CAM TIMING – BASIC NOTES.

31 August 2000

To avoid lots of swearing and unnecessary damage, check the timing gears slide neatly onto their respective bosses. If tight, first check for any high spots in the gear bores and key-way slots. Clean out using with fine emery cloth, medium Wet 'n' Dry paper, or some such. Remove the Woodruff keys then dress the bosses using abrasive material as mentioned previously. Re-check fitment before re-fitting keys. Check the key-ways and keys too before re-fitting. Get rid of unwanted sticky-out bits on the keys that would inhibit a slide fit. Clean out the key-way and de-burr top edges. I always file a slight 'flat' across them to give plenty of clearance to the gear key slot. If the pulley is a slack fit on the key, turn it anticlockwise before nipping the bolt up. ALWAYS fit it like this. It's imperative to fit cam (and followers in the case of solid wall blocks) following manufacturers instructions precisely using a good quality cam lube.

Sit the block/crank/rods/pistons/front plate/cam and cam retaining plate assembly on something that will allow full rotation of the crank without fowling. The gearbox is ideal, but needs to be stabilised by wedging with a thin sliver of wood or some such. Fit the flywheel retaining bolt and washer to facilitate crank rotation. Use something reasonably long as a lever to turn the crank with - jerky motion is to be avoided for accurate settings.

For those confused about which end is which of an engine, the FRONT is the water pump end, thus number one piston is nearest the water pump. Worth remembering as most engines are like this.

When timing cams in, two terms are continually confused - ADVANCED and RETARDED. To explain/clarify her are these terms applied to a common manufacturer recommended 106 degree setting as an example.

ADVANCED cam timing means that the valve events are occurring BEFORE the recommended point. Your measurement will therefore compute a reading LESS than 106. Generally this increases bottom and mid range outputs, but losses a little peak output. To correct this the cam will need turning counter-clockwise (anti-clockwise).

RETARDED cam timing means valve events are occurring AFTER the recommended point. Hence measurements and computations will give a value MORE than 106. Generally this increases peak outputs, but will lose bottom and some mid range output. To correct this the cam will need turning clockwise.

In both the above, I have stated just the CAM needs turning. To achieve this offset keys will be needed where non-adjustable cam gear drives are used, available in one-degree increments from 1 to 9 degrees. Also the above conditions are exaggerated when applied to small-bore engines. Modern cams have become such a developed art that sticking to manufacturers recommendations is usually the best course unless intimate knowledge of the type of engine build exists. Otherwise it could be tears at bedtime!!

The reason for taking readings either side of full lift as depicted in the methods is to get a true full lift point. A certain amount of 'dwell' exists at the cam lobe peak, so is difficult to ascertain true maximum lift point. The points used could be anywhere between 0.020" to 0.003". The nearer).003" the better as some cams have asymmetric lobes. These will cause inaccurate settings to be established if points further from 0.005" where used.

Two cam timing methods are explained - one where the customary DTI, etc. is available, the other for those without specialist equipment (mechanical method).

Relevant part numbers :

WKN1 OSET to WKN9 OSET	Offset cam keys where the figure indicates the degree offset required.
KCLUBE	Torco premium quality cam lube.