Dear Gang,

I notice the Water pump come with a plastic Red Indicator. When Installed it is directly over top of the crank shaft pulley. The pulley has a marking of 0.0 and other numbers. Does this meant if the Red plastic indicator is at 0.0. this is the TDC of cylinder no: 1 ?

Shark is still in the Porsche Workshop.

With kind regards......

William Heung


You are correct in thinking that I wanted to get to where the Intake tract was closed off. I am maybe wrong about where that occurs. Sitting at my desk this morning it is hard for me to remember where I set this without looking at it. I want to say that I set the motor at where the cam sprockets where marked for TDC and the water pump marker indicated 0|0. I assumed that this should be the starting point for the engine cycle and thus everything would be closed. Is my understanding off?? I did get air out of the vacuum leaks without too much pressure being blown into the tube...sorry if I have mislead anyone by assuming some things...Can anyone give me a correction here or maybe help me understand?

~Mark Drenzek

Each cylinder on the 928 engine operates at 45 deg after the last cylinder before it in the firing order, and 45 deg before the next cylinder in the firing order, so there is no point where every valve in the engine is closed.

TDC simply means Top Dead Center. Each piston goes to TDC once each revolution. The 0/0 on the crank pulley shows TDC for #1. This occurs once each revolution, once at TDC-firing (or TDC-compression), and once at TDC-exhaust. TDC-firing is the point where the marks on the cam sprockets should be aligned, and just after the ignition timing occurs.

It is common for mechanics to simply refer to "TDC" when they really mean TDC-firing, since not much of anything is referenced to TDC-exhaust. So, if you are reading something that tells you to "put the engine on TDC", they almost always mean, "position the engine crankshaft so that cylinder #1 is at TDC-firing".

At this point, all the valves in cylinder #1 will be closed - but there will be open valves in other cylinders. There are ALWAYS open valves.

If you want to pressurize the intake to check for leaks, the easy way to take care of open valves is to cap the exhaust outlets.

A neat way to check for intake leaks is to blow smoke into the intake.
Leaks are immediately visible. Joel at North Point, one of the best 928 shops around Atlanta, got a smoke machine last year, and he loves it. Be interesting to try to build one ....

Wally Plumley
928 Specialists

TDC marker on left (passenger) side camshaft

TDC marker on right (driver) side camshaft

TDC marker on crank damper pulley