Paul has been having trouble getting a pin into the flywheel of his tractor engine to locate 16 deg before top dead centre (TDC)…..

I’m currently working on a couple of 23c and trying to find the hole in the flywheel. I have, as per dvd, put a 1/4 in bar in the hole in the casing and turned the engine over using a socket on main pully. I’ve done this quite a few times and no luck. Is it possible that it has not got a hole in it? If so, what else can I do? Cheers.

Hi Paul,

Everything is possible.

Has it got a replacement flywheel I wander? – although you would expect that to be drilled as well. Otherwise how would the factory have set it up?

So you’re trying to determine the degrees before Top Dead Centre of the flywheel.

One way to determine the crankshaft angle without using the timing hole is by the TopDC and BottomDC markings on the flywheel. Using the timing marks on the flywheel and the datum mark on the back of the engine (next to flywheel) the TDC position can be determined. Then stick a 360 degree protractor to the flywheel and make a pointer which is attached to the engine block. You now have the facility to make a measurement in degrees of rotation. You should only turn the engine in the direction of normal rotation, so to get to 16 deg before TDC, you should turn the engine forwards 344 degrees.

Another method of determine the postion of TDC when the cylinder head is removed is to use a dial test indicator on the centre of the top of number 1 piston. The dial test indicator will show you when the piston is at the very top (ie. TDC). Then use the protractor method (as above) from there on to get to 16 deg before TDC.


Quick note. All designations of TDC relate to piston number 1 on its firing stroke. So you need to observe the valve movements to determine when the piston is at the top of its firing stroke rather than exhaust stroke. To do this observe the valve movement in relation to the piston. So when piston is raising towards TDC, then both valves should be closed.

The above method will give the same 16 deg before TDC as the 1/4 in bar into hole in flywheel.

It will be very odd if the timing hole is not there.

Hope that helps and makes sense.

Steve + Ian VTE.