Distributor advance maxed to early

[techbod]

This is for an '89 bus with a 1.9 DG wbx engine. Distributor is 0 237 024 035 / 025 905 205 Q (bosch/vw)

I'm working through a number of carb and distributor issues and have arrived at this one

The vacuum unit has been replaced as it was broken and the vacuum side of things performs as expected, but I seem to have an issue with the mechanical advance. The timing/advance info has been taken from Brick Yards data here: http://www.brick-yard.co.uk/VehicleSpec ... DGdata.htm. Measurements made using a strobe with advance wheel and a couple of different tachometers for the revs.

The van is set to idle when warmed up at 5' BTDC @ 900 rpm, vacuum off. Once the revs are increased the mechanical advance maxs out at about 28' by 2800-3000 rpm (depending on which tachometer I use). This is too early - it should be about 28' at 4200' rpm.

So I've stripped down the distributor to examine the weights and springs. It appears to only have one spring and although there is provision for a second spring, it does look like it might be designed for one: only one arm is weighted and there is no little plastic locating lug on the second un-sprung arm. There is no sign of a broken spring, though there were some small bits of plastic that could have been part of a 2nd spring locating lug. Its all lubricated, nothing dry or seized.

Picture here: https://www.flickr.com/photos/30324212@N04/14303573681/

I have searched the forum and web and I can't find any pictures or info to say if there should be a second spring or not. The nearest I have found is this forum posting http://forum.club8090.co.uk/viewtopic.p ... g#p7980993 which makes me think that a single spring might be correct?

Can anyone help with either confirming there should be only one spring in there? If so mine must be tired/stretched so I need to find one of the correct spec, who might sell one?

(I experimented with adding a second, weaker spring into the vacant position and tested it - it maxed out at 3500 which is a small improvement, though not sure what it does to the shape of the advance curve, but I'd rather have the correct parts in there than randomly adding bits)

Thanks for any help.

[itchyfeet]

My late q suffix dizzy has one spring but i also have an early c suffix which has two springs

[123-jn]

Is your dizzy an old one? Mine was the original from 1989 and only had 1 spring, I could not find out if this was correct so I fitted a new dizzy and now my advance is pretty much bang on. Perhaps they age badly? Ive kept the old one as a spare but the mechanical advance advances too much too soon and causes pinging. With the new one all is quiet ( apart from a tappet on number 4 of course!!!!) and a squeak from the suspension and a whine from the gearbox and a rattle from the cooker and a rumble from a wheelbearing etc etc etc . VW's are soooo great!!!!!!

[ghost123uk]

Is your dizzy an old one? Mine was the original from 1989.... I fitted a new dizzy and now my advance is pretty much bang on. Perhaps they age badly?

Umm, interesting. Shame you cannot just get a new spring (or I wonder if you can?) Maybe many of our vans might run a bit better if you are right about the springs weakening with age.

With the new one all is quiet, apart from a tappet on number 4 of course and a squeak from the suspension and a whine from the gearbox and a rattle from the cooker and a rumble from a wheelbearing etc etc etc .

[California Dreamin]

Bit Heath Robinson & not an exacting science but I suppose you could cut the end off the spring and reform a new end with the next loop..effectively increasing the springs tension and thus restricting the advance....just a thought.

Martin

[techbod]

Thanks for the replies.

So that confirms it - it is only supposed to have one spring. I've searched around but can't find anyone that seems to supply an advance spring for this dizzy. It looks like if it was a Lucas I would have no problems getting one.

I have found a couple of places that will make me a spring, but I need to know what the spring rate is, and I don't, (though I do have the rest of the required info).

I took it apart again today and replaced the second spring with a stiffer one - it now maxes out advance at about 3900, which is getting there, but the trouble with using two different rate springs I suspect I now have a fairly 'wavey' advance curve, as the 13-17' point is now at 2800 instead of 2400.

If I can't find someone that knows what the spring spec should be I might try taking out a loop, but there is no going back from that if it makes it worse. ATM I'm a bit loath to give up on an otherwise ok dizzy for the sake of a spring.

If I can't find one the next try might be to replace both springs with a matched pair and try again, though the dizzy is designed for one so no idea if it will ever work properly like that. I'll post if I come to a useful conclusion

[itchyfeet]

025 905 205 Q



025 905 205 C

[techbod]

Thanks itchyfeet.

Unsurprisingly my Q looks like your Q, same colour coded plastic bits as well. The C is interesting - it appears to be weighted on only one arm like the Q and to my eyes at least, the springs appear to be different. The one on the unweighted arm appear to be made of a smaller diameter wire, so it looks just like my Q does at the moment after I have mucked around with it. I wonder what the advance curve for the C looks like.

I'm waiting to speak to a local spring maker tomorrow and see what he has to say.

[bigherb]

Try these people for distributor parts they have always managed to sort me out.
http://www.ignitioncarparts.co.uk/Conte ... About%20Us" onclick="window.open(this.href);return false;

[techbod]

I decided to give the spring maker a go. As much for the interest as anything else. He took the spring and made various measurements, I then had to wait a little over a week before I could pick the spring up as he was rather busy. As he has a min charge, he made me about 8 springs which turned out to be useful.

When I picked them up, he said he had put plenty of initial tension on the springs - not knowing much about springs, I didn't really think about the consequences of that. He did say though the initial tension could be reduced or even removed by careful stretching of the spring. The original spring is stretched so that in resting position it has a fair gap between the coils, the new springs were all tightly wound.

First test didn't go as expected. Setup in the normal way, engine warmed up, vacuum off, with strobe and tachometer and starting increasing the revs. I got no advance at all until about 2500 rpm - I wondered what I had done wrong until I figured its the result of having a fair amount of initial tension. As I sanity check I sacrificed a spring by stretching it to match the length of the original, and tested it - sure enough it started advancing about the correct point and maxed out about 2500 rpm same as the original spring.

To cut a long story short I tried several springs with differing amounts of stretch (to reduce/remove the initial tension). The best I have so far is an improvement over the original spring, with the max advance maxing out at approx 3600 (instead of 2400). The rest of the curve is a reasonable approximation though not as similar as I might like.

As far as spring experiments goes, I may leave it there for the moment, its taking up alot of time and other things on the bus need doing. On the plus side I the time taken to strip, change the spring and rebuild the dizzy has come down to about 10 minutes. I may make some phone calls to some suppliers (thanks for the links) and see what bits they have, thought here must come a point when getting a replacement dizzy becomes a better option.