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Vintage Diesel and Oil Engines Fairbanks Morse, Lister, Petter, Witte and other pump injected Diesel oil engines.

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Detroit Diesel 4-71 Smoking and Missing


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  #1  
Old 05-02-2018, 12:34:57 PM
471DetroitKid 471DetroitKid is offline
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Default Detroit Diesel 4-71 Smoking and Missing

Hi all, I'm having trouble with a 4-71 Detroit Diesel. It is in a pecan tree sprayer. It started missing and smoking really bad the last time I was using it. My Dad and I took the valve cover off and held down each injector and isolated the problem to the #4 cylinder. When we held down the fourth injector, the smoke cleared up and there was no noticeable difference in the engine RPM. So we put a rebuilt injector in, but we still have the same problem! We ran the rack and adjusted the valve lash on the problem cylinder but nothing has changed. I also noticed it has diesel leaking around the exhaust manifold.(wet stacking) I ran it for about 30 minutes this morning under load to try and clean out the cylinder, but nothing improved. Any ideas on what the problem could be?
Thanks in advance!
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Old 05-02-2018, 12:46:24 PM
Tracy T Tracy T is offline
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Default Re: Detroit Diesel 4-71 Smoking and Missing

i am no diesel mechanic by any means but i would suspect something has caused that cylinder to loose compression based on what you have stated. first post i see, welcome to the stak! others more qualified will be by shortly.
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Old 05-02-2018, 01:38:42 PM
The Diesel Doctor The Diesel Doctor is online now
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Default Re: Detroit Diesel 4-71 Smoking and Missing

Sounds like low compression on that cylinder. Does your exhaust pipe point up? I have see many times where rain water enters the cylinder and bends the con rod. Pull of the air box covers bar the engine over by hand, Observe the piston movement. The one that disappears below the port would indicate a bent rod. ALso you can check for a leaking valve when shutting down the engine listen for a churping sound in the exhaust just before it stops AL.

Also don`t continue to put it in service, If it is a bent rod it will bend more and can punch a hole in the block. AL
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Old 05-02-2018, 06:32:40 PM
Bill Hazzard Bill Hazzard is offline
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Default Re: Detroit Diesel 4-71 Smoking and Missing

What color is the smoke? That will help with the diagnosis.
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Old 05-03-2018, 08:44:51 AM
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Toesmack Toesmack is offline
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Default Re: Detroit Diesel 4-71 Smoking and Missing

Also suspect is the copper cup the injector rests in. Cracks are not exactly common, but not unheard of. You can pull the injector and do a visual down the injector bore after you pull the intake box cover to check your con rod.
Don't continue operation without locating the problem. Sounds like enough fuel to wash down the cyl and also dilute the oil.
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Old 05-03-2018, 08:56:31 AM
471DetroitKid 471DetroitKid is offline
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Default Re: Detroit Diesel 4-71 Smoking and Missing

Thanks for the replies! We have since checked the compression, and the problem cylinder appears to be dead. No compression, not any! The smoke is a blue color which would seem to indicate burning oil, but the oil level doesn't go down much at all. Fuel consumption was up though, like 50%! We have decided to pull the head and see if something is obviously wrong in the top end. The exhaust points down and then runs horizontally for about 10 feet, so water in the exhaust would be next to impossible.
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Old 05-03-2018, 11:43:00 AM
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Default Re: Detroit Diesel 4-71 Smoking and Missing

When your compression goes from 550 PSI To 0, i bet you will find a very compromised exhaust valve. Have seen pie shaped pieces missing ,also the valve head broken off and embedded in the piston. Post pictures of what you find. ALOHA AL
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Old 05-03-2018, 12:35:03 PM
471DetroitKid 471DetroitKid is offline
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Default Re: Detroit Diesel 4-71 Smoking and Missing

I opened the air box covers on the problem cylinder and the one in front of it, and the pistons went down the same distance.(Neither of them went below the air ports.) So thankfully not a bent rod! Now for the head removal, I have to unscrew the rockers from the pushrods to get the head off, right? Or do I pull the push rods up and the pushrods and rockers come off in one piece?
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Old 05-03-2018, 01:26:52 PM
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Default Re: Detroit Diesel 4-71 Smoking and Missing

When you disconnect everything attached to the outside of the head including the governor remove the 10 cylinder head bolts. They take a 15/16 socket. There are lifting brackets on each end of the head. remove the 7/16 bolts that go down into the flywheel and front cover housings. The head will come off as an assembly. AL

Forgot to mention, you can leave the rockers in place but you need to remove the control rack. AL
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Old 05-03-2018, 01:49:39 PM
471DetroitKid 471DetroitKid is offline
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Default Re: Detroit Diesel 4-71 Smoking and Missing

It appears that I need to completely remove the governor for the head to slide up. Do I just take out the four 1/4" bolts that hold the governor to the front of the blower? Sorry for all the questions, but I've never done this before and I don't want to do anything I might regret!
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Old 05-03-2018, 02:26:08 PM
471DetroitKid 471DetroitKid is offline
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Default Re: Detroit Diesel 4-71 Smoking and Missing

Well, we got the head off! And, I think we found our problem! Now, do I need to take the head to a machine shop and get a valve job? Or, can I just buy a new valve and stick it in? The seat looks pretty good, it's not pitted really deep or anything.
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Old 05-03-2018, 02:27:26 PM
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Default Re: Detroit Diesel 4-71 Smoking and Missing

Allan is at work right now. But the answer to your question is YES.
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Old 05-03-2018, 11:48:41 PM
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Default Re: Detroit Diesel 4-71 Smoking and Missing

Clean the space between the broken valve and the valve below it with a wire brush and sand paper. It may be just the photo but it looks like it may be a small crack. The pieces that broke off the valve bounced around a bit before it went out the exhaust pipe. If the head is not cracked the damage does not look to bad. There probably some marks on the piston head . What you need to do is bar the engine over until the #4 piston top ring is visible in the liner port. Take a small screwdriver and push it in to see if it springs back. This will tell you if the ring groove got damaged. The cylinder liners may move when you bar the engine, just push them down until you get to the right spot. As what to do about the head. If it is cracked it should be replaced. You could replace and lap in that one valve and maybe get away with it. Replacing all 4 valves in that cylinder would be better. Best option would be to have a machine shop or Detroit dealer rebuild it. They also have exchange heads. You might also find a online. Good luck AL
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Old 05-11-2018, 08:24:15 PM
471DetroitKid 471DetroitKid is offline
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Default Re: Detroit Diesel 4-71 Smoking and Missing

Well folks, I am happy to say after getting a valve job on the bad cylinder, she is running like a dream. Thanks to all for your input. Special thanks to The Diesel Doctor. It would have been extremely difficult without your help!
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