VWDiesel.net The IDI, TDI, and mTDI source.
Engine Specific Info and Questions => IDI Engine => Topic started by: 410 on September 25, 2011, 08:43:09 pm
-
Has anyone ever seen a main cap break on a aaz block? As soon as I get a chance I'll post some pics. I just finished replacing an aaz block with a massive hole in it with the number 2 main cap being the culprit. I don't know if the bolt(s) broke first or if the cap itself failed and then broke the bolts. The most amazing part was the engine still ran!
I saw this a few years back on an aaz block with the identical failure and thought at that point that I would never see this again. That one also still ran. Basically, I want to do everything possible to avoid this again so I've decided to do the only thing I can do and that's upgrade the main cap bolts from 10.9 to 12.9. I found some 10mmx1.5 bolts through Acklands for less than a buck each but I would really like to know if anyone else has seen this.
-
Here's a couple pics.
(http://i1128.photobucket.com/albums/m488/410-photos/blown%20engine/IMG_0202.jpg)
aaz block with a window.
(http://i1128.photobucket.com/albums/m488/410-photos/blown%20engine/IMG_0204.jpg)
And #2 main cap gone.
I found both pieces of the cap as well as both cap bolts in the engine bay. I haven't uploaded those pics yet. Coming soon.
-
Looks like you might have trouble sealing the oil pan on this one. What is the history on the block blowout?
-
I built this motor up two years ago now. I pulled the rods so I could install ahu pistons but never touched the mains. The motor had close to 34,000km in the toyota pickup when she blew. This engine was making decent power but like I mentioned in my previous post, I saw the same thing happen on a bone stock aaz.
I'm not too concerned though. I had just bought a 1998 jetta tdi so the truck is back up and running. Just don't want to see it again!
-
Wow. That was from your mtdi? So the bolts broke?
-
i can fix that... i gots some jb weld... then ill buff it real good... ;D
mains are strech bolts i thought.. like rods.. id also assume that unless the drank was flexing real good i cannot see how that happens...
-
perhaps the main cap got between the crank and the back of the block causing this
-
I think the cap broke first from a possible casting flaw and then stressed the bolts until they broke. Then the crank decided that the cap was causing too much trouble inside the engine and threw them out the side.
My camera is still at work right now and I don't go back until Wednesday so no pics of the cap until then.
-
Any chance the bolts just worked themselves loose?
-
I think main cap went from fatigue, flaw , vibration or whatever, then wedged between big end and casing, taking b/e cap and side out... maybe.
What marks are there on the casing pieces, and caps?
-
Any chance the bolts just worked themselves loose?
Nope, The bolts snapped clean at the bottom edge of the cap. The rest of the bolts were still threaded in the block and came out very easily. There was at least 5/8" of the bolt still in the block. They look like they were sheared between the block and the cap.
No signs of fatigue where the bolts broke but it's hard to say the same from the cap. The break on the cap might show some signs of fatigue but the pieces got pretty beat up as they went through the side of the block.
-
Nope, The bolts snapped clean at the bottom edge of the cap.
Wow!
-
It would be nice to know what did it.
Is there any thread on the head end of the main bolts? If so it may be possible to see if the threads are stretched through over tightening or purely sheared. There are plenty of folks who overtighten as a security measure [yourself excluded of course ;D]
-
Same thing happened to me but on cap #5. Split in half. And the cap pieces got stuck between the crank weights and the block and left a big hole as a result, just behind the starter.
(http://www1.garaget.org/archive/64/63772/81419/81419-1199082.jpg)
-
It would be nice to know what did it.
Is there any thread on the head end of the main bolts? If so it may be possible to see if the threads are stretched through over tightening or purely sheared. There are plenty of folks who overtighten as a security measure [yourself excluded of course ;D]
It would be nice to know what did it! The bolts don't look stretched at all to the naked eye. I'll have a closer look on Wednesday when I go back to work.
Sierra94, Sorry that this also happened to you but it's nice to know that I'm not the only one that has seen this! Thanks for sharing. Any pics of the actual cap?
-
Same thing happened to me but on cap #5. Split in half. And the cap pieces got stuck between the crank weights and the block and left a big hole as a result, just behind the starter.
(http://www1.garaget.org/archive/64/63772/81419/81419-1199082.jpg)
Well that doesn't count; it's merely an extra blowby vent ;D
Sorry I couldn't help myself :'(
-
(http://i1128.photobucket.com/albums/m488/410-photos/blown%20engine/IMG_0204.jpg)
And #2 main cap gone.
I found both pieces of the cap as well as both cap bolts in the engine bay. I haven't uploaded those pics yet. Coming soon.
That ALMOST looks like the #1 rod twisted off and sticking down between the counterweights? What's going on there?
-
i think it was the putter that poked the hole with cap parts..
-
410: No, I only found half of it in the pan along with the 2 bolts (which were undamaged!!). The other part of the cap is still missing ;D
This happened a couple of years ago, and at that time I only took pics of the outside damage. I swapped the extra vented AEF (1.9 NA) for a 1Z and built a m-Tdi IP that I still run today.
-
Like I mentioned before, this engine still ran. All rods were completely intact. #2 rod did suffer some damage but I didn't notice until I removed it from the block. #1 piston also had a bit of its skirt broken off as well. All bearings aside from number 2 main cap were intact and believe it or not, the crank is in reusable shape. So, I guess I'm out one block, one rod and one piston. ;D
-
Okay, here's some pics of the cap and bolts. After looking at everything a little closer, it does look like one of the bolts broke first, then the cap. The cap then breaks the remaining bolt at which point everything got ejected.
(http://i1128.photobucket.com/albums/m488/410-photos/IMG_0229.jpg)
If you look closely at the break on the bolt on the left, the fracture shows signs of fatigue where the right side bolt was a clean break.
(http://i1128.photobucket.com/albums/m488/410-photos/IMG_0231.jpg)
Mark, I would have to agree with you that this bolt was probably overtightened eventually leading to the failure of the bolt. Either that or the bolt was flawed but I doubt that.
-
This kind of damage is typical of a kickback when starting a motor on ether. I have seen this a number of times and ether has always been the culprit.
-
Having done some reading; I have discovered that the fracture profile of those bolts are of flexing fatigue.
Clearly the left bolt went first and for some unknown period of time hammered together, strange in itself as it should have dropped out.
Not clear on the pic but the bolt face proably simulates a scallop shell, with the hinge spot being the actual last cling of bolt.
Where there are no concentric rings with their centre at the hinge, signifys a relatively rapid fracture. like the right hand bolt.
Conversely circular waves/ripples would have signified a gradual flexing failure due to a repeated lower force.
Pure shear in anything other than a guillitine effect in a very tight and close fitting pair of holes will result in a significant 'down the side' portion.
Pure stretch will result in more of a crystalline effect not unlike the snapped cap.
Are the cap faces perfectly flat? [looking for a source of rocking under load]
A picture of the shell bearings will tell much as they are so soft, and could tell you if it was a flexing crank, or bending conn. rod etc
I could of course be wrong, in all but the last paragraph ;D
-
The bearing on number 2 cap was squished into a ball.
-
good god this is some most unfortunate carnage pics. Especially after just changing my main and rod bearings last week...
I think im gonna change my re-used (three times now) bolts for some 12.9 ...