Busted my crank...

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Jerry D.

Jerry D.

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Joined
Mar 31, 2005
Threads
58
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Location
Citrus Springs, Florida
Any ideas or thoughts on how you bust a crank in a '91 4Runner 3.0 V6 with an automatic?:confused: Daily driver, rare off road use, no mud running, no rock crawling, no tractor pulling.

No oil problems, no heat problem, no shavings or trash in the pan or engine. Just started “knocking” like you get with a spun bearing. Busted between #1 and #2 rod journals in a very clear break.

I’m thinking is was a flawed cast to begin with, and luck ran out.

Ideas???

Jerry D.
4Runner crank 003.webp
4Runner crank 007.webp
4Runner crank 008.webp
 
Dayum!!!

Never heard of that one in a 3.slow. Didn't know it had enough torque to do that. Ya, I'm going with the "flaw in the casting" idea.
 
Seen 2 others... same place..both 4 runners no p-ups tho??
 
Wow only thing I would do is try to check it was sitting right in the block but damn thats a nasty break.
:eek:
 
Are you the original owner?


Mark...
 
I am not the original owner.

Bought the truck two years ago and it had a bad bearing then. Rebuilt the engine with a “re-ground” crank and all new bearings, rings etc. Block was not bored out as it did not have excessive wear. Did complete check on bearing clearance, thrust and rod side clearance. Rotated crank after each bearing, main and rod, were torqued. No binding or excessive effort needed to rotate crank. Engine ran great for about a year, then the crank snapped. The rod caps and main bearing cap nuts/bolts were still tight at removal. All the bearings from the engine after the break looked like new. No signs of oil starvation, scaring or wear.

Only noise from truck was driver was playing the radio TOO loud. Maybe the bass vibration cracked the crank…:idea:

Jerry D.
 
That type of failure is not related to bearings, oiling or normal problems. Either a flaw from the beginning, or a major shock to the crank which lead to a crack developing. Just like a prop strike in an aircraft. You have the crank spinning at high speed and it is suddenly is stopped immediately. Lots of stress.

Hard to do with an auto though.

I had a 2F crank fail this way. The engine had come from a parts rig that suffered a rollover. After the crank snapped a few months after the engine was swapped, the original wreck was re-examined. The rig had rolled at speed, gone airborne and come down hard on the rear tires. The impact had created major traction as the tires hit the ground (bent both rims) and the running engine was stopped cold. The shock loading created a crack which gave way later on.

But anyway, either the crank was flawed from the start or it experienced a major shock at some point. Possibly dropped while it was in the machine shop? But that would be on the low end of stress to creat that damage. ???


Mark...
 
Thanks for the replies.

I can go with the idea of high rpm and sudden stop of the tires as Mark pointed out. Must have been damaged prior to installing into this V6. And the shop that got the “re-grind” for me swears it was maga-fluxed before they ship them out…

Anyway, got another crank, start install today, hope to have Runner on the road by Sunday. And Capt. Jim, it is out of Jamie’s daily driver 4Runner…and I’m looking for a good base to mount the short end of the crank to so she can put it on her mantel.:D After this, will be working on Jamie’s 60, then Rick’s Runner, then the boy’s 40 and finally mine. Have to get the boy’s and mine ready for Texas in March.

Thanks again,
Jerry D.
 
a bad harmonic balancer will do that to your crankshaft, its pretty common on highway trucks and machinery. the balancer has a lifespan, and once it wears out your crankshaft will break in the not so distant future.
replace the balancer with a new one, you dont want to break another crank next year do you?
 
Dang Jerry - Looks like you're spending more and more time on the dark side :D.

Over at Jim's and he showed me this thread - that suks, are you sure one of teens wasn't driving like the last motor that got blown at the Annual a few years back?
 
Jerry D. said:
I am not the original owner.

Bought the truck two years ago and it had a bad bearing then. Rebuilt the engine with a “re-ground” crank and all new bearings, rings etc. Block was not bored out as it did not have excessive wear. Did complete check on bearing clearance, thrust and rod side clearance. Rotated crank after each bearing, main and rod, were torqued. No binding or excessive effort needed to rotate crank. Engine ran great for about a year, then the crank snapped. The rod caps and main bearing cap nuts/bolts were still tight at removal. All the bearings from the engine after the break looked like new. No signs of oil starvation, scaring or wear.

Only noise from truck was driver was playing the radio TOO loud. Maybe the bass vibration cracked the crank…:idea:

Jerry D.
Click to expand...

What bearings were bad? I'm betting the first couple.
The block my not be true and while you did check the clearance I bet with plastic gage I bet you only checked the top. It may have been tight or loose the opposite side and flexing the crank just a little and over time it failed.

The block probably needs to be line bored. Take it to a quality shop and have it checked.

The crack looks dark in places like it may have been failing for a long period of time. Did the machine shop magniflux the crank before turning it?
 
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