Amazon: Damaged JFUR4 distributor

[HRA]

I've got an Amazon saloon with a B20A engine. A while ago I set-up the ignition timing "according to the book" - 19 degrees BTDC at 1500rpm with the vacuum disconnected and plugged. The car ran well and felt lively enough but there was obvious pinking on acceleration in top gear up-hill. So I did the usual thing and backed-off the advance at the distributor. Things got a bit better, but still some pinking on acceleration up-hill. So I backed-off the timing a bit more, but the pinking is still there. OK, so I'm not heavy-footed and I don't often notice the pinking, but with the timing backed of some 10 degrees now the car isn't so lively.

Last night I finally got around to looking at the distributor. I wondered if there might be a problem with the centrifugal advance, and indeed there was. The mechanism is quite free and the light spring is fine. However, the heavy spring had become detached at the outboard end. On closer inspection it looks like the top of the attachment-point has broken off. This is a finger of sheet metal that should be wide at the top, thinner in the middle, then wide again. It looks like it has snapped off at the thin section.

A few minutes with a couple of files and I've managed to refashion the remains of the finger so I can get the spring back on. It feels reasonably-firmly attached but it is only a running-repair. I've managed it so that there is still some slack at the other end of the spring where it mounts on the round post, so all should be reasonably good when I set the timing-up over the weekend.

I'm going to look-out for a second-hand distributor - perhaps one that is going "for spares". Is this wise or is the damage I've seen a common failure mode? Is it worth a gamble on an old unit or do they all break in exactly the same way? Any advice would be much appreciated!

[Triple-S]

J, I've just sent you a direct mail in case you'd rather have such at your other address.

P

[Bracpan]

Although I have a B18 engine my dizzy is from a B20 and i'm getting very similar problems, after some good advice from the people on here I am thinking of going for a 123 Distributor that should i hope last for many many years...

[Ron Kwas]

HRA;

This is very interesting...please give the Bosch PN on side of the Dist, and I will see if I have Dist data and put further info together for you...bottom line is that this is, I expect a fairly rare failure (actually first time I've ever heard of it) but if you can file a new keeper notch into the spring mount, and be confident it will stay and not pop off in service, I expect it will be a good long-term fix, and replacing the Dist is not necessary.

It's great that you identified and repaired the root-cause of the issue...clearly the second advance Spring (for upper RPMs) was completely out of the picture, so your advance was too high too early, and that completely explains the "pinking" (on this side of the Atlantic: Pinging!).

Ref: https://www.sw-em.com/Volvo%20Igniti...CA%20Servicing

I'd also be interested in any pix you might have of the damage and repair.

Cheers

[Ron Kwas]

HRA;

I don't know if you have a type ... 099 version of the Dist (please confirm if possible!), but here is what your CA curve may have looked like:

...full advance at 1500RPMs...yikes!...welcome to Ping-City (not a place in china!)

I'd still love to see some detailed pix of damage and your repair if possible.

See also: https://www.sw-em.com/Volvo%20Igniti..._of_CA_Failure

Cheers

[HRA]

Thanks Ron-Kwas; that's pretty much how I visualised it. My distributor probably has a slightly different graph since the number ends 077. Looking at the 099 graphs, the heavy spring governs the last 5 degrees of advance. I had to back my timing off by about 10 degrees to stop the pinking (or pinging) so I maybe the change of slope of the 077 graph to starts earlier?

Mechanically my work-around seems to be holding-up. I tried to get some photos but the auto-focus on my phone wasn't having it - get close enough to see and all it wants to focus on is the background! However, even though the heavy spring is back in operation I still need to retard the timing nearly 10 degrees to be sure of no pinking.

That's set me wondering about the other causes of pinking:[LIST][*]Spark plug too hot[*]Low-octane fuel[*]mixture too weak

I'm running NGKSPARKA007037 plugs - I think they're pretty standard and I haven't seen any of the white deposits and damage that overheating causes.

I do usually buy the basic 95 RON unleaded fuel. In the past I did try higher octane versions but I didn't notice any difference apart from the price. Having said that, I filled-up again yesterday and added some Castrol Valvemaster Plus that's supposed to increase the octane number.

I've got a single Stromberg: I suppose it might be running a bit lean. I'm getting 30 mpg at the moment so it's certainly running "efficiently"! I set the mixture at idle using a glass spark-plug so I can see the flame-colour in the cylinder. The Stromberg could be running lean at higher revs though.

So, to my plan of action. Triple-S very kindly let me have a couple of old distributors. He described them as "rusty" but a soak in paraffin is getting them clean. I'll either swap-out the part I need for mine, or assemble a complete replacement. That should get the centrifugal timing right. I've already checked the vacuum advance and that seems air-tight.

While that's happening I'm cleaning the air-filter so I've got a level playing-field with the Stromberg.

I'll set the timing at 19 degrees at 1500 rpm. If the Valvemaster has done the trick then there should be no pinking. If not I'll see if richening the mixture slightly solves the problem. If it does then all well and good. If not I'll have to go back to retarding the ignition until the pinking goes away. With any luck I won't need to retard it a full 10 degrees!

I think that sounds like a plan - I'll update this when I've made more progress. In the meantime I've got to go back to the day-job!

[Ron Kwas]

HRA;

Thanks for update and additional info. I'll see if I have CA graph for 077 config. Pink(g)ing can also be caused by carbon deposits in Combustion Chamber increasing Comp Ratio to the point of compression ignition, or glowing hotspots (if you have access to a bore-scope camera to have a look in a spark plug hole to confirm)...you might need to decarbon Comb Ch.

Again, it's great that you sussed out and were able to sort the root cause...I think the spring-mount failure is quite rare, and if you are mechanically happy with the repair, I don't think it's necessary to consider replacing the Distrib. I understand about pix...too bad, but please think of it next time you have Distrib apart.

The glass spark plug (Gunson's?) is OK for setting mixture...the trouble is (and I tend to always point this out, because it is so important) checking and setting it at idle is only marginally useful, because at idle, engine is not under load (and not pink(g)ing!)...to be of any real value, mixture ideally needs to be checked under load/road conditions or on a dyne, where it is pink(g)ing, but that is a significant increase in cost/complexity...

Cheers

[c1800]

“ I'm running NGKSPARKA007037 plugs”

Not familiar with that number for NGK spark plugs. Are they labeled BP6HS on the insulator?

[HRA]

Sorry c1800, that was all the information I had to hand this morning. I've been out to the car, pulled a plug and it's a BP7HS. I think that means it's a bit cooler than a BP6HS, so at least I can rule-out the spark-plug being too hot.

I suppose that a cooler plug might be more prone to fouling but the tip of the one I pulled looks fine - a nice light brown colour - just what I'd expect if the mixture is about right. Fouling aside, is there any other disadvantage to running a slightly cool plug?

But in the process of checking the plug I found a more fundamental problem. With the car out of gear and the handbrake off I couldn't roll it back on a level garage floor. Flat tyre! It would have to be on the side that I can't get to easily - that can be a job for another day!

[c1800]

yes the BP7HS is cooler, but if they're running clean, all is good. I know of no disadvantage to using them. in fact I have set ready to go in my 1800.

Hope the tire can be repaired.

Cheers.