After 600 miles, I got 2 cracked main caps. What the heck.

[TonyTDTruck]

I was heading out of town fully loaded with camping gear for our first trip in our DoKa, and I began to hear a knocking sound.
First thing I said to my wife was, we ain't going nowhere past this point. My head went down and rested on the steering wheel for about two minutes.
Had it towed home and we got in the OTHER car for a normal camping trip.
I thought it chunked a rod bearing.
Number 4 and 5 main caps cracked in the same place. What could have caused this? I didn't torque the main bolts enough?
The crank was checked at Bearing Services here in Portland and the engine ran fine before I rebuilt it.
Could the main bolts have stretched? I have never seen this before. Any input would be much appreciated.
Do I need to go with race performance caps? Heck it's just an AAZ with a Giles pump.
At least I didn't destroy the engine.

Thanks
Tony

[CRSMP5]

aaz bad for that it seems... those streach bolts from factory too i beleive..

[Jetmugg]

If they were OEM Torque To Yield (TTY, or "stretch") bolts, that's the most likely culprit.

Any such fasteners are designed for 1 time use.  From a metallurgical standpoint, I'm not super happy about their use in general, but they are here to stay.

Steve

[410]

Sadly I've seen this twice before with my own eyes and in both cases the block was completely destroyed.


Count yourself lucky that you caught it.  The problem is you can't just throw main caps from another engine without a lot of machining. 

[TonyTDTruck]

WOW that's INSANE! Do they make aftermarket bolts that are better? I'm using stronger bolts on the head but I didn't think the crank bolts were necessary.
ARP I believe they were.
I do consider myself lucky after seeing this picture. Thanks 410.

Tony

[wolf_walker]

Huh, didn't know they were TTY.
ARP studs anyone?

[RabbitJockey]

arp makes hardware i am sure ud probably have to call them tho.

but u have some machining in your future.  that really sucks!!!

[TonyTDTruck]

By machining you mean I have to line bore the new main caps? I believe you are correct.
It does mean removing all of the components and starting all over. Yea it sucks.
Does anybody know where I can find a TDI crank? Just in case I may need one.

[RabbitJockey]

By machining you mean I have to line bore the new main caps? I believe you are correct.
It does mean removing all of the components and starting all over. Yea it sucks.
Does anybody know where I can find a TDI crank? Just in case I may need one.

yeah thats all i meant... atleast it won't be as expensive has a full rebuild...

[410]

It's kind of interesting that the mains are all breaking at exactly the same spot.  I figured that one main bolts broke [on my motor] and caused uneven stress on the main which cracked it at its weakest point but I see your bolts are still intact.

[theman53]

By looking at the bolts I would guess they are factory stretch bolts as they look fully threaded.

If you would measure them let me know if they are 80mm long or 65mm long. I had a theory that the shorter ones were the culprit, but it looks like those are the longer ones.

If I had to guess I would still say the bolt is the issue. Once they loosen a bit or stretch more, then the force of the crank has to go somewhere. I would venture that the spot we see breaking in these is where the force of the crank is coming down and spinning that direction. Guessing though.

[CRSMP5]

well i just did arp vr6 rods, mains and heads... rods/mains same as 1.9 diesel... in length/thread pitch... so they got the stuff/sizes..

my inital post says that.. read mk3 bently.. has aaz info.. just slipped in with the little tdi info.. they streach..

[TonyTDTruck]

It's kind of interesting that the mains are all breaking at exactly the same spot.  I figured that one main bolts broke [on my motor] and caused uneven stress on the main which cracked it at its weakest point but I see your bolts are still intact.

The bolts didn't break. We were on the freeway and all of a sudden a vibration was felt coming from the back. At first I thought it was a flat. It also sounded and felt like a bad U-Joint or CV joint. I let off the gas and the sound went away. So I gave it gas to keep going and all of a sudden the sound and feel got a lot worse. I figured that one cap broke and then another. Not both at the same time. I pulled over and at idle I could hear a thump thump. I thought it was a rod bearing.
After that it got a ride on a tow truck.
I'm looking for a set of main caps and a TDI crank. I know it's a long shot but I have to start some place.
Any ideas?
Thanks

[theman53]

I didn't say they broke, I was implying they let loose or stretched a bit more. Guessing is all I am doing. Without knowing exactly how long the bolt was going in and how much it would grow being TTY there is no real way of knowing if they grew a bit or not. I would still love to know which length bolts were installed.

Also, from what I gather the aaz and ahu have the same exact crank, block, and rods. Is your crank hurt or are you thinking that the TDI will be stronger or something?

[410]

The cranks are different between the aaz and ahu.  The ahu has the D  shaped crank nose and the aaz has the same crank nose as the 1.6.  The ahu crank also has a relucter wheel for the crank sensor.

My suggestion would be to get an AHU or 1Z short block and use the AAZ pistons if you want to stick with an idi.  The TDI blocks seem to be more robust.  I have never seen this failure on an AHU or 1Z.  I do feel your pain Tony.  Hopefully you can get up and running soon.