Timing is Everything

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POSTED ON October 30, 2017

When it comes to accurate, reliable and adjustable camshaft timing it is impossible to go past a quality toothed belt drive system. Fitting one, however, is often not as simple as making the decision to buy one. Leon Withnell from A1 Hi Performance in Myaree, takes us through the installation of an adjustable belt drive being fitted to a 347 Windsor. There are several advantages to running a toothed timing belt system. The first is longevity. In most cases these flexible belts will outlast even a doublerow timing chain, particularly in roller cam applications were high valve spring loads must be overcome to rotate the camshaft. Because the belt is flexible, rather than rigid like a chain or gear, it does not transmit the harmonics of the crankshaft into the camshaft. These harmonics can cause significant vibrations which can de-stabilise the valvetrain. The use of a third tensioning pulley also ensures higher belt tension for less play and greater timing accuracy than many chains can offer. Finally, due to its very nature, the inner section of the cam pulley can be moved in relation to its outer section which enables the cam timing to be altered very easily, even if the engine is in the car. These kits initially appeared on US Pro Stock engines but now they are available for almost any engine.

1. Before the timing kit even sees the light of day, Leon takes special care to examine the oil delivery path for the thrust surface of the camshaft. Early Windsors and SVO blocks (like the one in the photos) have no provision for oiling the thrust face at all. Clevelands have a tiny oil hole just to the side of the cam tunnel opening. In the case of this SVO race block, Leon grinds a small slot into the bottom of the cam bearing that intersects the oil supply hole and allows some oil to flow forward to lubricate the camshaft thrust area. While on the topic of cam bearings, Leon also performs another minor modification to bearings not already equipped. By drilling two small holes in the upper section of the bearing and then placing the shell in a lathe and turning a shallow groove around the entire outer circumference of the bearing, oil supply is tripled. If the engine should suffer a brief moment of oil starvation, it is possible to wipe the white metal off the bearing surface and block the bottom feed hole. But, if the two upper holes are drilled and connected by the milled groove, there is enough oil supply remaining to prevent a major failure.
2. Before the kit could be installed, two small locating dowels had to be machined to accurately position the alloy housing on the block. Beforeactually bolting the main housing into position it important to check the end float on the camshaft to make sure it has the desired amount of travel. An absence of end-float will not allow adequate lubrication of the thrust area which will result in severe galling. When these tolerances have been checked and adjusted if necessary, the front cover can be bolted into position, once the camshaft is installed. Before pressing the crankshaft pulley onto the crankshaft, apply a little sealer to the pulley’s inner surface and some oil to its outer surface.

Step 1 Step 2

3. Next, the camshaft pulley and belt are installed. The inner section of the pulley locates on the camshaft dowel and the outer section is lined up “dot-to-dot” with the crankshaft pulley. Note, at this point it is advisable to line the marks on the cam pulley to zero advance or retard until an initial camshaft degree check has been carried out.

4. With the belt on and the pulley lined up, the tensioner pulley can be bolted into place. In this kit, there were two of these pulleys, one larger in diameter than the other. Naturally, the larger diameter would make the belt tighter and this is particularly useful for blocks that have been line-bored which effectively raises the crankshaft slightly in the block and requires a shorter belt or chain. This pulley has a sealed bearing which does not require a direct oil supply.

Step 3 Step 4

5. Once the kit is installed, the camshaft timing must be checked using a dial gauge and a degree wheel. Then, if necessary, the six locking nuts can be loosened and the camshaft advanced or retarded by the required amount for maximum power and torque. Better still; the camshaft timing can be adjusted at a later stage, perhaps at the race track or on dyno, to give more bottom end torque or top end power. Leon assured us that with a little patience and some thought, such an installation could be carried out by any competent engine enthusiast. Once fitted, this is the ultimate cam drive system, and you can’t beat perfect timing!

Step 5 End Result

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