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Broken crank
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vugbug68
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PostPosted: Sat Nov 21, 2015 11:36 am    Post subject: Broken crank Reply with quote

My friends engine that had the crank snap in two. It is a forged German crank so I'm sorta puzzled as to why it broke, but then again I did find the GEX stamp so that might be the answer. It lasted 1 year of daily driving (in my friends car) then just broke. Pistons, cylinders, and heads were all in good shape.

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Brian
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PostPosted: Sat Nov 21, 2015 11:49 am    Post subject: Re: Broken crank Reply with quote

I was gonna say you need one of these, but I think the GEX says enough.
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PostPosted: Sat Nov 21, 2015 12:07 pm    Post subject: Re: Broken crank Reply with quote

vugbug68 wrote:
It is a forged German crank so I'm sorta puzzled as to why it broke, but then again I did find the GEX stamp so that might be the answer.

It was most likely cracked when they threw it together.
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[email protected]
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PostPosted: Sat Nov 21, 2015 12:45 pm    Post subject: Re: Broken crank Reply with quote

that case is awfully oily for a 1 year old engine, just saying. There were other issues you either aren't mentioning, or aren't aware of...
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PostPosted: Sat Nov 21, 2015 1:08 pm    Post subject: Re: Broken crank Reply with quote

vugbug68 wrote:
It lasted 1 year of daily driving (in my friends car) then just broke.


Ya, that's a good one. I used the same line when the trans on our riding lawnmower developed a hole in it. I'm sure it had nothing to do with the wheelies it was doing prior to the hole appearing....
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vugbug68
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PostPosted: Sat Nov 21, 2015 1:19 pm    Post subject: Re: Broken crank Reply with quote

[email protected] wrote:
that case is awfully oily for a 1 year old engine, just saying. There were other issues you either aren't mentioning, or aren't aware of...


The engine was built many years ago, it sat in my friends garage for a while and already oily when we put it in the car. I've seen engines that were much nastier than this with a perfectly fine crank. There were no other problems that would make me suspect the crank might break in half.
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vugbug68
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PostPosted: Sat Nov 21, 2015 1:24 pm    Post subject: Re: Broken crank Reply with quote

ps2375 wrote:
vugbug68 wrote:
It lasted 1 year of daily driving (in my friends car) then just broke.


Ya, that's a good one. I used the same line when the trans on our riding lawnmower developed a hole in it. I'm sure it had nothing to do with the wheelies it was doing prior to the hole appearing....


Wheelies on a riding lawn mower? Now that's a good one, you got a hemi in that thing?
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PostPosted: Sat Nov 21, 2015 1:57 pm    Post subject: Re: Broken crank Reply with quote

vugbug68 wrote:
[email protected] wrote:
that case is awfully oily for a 1 year old engine, just saying. There were other issues you either aren't mentioning, or aren't aware of...


The engine was built many years ago, it sat in my friends garage for a while and already oily when we put it in the car. I've seen engines that were much nastier than this with a perfectly fine crank. There were no other problems that would make me suspect the crank might break in half.


So, it wasn't built one year ago and done only daily driving since - as your first post implied?
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PostPosted: Sat Nov 21, 2015 2:04 pm    Post subject: Re: Broken crank Reply with quote

Lets see some close ups of the crank journals near where it's cracked. Sometimes if the crank is reground without a radius on the corners they will crack. Sometimes parts just break.
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PostPosted: Sat Nov 21, 2015 2:16 pm    Post subject: Re: Broken crank Reply with quote

Having never experienced a broken crank before, I gotta say I'm curious as to what exactly happens when it lets loose. I mean, does it all of a sudden go KAPWING! and sieze up right then and there, or does the motor keep chugging along just on the back two cylinders and for some reason the car doesn't go anywhere when you let out on the clutch?
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PostPosted: Sat Nov 21, 2015 2:20 pm    Post subject: Re: Broken crank Reply with quote

When the crank breaks, all 4 cylinders are still firing and all the pistons are going up and down the bores. It just makes a lot of noise.
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PostPosted: Sat Nov 21, 2015 2:47 pm    Post subject: Re: Broken crank Reply with quote

just wondering..what pully was on it?
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PostPosted: Sat Nov 21, 2015 4:20 pm    Post subject: Re: Broken crank Reply with quote

VWCOOL wrote:
vugbug68 wrote:
[email protected] wrote:
that case is awfully oily for a 1 year old engine, just saying. There were other issues you either aren't mentioning, or aren't aware of...


The engine was built many years ago, it sat in my friends garage for a while and already oily when we put it in the car. I've seen engines that were much nastier than this with a perfectly fine crank. There were no other problems that would make me suspect the crank might break in half.


So, it wasn't built one year ago and done only daily driving since - as your first post implied?


Yeah I didn't word the first post correctly, I assume GEX built it years ago, it was a longblock and we added everything to make it a turnkey which was a little over a year ago. It ran real good, never had a problem until it started clunking
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PostPosted: Sat Nov 21, 2015 4:46 pm    Post subject: Re: Broken crank Reply with quote

One more question: I can see how 2 and 4 would keep firing, but how the hell do 1 and 3 manage, what with no longer being physically connected to either the valve train or the ignition system? That boggles my mind!
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PostPosted: Sat Nov 21, 2015 5:10 pm    Post subject: Re: Broken crank Reply with quote

Floating VW wrote:
One more question: I can see how 2 and 4 would keep firing, but how the hell do 1 and 3 manage, what with no longer being physically connected to either the valve train or the ignition system? That boggles my mind!


I've broken two cranks, and both were hairline cracks all the way through. The crack was kind of jagged in spots, and went through at an angle. The engine will keep running for a while since the two halves are kind of wedged together. It just makes a minor noise at first but will progressively get louder and louder until you realize something catastrophic is wrong. I'm sure at some point it would stop running, but I would think most people have the common sense to turn the car off before that happens to limit the carnage. The first time this happened to me it was on a 36hp engine and it ruined the case. The second time was on a 1600sp and everything inside was fine.
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PostPosted: Sat Nov 21, 2015 5:57 pm    Post subject: Re: Broken crank Reply with quote

Smile Lugging an engine at LOW speed in 3rd or 4th gear will snap a crank.
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modok
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PostPosted: Sat Nov 21, 2015 6:08 pm    Post subject: Re: Broken crank Reply with quote

Hard to guess the cause.
It could have been damaged and not straightened properly, or maybe it has a million miles on it.
The few GEX cranks I've checked they were not ground straight at all. Must not have understood how to straighten them. Only worse work I ever saw far as runout was in a tractor engine rebuilt by a vocational training program.
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PostPosted: Sat Nov 21, 2015 6:46 pm    Post subject: Re: Broken crank Reply with quote

campingbox wrote:
Lets see some close ups of the crank journals near where it's cracked. Sometimes if the crank is reground without a radius on the corners they will crack. Sometimes parts just break.


X2. This happened to a friend's engine. Ran for maybe 1000 miles (I can't remember exactly), and the warning was a knocking and oil light flickering at higher and higher idle speeds. We pulled everything off look for the problem. Split the case and still didn't see anything. Went to lift the crank off the case half and only half of it came out! Bingo!


Last edited by KTPhil on Sun Nov 22, 2015 2:54 pm; edited 1 time in total
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PostPosted: Sun Nov 22, 2015 10:00 am    Post subject: Re: Broken crank Reply with quote

I had a friend bring us his duster and said the crank was broken in 2 peices... he drove it to our speed shop/chassie shop...said to just put a crank in it...or a motor witch was cheeper.so i pulle it out and......it was broken in 2 totaly seprate peices, he had been driving it for mover 2 months like that. I just stuck in another low cr 318 we had laying around.and away he went.cheep. I miss those days.
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PostPosted: Sun Nov 22, 2015 10:46 am    Post subject: Re: Broken crank Reply with quote

I broke one in dads ghia. It made a loud bang and clunked all the way home. No damage- threw a new crank and away it went- In the bus that towed the jeep and motorcycle to Or. from NJ.- THEN it had to be rebuilt.
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