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#2 main cap broke on aaz
by
410
on 25 Sep, 2011 20:43
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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.
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#1
by
410
on 25 Sep, 2011 23:01
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Here's a couple pics.
aaz block with a window.
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.
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#2
by
ORCoaster
on 26 Sep, 2011 00:09
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Looks like you might have trouble sealing the oil pan on this one. What is the history on the block blowout?
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#3
by
410
on 26 Sep, 2011 17:06
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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!
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#4
by
rallydiesel
on 26 Sep, 2011 17:37
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Wow. That was from your mtdi? So the bolts broke?
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#5
by
CRSMP5
on 26 Sep, 2011 17:41
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i can fix that... i gots some jb weld... then ill buff it real good...
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...
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#6
by
RabbitJockey
on 26 Sep, 2011 19:41
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perhaps the main cap got between the crank and the back of the block causing this
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#7
by
410
on 26 Sep, 2011 21:01
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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.
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#8
by
rabbid79
on 26 Sep, 2011 22:10
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Any chance the bolts just worked themselves loose?
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#9
by
Mark(The Miser)UK
on 26 Sep, 2011 22:18
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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?
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#10
by
410
on 26 Sep, 2011 23:05
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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.
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#11
by
rabbid79
on 26 Sep, 2011 23:10
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Nope, The bolts snapped clean at the bottom edge of the cap.
Wow!
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#12
by
Mark(The Miser)UK
on 27 Sep, 2011 05:21
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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 ]
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#13
by
Sierra94
on 27 Sep, 2011 06:48
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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.
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#14
by
410
on 27 Sep, 2011 10:09
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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 ]
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?