected to a long grind on the starter.
8. Do not idle engine during the first twenty minutes of operation; rpm should be kept at 2500 or above. In pushrod engines oil throw-off from the crank may not be sufficient to lubricate the cam followers. Also contact stresses at the nose of the cam are very high at low speed. If adjustments need to be made during the twenty minutes break-in period, shut the engine down. DO NOT IDLE.
9. In some OHC engines where re-profiled cams are used, you may need larger than standard adjustment shims.
10. When modifying engines that utilise finger followers, e.g. Ford Pinto SOHC engine, it is imperative that you ensure the followers sit in a horizontal position. Failure to do so will alter the rocker geometry. Increasing or decreasing the valve lift can result in failure.
11. HAVE YOU CHANGED YOUR CAM BELT? The importance of changing your cam belt at the manufacturers recommended intervals could not be over-emphasized. A failure of this item will more often than not result in massive engine damage. Our range of belts has been specifically designed to cope with the demands of a competition engine. If you are in any doubt as to the mileage your belt has covered…. CHANGE IT! Our up rated belts retail at prices very close to that of a standard replacement item. Do not take a chance, fit a Piper cam belt.
A Guide to Correct Timing
To check your cam timing, you will need a 360 degree protractor and dial gauge. The engine must be set at TDC and the protractor bolted to the crank pulley. Attach the dial gauge so that the foot is resting on the valve spring cap (or follower on OHC engine). Attach a pointer to the engine and zero the protractor. The engine is now at TDC with the protractor reading zero.
Turn the engine until full lift is first shown on dial gauge. Note number of degrees (e.g. 106 degrees ATDC), continue to turn the engine and note when lift starts to reduce (e.g. 110 degrees ATDC). True full lift position will, in this case, be 108 degrees. Your figures will differ but true full lift is at midway point.
The correct full lift position for your cam is shown on attached information sheet.