Alfa Romeo Forums banner
1 - 11 of 11 Posts

·
Registered
Joined
·
40 Posts
Discussion Starter · #1 · (Edited)
I thought changing my ignition HT cabling would be a simple exercise..

Simply take the old set of leads off and connect the new ones using the numbers on the rubber upper case seal to match up with the numbered distributor cap plugs, right?

Motor vehicle Automotive design Gas Auto part Engineering


Well that didn't work. All I got was some cranking and a backfire.

I double checked everything and same result. I even contemplated that I had the cylinder numbering in reverse, considering numbers 1-4 from the left viewed from the inlet side, but that didn't make any sense with the supplied lead lengths, assuming that the supplied rubber distributor case top was supplied with the leads correctly inserted.

There was only one position for the Marelli distributor cap to mount, due to a raised key on the mounting surface, and similarly the rotor had only one position due to a square and round key adjacent to each mounting screw.

Finally I went back to basics and first set the engine to top dead center by removing No1 plug and cranking an inserted pencil to max height. There was no valve edge visible, so I also pulled the No4 plug. When I still could not see a valve in No4, I removed the valve cover to discover the cylinder on compression by observing the cam lobe positions.

Vehicle Car Motor vehicle Automotive design Automotive air manifold


The above pic shows that it is only on No4 that both inlet and exhaust cam lobes are clear of their buckets, whereas No1 is in the "valve overlap" state where its exhaust valve is in the final stages of closing and its inlet valve is just starting to open. The direction of rotation of the cams can be confirmed by visualizing the fan rotation direction and thus, the cam chain moving upwards in the pic.

Clearly No4 should be catching the spark in this condition, however the position of the rotor was aligned with the distributor cap marking for No3, which was a 90 deg discrepancy!

Motor vehicle Automotive design Yellow Automotive fuel system Automotive exterior


It looks like the entire distributor and oil pump had somehow been mounted in an incorrect position, so as to cause the cap numbers to be rotated 90 deg in advance.

So Murphy's law can again be given credit for allowing a way of mounting the distributor 90 deg in advance, and yet another driver turned mechanic has been reminded to always check the numbers when disassembling!

I hope this helps someone else (similarly puzzled).
 

·
Premium Member
Joined
·
6,577 Posts
Number one. Top Dead Center should have both cam lobes pointing out.

Your picture shows your at TDC on number 4.

When replacing spark plug wires. Always replace them one at a time.
 

·
Registered
Joined
·
3,134 Posts
The oil pump has been out in your engine at some point. It was replaced in the “incorrect” position. Very common. On my race engines, I never worry about the position of the pump when they go back together. But I also don’t have numbers on top of the distributor cap to mislead anyone!
 

·
Premium Member
Joined
·
24,134 Posts
Yes, it doesn't really matter as long as you get it all timed right. The distributor, unlike some, can be placed in pretty much any orientation, so you can find the right relationship even if the oil pump has not been put in the original position.
Andrew
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #5 ·
Thanks Jim for spotting my error in the post (now edited), and the good advice.

Indeed, the oil pump was out in 1987 with the last full rebuild, which is too long ago now for me to recall whether the distributor cap was numbered at that time, however given my latest confusion with assuming ignition timing matching the distributor cap numbering, I figure I would have corrected it in 1987, if the cap was numbered then. I am pretty sure the cap has been changed since then, at some stage by others, who probably never thought it warranted to tell me about the issue at the time.

No doubt I will set the distributor orientation to match the cap numbers in the next overhaul, which is already past due.
 

·
Registered
1977 Spider 49-State
Joined
·
248 Posts
There should be a lock clamp under the distributor (not the hold down nut on the block for ignition timing). If you loosen this, you can rotate the distributor body to get back to aligning the marks on the distributor cap. It's possible your distributor could have been apart at some point for a rebuild and the clamp was disturbed.
 

·
Registered
Joined
·
40 Posts
Discussion Starter · #9 ·
Hi WA-Alfa,

What may appear to be connected to the coolant bleed screw is not.

I think what you are referring to, is the tube which is normally attached to a nipple mounted on the valve cover vent flange. The other end of the tube, (aft of the clamped pipe) is connected by green plastic tubing to the fuel tank neck, presumably as an anti-pollution vent.

These is no original or retro-fitted temp warning on the car, only the original temp sensor, partially visible at the bottom of the previous pic.

The pic below, of the reassembled valve cover etc should help, although now obscured by the ignition harness..

Cheers
Motor vehicle Vehicle Automotive design Auto part Personal luxury car
 
1 - 11 of 11 Posts
Top