Posted: 8/7/2010 8:38:24 AM EDT
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I have a D179 engine in my tractor. 1200 factory hours, no problem until IP rebuild.
It bends exhaust pushrods since that injector pump rebuild. The very rear exhaust is the first to go, I believe every time. The motor runs fine and will be functional for a while before push rod failure. Everything from the cam to the piston tops (I removed haead to rule out contact) has been visually checked by me and everything looks fine. It's solid lift. There is no binding in the valve train. I have ran the motor with crankcase cover (so I can see cam) and valve cover off and watched a push rod bend. The motor was running great when I cut it off due to the inpending failure. The ONLY two out of spec things I've found are: 1. The pump looks to be timed at 22 degrees instead of 14 BTDC. Shouldn't make a difference as far as I know. 2. I was setting lash at 12 on each valve, but did find one manual stating it should be 10 on intake and 12 exhaust. I do not believe that 2 thousandths would make a diffence but will start at 10 on intake when I get new push rods in. I am open to ANY wild guesses or suggestions. I cannot figure it out. I've communicated with some mechanics who also haven't a clue. |
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I know nothing about diesels in general but a couple of questions. Did the head(s) get milled at all? If they did, the pushrods MIGHT be too long now and the rocker arms are pushing on the edge of the pushrods instead of the center. Thats all I can think of off the top of my head. |
| Is this a 2 or 4 valve head? If it is a 4 valve head could the bridge be getting hung up? You say it runs for a bit then bends a pushrod, how long does it run before failure? Are you 100% sure the replacement pushrods are the correct lenght? How many have you bent? |
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Quoted: Check your valve guides if they were not reamed to size when rebuilding the head. Guides to tight can stick valves. Also check coil bind and guides left too long. I'm no expert by any means, so just throwing this out there. But along those lines... In the high performance diesel stuff, people have had problems with not enough valve guide clearance even though it is "in spec." Basically at low engine coolant temperature and running big injectors, some have seen "coking" on the valve stems which further reduce clearance, leads to binding, and bent pushrods. I know it's a different ball game that what you are dealing with....just a thought. |
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There is something missing here as far as details of the original repair. Why did the injection pump need to come off for repairs at 1,200 hours? How far was the engine torn down for repair/rebuild? Was the head rebuilt? Were the timing gears removed? Does it bend the same pushrod? If correct timing is 14 degrees, why is it at 22 degrees?
If you are ONLY bending the same exhaust pushrod, something is binding up in either the rocker arm or valve stem/guide. I believe that you say there are no indications of valve to piston contact, if there was the valve stem would be destroyed and probably worse. I would remove the injectors and rotate the engine and carefully measure the travel of the pushrod/ rocker arm in problem cylinder as compared to the other cylinders while somenoe rotates the engine. |
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-Two valves per.
-The replacement pushrods are right length. -Several push rods have bent on different cylinders. -The IP had to come off due to water contamination. -The engine wasn't rebuilt. -I removed head to check for valve/piston contact and checked valve stem travel by hand on teh bech, no binding. -I took valve cover and cover off side of crankcase and and watched the engine (cam to rockers) with motor running. -Inspected all cam lobes. -The guy who R&R IP advanced the timing I suppose. Still squirts with the valves closed. (I found he had a morphine problem I didn't know about so I'm not going back to ask.) Thanks for ideas. 17Z, I believe I will pull sheet metal and check teeth on timing gears tomorrow. |
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I know diesels are very timing sensative. Since all that was touched was the IP, it makes sense to me that is your problem.
If it is squirting fuel at the time the exhaust valve should be open or chamber pressure is too high holding the valve shut, that could bend push rods randomly. I bet you need to have the IP overhauled again and the timing is off internally, and it is just plain wrong. I have seen crushed pistons from over fueling. Look harder at the IP, a morphine addiction or "monkey on your back" may be the whole problem. |
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Quoted:
Sounds like the crankshaft/camshaft gears are a tooth or so off proper timing. I've seen the same issue with JD 359 engines, got overhauled, tech botched the gear timing, engine ran well enough....until it warmed up and bent pushrods. 
this would be my WAG =(wild ass guess) also.......way over fueling/way early fueling can and does do bad things in diesel engines. |