Cummins Locked Up
Thread Starter
Joined: Nov 2005
Posts: 4
Likes: 0
Cummins Locked Up
Hey everyone, I'm here to ask for help at work diagnosing a locked up Cummins diesel.
It's a 1994 3500 4x2 and the owner said that it locked up doing 70 mph on the highway. We tried to turn the flywheel and sure enough it won't budge. then we pulled the injectors to see if it hydro-locked - nothing there. Next we tried pulling the starter out to look for obstructions in the bell housing - nothing. So then we pulled the injector pump to look for the infamous injector pump nut that can lock these things up - it's fine. Last thing we've done is pull the timing cover to see if there's a timing gear that's fubar - they're all good.
We can figure out what's strong enough to lock an engine up that wouldn't leave a gaping hole in the block (no holes in the block btw). If anyone has ideas please let me know. If we have to pull this engine out we have to pull the torque converter with it, and we'll have to take the front end completely off.
All of the old Dodge mechanics we've talked to say they've NEVER heard of a Cummins locking up. One guy told us that he's heard of them melting pistons and rings.. but they still run.
Kevin
It's a 1994 3500 4x2 and the owner said that it locked up doing 70 mph on the highway. We tried to turn the flywheel and sure enough it won't budge. then we pulled the injectors to see if it hydro-locked - nothing there. Next we tried pulling the starter out to look for obstructions in the bell housing - nothing. So then we pulled the injector pump to look for the infamous injector pump nut that can lock these things up - it's fine. Last thing we've done is pull the timing cover to see if there's a timing gear that's fubar - they're all good.
We can figure out what's strong enough to lock an engine up that wouldn't leave a gaping hole in the block (no holes in the block btw). If anyone has ideas please let me know. If we have to pull this engine out we have to pull the torque converter with it, and we'll have to take the front end completely off.
All of the old Dodge mechanics we've talked to say they've NEVER heard of a Cummins locking up. One guy told us that he's heard of them melting pistons and rings.. but they still run.
Kevin
Professional
Joined: Aug 2004
Posts: 117
Likes: 1
From: 33.43.342, 84.21.602
RE: Cummins Locked Up
Ive personaly seen melted pistons and rings on Cummins engines and the thing still run like a top. even had a 8.3L Cummins come into the shop here with 3 droped valves into the same cylinder. engine still ran, albeit a little rough but it ran.
I would say check the lift pump it's probably dead. if the thing is getting fuel it'll fire, thats what I would check first
I would say check the lift pump it's probably dead. if the thing is getting fuel it'll fire, thats what I would check first
Veteran
Joined: Nov 2005
Posts: 401
Likes: 0
From:
RE: Cummins Locked Up
I am curious how hot he got it. I have seen a non-diesel motor with a few siezed pistons (could not spin the crank) because the motor leaned out and over heated due to the dummy who owned it pulled the head and put it back together without replacing the head gasket. I have also seen atv's sieze up tight due to overheating. Drew, have you ever seen a piston siezure in a diesel? I'm not a mechanic so I don't see a lot of misfortunes.
I guess I question if the owner is telling you the true story of how it happened. Could the wrong fuel overheat the motor? I dunno, never worked on a diesel.
I guess I question if the owner is telling you the true story of how it happened. Could the wrong fuel overheat the motor? I dunno, never worked on a diesel.
Professional
Joined: Aug 2004
Posts: 117
Likes: 1
From: 33.43.342, 84.21.602
RE: Cummins Locked Up
diesels are built to tighter tollerences and made from beefier parts than gassers. if a diesel is leaned out too mugh it will just loose power and stop running, plus EGT's will skyrocket which can burn the turbo up.
most diesels sieze up due to rust from not running, or a rod gets trown out of the block, crank breaks. basicaly something has to break in order for the engine not to run. diesels dont stop running like gassers since the rotating assembly is so much more massive and the rotating enertia is so mugh greater, if a piston does sieze the next thing that happens is the rod or crank being puked out of the bottom of the oil pan, or the head gasket blowing out.
but usualy the first thing to go on a Diesel that is running say Kerosene, JP-8, 4 or 2 is the injector pump burning up.
the Cummins 8.3 (250) that came in with the dropped valves was from over-revving. vehicle was moving and tranny was brought down a gear, clutch let out and engine reved to somewhere near the neighborhood of 4000-4500rpm. these engines are not built for that speed. redline is around 2700-3K. so what happened was the valves began to float, the piston slapped the valves and the retainers popped off allowing the valves to drop into the cylinders and CRUNCH. the rod was bent, piston was chewed up like an old dog toy, and head looked like it was shot up. Since the head on these engines is a three piece head where one head covers 2 cylinders, we just had to replace one head, pull the piston out, pull the sleeve and put new parts in and it was good to go.
the only way to turn a diesel engine over by hand would be with a breaker bar on the end of the crank. gassers normaly have 8-10:1 compression. the Cummins has about 17.5:1 so the compression is WAY higher and there is no way to turn that by hand like you can a gasser.
if the engine will turn, and you can put fuel to that engine, it will fire. thats why I point twards the lift pump. it died starving the injector pump killing the engine. change the lift pump, prime the engine back up and it's good to go.
Doug, my favorite engine to see die are Detroit Diesel 92 series V8's. they are two stroke, 903cid diesels with a turbo and blower sitting on top. the engine normaly reves to about 2500rpm max. however I had one run away on me while adjusting the govenor and run past 4000. put a clip board over the turbo intake to suffocate the engine. luckly it finaly stopped. the head gasket was sucked into the cylinders, the blower gasket was sucked in as well. however I have seen one literaly blow up. when the engine hits around 5K the turbo is producing so much boost the head bolts cannot hold the pressure and the heads blow off in a firey flash, then the crank gets puked out the bottom and rods fly through the block from the instantaneous no load. the blower casing breaks in half from the rotors spinning too fast and the turbo is ripped into about 15 different pieces. the only thing left are usualy the engine mounts
most diesels sieze up due to rust from not running, or a rod gets trown out of the block, crank breaks. basicaly something has to break in order for the engine not to run. diesels dont stop running like gassers since the rotating assembly is so much more massive and the rotating enertia is so mugh greater, if a piston does sieze the next thing that happens is the rod or crank being puked out of the bottom of the oil pan, or the head gasket blowing out.
but usualy the first thing to go on a Diesel that is running say Kerosene, JP-8, 4 or 2 is the injector pump burning up.
the Cummins 8.3 (250) that came in with the dropped valves was from over-revving. vehicle was moving and tranny was brought down a gear, clutch let out and engine reved to somewhere near the neighborhood of 4000-4500rpm. these engines are not built for that speed. redline is around 2700-3K. so what happened was the valves began to float, the piston slapped the valves and the retainers popped off allowing the valves to drop into the cylinders and CRUNCH. the rod was bent, piston was chewed up like an old dog toy, and head looked like it was shot up. Since the head on these engines is a three piece head where one head covers 2 cylinders, we just had to replace one head, pull the piston out, pull the sleeve and put new parts in and it was good to go.
the only way to turn a diesel engine over by hand would be with a breaker bar on the end of the crank. gassers normaly have 8-10:1 compression. the Cummins has about 17.5:1 so the compression is WAY higher and there is no way to turn that by hand like you can a gasser.
if the engine will turn, and you can put fuel to that engine, it will fire. thats why I point twards the lift pump. it died starving the injector pump killing the engine. change the lift pump, prime the engine back up and it's good to go.
Doug, my favorite engine to see die are Detroit Diesel 92 series V8's. they are two stroke, 903cid diesels with a turbo and blower sitting on top. the engine normaly reves to about 2500rpm max. however I had one run away on me while adjusting the govenor and run past 4000. put a clip board over the turbo intake to suffocate the engine. luckly it finaly stopped. the head gasket was sucked into the cylinders, the blower gasket was sucked in as well. however I have seen one literaly blow up. when the engine hits around 5K the turbo is producing so much boost the head bolts cannot hold the pressure and the heads blow off in a firey flash, then the crank gets puked out the bottom and rods fly through the block from the instantaneous no load. the blower casing breaks in half from the rotors spinning too fast and the turbo is ripped into about 15 different pieces. the only thing left are usualy the engine mounts
Thread Starter
Joined: Nov 2005
Posts: 4
Likes: 0
RE: Cummins Locked Up
Well, let me give some more info.
When the truck died the owner tried to start it again and only got a "clunk" sound as the starter tried to engage but couldn't turn anything. So, he thought it needed a new starter and he put one on himself. Of course the new starter didn't do any good either, it still just goes "clunk" like the starter gear is engaging but just can't turn the flywheel.
So, even if it's getting fuel from the injection pump it can't turn over - which is why we think we've had some part of the rotating assembly come apart. Yesterday I took the valve covers off to check for bent rods or dropped valves, of course nothing's out of wack there either.
We were just given the 'go ahead' to pull the motor and find out what's wrong with it, so we'll know probably sometime next week what went wrong. If it did throw something I'll take pictures, as it seems we've encountered the first Cummins with a lower end problem that wasn't obvious. From looking at how the rods are made (with the semi-circles ending at 1 and 7 o'clock instead of 3 and 9 o'clock like a regluard rod) it's possible that if one of the bolts holding the rod together backed out it could have seized the engine without leaving a hole in the block.
When the truck died the owner tried to start it again and only got a "clunk" sound as the starter tried to engage but couldn't turn anything. So, he thought it needed a new starter and he put one on himself. Of course the new starter didn't do any good either, it still just goes "clunk" like the starter gear is engaging but just can't turn the flywheel.
So, even if it's getting fuel from the injection pump it can't turn over - which is why we think we've had some part of the rotating assembly come apart. Yesterday I took the valve covers off to check for bent rods or dropped valves, of course nothing's out of wack there either.
We were just given the 'go ahead' to pull the motor and find out what's wrong with it, so we'll know probably sometime next week what went wrong. If it did throw something I'll take pictures, as it seems we've encountered the first Cummins with a lower end problem that wasn't obvious. From looking at how the rods are made (with the semi-circles ending at 1 and 7 o'clock instead of 3 and 9 o'clock like a regluard rod) it's possible that if one of the bolts holding the rod together backed out it could have seized the engine without leaving a hole in the block.
Thread Starter
Joined: Nov 2005
Posts: 4
Likes: 0
RE: Cummins Locked Up
Oh yeah, we already pulled the injector pump out.. which may have been a big mistake for us. We don't have the special service tool to put it back in, and we didn't know to set the engine at DTC Cyl 1 before taking it off. Not like we had a choice though, as the engine is seized and we couldn't have gotten it to DTC Cyl 1 if we wanted to.
Alldata says it's a 3.5hr job to put the injector pump back on IF you set it to DTC cyl 1 before you take it off. Heh. Assuming we can fix this engine without replacing it I guess we'll be sending it down to the Dodge dealership to let them do the hard work.
Alldata says it's a 3.5hr job to put the injector pump back on IF you set it to DTC cyl 1 before you take it off. Heh. Assuming we can fix this engine without replacing it I guess we'll be sending it down to the Dodge dealership to let them do the hard work.
Professional
Joined: Aug 2004
Posts: 117
Likes: 1
From: 33.43.342, 84.21.602
RE: Cummins Locked Up
I cant wait to see these photos.
as long as you havent moved anything with the injector pump and return the engine in the same possition after it is fixed it might only take a little timeing adjustment to get it running again.
as long as you havent moved anything with the injector pump and return the engine in the same possition after it is fixed it might only take a little timeing adjustment to get it running again.
Trending Topics
Veteran
Joined: Nov 2005
Posts: 401
Likes: 0
From:
RE: Cummins Locked Up
Drew- Thanks for the info., I always like to learn something new. I just got my first issue of TDR a few days ago. I seriously thought about buying a diesel but decided against for a few reasons. One was lack of knowledge, but I'm learnng more all the time.
Thread Starter
Joined: Nov 2005
Posts: 4
Likes: 0
RE: Cummins Locked Up
Well, here's the result. We pulled the tranny the other day, and the engine yesterday. The pan came off this morning. We couldn't find anything wrong right away, so we proceeded to loosen the main bearing bolts, and it still wouldn't turn. Then I noticed a crack on the bottom of piston #6. We took the rod bearing off piston 6 and then the assembly started moving. We knew that #6 had siezed, so we got permission to pull the head.
Here's the result:
Piston 6 melted and seized the motor. We can only assume the #6 injector failed and burned the piston. The intake valve was hanging like a loose tooth ready to be pulled out. So, I beleive credits go to Curtis Ainsworth for being the first mechanic to see a Cummins diesel come apart and lock the motor up.
Here's the result:
Piston 6 melted and seized the motor. We can only assume the #6 injector failed and burned the piston. The intake valve was hanging like a loose tooth ready to be pulled out. So, I beleive credits go to Curtis Ainsworth for being the first mechanic to see a Cummins diesel come apart and lock the motor up.
