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Camshaft Fitting & Timing

Camshaft Fitting

Due to the high number of phone calls we receive concerning the fitment and timing of camshafts, we have decided to include camshaft fitting instructions on this website. The first section describes what to look out for when fitting a camshaft to avoid premature failure. The second section describes a typical method for timing a performance camshaft.


Camshaft Fitting Instructions

Burtons do not recommend installing a performance camshaft in a vehicle fitted with an automatic gearbox. The installation and first few moments of running are critical factors in the life of the camshaft. Failure to install the camshaft correctly will have a drastic effect on the life of the camshaft and in the worst cases can result in immediate failure. The following instructions must be adhered to in order to obtain maximum performance from the engine and to ensure a long and trouble free life from both camshaft and associated components. These instructions are also provided in addition to the original manufacturers installation procedure. Where a camshaft is being replaced due to excessive wear, it would be highly recommended to strip the engine and fully clean the internals. Metal particles present in the sump, oil pump, bearings and oil galleries will soon play havoc with the new cam. It would also be wise to check the oil feed system. Low oil pressure due to a worn pump, blocked pick-up pipe or blocked oil galleries will quickly wear the new cam to the same state as the one being replaced. In other words, before replacing a failed camshaft, make sure you find out the reasons for the failure and correct it! Before fitting the camshaft, check that it is identical in every aspect (with the exception of the lobe profiles) to the one being replaced. Special attention should be given to the oil feed positions and journal diameters as variations may occur during the manufacture of the engine. Also check that any gallery bungs present on the old cam are also in place on the new cam. Do not remove the black phosphate coating from the new cam lobes. Liberally coat both the camshaft and cam followers with a proprietary cam lube or engine assembly compound.

 

Valve fully closed
Valve fully open

At Burtons, we recommend and use Graphogen, a colloidal graphite paste. Failure to do this can cause scuffing between the surfaces of the cam and followers, which will result in premature wear. Ensure that followers are free to rotate in their bores where applicable. It is essential that new followers are always fitted, regardless of the condition or limited use of the old followers. Failure to do so may cause premature components failure and consequently will invalidate any warranty claim. Upon installation, the valve springs must be checked to ensure that:

i) the fitted length (installed height) of the valve springs match the figure provided by the manufacturer (see fig. 1). If too small, then the valve seat areas in the head will require machining. If too large, shims can be added to the spring seat. Due to varying manufacturing tolerances of cylinder heads, all springs should be checked and measured for clearance.

ii) coil binding does not exist at full valve lift. This is the condition where the spring is fully compressed (see fig. 2). As a guide, at full cam lift the spring should be able to compress a further 0.060” (1.5mm) before the coil bound condition is reached. This can be checked by inserting feeler gauges between each coil of the spring and adding the results together to get a total clearance figure. Due to varying manufacturing tolerances of cylinder heads, all springs should be checked and measured for clearance.

Check the clearance between the bottom face of each retainer and the top of the guide or stem seal at full lift (see fig. 2). This should be a minimum of 0.080” (2mm). If this clearance cannot be achieved, the top of the guides must be machined. When double valve springs are being installed in place of singles, ensure that the inner spring is correctly located and the correct retainers and platforms are used where applicable.

When modifying engines that utilise finger followers i.e. SOHC Pinto, it is imperative that you ensure the followers remain in the original attitude relative to the cylinder head. Failure to do so will alter the rocker geometry, increasing or decreasing valve lift and can result in failure of both cam and followers or excessive valve stem/guide wear.
For OHV engines, attention should be paid to rocker arm geometry for the same reasons.

 

Camshaft Timing

Determining True Crank TDC Position: Head off Block

 

Although the crank pulley will have a mark to show TDC position, this point may not be accurate due to manufacturing tolerances. It is always recommended to calculate the actual position of TDC rather than rely on the mark on the crank pulley. Fit the timing disc to the front of the crankshaft. A pointer for the timing disc can be made from a piece of bent wire secured under a suitable front cover bolt. Position a dial gauge to measure the travel of No 1 piston (see right). Turn the crank until the piston is at its maximum height and zero the gauge. You will find that there is a dwell period of approx. 10 degrees where the piston is at its maximum height. True TDC position is at the centre of this dwell period. To accurately measure the position of TDC, rotate the crankshaft and stop at a figure just before TDC, for example 0.020” on the dial gauge. Record the figure on the timing disc from the pointer. Now rotate the crankshaft and stop at the same figure (0.020”) after TDC. Record the figure on the timing disc again. True TDC is positioned in the middle of these two figures. The TDC position can be calculated by adding the two figures together and dividing by two. Adjust the timing disc so that it reads zero on the pointer at true TDC.

Using a crankshaft timing disc

 

Determining True Crank TDC Position: Head on Block

If the head has not been removed when changing the cam, it is still possible to measure the true TDC position. The procedure is the same as before but the movement of the piston is recorded by using an extension resting on the piston crown (such as a socket extension or our special tool on page 114). Access to the piston crown is made through the spark plug hole.

 

Timing in the Camshaft

 

Camshaft timing using a dial gauge

Rotate the crankshaft clockwise to 90 degrees after TDC. This will make sure all the pistons are half way down the bore. Now position the dial gauge so that it can read the lift of the inlet valve of number 1 cylinder from the top of the valve retainer (see left). Rotate the cam until the gauge shows that the valve is at full lift. As with the crankshaft, there will be a dwell period where the valve is at full lift. True full lift is at the centre of this dwell period. Roughly position the cam at true lift position. Now rotate the crankshaft clockwise to the full valve lift position (as specified on the camshaft data sheet - this figure is typically from 100 to 120 degrees after TDC), fit the timing belt or chain and set up the tensioner. 

Now rotate the crank clockwise until the inlet valve of number one cylinder is just off full lift position (such as 0.005” or 0.15mm). Record the figure on the timing disc from the pointer. Then continue to rotate the crank clockwise until the valve has fully opened and then closed by the same distance as previously used (0.005” or 0.15mm). Read the figure on the timing disc again. The position of full lift is the middle of these two figures. The full lift position can be calculated by adding the two figures together and dividing by two. Adjustments can then be made to the camshaft timing, using an adjustable cam pulley or offset dowels, if this figure does not agree with the one on the data sheet. Check the timing again after adjustments using the same procedure. Having timed the camshaft, check that there is no piston to valve contact. Minimum clearance is 0.060” (1.5mm). This can only be checked by dummy building the engine with a piece of Plasticine placed on the crown of the piston. As the engine is turned, the valves will indent the Plasticine. The clearance is then measured as the thickness of the Plasticine between the piston crown to the bottom of the valve indent. Before starting the engine, turn the engine over by hand to ensure that it turns freely. Prime the oil system and check that everything is set to ensure that the engine starts straight away. The engine must not be turned over for any length of time on the starter. Once started, do not allow the engine to idle for the first 20 minutes and keep the revs to a minimum of 2500 rpm. This will ensure adequate lubrication of the cam and followers and reduce the contact force between the cam and follower. If any adjustments need to be made within the first 20 minutes, then shut the engine down. Do not allow the engine to idle. Please note that new hydraulic lifters may in some cases operate with excessive noise for a few minutes before they are fully charged with oil.

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