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Have you heard of these early hemi failure modes?
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56D500boy
Posted 2018-02-04 2:01 AM (#557474)
Subject: Have you heard of these early hemi failure modes?



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I've been talking to a couple of local guys with 55 and 56 Dodges with hemis (55 = 270; 56 = D500 315 (not mine)). In these discussions, two strange (to me) failure modes came up. Anybody heard of these?

1. The 55 owner was relating a story about when he had a 55 2dr 270 hemi hardtop back in the day, i.e. in 55-56. He used to street race it a bit. One day while racing a 49 Ford that had an early Olds Rocket V8, he broke his crank just at the point when he shifted the Powerflite from L to D (he didn't have a tack but he said that "it was pretty wound out".) In the post mortem, it was discovered that the block had actually shrunk, i.e. the block casting was too "green" when it was initially machined resulting in the rear-most crank bearing pulling up by 3 thousandths. Normal driving no problem. Wound out too many times that put too much stress on the crank and it broke somewhere near the back (Like at cylinder 7 area). The solution was to re-line bore the crank mains taking into account the 3 thou and then machining the caps accordingly. And a new crank obviously. That fixed the problem.

2. The 56 owner told me that he was driving his 56 La Femme D500 after he got it and eventually it started to stall at idle a lot. Nobody could figure it out. Eventually the removed the engine and tore it down. In the process, they found that the water pump manifold/cover had been attached to the block during a previous rebuild with at least one bolt that was too long. The bolt in question had (supposedly) pushed the No. 1 cylinder wall and made a bulge in the cylinder wall that was causing the engine to stall.

On this last one I was skeptical until I saw a 2013 WPC Museum video earlier today and stopped it at the hemi cut-away. Then I could see that it was possible to have that issue if the water pump manifold was attached with a bolt that was too long. I've circled the potential problem bolt in yellow in the screen capture.

Anybody heard of this one?



Edited by 56D500boy 2018-02-04 2:07 AM




(55-57GenericHemiEnginePartsDiagram.jpg)



(WPCMuseumYouTubeVideoD500ScreenCapture_8_annotated.jpg)



Attachments
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Attachments 55-57GenericHemiEnginePartsDiagram.jpg (199KB - 115 downloads)
Attachments WPCMuseumYouTubeVideoD500ScreenCapture_8_annotated.jpg (122KB - 112 downloads)
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60 dart
Posted 2018-02-04 6:58 AM (#557480 - in reply to #557474)
Subject: Re: Have you heard of these early hemi failure modes?



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pretty much what/why i was told of 56 desoto getting an upgrade torqueflite ,,,, broke cranks-------------------------------------------------later

Edited by 60 dart 2018-02-04 7:00 AM
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Powerflite
Posted 2018-02-04 10:09 AM (#557487 - in reply to #557474)
Subject: Re: Have you heard of these early hemi failure modes?



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i seriously doubt it was due to a shifting block. .003" is a huge amount for a solid metal to move in one spot. Sounds like it was just machined improperly from the get-go; or else it was solely the problem with the crank and they line bored it just in case the block was out of spec, for added insurance. Either that, or the broken crank caused the bore to go out of spec - which is the most likely reason. Claiming that the block was "green" when it was bored is a wives' tale.

Also, if the block really was out by .003", the crank wouldn't turn at all. Tolerance on that bore is more like .0003", or 3/10th's of a thousandth.

Edited by Powerflite 2018-02-04 10:21 AM
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58coupe
Posted 2018-02-04 1:13 PM (#557497 - in reply to #557474)
Subject: Re: Have you heard of these early hemi failure modes?



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I have read that the early Dodge hemi's (241,270) with the smaller diameter crankshaft had a tendancy to break when "hotrodded" developing more power.
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Mopar1
Posted 2018-02-04 2:08 PM (#557500 - in reply to #557497)
Subject: Re: Have you heard of these early hemi failure modes?



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58coupe - 2018-02-04 12:13 PM

I have read that the early Dodge hemi's (241,270) with the smaller diameter crankshaft had a tendancy to break when "hotrodded" developing more power.
No vibration damper from the factory contributed, if not the main cause, of failures on low deck Dodges.
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Mopar1
Posted 2018-02-04 2:13 PM (#557502 - in reply to #557474)
Subject: RE: Have you heard of these early hemi failure modes?



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"In the process, they found that the water pump manifold/cover had been attached to the block during a previous rebuild with at least one bolt that was too long. The bolt in question had (supposedly) pushed the No. 1 cylinder wall and made a bulge in the cylinder wall that was causing the engine to stall. " I'd think it would be more likely to crack/break out the wall.
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