Crank breakers wanted

Small Block Mopar Engine

  1. K.O. SWINGER

    K.O. SWINGER Meeting in the alley since 1976

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    So tell your story, have you broke a crankshaft? Was it cast was it forged and why did it break. They say the factory cast units will handle the riggers of super stock racing? And you know that's some stress! I personally am not to interested in theories or hypothesis nothing but facts ma'am.
     
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    • SSG_Karg

      SSG_Karg Heeeeeres Johnny!

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      ......crickets.......
       
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      • JDMopar

        JDMopar Well-Known Member

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        I didn't break it....but in 1975, I bought a Duster 340 parts car that had been rear ended pretty hard. I paid $50 for it, and it was an FC7 340 4 speed car. I took all the 4 speed stuff out to swap over in my 70 Duster. The original 340 in the parts car had a broken crank. It was broke in the 2nd main journal, and it started up and ran. I started it up and backed it into our basement after my Mom towed me home with a rope! The balancer barely wobbled, and it didn't knock until you revved it up pretty good. I sold the rest of the car for $50 and put everything from the flywheel to the 8 3/4 with springs in my car. Not much of a story....but it's the one I've got! LOL
         
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        • MoparMike1974

          MoparMike1974 FABO Gold Member FABO Gold Member

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          Here is a crank out of my 74 cuda 318. It was non-running when I got it and this is what I found when I tore it down. No other issues found in the engine, everything looked great.

          Brokecrank.jpg
           
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          • 12many

            12many Well-Known Member

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            I’ll bite. Not a small block but in 2008 or thereabouts I rebuilt the 225 slant six w/forged crank in my van, after brainwashing myself on Slantsix.org posts about hopping up the slant:rolleyes: so I had the block decked to bump the compression, some head work with bigger stainless valves and light porting I did, typical long block rebuild otherwise, Erson custom cam, modified single barrel intake into a two barrel, hogged out exhaust manifold to accept 2-1/4” pipe, HEI conversion, etc etc. Was peppy, it moved somewhat impressively, sounded good through a Dynomax Super Turbo. So one night hauling ass down the interstate at about 80 or so out of the blue BANG!!! Loud as fuck metal explosion of some sort, engine was still running (it was brief) but clanking like we have a major problem and then the motor went dead. This all happened under the doghouse which is right next to the driver seat. Was very loud and startling. Coasted over to the shoulder and being dark I could barely see under the doghouse lid but I could just see under the intake/exhaust manifolds on the side of the block a big ass hole and the crankshaft. Uh oh:eek: So after towing it home I grabbed a flashlight and could see the crankshaft was in two pieces! Must have been all it could take and it couldn’t take no more! Ended up scoring a remanufactured long block (from the late 80’s) that was still in the crate sitting in a warehouse that was being liquidated, the engine had all American made components upon thorough inspection. So I put the Erson cam in it, the ported head, along with the manifolds and was back in action! So I am a “crank breaker” yup:(
             
            Last edited: Jan 28, 2021
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            • 70aarcuda

              70aarcuda Master Hoader of SBM FABO Gold Member

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              Emailed friend who raced a 360 in SS a few years ago....He said he used cast crank and never had a problem....Volare that GT/IA
               
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              • Garrett Ellison

                Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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                I had a '73 400 cast crank I had taken out of an engine that had spun the rod bearing and was grooved out beyond repair. I had some use out of it as a "hammer" while playing a game of Chrysler Vs. GM and Ford by throwing it at other pieces of junk cast iron from a height of six feet. It broke everything I threw it at without itself breaking and left some pretty good chips in the cement, too. The '73 360 crank I have right now sounds like a forged steel crank when tapped with a hammer. I wish I had crack checked the B crank before hauling it away to see how much damage I may have done to it. But after that, I believe the early seventies cast cranks they produced could withstand anything this side of nitro if used with aluminum rods.
                 
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                • Demonracer

                  Demonracer 71 Demon 00 Ram 16 Chrysler 300S 05 Caravan FABO Gold Member

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                  Bob Murray & I were running Super Gas with a 69 Barracuda that had a 440 with a 5/8" stroker crank in it & Max Wedge stage III heads, severely ported. We went to an NHRA divisional race close to Tyler, TX & on our second round of eliminations we slowed down a full second. We won the round because the other car red lit. We pulled plugs & started diagnostics & came up empty, so we loaded it up on the trailer. We stayed to watch the rest of the races & then went back to his shop to see what went wrong. Bob pulled the engine down the next week & I got there that next Friday night after having to work all week. I was under the car pulling the pan, getting ready to pull the engine. The light shined just right & I saw what I thought was a hair line crack in the center main web. We got it out & sure enough the center main web was cracked all the way up into the cam bearing area. After we found the crack, Bob sent the crank off to be x rayed & found cracks on five of the rod journals. We were told that the cracks could be welded & the journals turned back down but there were no guarantee that it would hold up. Needless to say, we passed on that idea knowing the stress we were putting on that engine. I still have the crank stored away in the back of my storage area, I just don't know why I hung onto the crank other than we were having a blast running the 9.90 index with just a transbrake & no electronics.
                   
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                  • Hellrats

                    Hellrats Just another dumbass FABO Gold Member

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                    I ran factory cast crankshafts for years in Mopar 360 engines in circle track dirt cars. Never did break a crankshaft.
                     
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                    • moper

                      moper FABO Gold Member FABO Gold Member

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                      Never broke one personally. Had blocksvfail. No cranks.

                      a friend did. Used an ex-fueler crank in the days before big aftermarket support of longer strokes. Had cracks but his builder assumed “if it held 4000 it will hold 1200”. It held it for the dyno. Came apart at 1000’ on its maiden run, taking the side of the block and a front tire with it. Car in the wall.., etc etc etc.
                       
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                      • Oldmanmopar

                        Oldmanmopar Going left turning right FABO Gold Member

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                        I snapped a 69 440+6 crank right in front of the flywheel in 1974. Hard launch 4spd. Dana 410's 69 Coronet with Race Masters. Put a magnum 4bbl in out of my other wrecked R/T . I did many of the same launches with no problems. I would say some things are just flawed and those are the risks of the game.

                        I was always a confirmed believer in steel cranks. I won't build a High torque motor for myself without one . Why? Because I like the big torque on the bottom and high 8000 rpm HP on the top . I never broke a Cast Crank but I never had one in a Race motor. I just was worried about all the other parts it would destroy .

                        I did have a RB rod shove two cam lobes up through the intake though.
                         
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                        • Hellrats

                          Hellrats Just another dumbass FABO Gold Member

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                          I'm sure the hard launch at the drag strip is the hardest on cranks.
                           
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                          • dirty white boy

                            dirty white boy 50 yr old Juvenal delinquent

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                            dirt track racing can be extremely bad on cranks especially if tracks acorn field bouncing from one hole to another will snap a crank or a axle,..rear end, hole drive train for that matter!
                             
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                            • AJ/FormS

                              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                              I love reading these stories.
                               
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                              • K.O. SWINGER

                                K.O. SWINGER Meeting in the alley since 1976

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                                They're all great stories! Sad but great.. I just believe a lot of horror stories about broken cranks are due to other catastrophic failures something seizes something breaks loose causing unbalanced stress, or as stated just a flaw in that particular crank. There is no doubt that forged crankshafts are superior but I am amazed with the strength of a quality cast unit and how many of them put up with the flogging that they do.
                                 
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                                • RammerJammer75

                                  RammerJammer75 Well-Known Member

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                                  My Dad killed a couple Callies cranks during his dirt track days, but all of them were due to a rod or main journal being set too tight and killing the crank. He had a rod journal so tight one night it warped the crank. He raced out of his own pocket, so most of the time the cheaper fix was the right fix to race the next week. He had a local shop try to straighten the crank, but they wound up weakening it. The following week, it wound up braking right in that spot and killed the engine.
                                   
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                                  • pittsburghracer

                                    pittsburghracer Well-Known Member

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                                    Being this is posted in the small block area I won’t go into the destruction I’ve done to big block cranks but I’ve never hurt a stock small block crank. Knock on wood.
                                     
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                                    • teringer

                                      teringer FABO Gold Member FABO Gold Member

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                                      bin up in the air with the pedal on the floor and coming back down to earth on a very tacky track with 10'' tires a couple of times never broke a mopar part (360) or a 8.5 gear but I've seen others not survived /mostly chubys
                                       
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                                      • gregcon

                                        gregcon Well-Known Member

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                                        Last week, a guy I work with was driving down the highway at 75MPH in his F250 with 6.7L diesel engine. This is a truck he bought new, always maintained, and had a little over 100K miles on. It is a 'cowboy Cadillac' truck, he never used it for much other than driving around in.

                                        The engine light came on, the engine stopped running. He pulled over. A few hours later, the dealer they towed it to told him they could rotate the engine with the starter and the pulleys weren't rotating. After pulling the pan, they confirmed the crank was now a two-piece affair.
                                         
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                                        • yellow rose

                                          yellow rose Overnight Sensation FABO Gold Member

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                                          Damper and crank failures on Diesel engines is a real issue.

                                          The VAST majority of broken cranks is because the damper was wrong for the application or it was worn out.

                                          It would be interesting to see what type of damper was on that crank.
                                           
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                                          • 79410aspenrt

                                            79410aspenrt Well-Known Member

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                                            never broke a cast 360 crank yet. i did however find out the strength of factory rod bolts
                                             
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                                            • Oldmanmopar

                                              Oldmanmopar Going left turning right FABO Gold Member

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                                              Never pays to use old bolts on the rods . Many learned the hard way including myself
                                               
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                                              • Garrett Ellison

                                                Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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                                                What rpm, piston mass, approximate hp level, and type of usage was that point for you?
                                                 
                                              • Garrett Ellison

                                                Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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                                                Thank you! I halfway thought about it but I'll put the little extra insurance into it. I'm cheaping out badly enough on this 360 build as it is with a set of 14,000 mile '73 HD truck pistons that run .008 deck clearance with a 9.6 inch deck. But I believe I'll probably upgrade there, too, by the time it's over. The snowball priniciple.
                                                 
                                                Last edited: Jan 30, 2021
                                              • 79410aspenrt

                                                79410aspenrt Well-Known Member

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                                                6800 RPM, Aries forged pistons on stock rods, no dyno #'s but ran 10.20 @ 130 MPH @ 2900 lbs
                                                 
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