Not as lucky as I had hoped

[Smoker]

Hi, btw.  First post... I've been lurking for a while. Tons of good info here.

I bought a mk3 Jetta yesterday.  It was advertised as having a 'blown engine'.  I called and asked if the t-belt had let loose, or what exactly the problem was.  "I don't know anything about cars", he says... "it just runs really bad and smokes a lot.  My mechanic says the motor is blown."

It was cheap enough that I can't lose, and I was hoping for an injector problem or something.  I also have a B4 Passat here that had an intermediate shaft failure, and I was hoping I could make one good car out of two, then rebuild the bad motor to stab in my Dasher.  Not the case...





Uh... where did my follower go?? The only thing that makes sense to me is that the valve seized and the cam lobe beat the follower to pieces, unless I'm missing something.  I guess it's time to pull the head to investigate further.

Anyone have a complete head to sell me?

[vanbcguy]

Yowza...

Pull the head for sure - most likely you'll find some evidence of piston to valve contact.  With any luck you'll only need a new cam, follower and a few valves - there's a number of engines running around here with significant valve impressions in their pistons but no ill effects once the broken stuff has been replaced.

[burn_your_money]

You'll probably need to machine the crank. TDIs have crank failure problems as well (which is my guess). You should get a clutched alternator pulley for it as well.

Where are you located?

[Smoker]

I'm in central VA, although if I hang around here too long I may need to move north of the border...

What would the crank failure be? It still runs, and sounds normal (as normal as it could sound on 3)



Maybe I should paint the full picture:

I paid $400 for the Passat.  316k miles, and is actually pretty straight and clean except for that whole busted motor thing.  The PO claimed that it's still on its original turbo and clutch (!!)

I paid $600 for the Jetta.  I basically bought it hoping I could make one good car out of the two, keep the swap parts for my Dasher, and part out/scrap the rest and break even.

I've owned at least 30 VW's, a few diesels, but never a tdi.  Obviously my next step is to dig deeper into both to get to the bottom of what I'm dealing with... besides that, any advice?

[vanbcguy]

The crank failure issue is a design flaw in the AAZ.  The timing belt pulley on the crank itself gets loose over time and then eventually lets go - this is a very common cause of timing belt failures on AAZ engines. 

The AAZ uses the same style of crank nose as the later 1.6 engines, but they switched to a serpentine belt.  Turns out the serpentine belt is so much more efficient at transmitting power that the crank nose couldn't take the stress.  Basically every time a piston fires it causes the crank to accelerate, and then as the next piston starts its compression stroke it slows down again, that piston fires it accelerates, slows, accelerates, etc.  The alternator however has a big spinning mass that wants to keep going at a constant speed.  The 'pulses' from the engine going about its business would fight against the alternator, hammering the pulley back and forth on the crank.  Eventually the keyway starts getting chewed up and it causes the big bolt at the crank itself to start backing out, then it tosses the pulley enough to throw the timing belt.  That big bolt is a stretch bolt btw so it is supposed to be single use.

There's two fixes that should be combined if you are planning on keeping the engine.  As burn_your_money mentioned, the crank is probably chewed on yours given that it has experienced a previous timing belt failure.  The first fix is to machine the end of the crank so it can accept the newer TDI-style crank pulley.  It can be done in-car, a few folks on here have done quite a few of them.  The TDI pulley is fairly cheap and not that hard to find.  The TDI pulley has a "D" shape as opposed to the keyway design on the old ones.  The "D" spreads the load out over a much larger area reducing the stress on the crank nose.

The second fix is to switch to a clutched alternator pulley.  The later AAZs plus most of the TDIs came with a clutched pulley that lets the alternator keep turning when the serpentine belt slows down.  This way the 'accelerating' forces from the engine still act on the alternator but the 'decelerating' forces do not, this reduces the hammering on the crank pulley.

The recommended best practice for an engine you are planning on keeping and doing any kind of mileage on would be both of the above - go to the TDI style crank pulley and the clutched alternator pulley. If you don't have a lot of love for the vehicle you may be able to get away with just one of the two fixes. 

At the very least though, even if you only plan on keeping the car for a year or you plan on selling it on, buy a new crank bolt and inspect the pulley.  Maybe the pulley is fine, maybe it is chewed up beyond recognition.  No matter what I'd want a good bolt in there installed as per the Bentley manual.  As I mentioned above, the bolts are single use.  Given that whomever did the "work" on the engine chose to leave it with a missing lifter I would not in any way assume that the current crank bolt is installed correctly or hasn't been reused.  The bolt is cheap but will definitely fail if not installed properly.

[libbydiesel]

I think the two cars are both TDIs.

[vanbcguy]

I think the two cars are both TDIs.

Now see there's a bit of info that'd be particularly relevant and helpful here... So OP, what DO you have anyhow?? That does look kind of like a TDI head upon closer inspection...

[libbydiesel]

Also, the lifter isn't gone, just the top of it is.

[Smoker]

Sorry, gents... I never thought to clarify. Both cars are tdi's.

[Smoker]

I'm just used to thinking within the U.S. market.

[R.O.R-2.0]

pull that head, we need pics!!

[Smoker]

I would imagine that made some noise, whatever it was... nothing looks amiss on the other end of things.  There was a loose, cylindrical something sitting on top of the remains when I pulled the cam.  I forgot to set it aside for a pic. 

I have the heads off both cars, and taking them to the machine shop in the morning.  Hoping we can make one good head between the two and at least get one of these cars on the road.  The passat head has at least one bent valve and one cracked lifter.

[burn_your_money]

The crank failure issue is a design flaw in the AAZ.  The timing belt pulley on the crank itself gets loose over time and then eventually lets go - this is a very common cause of timing belt failures on AAZ engines.

To add to this, there are quite a few documented cases of TDI crank failures, exactly the same as the AAZ. I've personally repaired one. I'd say that the clutched alternator pulley is mandatory with a serp belt. Many TDI guys are pinning their crank gears to avoid this issue as they feel the clutched alt pulley is not sufficient.

[R.O.R-2.0]

The crank failure issue is a design flaw in the AAZ.  The timing belt pulley on the crank itself gets loose over time and then eventually lets go - this is a very common cause of timing belt failures on AAZ engines.

To add to this, there are quite a few documented cases of TDI crank failures, exactly the same as the AAZ. I've personally repaired one. I'd say that the clutched alternator pulley is mandatory with a serp belt. Many TDI guys are pinning their crank gears to avoid this issue as they feel the clutched alt pulley is not sufficient.

was this much of an issue with gassers?

or am i just ASKING for problems by running a serp setup on my 86 GTI?

pretty sure VW used that crank design to the bloody end on the ABA, and you dont hear of them failing like a TDI?

im under impression that it is the high compression of the diesel that kills the nose of the crank? 10:1 is ALOT less than 24:1..

[burn_your_money]

I have a theory that is has to do with the pulses of the alternator and the injection pump but I really don't know. The high compression is probably also a factor.