Refreshing a DVDA or SVDA distributor - my photographic tale

[busdaddy]

Looks like it'd be adjustable to me, when installed varying the length of that stop would allow more or less advance as that sloped section of the arm contacted it.
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[Tcash]

Note the pin on the adjustment screw is not centered. So as you turn the screw is moves the pin toward and away from the actuating arm stop. It would allow you to limit the total vacuum retard advance.
Tcash

Thanks for the pix. What are you shooting them with?

edited
Tcash

[NASkeet]

[airschooled]

[SGKent]

About 1980 VW changed the dual advance mechanisms that were sold as replacements by the dealer. If you bought one from VW in 1976 it was identical to the old one. If you bought one about 1980 it came with a set of instructions and an allen wrench. You found the distributor can model you needed on the instruction list where it gave a number of turns. You put the allen wrench through the vacuum nipple and turned it to that number of turns off the stop. I do not know if they were always this way and VW stopped setting them at the factory, or if this was a one part fits all device. I bought one of these and remember asking the Econo parts manager (a friend) show me that the fiche called out for this weird set it yourself model. It did show that it had superseded the original part.
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[wcfvw69]

I was just looking at this old 853 vacuum can again. If you look at the pictures of the adjustment screw, it appears to have been locked by brazing it at the adjustment threads.

I think SG Kent is probably on point. It may have been a "one size fits all" can though I still question how much adjustment it really had? The cut outs on the vacuum arm appear to only move so much before they would bottom out against either the peg or the back of the vacuum can body..

I tested this used can and shockingly, it only holds vacuum on advance as the retard section is blown. I may carefully disassemble it and see what the material is inside.

I circled the areas where the arm stops hit.
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[busdaddy]

So the advance is fixed and the adjuster is for the retard only, interesting. If you clean it up is there any marks on that adjuster like 1-2-3 or something?, different years used different amounts of retard, it's likely as SGK suggests one adjustable part to replace many preset ones.

And yes Nigel, you guys may have a rediculous amount of laws and regulations, but at least you didn't have to deal with smog equipment too.
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[SGKent]

[NASkeet]

[tasb]

The correct for NAm distributor for a manual trans 1973 bus would have been an 043 905 205 J distributor which was a DVDA unit. It would look very much like the above.
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[Peabody]

I have the small washers that go under the weights as well as the shaft "fiber shim" washers. I also have access to order the bushing that goes over the shaft to space the weights correctly (It's expensive unless we get a bunch of them and it doesn't seem to break easily but does appear to wear according to my measurements). I also have metal shims in .006" and .012" thickness for the axial shaft play.

Let me know if there's any interest in these. Thanks
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[wcfvw69]

[Peabody]

[tasb]

McMaster Carr has been my friend for years.
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Roads Scholar &
1957 Kombi low mileage 36 hp governor equipped M 178 Slow Drag Winner 2014, 2015, 2018

1965 hardtop Deluxe Microbus owned since 1990 M 620 factory 12 v 1500cc

1961 (October)Single Cab- Road Trip Workhorse

[surfbus23]

I think I'm running into the same problem Robbie had. My distributors are having trouble resetting to what I will call the home position. That is if I set it to 7.5* BTDC one it revs up a bit it doesn't return to 7.5* but rather something like 10-11*.

I have two distributors, an 009 and a 205S for a bus that I refreshed and everything is well greased and oiled. They have not mechanical issues outside of the bus but once I test play in the bus it does exactly as happens in Robbie's video below. If I advance the rotor it springs back but not back to where it started. I have to manually go back the rest of the way. If I turn the engine off it will also reset itself properly.

Robbie suggested that his was fixed by adjusting his spring. That didn't seem to do anything for me. Does anyone have any ideas about how to solve this?

Thanks!

[airschooled]

Hi surfbus23,

I'm sorry I can't help more, but that solution was ultimately washed out with new parts. It was a combination of excess distributor drive gear end-play, excess crankshaft end-play, and my need to get to work every day on time looking sharp. This is not likely to be your problem unless you had a DVDA like a 205Q. (I'm assuming your 205S is in a fuel injected Type 4 engine as well?)

When fully warmed up, can get your 205S idle reliably at 600-700 RPM while timed to 7.5° BTDC with the hose disconnected? This will establish a base line timing map, where anything that happens above it can be traced.

Robbie
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[surfbus23]

I've got a 2.0L with dual Weber IDF 40s, so the 205S/205P seemed the closest I could get.

Yes. I can get it to idle reliably, but keeping it at 7.5° is my problem. It's not like it jumps around. Just if it gets enough RPM to advance it will then have trouble returning to 7.5°. I found when I was out tuning today that advance was kicking in and throwing off the timing. I'll try keeping it at a lower RPM in the morning and see if that keeps the 7.5° in place for a LBI tune. I anticipate some idle weirdness though as I drive around and it only comes back to 11°.

I'm also going to check the linkage in the morning.

[wcfvw69]

[Peabody]

I agree with Bill. Your sticky area of the rotation is likely due to friction in the rotating assembly of the advance plate. Take it apart again and make sure everything is clean and lubed (don't use too much lube). Make sure everything moves nice and smooth. Then ensure the springs return the timing plate to it's home position without help. If they don't you may want to source replacement springs (not sure if the part number is the same from model to model so check on that when sourcing).

I'm not sure how Robbie's distributor advance plate could behave differently while installed in the bus other than binding of the shaft due to play in the housing bushings that the shaft rotates in. If the shaft has some misalignment due to the play I can see the load of the drive gear causing the tile of the distributor shaft causing the advance plate to be tilted and having more force (friction) on one side.

Pull the distributor and wiggle it around and see what you find. I'm curious.
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'74 Westy (parts)

[surfbus23]

Well... won't be testing this one out any more. I felt pretty confident in how well it was lubed up, but I remembered that the bushings did sort of bind when I went to push it in last time. The idiot that I am I was tapping it out and it wasn't going so I gave it a harder wack. It was caught on the lips of the housing and I bent it over. Will I ever learn. But here's a picture to show that it WAS nice and clean and well lubed. Now it's just a piece of junk.