downunder

This is the timing wheel I use. It's just a 360 degree protractor as used in schools or whatever with a hole drilled through the exact centre to mount it to the crankshaft. The pointer is just a bit of soft wire bolted to one of the engine mounts or any other suitable screw holes. Soft wire allows a bit of bending to fine tune the pointer to exact TDC.

If you just want to find duration of any ports then it's not necessary to have the pointer at exact TDC but with the crankshaft port you really need to know its opening and closing times which means finding TDC.

There's a couple of ways to do this quite accurately. One is to slip a bit of paper into the exhaust port and get the same reading either side of the 180 mark when the piston just nips the paper on the way up. This works for 99.9% of all engines, the rest have what's called Desaxe crankshafts which gives non-symmetrical timing.

The most accurate way is to use a piston stop tool (and this is the only time one of these things should be used, they should never be used to help tighten a flywheel). Set the stop tool so it contacts the piston just before the piston gets into the pinch but around 20 degrees total movement either side of TDC is good. The aim is to get the same reading either side of TDC by turning the crankshaft in one direction then back around in the other direction. This is where the bendy pointer helps. When it reads exactly the same either side then the pointer will be right on the 0 mark at TDC.

With the head off the engine, use a head screw or backplate screw (they're a bit shorter) to lightly clamp the liner so it won't lift if there's a good pinch. I check the exhaust timing by looking through the exhaust with a bright light shining down the bore and turn the crank until there's just the slightest glimmer of light showing. Doing this in both directions should give the same reading but always do it with the piston going up the bore to load the rod bushes and take out any clearances. I like to use a magnifying glass to check the other ports because they can be a bit hard to see properly. Usually I'll check them 3 or 4 times to make sure I'm getting a consistent reading.

For the opening point of the crankshaft, I prefer to turn it backwards because it's much easier to pick when the crankshaft port just closes rather than just opens. Once again, I use a magnifying glass for that.

How you record the timings is a matter of personal preference. I prefer giving the exhaust and transfer timings just as their opening time which is exactly half the total duration. Either way it means the same thing. In supertib's engine I'd have written the exhaust as 88 and the transfer as 56 so I'd know immediately there was 32 degrees of blowdown.