Source for dizzy advance springs in the UK?

[techbod]

Long shot but anyway...

Anyone know of a source / manufacturer/ little old man in a shed, preferably in the UK that can supply distributor advance springs?
I can find one supplier for Lucas based dizzys but in this case its for a Bosch - and its a single spring design so I need to find someone that knows the spec.

Thanks.

[erictharg]

Worth giving Aldon a call. Not sure they do much with Bosch, but if not they might know someone who does...

[Westfield 129]

Any Porsche tuner specializing in the 4 cylinder cars, especially if they do vintage race engines. Pertronix might be able to help as well.

The distributors are still used in FFs, so I imagine that the parts are on the shelf at many of the racer supplies that cater to the X flow racers.

Any distributor shop with a distributor test machine should be able to supply the springs in various tensions as well.

Bosch has a vintage parts department that might be able to help.

I did a quick Google search for "Vintage Bosch Distributor Parts" and got half a dozen suppliers here in the US.

Are you missing the springs, or is there some other problem with the advance curve?

[techbod]

Thanks for the replies chaps.

Yes its an issue with the advance curve - it should max out at approx 28 degrees (with vacuum off) at 4200 rpm, but it is actually maxed at 2800 rpm. I can find nothing else wrong with the dizzy so in the first instance I'm going to assume the current spring has stretched or is just tired - its probably 25 or so years old, so its not unlikely. This is an old VW btw - nothing exotic I'm afraid

I'll give Aldon a call tomorrow and good thought on the vintage side of things - I'll have a search.
I have also found a local spring maker - if I give them the old spring I imagine they can have a good go. I know what the advance curve should look like so even if I have to go round a couple of times, it might be a reasonable option if all else fails.

[Westfield 129]

The simple fix is to set the timing at max advance RPM and see where it comes out at idle.

Use a dial back advance timing light, setting at the "0" degree mark with your specific timing dialed into the timing light. This should give you the correct max advance, and the idle should work out OK.

Those springs are easy to find from any VW/Porsche parts supplier. Nothing special, and they are cheap. But I doubt that the springs are the problem.

Set the timing at the max advance setting (around 3000 RPM) rather than at idle. That should fix your problem.

Note that this is how we set the timing on most every engine that has a dizzy. Max advance at max advance RPM. Usually around 28~32º BTDC, using a dial back timing light.

[techbod]

Thanks - that's a good tip, I'll use it for doing the timing when I've finished getting to the bottom of the current investigations.

It wont work satisfactorily for me at the moment, the whole advance curve is 'telescoped' into almost half the length it should be. Setting the timing at max advance (approx 4200rpm in this case) setting gives me an idle that is at least 10deg or so out of spec.

So I went the glutton for punishment route first (partially because I'll learn more this way) and went to a spring maker. He has made me a handful of springs based on the original springs' dimensions and properties.

Results are, errm, interesting.

First new spring test started well. Max advance 28 deg at approx 4100 rpm, near as dammit the book spec. Idle is correct, so the curve bookends are ok, but what happens in the middle isn't. As the rpm is increased from idle I get virtually no change in advance until say 2800rpm and them it crams the whole advance curve into 1200 rpm.

The spring maker chap did tell me he had put 'plenty of initial' into the springs, I just said OK because I hadn't really thought about the implications of what that meant until I got the results above (I've not really thought much about spring properties before). I'm guessing from his description I don't really want much in the way of initial tension, the advance curve should start increasing from not much above idle. The spring maker did tell me I could reduce the initial by stretching the spring. He suggested an iterative approach to doing this.

First spring I stretched too far - in fact its as stretched as the original bosch spring, and when in the dizzy, it has a very similar advance curve i.e. it max's out to soon. The second spring I just tweaked to have the merest hint of coil separation at rest. The advance curve is slightly better - maxed out at 4000 rpm and starts to climb about 2000 rpm, but thats still to late - should be about 13 deg by then.

However the difference between the first and second spring length is pretty small, and I'm not confident that I can get the required level of accuracy with a pair of needle nose pliers and guessing. This all needs to be sorted and running in a weeks time, so I'll have another go on Friday, if I can't get a reasonable approximation of the spec advance curve I'll have to ship some parts in, or even just buy a new dizzy.

[Westfield 129]

Which version of the Bosch distributor do you have? Do you have a manual or exploded drawing of it? Is it a JFUR4 (vacuum advance) or a JF4 (mechanical advance only)?

I happen to have a JFUR4 from a Porsche 912 that is in very good shape.

Generally, the springs control the rate of advance, not the total advance. The total is controlled by the flyweight travel.

Other than the perception of too much advance, too quickly, what is the problem with how the engine runs?

Why not set the idle advance, then check the total advance. What do you get? At what RPM do you get max advance and how does it run?

[techbod]

Its a 0 237 024 035 Q as fitted to the t3/t25/Vanagon. Its a vacuum type.
I must be clearer:Total advance in terms of max degrees is correct. Vacuum only advance is correct.
Centrifugal only advance is correct in terms of max degrees achieved, it just happens too early - It is the rate of advance that is the issue.
It should look like the blue trace, DG, shown here: http://wiki.club8090.co.uk/index.php/Pe ... nce_curves. If I were to plot the results from mine it would look similar except with a steeper gradient, so it is 28 - 30 deg or so max advance at 2500 rpm or so instead of at 4200 rpm.
Replacing the spring (singular) does improve things and reduce the rate of advance, which is what I have been trying, I just haven't yet found one that gives me the required curve.

Hence all the faffing around trying to find the correct spring...

The vehicle has been in storage for the best part of 3 years and has numerous issues I am slowly working through. I don't expect it to be a sports car but its acceleration seems pretty poor, so I started digging around and the advance curve issue showed up. It may not be the reason for the poor acceleration but I'd like to tick it off the todo list. Carb has been rebuilt, brakes aren't binding, vacuum hoses have been replaced, new fuel filter etc etc. I'd like to get to the bottom of why the dizzy doesn't appear meet the published spec anyway.

I didn't really intend to take up space on the forum with T25 issues - its probably about as far from a W11 as you can get. Talking to Matthew at the kit car show about the forum and what it might cover, he came up with the suggestion that anything that was a Le Mans replica type car was probably in the spirit of the board. An excellent suggestion - but it would be a stretch to include the T25 in that.

[Westfield 129]

I doubt that the problem is too quick or too steep an advance curve. Usually, we set up the distributors to advance quicker to build power quicker. If you are not getting any problems with pinging, the advance curve is likely helping rather than hurting. And... The Vanagon was hardly a performance machine. If you are used to a bicycle, the Vanagon may feel slow... Really slow... Especially going up hill.

Have you checked the valve adjustments or done a leak down test on the cylinders? Tight valve clearances can cause the problem you are experiencing.

Does it have points? (I have yet to run the part number). If it does, check the alternator output. If over 15V, check the points for burning and a change in timing.

[techbod]

No points, its a Hall effect sensor, tappets are hydraulic. Not down a leak down test yet - might not like what I might find
Had another go today at trying to get the correct (by the book) advance curve by modifying a new spring.
Got a reasonable improvement over the original spring, but still not correct. Anyway I'll take it out for a tomorrow and see how it actually feels on the road.