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Discussion Starter · #1 ·
A few months back I installed a "ran when parked" GTV motor in my '74 Spider. I remember specifically that, in order for the engine to fire correctly, the plug wires on the Magneti Marelli electronic distributor had to be placed in such a way that the numbers labeled on the distributor did not match the actual cylinders. No big deal, I have read that some later distributor caps are mis-labeled.

The mystery now is, after replacing the "ran when parked" head with my old head, why does the motor now only run correctly when the numbers ARE set to match the corresponding cylinders.

The distributor has not moved. The motor was not turned at all while the head was off. I lined up the cams to the notches upon reassembly.

Am I crazy? Are Spider and GTV cams different and so offset that they alternate which stroke the motor is in? Do I have some king of exotic cam set-up on one of the heads? What could I have screwed up?
 

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TDC mark on the crank doesn't mean the distributor rotor is pointing to the 1-st wire. It was set to the 4-th before, I think :D
 

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There are two marks on the cams. Lobes pointing outward is TDC #1, lobes pointing inward is TDC #4. With the head off and both #1 and #4 at the top of the stroke it will depend on the position of the distributor rotor as to which one is at TDC.
 

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Discussion Starter · #4 ·
Thanks for that info, but it doesn't really solve the mystery...

Picture the scenario;

- Motor runs
- Plugs wires are removed and laid to the side (felt pen numbers on the plug caps)
- Head is removed and a different head is installed
- Plug wires are replaced in the exact same order
- nothing else has changed
- motor no longer runs until the wires are moved to different positions
 

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Kcabpilot has the likely answer. When you removed the old head were the cams positioned such that #1 lobes were facing apart or towards each other? When you installed the new head were they positioned the same? Was the crank turned while the head was off?
 

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kc explained it quite nicely, I thought.

To put it another way, the cams in the new head and the cams in the old head were timed 180 degrees apart.
 

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Discussion Starter · #7 ·
There are two marks on the cams. Lobes pointing outward is TDC #1, lobes pointing inward is TDC #4. With the head off and both #1 and #4 at the top of the stroke it will depend on the position of the distributor rotor as to which one is at TDC.
Sorry, I didn't see this when before I wrote my second post. That is helpfull and makes sense.

So now my question is, does it make a difference if I just keep running it this way? Or do I need to go back in, undo the chain, flip the cams and rearrange the plug wires again?
 

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does it make a difference if I just keep running it this way? Or do I need to go back in, undo the chain, flip the cams and rearrange the plug wires again?
Just leave it as is. It seems that you inadvertantly fixed a minor problem without realizing it!

You do understand that once you admit to owning a 37-year old Alfa Romeo, there is only one answer to the "am I crazy?" question.
 
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