924Board.org

[caswah]

A newbie question, but Ive tried to understand this for some time now...

When i set piston # 1 at TDC, the distributor rotor should be pointing towards the mark in the distributor body as well as towards spark plug # 1 connector, fine, but if I crank the engine until next TDC for piston #1 the distributor rotor points at the exactly same position.

The first time piston #1 reaches TDC, the cylinder is full of compressed air/fuel mixture and we want an ignition/spark (1st stroke), but the second time it reaches TDC the cylinder is full of combusted fuel/exhaust being pushed out through the valves (3rd stroke).

How does the engine "know" whether to ignite in piston #1 or not when the piston is in TDC ?

Hope you know what I mean, but if the distributor alone was to decide when to ignite, the engine would ignite every time a piston reaches TDC (both when filled w compressed air/fuel and when filled w combusted fuel/exhaust)...
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Euro ´81 924 - Interior being restored

[!tom]

[D Hook]

Even if you could get them to go at the same speed, what's to ignite?

And no compression since the exhaust valve is open to let the piston push the exhaust out.

Tell the truth....did you put one of those Tornado things on your engine?
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'80 924 n/a SOLD

[caswah]

But im not rebuilding anything, using all parts I had from the start. All I did was remove the distributor and then reinstalling it.

Did I miss something.. ?
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Euro ´81 924 - Interior being restored

[968rz]

I bet you lost track while turning the engine. Pull #1 plug and use a plastic drinking straw on the top of the piston as you rotate the engine by hand. For every 360deg turn of the dist rotor you should see the straw move up twice.
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Rick
79 924 coupe Petrol Blue 3spd auto (wife's DD)
93 968 coupe Amazon Green 4spd Tip (my DD)

[Ozzie]

Impossible.
You missed a TDC.

The cam turns at 1/2 the speed of the crank.
Try it again.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[daniel]

A method I have used many times:
Bring no1 cylinder to the top, then observe where the rotor button is pointing. rotate the dizzy until the button points towards a lead socket on the cap. This is now no.1. Now insert the next 3 according to firing order and rotation direction. Try to start, if the engine does not start, you are 180 deg out. So move every lead two positions around. If the engine dosnt start now either you have messed up the above steps or something else is wrong.

Best of Luck
Daniel
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Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

[caswah]

Thank you for your answers!

Think I just realized what Ive been doing wrong: I check the TDC by removing the #1 spark plug, inserting the thumb and cranking the engine by hand until air stops blowing out of the spark plug hole.

Works fine but...the next time the piston reaches the same position the valves are open, letting exhaust out = no compression, so I cant feel when the piston reaches the top but must use something (such as the suggested straw) or remove the vent cover shield (or what you call it in english).

Stupid stupid me.. will try again. This does however not solve my problem, see my other recent topic.
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Euro ´81 924 - Interior being restored

[Ozzie]

check your TDC using the marks on the oil pump and crank pulley.
check your flywheel mark and if that also lines up then use that as it is more accurate.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance