AAZ crankshaft snout tdi "D" mod

[scopefrfd]

I was going over some posts on the inherent weakness of the AAZ crankshaft keyway.  Some repairs, the crankshaft keyway is welded up and the crank snout is reground to accept a tdi "D" crank gear.  Others the crank snout is machined 180 degrees opposite of the factory key way.  

My question is why can't the crank snout be ground where the keyway is, without welding.  Doesn't the new machined outer edges of the new "D" crank gear basically take all the load?  I believe the keyway is cut a little deeper on the crank but that "gap" would be in the center of the D-crank gear.  I can't imagine the center of the crankgear being subjected to that much force.

[mdonau]

hi,

the load is not transfered by the snout!
it is just for centering the crank-gear, the load ist only transfered by the surfacepressure done by the bolt.

due to vibrations, reused bolts, non plain contact surface and other factors the bolt gets loose or breaks.

after some time VW changed the bolt from 10.8 (6 edges) to 12.9 (12 edges)

especially the heavy wheel /w rubberdamper for driving the generator/powersteering etc. belt seems to have a negative effect when the rubber gets worn out and the wheel isnt longer balanced.

greets, michael

[nkb]

my understanding is the welding builds up the snout back up to stock dimensions or more so the gear fits properly.
 i don't see why it couldn't be machined in the same spot?

[QuickTD]

I always weld them up because the face and the outside diameter is usually worn and no longer true. While I'm at it I fill in the old keyway. Welding also allows me to make the crank snout slightly oversize for a light press fit in the pulley and on the "flat". An undamaged crank could probably just be machined across the old keyway, but I've never worked on an undamaged crank...

[wyldman]

I do them the same way as QuickTD.

I have done many undamaged cranks,but still weld them up and remachine to slightly over size,so the gear is a light press fit.

The TDI gear is a D shape inside,but it does not go all the way trough the gear.The actual area where the flat sits on the crank is only about 1/8" deep.If the gear does not fit tight,it will rock and wobble,and then it comes loose and spins.

I've seen some guys attempt this repair and never have success,as they are not precise,or don't weld up the crank first.When you entire engine (big $$$$) is at stake,don't cheap out on the proper repair.It costs a little more to weld and remachine,but it's worth it.

[Spokerider]

I realize this is an old post, but I have some questions about repairing / modifying the crank nose on my aaz.

For welding, what part of the crank are you building up with weld? The face and the circumference, along with the keyway?.........and then machining it all to allow for a tight press fit to the AHU "D" gear?
My crank is in good shape and the keyway is not buggered..........so just weld the keyway or? I want to do the mod before it gets buggered.
 
Also, does it matter how the "D" is oriented on the crank in regard to timing marks and timing the engine?

Lastly, buy an oem Febi gear or a $15 Chinese copy.........is there an appreciable difference?

Thanks

[Gizmoman]

I don't see any reason you couldn't machine it where the key is now.
I welded mine up but it was just cause I could, so I did.
The 22 tooth sprocket really doesn't need to be timed exactly from what I've heard. I maintained the timing pretty close when I milled the flat for the new sprocket. Again, why not if it's possible. The fit was good and as mentioned, it's the new, properly torqued bolt that does all the "holding".


I think the off-shore sprocket will be fine. It is an important bit though so if you have doubts and a more familiar brand will make you feel safer, I'd go for it.

[745 turbogreasel]

What are you guys welding with, I'd be worried about making things worse with  the flux core in my MIG...

[Gizmoman]

What are you guys welding with, I'd be worried about making things worse with  the flux core in my MIG...

I preheated it a bit so it wouldn't get hard and if I recall, ground out the key way some to remove the sharp corners in the bottom (to avoid pinholes). I used .035 wire and 75% argon. It was scary but it turned out good.

Flux-core would do it, just not as easy to control (too hot for me anyway). I don't really think it needs to be done though if the fit is still good. My original keyway was fine and so was the sprocket. I am also running a V-belt so probably didn't need to do anything but use a new bolt.

[745 turbogreasel]

that seems reasonable enough, I was thinking more of the folk adding materiel to the OD of the thing.

[Spokerider]

I think QuickTD and wyldman  weld up the face, the outer circumference, the keyway, and then machine the whole crank end to mate with a light press fit, to the specific sprocket that they have selected for the repair. One of them dishes the face so that the sprocket won't roll around on the bolt. I'd like to hear more about the dishing of the crank face, as in how many thousandths deep?

I am going to have a machine shop do this repair, however, I do not want to leave the process to someone who really doesn't have an idea of the problems [ and required fix ] that the AAZ has regarding the sprocket keyway, and the torsional loads placed upon the crank from a non-decoupler pulley alternator. I want to be able to provide the appropriate answers and direction to the machinist [ who has likely never seen this problem before ] so that the repair is done right.

The TDI AHU sprocket is $62.00 from my local VW dealership.
Does anyone know if the crank bolt for the AAZ and the AHU are the same part number? Or are they different bolts altogether? Same for the rear crank gasket? Same gasket for both the AAZ and the AHU?
Would be nice to get all of this online at one place, but id parts does not have any AAZ parts listed, only AHU.

[Gizmoman]

I think QuickTD and wyldman  weld up the face, the outer circumference, the keyway, and then machine the whole crank end to mate with a light press fit, to the specific sprocket that they have selected for the repair. One of them dishes the face so that the sprocket won't roll around on the bolt. I'd like to hear more about the dishing of the crank face, as in how many thousandths deep?

I am going to have a machine shop do this repair, however, I do not want to leave the process to someone who really doesn't have an idea of the problems [ and required fix ] that the AAZ has regarding the sprocket keyway, and the torsional loads placed upon the crank from a non-decoupler pulley alternator. I want to be able to provide the appropriate answers and direction to the machinist [ who has likely never seen this problem before ] so that the repair is done right.

The TDI AHU sprocket is $62.00 from my local VW dealership.
Does anyone know if the crank bolt for the AAZ and the AHU are the same part number? Or are they different bolts altogether? Same for the rear crank gasket? Same gasket for both the AAZ and the AHU?
Would be nice to get all of this online at one place, but id parts does not have any AAZ parts listed, only AHU.

I don't think it's that big of a deal but do whatever you feel is needed. I believe the specified torque of a new bolt (TTY) is the ticket. The bolt (when torqued properly) is a very serious "spring". I believe the working mate is made between the inside flat face of the sprocket and the end of the flat crank. An interference fit is still radial and while it may insure concentricity, it is a radial fit and won't help resist (radial) torque as well as the properly mated faces.

If you can't rely on the bolt, everything else you do (short of a heat-shrink fit) is moot. Once it moves, it's all downhill from there.

If you need to machine the crank because the crank is buggered (welding it up before hand), a light press fit is certainly no harm. Maybe just take the sprocket with you and tell the guy what you want - he really doesn't need to know why.

[libbydiesel]

I made a nice jig for making the front face of the crank true in-car.  I have welded up the crank before, but don't typically.  I just cut the new keyway opposite the old one.

[wolf_walker]

Scarry stuff but I'm glad people are capable of it.  I have yet to remove the crank bolt on the AAZ in the 82.  Plan to avoid it as long as possible.
And to stay with V belts.

[Gizmoman]

Scarry stuff but I'm glad people are capable of it.  I have yet to remove the crank bolt on the AAZ in the 82.  Plan to avoid it as long as possible.
And to stay with V belts.

I agree with the v-belt concept - simple but effective. I'm sure others who have the serpentine set-up could chime in here but I am a machine designer and have used sprag (one-way) clutches before - they fail eventually and if you consider how many times your right foot lets off the throttle, it can happen sooner than you think. Shortly after that the sprocket starts to get hammered by inertia with no forgiveness.

I only did the "D" fix because it was easy at the time. Under different circumstances, I'd have left it alone (with the exception of a new bolt and proper torque).

For anyone reading this that may not know, a serpentine belt is extremely good at transmitting 100% of the torque produced at the crank  - meaning zero slip. The alternator is a heavy mass of spinning copper and steel. Every lift of your right foot from the accelerator pedal immediately changes the speed of the crank and the alternator mass doesn't quite keep up with that change. The difference between the two components gets transferred to the connection between the sprocket and crank. Hence, the need for the best connection possible.

A V-belt allows a bit of slip and will soak up most of the variation of the two.

I think I need an intervention