Is there a way to verify flywheel TDC?

steve · Post by **steve** » Thu Apr 13, 2006 2:10 pm

Is there a convienant way with the head on to verify that TDC on the flywheel is actually TDC?

I figured that if that is off just a little bit that it could make a difference. I don't recall exactly but isn't the flywheel just bolted onto the crank? No alignment pin? So it seems like you could get some misalignment. Maybe not... I wonder how much could it vary?

Oh, I just thought of something. Take the timing belt off and turn the crank till it touches whatever valve is open. Mark that location on the flywheel. Then turn the crank the opposite way till it again touches the valve (should be the same valve right? I'll have to look at what valves are down) Then mark flywheel again and determine the midpoint between the marks. It should be the TDC of the crank and should hopefully be close to the tdc on the flywheel.

libbybapa · Post by **libbybapa** » Thu Apr 13, 2006 2:35 pm

You can remove an injector and use a feeler wire.

Andrew

steve · Post by **steve** » Thu Apr 13, 2006 2:42 pm

But it's got to be solid and of a fixed length/position so that the exact same piston location can be achieved on either side of TDC. I've heard of people welding a bolt on the end of a spark plug. But that idea won't work because it won't get down past the diesel prechamber.

GreyRabbit · Post by **GreyRabbit** » Thu Apr 13, 2006 4:25 pm

As long as you've got OEM flywheel bolts I'd be pretty surprised it it was off at all. The bolts are pretty tight where they go through the flywheel.

The holes are offset so you can't assemble it wrong as well.

tylernt · Post by **tylernt** » Thu Apr 13, 2006 9:45 pm

GreyRabbit wrote:The holes are offset so you can't assemble it wrong as well.

That's what I thought too, until I did a clutch job and my TDC mark went missing after putting it all back together. I did find a mark on the flywheel about 60 degrees off though.

steve · Post by **steve** » Mon Apr 17, 2006 10:30 am

I'm mostly concerned about any looseness upon installation or tolerance buildup that would allow the flywheel to be off by some amount that would cause any IP and cam timing settings to be off without you knowing it...

tylernt · Post by **tylernt** » Mon Apr 17, 2006 11:12 am

When I put my flywheel back on, I don't remember any slop between the bolts and bolt holes (not that I was looking for any). So I wouldn't be too worried, but as libbypapa says a feeler wire will make it past the precombusion chamber to touch a piston top if you remove an injector. Don't forget to replace the injector heatshield.

81rabbit · Post by **81rabbit** » Mon Apr 23, 2007 9:50 am

tylernt wrote:That's what I thought too, until I did a clutch job and my TDC mark went missing after putting it all back together. I did find a mark on the flywheel about 60 degrees off though.

I just helped a buddy take the pump off his '86 TD. I couldn't find the TDC mark on the flywheel. So we spun it around and there it was about 60 deg off. I'm 99% sure the car was running fine before removing the pump (the cold start seal was leaking so it wouldn't run - hence why he got the car cheep) but I'm wondering if there's a possibility that an "incorrect" flywheel was installed when the clutch was replaced a few years back.

Anyone else have any feedback on the issue?

thanks,

-J

calebc3 · Post by **calebc3** » Mon Apr 23, 2007 10:27 am

I have had a car with a correct flywheel that had been put on wrong by a shop that did a clutch job for previous owner. Car drove a lot like some older VW's I have had, ie not perfect. I started suspecting a problem when I was removing a leaking IP and couldn't find the TDC mark.
So, your scenario is possible. If I remember correctly, my problem stemmed from the pressure plate being put on wrong and the alignment pins being crushed. The flywheel then gets put on wrong because of the incorrectly aligned plate.
I dropped the tranny, redid the clutch and the new owner drives it daily.

audiesel · Post by **audiesel** » Mon Apr 23, 2007 9:53 pm

About three months after buying my car I had to do the IP because of a leak. The previous owner had had the engine rebuilt at some point, so obviously the clutch was done too. When I looked for the TDC mark, it definitely off. I used a stiff wire for a feeler gage and found TDC. Low and behold, I could barely see a mark someone had painted at the current flywheel position. I made the mark darker with a sharpie.

Don't know how it got like that, but that's my story.

libbybapa · Post by **libbybapa** » Mon Apr 23, 2007 10:44 pm

You can assemble the pressure plate to engine in all six positions if one bolt is left out. The flywheel can go in three different ways, but an alignment pin will get squished.

Andrew

CoolAirVw · Post by **CoolAirVw** » Wed May 02, 2007 8:06 pm

steve wrote:Oh, I just thought of something. Take the timing belt off and turn the crank till it touches whatever valve is open. Mark that location on the flywheel. Then turn the crank the opposite way till it again touches the valve (should be the same valve right? I'll have to look at what valves are down) Then mark flywheel again and determine the midpoint between the marks. It should be the TDC of the crank and should hopefully be close to the tdc on the flywheel.

Thats what the pro's do. There's a special tool that installs in spark plug hole for some engines that "stops" the piston just for that measurement.

Former VWDieselParts.com Forum

Is there a way to verify flywheel TDC?

Is there a way to verify flywheel TDC?

Top Dead Center Mark ~60 degrees off???

Re: Is there a way to verify flywheel TDC?