blown99 Posted April 3, 2020 Share Posted April 3, 2020 12' Superduty. Came in not running and had been at a few other shops. Customer had replaced the oil and filter prior to bringing it to me. I charged the batteries, it had a long crank, then started, popping back through the intake, ran for about 30 seconds then stalled. Had a slow crank after that. Pushed the truck inside, began disassembly assuming cam/lifter issue due to the popping back. Found failed lifter on #5/worn out cam lobe. Replaced cam, all lifters, checked valves reassembled. Checked piston protrusion to check for bent rods, cylinder walls looked very good. Try to start - long crank but it will start. I am able to keep it running for a few minutes, then it will stall. Engine runs rough, power balance is all over the place. When it stalls, I have a slow crank, acts like a slight hydro lock condition. I have no cam/crank sync and it is running. No codes for cam or crank sensors. I will get codes for random misfire and a #7 contribution. Relative compression test is erratic. Listening to it while it cranks - initially I had some uneveness when cranking like you typically do after an engine has been apart and everything is dry. After it ran for a bit and I attempted a restart I had uneven cranking. I removed the injector in #1, remove the vac pump, dial indicator down onto #1 piston and bar the engine - timing appears to be ok. Upper timing mark is on point with the piston being at tdc. Remove cam sensor, leave it plugged in but crank the engine and I get a cam fault when cranking. I have read a few cases of broken cranks and slipped crank gears. At this point after dial indicating, I am not suspecting the slipped crank gear. But this engine was loud...deep noise to it when it ran. Where are these cranks breaking? symptoms? Quote Link to comment Share on other sites More sharing options...
Brad Clayton Posted April 6, 2020 Share Posted April 6, 2020 They tend to break in the front, if it was broke you would know it because it makes a deafening noise like a broken flex plate times 10. Also the belt puts a lot of pressure on the front of the crank and it would flex a broken crank that is near the front and it would puke oil out the front crank seal at an alarming rate. Generally the main bearings spin and eventually clamp down on one or more portions of the crank thus slowing it's rotation (lugging the engine) and if the conditions are right the crank breaks instead of just locking the engine up. If the engine is still determined to run after such a wallet crushing event, then the counter weights will actually drive the crank (between the break) and she will raise hell. Quote Link to comment Share on other sites More sharing options...
cbriggs Posted April 6, 2020 Share Posted April 6, 2020 How far apart did you have it? The 12's were the most common ones to lose main bearings. I have had a few act a lot like this. Run it till it dies and then try to bar the engine and see if its tight. Also now that you have run it and circulated some oil cut open the oil filter, and possibly take a sample from the oil pressure sensor hole while cranking. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.