1989porsche928

I lost the 45 degree mark I put on the pulley it must have smudged off. Will the Porker 928 timing tool help me find it? I cannot rotate the gear pulley to 0 degree notch like the 928 engine training video said to. It keeps jumping past it.

Leon Speed

Okay the fundamentals to keep in mind are that when the engine (crank) is at TDC 0|T, the notch in the cam gear (which you refer to as pulley) should line up with the notch in the cam backing plate. Also, the crank rotates twice for every one turn of the cam gear. So, if the crank is at 45 BTDC, the cam gear should be at half that timing: 22.5 degrees BTDC. This corresponds roughly with 3.5 teeth on the cam gear.

So to get the 45 degrees BTDC mark on the cam gear, make a mark at 3.5 teeth clockwise from the notch in the cam gear. See the picture, the red dot indicates the mark:



Once you have strung the belt and have managed this rough setting, and the belt is tightened to spec, you move the crank to TDC 0|T and use the Porken 32Vr for fine tuning the timing.

1989porsche928

Thanks for the reply leon speed. Just a quick question about the 0 fine tune. Will it jump once I loosen the belts again?

Leon Speed

The cam gear will try to move, yes. But why would you want to loosen the belt again? Belt tension influences gear timing, so to get both timing and tension correct, you need to 'play' with both until correct. Basically, do the rough alignment on 45, then set the belt tension, then fine tune timing. Rotate the crank as few times, check both tension and timing, and adjust as needed (tension first, then timing).

1989porsche928

I just didn't think you could fine tune timing without loosening the belt.

SeanR

I'd like to see some pictures of what's behind the gear now that it is taken off.

1989porsche928

Will post pic give me a few minutes have to download then upload from phone. I wish their was a measurement between the trigger ring edge and back of cover.

1989porsche928

Leon Speed

Some rubbing but that was to be expected. Note that the cam is on the exhaust stroke and needs to be rotated so that the key is pointing up before the belt is strung. Only do this with the crank on 45. Obviously same goes for the drivers side.

1989porsche928

Here is the picture of the old hall sensor, not the new one that was destroyed. Does it look damaged?

1989porsche928

Leon the crank is set at 45, this is the one that I lost the mark on. I should probably draw a line to the key so I know where the key is

Leon Speed

Yes I understand but my point is that if you fit the gear with the key pointing down like in your pic the notch in the gear will on the bottom and not on the top like it should be in order to set timing. And if this cam is pointing down the drivers side is pointing down as well and should also be pointing up otherwise the cams are not aligned.

Rob Edwards

Hold on a sec- are we 100% sure that the crank is stopped at 45 BTDC on _cylinder 1_? Do you have a picture of the Driver's side cam gear?

When you moved the engine from TDC to the 4|5 mark, did you rotate the crank 1 plus 7/8 turns, or only 7/8 of a rotation?

Your driver's side cam gear (still attached) has two nubs on its face that should be pointing towards roughly 2 o'clock, along with the metal contact of the rotor. Are they pointing to roughly 2 o;clock?

Leon Speed

Rob, maybe my thinking is flawed but there is only one 45 at position at the crank so the piston is always in the same position. The position of the cams determine what stroke the engine is in.

Rob Edwards

True, there's only one 4|5 mark on the damper, so no matter whether the mark is at 45 degrees BTDC for cylinder 1 or for cylinder 6, you ought to be able to spin the cams without damage.

As long as the crank never moves.

But as soon as a new cam gear that is oriented 180 degrees 'out' with respect to the crank starts rotating, you'll encounter significant issues.


Below is a pic of a crank- the rod journals for 1/5 and 2/6 are 90 degrees apart, so you imagine if the rod for cylinder 1 is at TDC, so is the rod for cylinder 6.

At TDC #1, the woodruff key slot in the crankshaft should be pointing towards 4 o'clock and the cam gear rotors should be pointing to 3 o'clock. So at 45o BTDC on cylinder 1, the crank key is at about 2:30, and the rotors are pointing at around 2 'o'clock.

Just making sure that we're working at 45o BTDC on Cylinder 1.