Instructions for timing a camshaft
Most of us will have stripped & reassembled an engine at some time. Usually the cam is put back as it came using the existing timing marks on the pulley. Alternatively they can be set up with the valves “on the rock.”
Things can be different when a non-standard or reprofiled camshaft is used. For best results these have a specific timing setting, usually quoted in degrees ATDC (after top dead centre of No1 piston). If you get the timing far out you may loose performance or drivability in the lower ranges, or even worse have the valves and pistons meet with expensive consequences.
The following instructions are an amalgamation of some instructions I was given years ago by Chris Carter (of the then Chestnut House Sports Cars) and my own experience.
(1) Timing protractor – most cam suppliers will sell you one. (It’s a plastic disc with degrees marked on it, with a hole in the centre for attaching to the front of the crankshaft.
(2) Dial gauge (DTI). This device measures small movements of the piston or cam lobe to enable you to establish when the cam is maximally opening a valve. These can be bought along with a magnetic base for as little as £20 new from auto jumbles. Don’t buy them from retailers such as Halfords because they will charge a fortune!
Build the bottom half of the engine. Install the camshaft into the block making sure that it is properly lubricated with a special lubricant such as Camlube or similar. Similarly lubricate the cam followers & install them.
Mount the DTI to the top of the cylinder block so that the pointer rests on the top of No1 piston crown.
Determine true TDC by moving the crank to & fro to establish the middle of the dwell Attach your timing protractor to the front of the crank and align it’s 0° (zero°) point to a suitable fixed pint to act as a pointer.
Rotate the crank in its normal direction until the correct timing figure for your camshaft aligns with your pointer. (e.g. 103° but this specific to your chosen cam) DO NOT MOVE THE CRANK AGAIN AFTER THIS.
Fit the cylinder head, tightening it down in the usual manner to the specified torque.
Fit the rocker gear & set valve clearances to cam specifications to ensure that the cam is equally loaded.
Set the DTI so that it measures valve movement on the No1 inlet valve. Establish maximum lift on this valve by rocking it either way to identify this point. DO NOT MOVE THE CAM AGAIN AFTER THIS.
Fit the timing chain to the cam wheel, loop it around the crank sprocket & offer it up to the camshaft so that the two holes line up exactly. If it doesn’t do this you may need to move the chain on a tooth or two. Further fine-tuning can be achieved by rotating the cam wheel 90° to give half a link extra movement. Take your time and get the best possible match. REMEMBER NOT TO ROTATE THE CAM OR CRANK AT THIS POINT AND TO MAKE SURE THAT THE SLACK IN THE TIMING CHAIN IS ON THE TENSIONER SIDE ONLY.
Bolt the cam chain wheel to the camshaft (don’t forget the lock tabs) and remove the protractor and DTI.
You can now safely rotate the crank/cam assembly to make sure valves & pistons don’t meet. (They shouldn’t unless you have made a dog’s dinner of this!)
Continue with the rest of your engine build!