Ignition timing

[c1800]

Hi, I responded to Doug’s post in the wants section before seeing this thread. Lots of good info has been provided by 142Guy and others, but I’ll just repost what I provided earlier in the interest of completeness.
As stated it is a vacuum retard, I have read though rather than blocking the port on the vacuum unit , just leave it open, so as not to interfere. I assume you’ve got the port on the intake manifold blocked off.

What I said earlier

“ Yes, certainly could be worn out. If you want to take a deep dive into the inner workings of distributors here’s one source:

http://www.sw-em.com/Volvo%20Ignitio...CA%20Servicing

Sticking or broken springs in the distributor could cause your problem. Finding a source to rebuild your Bosch distributor might be worthwhile. Classic VW distributors are similar so you might find a classic VW place that could help you.

Or replace it entirely with a 123 Distributor. Yours is somewhat unique as I you’ve got the D-Jet FI distributor but running carbs. Might require a different advance curve with carbs. Don’t know. 123 Distributors can be programmed with many different curves. ”

[packers1712]

Thanks C1800 I’m not too worried about the “curve” just want to try and eliminate the inconsistency and manage a maximum advance degree figure of some where in the region of 35 - 38 degrees and can’t see any reason why my existing unit can’t achieve that! I have already managed 33 degrees when I first took custody you the car and recommissioned it so I believe it is achievable just want to understand what a “knackered “ unit looks like so that I can figure out what to repair.
There appears to be no excessive play or wear and I think I’m correct in saying even if the springs had weakened I would still achieve maximum advance just at lower Revs, I’m not giving up on my distributor just yet if I can stabilise the base timing setting then I’m prepared to work with it!
I couldn’t get the link to work!

Doug.

[powen1]

Doug sent you a PM

[c1800]

Trying that link again

http://www.sw-em.com/Volvo%20Ignitio...%20Scratch.htm

[142 Guy]

Originally Posted by packers1712

Wow thanks 142guy, when you say my mechanical advance might be knackered exactly what is knackered, it all moves freely and springs back when manually operated so what constitutes as knackered unit?

Doug

I don't know that it is knackered because I don't know what exactly is going on with your car and I don't know how you have been setting the base ignition timing (static method or using a timing light on a running engine?). The service manual says that the mechanical advance should provide 25 deg of advance as measured at the crankshaft starting from 'around' 900 RPM to 3000 RPM. If it is achieving that range of advance then it is functioning as designed. This can be confirmed by setting the advance to 35 deg at 3000 RPM and then checking the advance at 850 - 900 RPM. That change in RPM should give you full operation of the advance.

A really high idle speed can create advance problems. If the car idles significantly above 900 RPM and you use a timing light to set the idle advance to 10 deg, you will not achieve 35 deg BTDC at all because you are effectively retarding the distributor to give you 10 deg at idle.

Weak springs will cause the advance to come in early. The mechanical advance should be providing approximately 0 deg advance at idle speed. The distributor is rotated / adjusted to provide 10 deg of static advance which establishes the starting point. If your springs are weak the mechanical advance may be providing X deg of advance at idle when it should be providing 0 deg of advance. If you have set the idle timing at 10 deg using a timing light you will have reduced your maximum advance by X deg. One way to check for weak springs is to set the ignition timing to 10 deg BTDC using a static method (engine not running). Start the engine up and use a timing light to measure the advance at idle. If all of a sudden you have significantly more advance at idle then you know that your springs are tired or you have some kind of problem with the pivots for the weights that is allowing erratic movement.

You mentioned that the mechanism moves freely. Have you checked the pivots for the weights and the whole timing plate pivot for wear. This could allow free movement; but, result in erratic performance. Finally, since you are not running vacuum retard have you done anything to prevent movement of the vacuum apparatus? It has been 7 years since I completely ditched my distributor and I can't remember exactly how the vacuum apparatus rotates the contact plate. You wouldn't want unplanned movement in the contact plate to cause timing errors.

[packers1712]

Excellent guys thank you very much, 142 guy your explanation is perfect and I now understand what I’m looking for and will report back after some more investigation, it might not be for a week though as I don’t have permanent access to a strobe timing light and need to rebuild my distributor and get it back in the car for the next phase of tests that you describe!

Also thanks to C1800 the link worked and is great, with it and 142guy’s information I should be able to at least diagnose my distributor even if I can’t fix it!

Paul the last PM that I had from you was in August, I thought that I’d replied to it, did I not if so sorry I will!

Doug.

[Burdekin]

Originally Posted by packers1712

Excellent guys thank you very much, 142 guy your explanation is perfect and I now understand what I’m looking for and will report back after some more investigation, it might not be for a week though as I don’t have permanent access to a strobe timing light and need to rebuild my distributor and get it back in the car for the next phase of tests that you describe!

Also thanks to C1800 the link worked and is great, with it and 142guy’s information I should be able to at least diagnose my distributor even if I can’t fix it!

Paul the last PM that I had from you was in August, I thought that I’d replied to it, did I not if so sorry I will!

Doug.

Doug, Adam Twose is the man to talk to about distributors, repairing them, which one to run and setup etc. He use to restore them as well so might have one he could exchange. There’s also a company down in southern England that restores them but don’t know the details.

[packers1712]

Originally Posted by Burdekin

Doug, Adam Twose is the man to talk to about distributors, repairing them, which one to run and setup etc. He use to restore them as well so might have one he could exchange. There’s also a company down in southern England that restores them but don’t know the details.

Thanks Mitch I may well contact him then even if it’s just to pick his brains!

Doug.

[142 Guy]

Falling into the knackered category, some things to examine are:

1. the pins that retain the advance springs - grooves developing in the pins where the spring is retained
2. the point where the springs attach to the advance weights - grooves developing where the end loop of the spring loop fits on the weight
3. the pins that the weights pivot on

You are looking for anything that allows for movement of the weights when the advance mechanism is not rotating. In this case free movement is not necessarily a good thing.

In my rather fuzzy memory, the mechanical advance operates by the weights moving outward causing the breaker cam to rotate it relative to the distributor center shaft. My recollection is that it is the springs which transfer this motion from the weights to the breaker cam. That is why slop in the spring attachment points is undesirable.

The vacuum advance operates by rotating the contact assembly relative to the breaker cam. Normally, the vacuum servo would hold the contact assembly on the breaker plate in its 'correct' position. If you are still relying on the vacuum servo to hold the contact assembly make sure that the servo diaphragm and the attachment to the contact assembly is not allowing for unwanted movement in the contacts relative to the breaker cam. Since you are not using vacuum advance / retard I personally would be inclined to glue / solder the part of the breaker plate that allows the contacts to be moved relative to the cam into a fixed position.

[c1800]

Originally Posted by 142 Guy

Since you are not using vacuum advance / retard I personally would be inclined to glue / solder the part of the breaker plate that allows the contacts to be moved relative to the cam into a fixed position.

I don’t believe that is necessary, my B20e has been running fine for years with the vac Retard disconnected. I’ve relied on several expert opinions, never a mention of doing that.