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1925 BROKEN CRANK


brian1925tourer
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THE CAR WAS DRIVING NICELY WHEN THE CRANK BROKE JUST LIKE THAT, STILL KEPT TICKING OVER BUT VERY NOISY, BROKE AT END OF NUMBER ONE CONROD.THIS MOTOR HAD DONE ABOUT 800K'S SINCE REBUILD. ALL BEARINGS STILL LOOK GOOD, ANYONE WITH ANY IDEAS WHY THIS BROKE. IS IT A COMMON PROBLEM :(

Did you crack check, before you ground the crank? Was it ground on center line that the time gears match, if they needed? Were the rods checked for, Twist, Bend, and Off Set? Did the grinder put the correct Radius back in the crank, or did he just run his cut up to the old Radius, and stop there, and leave a Right Angle?

Pictures always help!! BJ, thanks Herm.

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Guest John1918

A friend's '16 roadster broke a shaft just motoring sedately along the street when there was a loud bang from the engine. People came running from their houses to see what happened. Another friend's '17 also broke a crankshaft. Perhaps there could be a weakness, definitely worthwhile getting the replacement crack-tested before installing.

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I agree with Herm111 completely! When you have a "Old" engine rebuilt insist that the machine shop line bores the mains. AND Insist on a heavy radius on the journal ends when the crank gets ground. This eliminate the "break" in the steel.

I don't know how dodge balanced their engines but it would not hurt to have the crank dynamically balanced. (Rotating) Don't static balance! (Not rotating)

Just my 2 cents again........

Bill

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On reading your post again, it looks as if the crank has been square cut like Herm suggested but if the break did not occour 'in the corner' as you say then there was probably a crack present all along. You have my sympathies but the crank should have been crack tested before grinding as well as journal ends radius finished. Apart from line boring the mains and checking con rods as suggested, next time, also check for cracking at rear main as this takes most punishment from the flywheel & clutch assembly. I would be interested to learn if crankshaft breakages were common in the earlier cars and if so, did it have an influence on the decision to go for the C type engine with five main bearings? or was this an attempt to make the four cylinder engine run more smoothly?

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Thankyou Willy for your offer, I have 2 spares so hope one of them will fit. I will be doing the work myself this time around as I did have some earlier problems with the rebuilt motor, and I know a bit more about them now. The person who did the work is on holidays at the moment so I can not confirm if crank was crack tested or not. I have started removing engine so should soon know if my spares will fit. The motor has 3 main bearings not five, I am thinking all sorts of reasons why crank broke, starting with my lousy gear changes, maybe pushing a bit hard on take off, noisy clutch, out of balance, could have been just one of those things that happen. Should I get the crank, flywheel and clutch balanced.

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