Ignition issue

[Derek UK]

To reinforce my comment and Ron's about the rotor being wrong or wrongly fitted it should be noted that the arcing at that post is to the base and not to the machined away area. This would indicate that the rotor "blade" is too high.

[Ron Kwas]

Nive, Derek;

Could it be as simple as the Rotor not having been pushed and seated fully "home" onto the Distrib Shaft? ...if the Rotor was not fully "seated" and "home" and a much too high in position, it would foul on the Cap which would be pretty obvious through contact noises and (IF Dist was uninstalled at the time, likely inability to turn the shaft at all!...but if Distrib was installed at the time, this might not be noticed and on first turning of the Rotor, things might hit and fracture...then again, the Cap might not even be installable under such a condition).

Such a gross misassembly would be quickly noticed and corrected. But what if Rotor was just "not quite home", but seated far enough that Shaft could turn, Cap could be installed and everything seemed quite normal...its raised position could set up the condition to (possibly) cause the arcing to the surface because it was so dirty and conductive (two conditions combine once against to cause a failure!)...whadyathink of such a possible failure analysis?



Proper position of Rotor is is clearly quite important (axially AND vertically!)...I've always noted that the Rotor can be quite snug on the Shaft axially, and once the key lines up in the Keyway them must be pushed fully "home" (against securing force of the spring...)...maybe it wasn't quite 'home"...

Cheers

[niveketak]

The cap was brand new as was the rotor as was the case in the first failure. I am sure as I can be that I fully instal the rotor so it is in the correct position and always make sure the cap is aligned so the clips fit easily. As to whether its the correct rotor, I can only go with what is sent from Simon, all the rotors have looked the same, same length same height.

[niveketak]

Ron, I did wonder whether rather than the rotor not being seated properly there was an issue with the spring not pushing the contact far enough hence the arcing onto the contact and weird shape. I have taken a picture of the button and spring as removed just now and to the naked eye it looks OK to me.

The dirt seems to be metal particles presumably from the contact.

[niveketak]

DSCN3410.jpg

enlarged2.jpg

Unless I am missing something the spring loaded contact looks OK but its the first time I have pulled one out to look

[niveketak]

Originally Posted by Ron Kwas

142G;

The issue that I am aware of with early/late Distributors is related to the two-piece vs one-piece Points. With the later, the through-hole for the points connection did not require the partial circular clearance cut-out in the Cap base as the earlier one-piece points required...that suggests to me an early Cap and Rotor can be fitted to a later Dist, with no fit issue, but not the other way around!
You could even modify a later Cap by grinding in that clearance, and fit it to an early Dist...it's not that huge a deal...but what glares at me immediately is where it was arcing to...(and all the dust in there...)

Cheers

I have owned the car for 8 years Ron and it ran fine mainly for 7 of them. This seems a recent event and I am wondering how the Quinto Hazel cap will go on, will be removing it on a regular basis.

[niveketak]

The car runs really well with a new cap so that would rule out any timing issues. Is there any way of telling which Dizzy is in the car IE is it an early or later one, it has the two part points and they have been replacements over the years for other 2 part points.

Originally Posted by 142 Guy

Legitimate back firing through the carbs (as opposed to the more common misfire) is uncommon and is typically a sign that the ignition timing is really advanced or really retarded. The back fire is caused by ignition occurring before the intake valve is fully closed (really advanced) or as the intake starts to open (really retarded). A problem with the condenser will not cause the ignition timing to change leading to back fire, so that is not the cause of the back fire issue.

Back fire can be caused by the valve timing being really out; but, that seems unlikely in these circumstances. If the distributor came loose and rotated that can cause the timing to alter leading to back fire. However, given the evidence inside your cap distributor cap, I suspect that the back fire may have been cause by the distributor rotor arcing to the contact for an adjacent cylinder rather than the correct cylinder.

I marked up your photo of your cap. In the areas circled in color there looks to be residue on the inside of the cap that appears to have metallic particles in it. If this is correct and not a visual illusion then it suggests, as Ron Kwas has mentioned, that there a mechanical fit issue which may be leading to wear. If those particles are metallic you could have some 'rotor or cap out of position issue' combined with the metallic contamination leading to flashover to the incorrect post (and a misfire).

My university friend from long ago had an Amazon and as I recall when doing a tune up you had to be specific on the year of the engine because there was a change in the distributors during the Amazon's production run. The last time I saw that particular Amazon was 40+ years ago so I can't remember the details - whether the caps and rotors could be physically interchanged; but, not work correctly or whether the differences between the early and late distributors was so distinct that you could not fit the early cap / rotor to a late distributor or vice versa.

The inside of your cap suggests some mechanical damage to the rotor or cap that might be caused by the incorrect cap, incorrect rotor or both for your particular distributor. I suggest that you check to make sure that you have the correct cap and rotor for your particular distributor. I will hazard a guess that you are not the original owner of your 122. Is it possible that you have an early car with a late distributor that has been fitted as a replacement?

[142 Guy]

Originally Posted by niveketak

The car runs really well with a new cap so that would rule out any timing issues. Is there any way of telling which Dizzy is in the car IE is it an early or later one, it has the two part points and they have been replacements over the years for other 2 part points.

There appears to be a dog's breakfast selection of ignition parts for the Amazon. The change in design does not go strictly by production year. The changeover year appears to be 'mostly' 1965. But, it appears that some versions like the B18A continued with the same distributor right up to the end. One piece versus two piece points does not appear to be a defining requirement as it appears that there is more than one set of two piece points (238859 and 240149 both being two piece points). It appears that two piece points were on some versions of the B18 right up until the end of production.

To find out what distributor you have you need to remove it. On the base of the distributor you will find numbers stamped in the housing or an oval tag (older distributors) mounted on the housing with the Bosch part number. The CVI website below has parts diagrams and they list some of the corresponding Bosch part numbers for the different engines. If you can match up your Bosch part number with the diagram you should be able to get the correct parts.

VP Auto offers up an even greater set of mix and match distributor options for the B18. They show 4 variants of the B18 ignition system.


https://www.cvi-automotive.se/en/art...14418/2-b18b20

https://vp-autoparts.com/en/artiklar...m-5/index.html

Aside from the points differences, according to both CVI and VP Auto the same Bosch distributor cap works on all the variants (Volvo part number 87069). There was a change in the rotor in the 1965 and later cars that appears to be consistent across all the versions of the B18. Thinking back 40+ years to my friends B18, it was probably the replacement rotor that was the problem. I don't know whether it didn't fit; but, it didn't look the same as the old rotor that came out of the distributor which sent him scurrying back to the parts shop to find a rotor that matched what was in the car.

Since rotors don't have Volvo part numbers on them, aside from ordering a replacement based upon your distributor Bosch part number the best you can do is look at the pictures on the Skandix, VP or CVI websites to see which part they look like and then figure out whether that is the correct part number for your distributor.

Given that the parts listing says same distributor cap for all the B18 variants, I don't think the problem is in the cap unless there was a manufacturing flaw. I suspect that the problem is related to the rotor - either an installation problem in the original rotor or the incorrect rotor.

[Ron Kwas]

Nive;

Your brush looks fine...see: http://www.sw-em.com/Check_Your_Dist..._Cap_Brush.htm

Cheers

[niveketak]

Originally Posted by Ron Kwas

Nive;

Your brush looks fine...see: http://www.sw-em.com/Check_Your_Dist..._Cap_Brush.htm

Cheers

Yes it does apart from the burnt part on the end.