Another broken crankshaft - I'm gonna cry.

[ShawnR]

I bought the truck 4 years ago with a broken crankshaft. The engine was a GM crate engine but past the 1 year warranty. I rebuilt the bottom end, new oil pump and of course a new balancer. Bad balancers break crankshafts, right?

It has now been about 12,000 miles later and BANG. I haven't pulled the pan yet, but deep down I know what has happened. Starter turns flywheel, front accessories don't turn.

"If" the block isn't cracked, I might just replace the crank.

I hear that SCAT makes a good one? Opinions? If I put in another stocker, I am selling the truck right afterwards since I will never trust it.

If the block is cracked. What options are there?

Cummins conversion?
gas conversion (5.7 out of a donor truck)?
complete replacement 6.5 engine?

The body is in farily good shape, rust is starting to kick in.

I am open to all suggestions.

 

[Matt Bachand]

What were you doing with the truck at the time of the let go?

 

[ShawnR]

Just pulling away from a stop sign. No trailer or anything. I had just spent 4 hours replacing glow plugs & all wires on the turbo side. Probably at half throttle. Low boost & RPM.

 

[NVW]

Generally to break a crank the balancer is bad, had this happen on a 427. A rebuilt with bearings shouldn't be to bad if you want to do it cheap. Leo

 

[Acesneights1]

That is really odd. something is missing here. Cranks don't break that easy.

 

[Michaeljp86]

Were you ever hard on it lately? Maybe it cracked or twisted a little and just now broke. Ive seen that happen on lawnmower parts alot, a shaft will break in half and you can see where part of the break was rusty like it broke 1/2 way years before.

 

[ShawnR]

No rough stuff recently at all. No heavy tows or anything. It did seem to be clattering slightly louder than "normal", but I just attributed it to not having driven it for nearly a month. I'll pull the pan tomorrow and snap a few pics. I am just hoping that there is no damage to the block and I can put a SCAT crank in. Probably a girdle on the main caps as long as I am in there. When cranking, the entire engine rocks from side to side and the downpipe hits the frame.

I was laid off at the beginning of the month so this is really not a good time for an expensive fix (18:1 pistons, head studs, etc.). I do have plenty of time though!

 

[NVW]

On my 427 I had noticed a vibration for a long time in my transmission. I always thought it was the tranny. After the repairs, with a new balancer all vibrations were gone. Leo

 

[Michaeljp86]

Ive heard the 6.5 will run with a broken crank, maybe the crank was broke for a while making the clatter. I heard the SCAT cranks need to be sent to a shop and machined better.

 

[JiFaire]

This smells funny... trucks don't just eat cranks. Especially with new balancers (you did replace both the harmonic balancer and the pulley, right?

Have you weighed your rotating mass? Weigh each of your pistons with their connecting rod and cap and see if they come out reasonably close...

Have you measured your block to make sure the journals are true?

Inspect webs for cracks that could allow for some flex.

Do you have an automatic or standard? Have you checked your flywheel or TC for balance?

Some of these ideas sound flaky, even to me, but jeez, cranks don't just break without cause. Two on one engine is unheard-of...

 

[hereismylife]

Another thing to think about is a fluid dampner. I was going to run one till I went with a different project:thumbsup:

Like the others said something does not sound right...:mad2:

 

[Michaeljp86]

Another thing to think about is a fluid dampner. I was going to run one till I went with a different project:thumbsup:

Like the others said something does not sound right...:mad2:

Aren't those like $200?

Maybe the block needs to be taken to a machine shop and have one of those things run through where the crank goes to machine the journals all in line.

 

[MBBOB]

It may not sound right........but sure sounds familiar.

I still cannot come up with a logical (or illogical) reason why mine broke!

 

[mitchedo]

Aren't those like $200?

Maybe the block needs to be taken to a machine shop and have one of those things run through where the crank goes to machine the journals all in line.

$200? Don't I wish. My Fluidampr was $450 shipped.

I agree with the second statement as well. Disassemble the engine and take it to a competent shop to have it magnafluxed and mic'd. Get the reciprocating assembly balanced and put it back together. Buy new bolts for the bottom end and get it all align-honed with the girdle if you choose to install a girdle.

Peninsular sells forged cranks, but they're like $900. You can also get the new engine with the girdle and forged crank (P400?) for some $7000 + whatever it costs for a custom oil pan.

My GM crate engine (manufactured by GEP in 2003) was poorly machined, resulting in premature bearing failure at 49,000 miles. At least the block didn't crack. ...yet.

Rusty truck, broken crank, and cracked block? If mine had all three, I'd part it out. Of course, I live in a smog nazi state where a gasser engine swap is out of the question.

 

[jbsaxman]

$200? Don't I wish. My Fluidampr was $450 shipped.

I agree with the second statement as well. Disassemble the engine and take it to a competent shop to have it magnafluxed and mic'd. Get the reciprocating assembly balanced and put it back together. Buy new bolts for the bottom end and get it all align-honed with the girdle if you choose to install a girdle.

Peninsular sells forged cranks, but they're like $900. You can also get the new engine with the girdle and forged crank (P400?) for some $7000 + whatever it costs for a custom oil pan.

My GM crate engine (manufactured by GEP in 2003) was poorly machined, resulting in premature bearing failure at 49,000 miles. At least the block didn't crack. ...yet.

Rusty truck, broken crank, and cracked block? If mine had all three, I'd part it out. Of course, I live in a smog nazi state where a gasser engine swap is out of the question.

Utah sucks @$$, doesn't it?

God I hate it here.

 

[Acesneights1]

Yeah somehting is wrong. it sounds to me like the block need a line bore or you have a piston in backwards or something. 2 in a row ? Better chance of winning lotto. I would look carefully at everything during dissasembly. You need to know why this is happening.

 

[midniteplowboyy]

How far is the IP advanced? Is it a manual trans?

 

[ShawnR]

I just got back from pulling the pan and doing the initial check of the damage.

The crank is broken in 2 separate places. The connecting rods for 5 & 6 pistons were still attached to the chuck of crankshaft that broke. Here are a couple of pics of the piece.

Here is a diagram of exactly where it broke this time.

When I bought the truck, the crank was broken here:

The 5 & 6 piston skirts are damaged and I assume that the rods are bent. There is a small hole in the side of the oil pan as well. I will go ahead and pull it and check the block for cracks. If it isn't cracked, I might rebuild. I did give the balancer a good look and there is nothing obviously wrong. I paid around $175 at the dealer less than 20K miles ago.

I am either going to just part out the rest of the truck, or stick in a replacement motor and sell it. I won't put in a "new" motor as the truck just isn't worth it. It has 225K miles and it starting to rust out. It is fixable, but it just isn't worth it in my opinion. I will start watching craigslist for a shortblock but I don't have a warm fuzzy feeling about it.

With a good running engine in it, the truck will probably be worth around $3500. I should be able to get at least $1000 out of stripping it out as everything else is in decent shape.

Thoughts?

 

[Michaeljp86]

wow, something went wrong there, I never seen a crank do that.

 

[Turbine Doc]

where did the previous replacement crank come from, maybe the way the pic was taken but color where it was broken doesn't look rite like maybe poor cast material, cranks are tough to break, I cut a piece once with chop saw and it was tough getting through it