broke my crank yesterday
 

car cut out on the track at 60ft mark. what I thought was something in the oil pump locking up and breaking the roll pin in the dizzy drive, turned out to be the oil pump shaft broken and a broken crank.

not sure what broke first, the crank or the oil pump shaft which then jammed the crank.

also found what looks like a dowel pin in the pan?

not took it all apart yet to check for any damage but it`s going to be expensive I guess.

What kind of crank was it? I did this years ago with a Chinese cast aftermarket crank in a low 10-second car. I managed to split the block lengthwise as well. I'm sorry you had the problem, but glad no one was hurt. It's good it happened early in the pass.

Jim

2007 Eagle cast stroker crank. shifting at 5500 crossing line at 5800 until this year when had to switch to shorter slicks and the 3 runs before it broke, shifting at 5500 crossing line at 6100.

block looks intact, didn`t spill any fluids

Dowel in pan is NOT encouraging sign. Not a fan of the cast china cranks... IMO they are inferior to factory cast cranks.
Sucks when things break.

where has that come from Bruce?

From what I have seen when a main dowel is in the pan then the block usually has a crack. Sorry for you problems.

oh ok thanks

Dowell holds the main cap in the proper location.

For you to find a dowell in the oil pan the dowell had to come out of the block/cap it was locating. It is "trapped" in its location normally.

Expect some interesting findings when you get the engine apart and everything gone over on the block. If the main caps split without hurting the block other caps can be installed (line bored/honed), and possibly you can save the block.

Tom V.

ok thanks Tom

I would not run one of those aftermarket cast Cranks without getting it Cryo treated for added strength, pure and simple!

a few more pics.

the dowel was from number 2 mains and the crank broke at number 5. what I did notice taking it apart, there are studs for number 2 and 4 and number 2 were loose after undoing the nuts, I could unscrew the studs by hand.

block looks intact but I will get it checked professionally before I decide what to do.

looks like it was eating the thrust bearing. this was changed in 2008, never saw any gold in the oil changes though and I had just done one 2 days before this happened.

the cam was in great condition and all the con rod bearings were good as well.

That #2 dowel pin may have fallen out at any time since the pan was off the last time. Looks like the cap may have been moving around some. How tight does the dowel fit in the block?

Main studs should not be tight in the block. If you could remove the studs by hand after the nuts were loosened, that's normal.

Looks like you might have gotten very lucky. How did the oil pump drive come out of place? Is the shaft locating pin missing from the oil pump?

I didn`t try the dowel as it had broken off and didn`t think to.

interesting about the studs as the number 4 ones I couldn`t undo.

not sure on the pump drive, but there are no pins on it, it`s smooth and looks like they`ve been ground off. is that what you do if it has to be installed from the top?

[ Post #1 FCMan: "car cut out on the track at 60ft mark. what I thought was something in the oil pump locking up and breaking the roll pin in the dizzy drive, turned out to be the oil pump shaft broken and a broken crank.

not sure what broke first, the crank or the oil pump shaft which then jammed the crank."]

The Number#2 main sees the stress in the engine first. Have seen several engines (cast main caps) where the #2 main cap was split up the main fastener hole. Your pics show no evidence of that happening in this case.

The crank does not normally break at the #5 main location.

Yours did which makes me think that the oil pump shaft got jammed up in the #5 crank counterweight area. If the block checks out you can put steel caps on the block is the block shows no other damage. Inspect the block for the oil pump shaft guide (cast in the block) still being there and in good shape.

Brian H broke the oil pump shaft guide on his IA-2 Block when he had a engine failure some years ago.

Tom Vaught

Tom

do you mean I shouldn`t use the existing main caps if the block is ok? also that shaft guide, what`s it made of?

thanks, Rick

I broke a factory "N" 455 crank about the same point on the track once. It was like I killed the ignition. No bang just stopped. I broke the #5 rod journal right off the crank. In our opinion the journal fillets should have been larger creating a stress concentration piont. The power from all the cylinders has to go through that #5 rod journal since the resistance on the engine is the flex plate. Just my 2 cents. Sorry about your engine.

I can easily see some excess heat (ie: blue'ing) in the area of the break around that rod journal/counterweight.

My WAG,it spit the OP shaft outta it,then it obviously lost oil pressure,rod grabbed the crank,bam broken crank,only odd part here is the OP says the rod bearing itself looked ok.

Was the big end of that specific rod discolored @ all???

That discoloration is away from (opposite side of) the main journal that has the thrust bearing on it,but despite that (one way or the other) I feel that the thrust issue could be the root cause of the crank breaking here.

Now were that the case,how about this chain of events,in this scenario the excessive thrust could easily be what took out the OP shaft,that's a no-brainer,that back counterweight is like right there,so that seems easy enough to see happening,I just dont think we'd see that obvious heat discoloration if the shaft jammed in there and caused the crank to break.

And the dowel pin is sorta the same deal.

I mean you can clearly see that specific main cap was fretting,and that's likely why the dowel fell out.

I dunno,looks to me like a couple of different things were going on @ the same time here.

Thrust is all outta whack,crank is sawing back & forth in the block,that causes the cap fretting situation first,so yeah it drops the dowel outta there,eventually the rearmost counterweight takes out the OP shaft,instant loss of oil pressure,then bam a rod grabs the crank,and the crank breaks.

Just curious,what casting no. is this block?

If it's a 557 block,that might explain some of this.

:noidea:

Bret P.

Have to agree that a lot of things were going on with this engine that could have contributed to the crank failing.

We had some cap/block fretting on the 863 HP boosted engine with 2 bolt caps and studs. The theory now is that the dowel pin register was not good enough on that deal.

Maybe the OP can post up the pictures of the main and rod bearings for us.

Tom V.

If it was a 557 block ........Tick Tock.

Brett

no this was a 72 block. all the con rod bearings were fine as were the crank journals themselves. yes the thrust bearings were worn but no other damage.

this happened at the 1-2 shift at 60ft mark.

I`ve had problems with it shearing the roll pins on the dizzy gear drive, would that have been caused by the crank moving due to the thrust wear?

Not much actual room (flexibility) for the crank to be in the wrong spot and not have the roll pin, distributor gear, etc see a lot of stress.

Tom Vaught

sorry Tom, I`m not understanding the answer, could you put it in simple terms for me, yes or no haha.

Looks like the break point started at the drill hole, likely started by a sharp edge!

Rick,
X2 on Tom's post....don't reuse the caps and get some steel caps.

If that's a 2-bolt block I'd consider splayed caps.

Either way sorry to see the destruction.

I'd wait and see what the block looks like when tore apart.

I'd say the block is cracked somewhere in the main bulkhead.

:(

Well I tried in simple terms and it was still taking too much typing so I bailed out on a reply :)

Tom V.

If it is a easily replaced 2 bolt block, nothing special sort of deal I would not even think about running that block again in a performance build. Could not sleep at night myself.
Sorry about your engine. But those offshore cast cranks have had issues eating thrust bearings and or failing where they should not.
I have flogged PMD cranks and never hurt one of them.

X2 I know your not in the U.S. But I would try real hard to find another block.

Unless it's the picture, to me it looks like the crank was cracked for a while....

great data point.

Looking at the dark areas in the crack it does appear to have started cracking a while back. Definitely got some cap fretting,what are you revving it to? And why are there main studs on only number 2 and 4 mains?
You could also do with modifying the thrust bearing, file a small chamfer along the parting lines of the shells- about 0.020" will do it. Have you restricted the oil flow to the converter/cooling circuit in the TH400? You sound like you have a recurring problem with the thrust bearing and modified TH400's are notorious for causing engine thrust bearing wear. Increased trans line pressure translates into higher cooler circuit pressure which can force the converter forward,causing thrust bearing problems.

I see what you are talking about, but I don't think they are "beach marks". I don't see a growth pattern

Yes, definitely. I experienced thrust issues with my '64 GTO engine until we made these two mods.

Jim

shifting at 5500, max ever revved to 6200 but usually 5800 at finish line

don`t know about the studs, that`s how it was built. the Milodon windage tray was bolted to the studs

both of those mods were done

I wonder if post #2 in this thread answers your question?

http://www.gtoforum.com/f50/455-main...uestion-55713/

The beach marks are a true yield strength limit indicator, yet was it organic defects in the material or a machining "stress riser" that got allowed to propagate. Hmmmmm.

You know, I never know what the heck you are talking about, but I always get the feeling you know exactly what you are talking about.

LOL.

Very well said :)