ahu crank pulley question

[Smoker]

I acquired another mk3 ahu today, non-running.

I could tell it was getting fuel, and every few rotations it would sorta kinda fire for a second.

First step, check timing.  With the cam and pump locked, the mark on the flywheel was nowhere to be found.  So I took the belt off and moved the crank till I found it, I want to say it was maybe the equivalent of a tooth or two...  so my question is this:

I remember reading about some tdi's that had trouble with the keyway/notch getting worn and letting the pulley spin enough to cause problems.  Is the ahu one of them?  And if that's the case, can it normally be fixed?  Or is my crank now a paperweight? 

[theman53]

typically the TDI's were ok with the crank the aaz were more problematic. I guess the TDI's did do it on occasion but nothing to cause a pattern about. I would just have a look at the key way. If everything else is ok and the valves weren't hitting, then you may have got lucky

[Smoker]

Ouch

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[Smoker]

More evidence of ouch.



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[libbydiesel]

I have seen that before on an AHU but only when the alt pulley no longer freewheeled on overrun. 

The crank looks decent.  You might try a new sprocket and see how well it fits.  If it wobbles then it would be very wise to address the crank.

[theman53]

not so lucky. I agree with libby, if the new sprocket is still a mild press fit then you can continue. Rebuild the head as the valves will be a problem at some point.

[Smoker]

I think at this point I'll pull the motor from my rusted out daily and put it in this car. Then I can take my time and make sure I make this right. I can't imagine the valves survived, so it's time to pull the head and really assess the situation. Also, that flat spot on the crank looks very much like a homemade hack job... It isn't square or uniform at all. Aren't ahu's supposed to have a notch instead of the d shape? My spare motor is at home, otherwise I'd look...

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[theman53]

nope, the TDI's should all have a D shaped crank

[Smoker]

Interesting. Thanks for the info. Maybe I'll swap the pulley before I pull the motor. If it's already broken, it can't do any harm...

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[theman53]

Wait to see if the rods aren't bent. Compared to the 1.6 rods the 1.9 rods are weak looking. Once the rods are ok then yes you could put the new pulley on, but while you are there why not replace the oil seal since that gear has to come off to do it.

[Toby]

The best course of action would be to put the new pulley on a and see if it has compression. If not you know you have bigger problems. If it does have compression start it up and see how it sounds.

It is highly unlikely that you would bend a rod w/o a catastrophic failure and usually that means the motor won't turn 360*, because the broken bits are in the way. He has already pulled the cam cover so we know the cam has not been blasted into several pieces taking a cam tower or two with it, so I bet it will at least run with a new cam pulley.

[libbydiesel]

I drove an AAZ into my driveway that had bent rods.  It ran a bit crappy but otherwise had no outward signs.

If the valves have been tapped by the pistons it is not uncommon that the head of the valve will break off at a later date even if they currently seal well enough to run decently.  I have two heads here at my place that 'prove' it.  With that much damage to the sprocket I would pull the head before running it  and replace any valves that have hit the pistons (exhaust) unless you really don't care if it drops the head off a valve and destroys the head, piston, rod and sometimes block.

[Smoker]

To be completely honest, considering what I have invested in this car, I think it's worth the risk to just see if it'll run with a good pulley, which I just ran home to get. But yes, I'll replace the seal, I've got a few new ones on the shelf.

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[Smoker]

I keep changing my mind. This is too much play for me to feel comfortable 'slapping it back together', even if it's just temporary. At some point, I need this engine to be good, whether it's for this car or a swap I have lined up for a friend. Might as well just pull the motor and do it right.

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[libbydiesel]

I have two custom jigs that allow me to machine the face of the crank and the keyway with the engine still in the car.  I've even gone so far as to weld up a worn crank and re-cut it to its proper shape.