TDI Syncro--Finding TDC for Timing Belt Change

[HBB]

I'm getting ready to change the timing belt on a 1990 Syncro converted to an ALH variant TDI. Bought the van with the ALH conversion already installed, so I am not sure what, if any, steps were taken to allow for determining when the crank is at TDC. It seems like its in proper time now, but I would rather not guess and lock the crank when the IP and cam and lined up and assume everything is correct.

I'm not seeing any way to get a look at the flywheel. Even if I could, I have no idea if the flywheel has a properly aligned TDC marking.

Am I stuck with pulling a glow plug and trying the old-school method of sticking a rod of some sort in the hole and rotate the engine while carefully marking the protrusion of the rod from the hole? And once I find TDC, what is the preferred approach for marking it so I don't have to go through this exercise again?

I have the metalnerd tool set and the dieselgeek timing belt kit, and everything is so easy to access that this belt change should be a quick and simple job if I can be sure I've got the crank in the proper position.

Thanks in advance.

[Jeff's Old Volks Home]

Why not use the mark on the crank pulley and front cover? It's very accurate. Plus you'll use VCDS to set the pump timing when you're done...
Jeff
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[tjet]

This is for a later engine, but it may be helpful...

http://easylearns.in/LearningVideos/EEE/watch/fAi667H7M2Y

[jackbombay]

There may/should be a hole in the adapter plate, when the engine is at TDC there will be a punch mark that will be in the center of the hole.
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[HBB]

[HBB]

[Jeff's Old Volks Home]

[hans j]

On my Mexican bell housing from Eurospec, the flywheel marks did not line up correctly at TDC. The flywheel they supply didn't come with any marks and I had to add them so it lined up correctly in the bell housing window.

The crank pulley is definitely really close with it's marks, and if you have the crank toothed gear holder with the timing belt kit, there won't be any issues. Just make sure to have the rest of the holders in place and tension the belt before tightening the camshaft. Don't forget to set injection pump timing after the belt is done. Personally I like to run about 1/4" above the center line in the VCDS graph and an IQ of around 3.5.
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1986 Canadian Syncro Westy TDI - 1989 Syncro Single Cab - 2001 Audi S4 - 1981 VW Caddy ABA - 1980 VW Caddy EV - 1973 VW T-181

[Tristar Eric]

I'm pretty sure the cam lobes for #1 are pointing up at TDC #1, also there is a witness mark on the tin of the crank. I use the belt change tools from diesel geek. It's pretty much a no brainer. Get TDC #1, pin locks IP, slide in the cam lock, and bolt on the crank lock. ( loosen the cam bolt before inserting cam lock).
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[HBB]

Thanks for the responses, I'll plan on going by the crank pulley when the time comes.

[njt1rider]

http://pics2.tdiclub.com/pdf/a4timingbelt.pdf

[markd89]

[HBB]

[svenakela]

When the belt has been of for some reason I've done it like this several times with good results.

1. Everything is referenced with the first cylinder. Remove the glow plug or the even better the injector for the first cylinder.
   
   
2. Use a long metal rod (welding rod is perfect) and let it rest on top of the piston. Turn the engine slowly until you reach the point where the rod is standing still and starts moving down again. Vision is good but with a finger resting on the rod you'll be amazed how accurate you can be.
   
   
3. Turn the engine back and forth a few times to find the two points where the rod stops moving and the point where you have the smallest movement noticeable again.
   
   
4. You have now found the two points that are the entrance and exit points for the crest of the TDC. This means, right in between these two points you have TDC.
   
   
5. If you can you should now mark it up with a drill mark or similar on the flywheel.
   
   

Actually, the TDI tools used to find TDC comes with pretty bad tolerances (the locking pins that are used can make the TDC float several tenths, over a degree in flywheel angle) and a tuning workshop or performance tuner always measure the TDC each time to make sure they are spot on.
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[HBB]

[HBB]

Ok, so I finally dug into this project today.

For future reference, here's what the mark on the harmonic balancer looks like when lined up with the corresponding mark on the lower timing belt cover:

As I feared, however, when the camshaft and injection pump are locked in place, this mark is way off, possibly a tooth or two off:

Mark when cam and IP are locked:

#1 lobes up:

Camshaft lock in place:

IP lock in place:

I have pulled the #1 cylinder glow plug, and am trying to find TDC using the old school method described elsewhere in the thread. I'll be interested to see if the marks actually line up at TDC.

I have no reason to believe that anyone who worked on this vehicle previously had the slightest idea what they were doing, and I would not be at all surprised to find that the timing had been a tooth or two off.

[markd89]

Please DO post back when you find that mark. When my timing belt is due, I need to find TDC and plan to use the same method...

Thanks,
Mark
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78 TDI Sunroof Bus
Los Angeles

[HBB]

Well, with the marks lined up (and #1 lobes up), a rod inserted in the glow plug hole confirms TDC. There's a few degrees of "float" at this point.

Just eyeballing it, it looks like the crank is a tooth behind. I understand that there is a bit of margin for error on the ALH before you'll get piston/valve contact, sounds like it's not that uncommon to end up out of time by this much due to improper tensioning of the belt. The guy I bought it from had told me he swapped in a metal impeller water pump at some point, so it's possible that this was when the timing error was introduced.

[?Waldo?]

[?Waldo?]

One VERY accurate method I have used to confirm the TDC mark is to remove one glow plug and insert a clear hose into the glow plug hole. The clear hose should be 3-4' long and should fit the glow plug hole tightly so that it does not leak air around the hose (you could add grease around the hose to seal it and be sure it doesn't leak). Rotate the engine close to TDC and then insert the other end of the hose into a clear glass jar that has a little water in it. Watch very closely while a helper rotates the engine to TDC. Air bubbles will come out of the hose and the exact point where the bubbles stop and instead, the water starts to go into the hose is TDC. Take care not to suck water into the engine (duh). I have found this method to be easier and far more accurate than using a dial indicator on the piston crown.
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