Vacuum advance dist. for Model A

[Hitman]

Originally Posted by ModelA29

#3 cylinder on old VWs ran 3 degrees of retard. That cylinder was shrouded by the oil cooler and they retarded the spark to keep it a little cooler. The Porsche 356/912 distributors had evenly spaced distributor cams.
The air cooled VW used a clockwise rotation distributor and the Model A is CCW.

This is not correct as you stated. VW did this only for a handful of years, and not for the reason you stated. It only occurred in the 69-72 VW’s that were 1600cc before they went to the doghouse cooler.

This didn’t happen with the 356/912 distributors. Those cars used different distributors. The distributor rotation has nothing to do with any of this.

[ModelA29]

Originally Posted by Hitman

This is not correct as you stated. VW did this only for a handful of years, and not for the reason you stated. It only occurred in the 69-72 VW’s that were 1600cc before they went to the doghouse cooler.

This didn’t happen with the 356/912 distributors. Those cars used different distributors. The distributor rotation has nothing to do with any of this.

ALL the early VW (1949 to 70 style cooling) and even the early mechanical only 009 (developed by Bosch for VW and installed as stock on some cars and stationary engines) had the retarded cam. After 1971 it wasn't needed. The trick mechanical (no retarded cam lobe) distributor has always been the hard to find Bosch Porsche 010. Yes distributor rotation of a VW/Porsche dizzy used on a VW or Porsche doesn't matter but it won't work right when you spin it backwards. Today you can buy a new ChiCom 009 on ebay for less than $30 cheap enough to play with.

https://www.vwnos.com/0-231-129-010?...caApahEALw_wcB

VW-resource.com wrote: A problem occurs in mismatching the 009 distributor with the doghouse-type oil coolers. Up to and including 1970, the oil cooler was internal to the fan shroud, and this meant that the #3 cylinder (left front) got warm air for it's cooling and therefore ran hotter than the others. So VW altered the timing on the #3 cylinder only -- the cam in the vacuum distributors has #3 cut 2-3 degrees later than the other three cylinders, to reduce the heat load on that cylinder a little. The early 009 distributors also had this feature.

But since 1971 the engines have a doghouse oil cooler that sticks out the front of the fan shroud. After passing through this oil cooler, the hot air is dumped overboard through some extra tinware. The fan itself is a little larger to supply this extra air. You should be able to see/feel this cooler sticking out the front of the fan shroud (front is front of car), slightly left of center. When you're under the car you should be able to see the rectangular air outlet in the tinware just above the bell housing. If the shroud is smooth/straight right across the front of the shroud, you have the earlier type of "in shroud" cooler.

So with the newer type oil cooler, the #3 cylinder now gets nice cool air for cooling, and the retard on #3 is not needed. The double vacuum distributors therefore have no retard on the #3 cylinder (double vacuum distributors were only used on '71 and later engines). VW dropped the retard on 009 distributors about 10 years ago too. So some 009 distributors have the retard, some don't. You need to make sure you have the right one. The only way to tell is to time the engine on #1 as it should be, then look at the timing for #3 (turn the engine 360 degrees). If the points open at the same time, okay; but if the points are opening later (the timing mark is now more about 4-5mm to the right), it's the wrong 009 distributor for a doghouse cooler engine.

[Hitman]

Originally Posted by ModelA29

ALL the early VW (1949 to 70 style cooling) and even the early mechanical only 009 (developed by Bosch for VW and installed as stock on some cars and stationary engines) had the retarded cam. After 1971 it wasn't needed. The trick mechanical (no retarded cam lobe) distributor has always been the hard to find Bosch Porsche 010. Yes distributor rotation of a VW/Porsche dizzy used on a VW or Porsche doesn't matter but it won't work right when you spin it backwards. Today you can buy a new ChiCom 009 on ebay for less than $30 cheap enough to play with.

That’s not correct. The Bosch 010 distributor was a VW bus distributor used only one year, and used in industrial applications for years after that. The Bosch 009 distributor was a two year VW bug distributor and used extensively in industrial engines later. The 009 never had the #3 cylinder retard. I don’t think the 009 distributor is good on T’s or A’s because they are centrifugal advance and don’t fully advance until 3000 rpm. Quality points and condensers are extremely hard to find these days.

VW’s ran hot on the #3 for reasons that had nothing to do with the oil cooler.

[Bob C]

Originally Posted by Hitman

That’s not correct. The Bosch 010 distributor was a VW bus distributor used only one year, and used in industrial applications for years after that. The Bosch 009 distributor was a two year VW bug distributor and used extensively in industrial engines later. The 009 never had the #3 cylinder retard. I don’t think the 009 distributor is good on T’s or A’s because they are centrifugal advance and don’t fully advance until 3000 rpm. Quality points and condensers are extremely hard to find these days.

VW’s ran hot on the #3 for reasons that had nothing to do with the oil cooler.

And the reason was??

[Hitman]

Originally Posted by Bob C

And the reason was??

Briefly, the #3 cylinder on a VW is like the #4 cylinder on an A. It's out of the way and doesn't get as much cooling as the other cylinders do. The #3 in a VW is the forward most cylinder due to crank journal spacing, and it's out of the direct airflow from the cooling fan. The #4 receives air directly on that side. It runs hotter due to the lack of air flow, and even then only ran hotter when they went to a 1600 cc engine with a higher compression ratio.

Pre 1971 the oil cooler is in the cooling airflow path of both the #3 and 4 cylinders, but only #3 runs hotter.

Happy to discuss further offline since this is off topic.