Broken crankshaft? - Diesel Forum - TheDieselStop.com
'99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the '99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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post #1 of 10 (permalink) Old 05-22-2019, 07:27 PM Thread Starter
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Broken crankshaft?

Truck has 330k miles, exhaust, intake, boost fooler, 1.0 ar housing, stock otherwise. Runs loud as **** at idle, but as soon as I get past 1/4 throttle, runs perfect. Diesel mechanic said it's not a flywheel, sounds like crankshaft or a spun bearing.
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post #2 of 10 (permalink) Old 05-22-2019, 08:27 PM
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A truck with a broken crankshaft isn’t going to run perfect at any speed. Shouldn’t run at all given the front wouldn’t be spinning and the cam is driven from the front. I’d guess a bad injector would be more likely.


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2003 F-250 XLT Crew Cab 7.3L, Chrome BigTex Grille Guard, Quad pillar - 3 ISSPRO gauges (trans, pyro, boost) and DP-Tuner F6; Roush fuel pressure / temperature / oil pressure gauges, Ford Severe Duty AIS, 31 row 6.0 transmission cooler, ScanGauge II, Marinco mod, Walker BTM, Full Force Stage 1 injectors

IF MY BODY IS EVER FOUND ON A JOGGING TRAIL JUST KNOW THAT I WAS MURDERED SOMEWHERE ELSE AND DUMPED THERE
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post #3 of 10 (permalink) Old 05-22-2019, 11:32 PM Thread Starter
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Even if it's an odd break that only allows minimal play in the bearings?
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post #4 of 10 (permalink) Old 05-23-2019, 08:42 AM
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I've never personally experienced it but I have heard of crankshaft fractures where the shape of the break keeps both "pieces" more or less aligned so the engine will still run. Obviously its going to make a hell of a racket.

The only broken cranks I have experienced were on 6.2 Chevs - 2 of them on the same truck - and they were catastrophic show stoppers. After the second one I put a 350 in the truck and traded it on a Ford. That was 2 Chevs in one for me - 1st and last.

2006 F250 6.0 4x4
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post #5 of 10 (permalink) Old 05-23-2019, 08:52 AM
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I still can't see any scenario where the crankshaft would break in a way where it would be noisy at idle and quiet at speed. I have seen out of round rods that were quiet at idle and got progressively louder at speed. Can't imagine a break where the bearing play would be increased. You could spin a bearing or destroy a bearing, but that isn't going to get quiet at speed.

An injector that is overfueling can produce a real racket at idle and might clear up when the engine speed got to the point where it could handle that fuel. Are you getting any smoke at idle?

2003 F-250 XLT Crew Cab 7.3L, Chrome BigTex Grille Guard, Quad pillar - 3 ISSPRO gauges (trans, pyro, boost) and DP-Tuner F6; Roush fuel pressure / temperature / oil pressure gauges, Ford Severe Duty AIS, 31 row 6.0 transmission cooler, ScanGauge II, Marinco mod, Walker BTM, Full Force Stage 1 injectors

IF MY BODY IS EVER FOUND ON A JOGGING TRAIL JUST KNOW THAT I WAS MURDERED SOMEWHERE ELSE AND DUMPED THERE
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post #6 of 10 (permalink) Old 05-23-2019, 11:05 AM
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camshaft end play will cause crap like I think you are describing. Rough idle that will make cyl deviation numbers all over the place. The sensors used as the recall fix sensors have sensitivity to the poles on cam being too close. I have two trucks running around with thinner gasket paper cut out shims I made by hammering sockets of two different sizes into the paper to cut the OD and ID that would let it slide over sensor. The o ring on sensor seals just fine with the sensor out .015-.020 inch.

There are grey and dark blue sensors and some say the blue fix the issue as they are less cranky about the pole to sensor tip clearance. Blue one did not fix the trucks I shimmed.

2015 F350 Platinum Max Tow What a beast with the 4.30 gears!
2006 F450 CC Hauler bed 4x2 6.0 L 6.0 auto, Lariat, 4.30 r/a, SCT, 4in exh. 103K New heads to repair diesel in coolant, 148K.
2006 F350 Lariat CC Dually 4X2, 6.0 auto 4.10 LS, SCT, airbags, 4 in. exh. 154K Rebuilt engine to repair damage from burned piston. One head to fix fuel in oil problem.
36 feet on the floor Elite/Outlaw LQ horse trailer.
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36 foot double tandem axle flatbed trailer
36 foot Platinum 6 horse LQ, side load, full width back tack
2003 EB Expedition 171K (no engine repairs, gas burners are the new longevity leaders)
2004 Volvo V70R AWD-high miler in fleet, 253K (no engine repairs) Hail totaled it but I kept it. Looks like a golf ball now.
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post #7 of 10 (permalink) Old 05-27-2019, 03:12 PM Thread Starter
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I still can't see any scenario where the crankshaft would break in a way where it would be noisy at idle and quiet at speed. I have seen out of round rods that were quiet at idle and got progressively louder at speed. Can't imagine a break where the bearing play would be increased. You could spin a bearing or destroy a bearing, but that isn't going to get quiet at speed.

An injector that is overfueling can produce a real racket at idle and might clear up when the engine speed got to the point where it could handle that fuel. Are you getting any smoke at idle?
No smoke at idle, just a lot of racket.
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post #8 of 10 (permalink) Old 05-27-2019, 03:25 PM
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Take your fan belt off and start it to see if it clears up.

2003 F-250 XLT Crew Cab 7.3L, Chrome BigTex Grille Guard, Quad pillar - 3 ISSPRO gauges (trans, pyro, boost) and DP-Tuner F6; Roush fuel pressure / temperature / oil pressure gauges, Ford Severe Duty AIS, 31 row 6.0 transmission cooler, ScanGauge II, Marinco mod, Walker BTM, Full Force Stage 1 injectors

IF MY BODY IS EVER FOUND ON A JOGGING TRAIL JUST KNOW THAT I WAS MURDERED SOMEWHERE ELSE AND DUMPED THERE
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post #9 of 10 (permalink) Old 05-29-2019, 01:17 PM Thread Starter
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Take your fan belt off and start it to see if it clears up.
that seems like it would cause more damage than it would help.
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post #10 of 10 (permalink) Old 05-29-2019, 02:59 PM
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NO. Removing belt to eliminate any of the engine driven accessories as cause is a very commonly used method. You don't go drive and tow with no belt as water pump is not being driven. Running the engine even 5 minute unloaded is not going to cause a problem with overheat as thermosyphon will still cause some circulation.

2015 F350 Platinum Max Tow What a beast with the 4.30 gears!
2006 F450 CC Hauler bed 4x2 6.0 L 6.0 auto, Lariat, 4.30 r/a, SCT, 4in exh. 103K New heads to repair diesel in coolant, 148K.
2006 F350 Lariat CC Dually 4X2, 6.0 auto 4.10 LS, SCT, airbags, 4 in. exh. 154K Rebuilt engine to repair damage from burned piston. One head to fix fuel in oil problem.
36 feet on the floor Elite/Outlaw LQ horse trailer.
35+5 foot double tandem axle flatbed trailer.
36 foot double tandem axle flatbed trailer
36 foot Platinum 6 horse LQ, side load, full width back tack
2003 EB Expedition 171K (no engine repairs, gas burners are the new longevity leaders)
2004 Volvo V70R AWD-high miler in fleet, 253K (no engine repairs) Hail totaled it but I kept it. Looks like a golf ball now.
Suzuki Carry KEI truck, 660cc 3 cyl DOHC EFI 4X4 5 speed RHD. Sort of a Smart Car sized pickup. Eats Gators and Mules for lunch.

Last edited by jimmy; 05-29-2019 at 04:21 PM.
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