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803 Bogs Down and dies at 85% Load

csheath

csheath

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Possible the valve stuck in the guide? I would pull the springs and make sure they all slide in the guides as they should.
 
pjwest03

pjwest03

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csheath said:
Possible the valve stuck in the guide? I would pull the springs and make sure they all slide in the guides as they should.
Click to expand...
Or the lifter sticking in the bore. At some point the valve is/was nearly fully open when it shouldn't have been. The valves and lifters should all move easily. I would also check the valve stem for straightness. It should also be nice, shiny, and clean.
 
U

USAMilRet

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Think I am going to replace the lifter, push rod, and valve if it is damaged.

Are you kidding me? The price for a single hydraulic valve lifter? Used one from $20, new one from $44 or buy all 8 lifters for $186. Dang, what are these things made of - GOLD? The lifter should be an off the shelf item that fits many many items so how do I find the proper cross references for these parts? Looking in the manuals but have not found what I am looking for.

Yes, I am going to take the intake valve on cylinder 3 apart to make sure it is OK and not bent. I ran a bent intake valve for years in a Audi Coupe that I had in West Germany and that sucker still traveled at 140mph on the Autobahn.

So I am looking for parts and I might as well just pick up another genset for parts.
 
J

justacitizen

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is there anything obviously wrong with the lifter? i think you would be wise to replace the lifter pushrod rocker and have the valve checked or replaced. if the valve drops it will ruin the engine. sorry this hasn't worked out to be as simple a fix as it could be but you are lucky the only thing broken is a rocker.
 
U

USAMilRet

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390
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Tampa, Florida
justacitizen said:
is there anything obviously wrong with the lifter? i think you would be wise to replace the lifter pushrod rocker and have the valve checked or replaced. if the valve drops it will ruin the engine. sorry this hasn't worked out to be as simple a fix as it could be but you are lucky the only thing broken is a rocker.
Click to expand...
If that is the ONLY thing so far.

I do not know if anything is wrong with the lifter. What take the chance that it could happen again by replacing the lifter? There does not appear to be anything wrong with the lifter sleeve or any othe4r part that would have caused the lifter to stick unless it was an internal thing. Will see when I take the lifter apart to check it.

As I have the rebuild gasket kit, I may just replace all the parts that came in the head packet for the valves.
 
U

USAMilRet

Member
390
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Location
Tampa, Florida
Well, after manually testing all the lifters, it appears that they are all working correctly. So the lifter is not the problem that caused the rocker arm to break.

I had to use my drill press to press the lifter caps down to get the oil out of the lifters to test them. They were rock solid and could not be moved until I used a great amount of force and pushed the top piston down to get the oil out, They are really simple mechanism's. The case, a plunger, spring, cap, cover with a hole for the push rod, and a spring retainer. That is it. Once charged with oil though, they are almost impossible to move until the oil is removed from them.

Also, an examination of the block and cam shaft indicated no visible reason that the lifter would have stuck. Metal faatigue does happen and I think that this was the cause. The only reason I can think of the valve hitting the piston thing is that when the rocker arm was breaking (not a clean break) but over a couple of cycles, it may have been intack enough to push the valve further then it should have. Considering the clearance between piston head and valve is measured in the thousands of an inch, this is the best explanation that I can come up with
 
DieselAddict

DieselAddict

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Efland, NC
Something that can happen is if your oil pressure goes really high it can cause the lifters to pump up. Since the clearances are tight in these engines it could cause a valve interference issue.

After you worked on the oil pressure relief spring did you see the oil pressure spike when you started it up?
 
U

USAMilRet

Member
390
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Location
Tampa, Florida
DieselAddict said:
Something that can happen is if your oil pressure goes really high it can cause the lifters to pump up. Since the clearances are tight in these engines it could cause a valve interference issue.

After you worked on the oil pressure relief spring did you see the oil pressure spike when you started it up?
Click to expand...
Oil pressure does not spike. It did go from about 22psi cold (7psi warm/hot) to about 55psi cold, well within the limits, after the adjustment to the spring, but I knew that it was not a solid solution. At least it upped the 7psi at the end to 22 psi. But after a couple of minutes, the pressure drops to about 22psi when the oil is hot. This was only a solution to get the oil pressure to above 7 psi for the time being.

Now I am using a 10W30 break in oil (was using, all but garbage now due to the broken rocker arm and the possible metal contamination of the oil) and that can cause the oil pressure to be a little low but I believe that the plunger in the relief valve is not in specs (to large a clearance around the plunger) and that is allowing the pressure to stay low. Now because I am very poor and do not want to have an oil starvation incident, I am going to place my wife outside watching the oil pressure gauge while the genset runs to monitor it to prevent catastrophic damage to the engine. When I mentioned this to my wife, she said to go ahead and spend the absurdly amount of $69 for this certain piece and get a new one. Alas, a new relief valve is also on order.

Well, I ordered the replacement rocker arm. Will take till next Thursday to get here, hopefully sooner. Still looking for a push rod though. Can not find a new or used one and usually my google fu is pretty good for finding stuff.

So if anyone wants to donate a push rod for the MEP803A, it would be highly appreciated. Then individual I had an PM out to about parts for the genset said he was unable to provide me with these items because it would be awhile before he could get to them and did not know the condition of them since this was a bad engine....
 
U

USAMilRet

Member
390
15
18
Location
Tampa, Florida
Some pictures of the head around the valve in question, the valve on intake 3 (3nd cylinder from the rear/flywheel 5th valve in sequence from the rear/flywheel), and the rocker arm break. Still looks like a fatigue break to me as it does not have the sharp surface of a clean break. but lighter metals break this way (white metal) but usually heavy metals like the rocker arm materials would have a clean break unless it was metal fatigue. My opinion and it could be wrong but comments on this are welcome from any side to figure out what happened.




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BTW, the rebuilder/seller indicated that the head was sent out for servicing while he did the lower. From what I can see, you can tell that this is a newly ground valves, and valve seats and that the head was shaved. Also told me that two valves were replaced.
 
Last edited:
M

m32825

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Central Florida
I'm glad you found something definitely wrong. I hate it when I do a bunch of investigation with nothing specific to show for it. I hope I never have to get into my engine like this, but it gives me confidence to know that I can draw on the expertise of all you rocket genuises if I do!

:)
 
J

justacitizen

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Location
oklahoma
so much for the master diesel mechanic. i would suspect everything he touched. a complete disassembly and check is in order while you still have something to work with.
 
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