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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old July 5th, 2019, 12:05   #1
Digital Corpus
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Default Mechanical Timing off, but doesnít make sense

The $180 DMF a few have noted from Amazon is a great DD clutch, but I donít know if itís TDC mark is right. Iím in the process of resetting mechanical timing on this B4 with one and the facts donít make sense to me. This is what they are:
  • IP and cam shaft are in-time with each other.
  • Flywheel/crankshaft is 14 teeth behind the other two.
  • VCDS reports N108 @ ~65% to have pump in time with the crank/flywheel.
  • The 14 teeth is where I marked TDC on the flywheel due to where the cam and IP hit TDC themselves relative to a mechanical punch assumed to indicate TDC on the DMF flywheel.
  • This measures out to ~37-38į which is inside of the +/- 55į lobe separation and Iíve confirmed no valve-piston contact, which makes sense, but moving the engine back and forth with the cam at TDC points to the mechanical mark as true.

Why was this engine able to run? Is the mechanical TDC mark off because of the different transmission housing the DMF (Luk 17-050) has a different viewport? What do I trust, the physical matching of the IP-cam, or the VCDS matching of the IP-crank which matches fuel injection from the 3rd injector to the timing output of the crank position sensor?

This occurred before and after resealing the IP, which I opted to do off the car. I know the history of the car with no hard starts and regular levels of smoke. Iíve been in VCDS before and after and Iím having a hard time understanding how the crank can be so far off and the car run normal.
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Last edited by Digital Corpus; July 5th, 2019 at 12:10.
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Old July 5th, 2019, 15:05   #2
scurvy
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My LuK RepSet 17-050 flywheel had a TDC mark that looked like this:




Perhaps the B4 viewing window is offset versus the A4?
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Last edited by scurvy; July 8th, 2019 at 07:04. Reason: removed & reuploaded clutch replacement pix
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Old July 5th, 2019, 16:40   #3
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Nope, not on this one. It's a divot like a center punch mark. I was thinking that the viewing window is different too, but the couple of manual A4's I've looked at under the hood didn't seem that way.
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Old July 5th, 2019, 20:42   #4
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Wouldn't the valves and pistons meet at 14 teeth out?
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Old July 5th, 2019, 20:48   #5
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You didn't compare TDC marks on the flywheels before you installed the new one?
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Old July 5th, 2019, 21:53   #6
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Quote:
Originally Posted by Seatman View Post
Wouldn't the valves and pistons meet at 14 teeth out?
If the cam is kept in time with the crank, no. If the cam is stationary, yes.


Quote:
Originally Posted by turbodieseldyke View Post
You didn't compare TDC marks on the flywheels before you installed the new one?
Honestly don't remember from a couple of years ago. Went hunting for the other DMF that was previously in the car, but it's MIA. Even before firing it up, I spun the engine with a wrench and didn't have an issue.
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Old July 6th, 2019, 04:11   #7
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Okay. Found the TDC mark with two additional marks that appeared to be indicator arrows. This TDC mark was a mechanical depression that differed from the previous photo, which matches a Sachs stock DMF, and is positioned and shaped such that during the daytime, it appears to be a shadow. Final count was 4-4.5 teeth of 132 teeth, or 10.9-12.3į off with the cam and IP advance, or crank retarded if you prefer.

Oh, and the other mechanical marks, there were 4 and they were not evenly spaced. I marked the TDC-neighboring starter ring gear teeth with a gold and silver paint pens.
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Old July 8th, 2019, 06:27   #8
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The flywheel bolts are not equispaced on the PCD so it can only bolt on one way. When lining up with the Sachs unit removed from my Golf, the marks looked the same and were in the same spot.


My wife's (sold) NB had a flywheel with not one, but two TDC marks! JasonTDI found that one out the hard way when doing the timing belt. I rediscovered it when doing a pump replacement. The proper mark was made more prominent with a chisel and a paint marker.



Glad you found the TDC mark - you may consider the use of a chisel as marker can fade or come off with solvent or oil.
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