MEP-803A - New to me, excited to get it going.

Ray70 said:

How does the motor sound when cranking? does it spin abnormally easy and smooth ( lack of compression pulses? )
The black goo leaking from the muffler joint indicates a fair amount of wet stacking has happened.
I've seen several 803's where the carbon buildup was causing the exhaust valve to not seat fully, resulting in Zero compression.
It was easy to fix, but wouldn't start otherwise.
If it cranks fast with little change in sound when pistons come up on compression ( combined with the pulsing you feel in the air cleaner ) leads me to think your valves may be hanging open a little.

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No, it spins with some compression. Not as smooth as my 3 cylinder Yanmar on the John Deere. I am very suspicious about a stuck valve at the moment. It seems to be sucking and exhausting through the intake. I have got to figure out how to get this out of my truck and onto the ground. Such a pain climbing into the pickup bed to work on it.

If no equipment is available, do you have a garage you could back into and set up a chain fall or come-along on a beam spanning a few roof trusses / rafters, or a decent tree branch outside you could back that Ram Dually ( I can tell ) under??
Pick it up and drive out from under it.

Ray70 said:

If no equipment is available, do you have a garage you could back into and set up a chain fall or come-along on a beam spanning a few roof trusses / rafters, or a decent tree branch outside you could back that Ram Dually ( I can tell ) under??
Pick it up and drive out from under it.

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I wish. I don't have any trees I can trust either. I'll probably end up yanking it on to my gooseneck trailer till I can acquire a different trailer to dedicate to it. Sure would be nice to find an affordable trailer that was made for these. My wife is already getting suspicious about my great price.

Took the covers off the top last night. What a pain to unglue the sealant on the electrical bays. Just a small amount of leaf litter in the high voltage section. At first my heart sank thinking it was a mouse house, but alas zero signs of rodent mischievousness. I belive it is just fan blown litter from when a door was open.

All the connections look great too, very clean and no apparent oxidation. This also made it possible to vacuum out the radiator bay where some debris had accumulated.

No thats absolutely the start of a nest. You are lucky thats where it ended. Not all machines have the RTV sealant at the top. You will want to properly rodent proof the set once its out of your bed and into its final resting place. Its been covered in the forums, a bit of searching will yield your best results.

Make sure to contact clean everything, that you can and cannot see. Especially inside the orifices of the switch bodies.

Before you replace the cover I would use Deoxit5 contact cleaner ( think you already got some ) and thoroughly clean the main AC select switch. spray it on the small openings around where the contacts come out the sides, then vigorously exercise the switch, rinse and repeat! D o the AM/VM switch on the main control panel too.

You will also want to do the S1 start switch with the same effort. Also there is a little jumper cable between 1 and 7 positions on the start switch. It appears its in place, but its got a directional component soldered into it. Wouldnt hurt to share some photos of what you have, to confirm its wired right, and in the right direction.

I most definitely have a valve issue. Got the exhaust off and the center caps over each cylinder off. From the front of the engine (fan end) the second rocker, the fourth rocker, and the sixth rocker are all loose. But the 2nd takes the cake. I can pull the push rod completely off to the side of the rocker. I bumped the starter over a little at a time and I can see all of them move the valves except the second. The push rod goes up and down, but there is so much sloppiness it doesn't try to move the valve. I am going to try and tap it with a rubber mallet and see if it bumps. I have a feeling every valve needs to be adjusted so going to be opening the book and reading up.

Okay. I may be in over my head. I can not find a way to adjust the valves in the manual. In TM 9-2815-253-23 in Section X 3-26 it begins talking about the Rocker Lever how to remove and how to inspect the push rods. It does say to tighten the nut to 25 ft-lbs. But, there is no instruction on how to actually adjust clearance from the rocker to the valve. I downloaded an actual Lister Peter LPW4 manual and it has a little more information, but still does not tell me how to actually adjust it. One YouTube video I found that looks like it was made with a 1999 flip phone says that you file down ears to adjust. However that is not written anywhere that I can find. I am searching the forum, but what I seek does not seem to be jumping out at me. Any recommendations?

Well this is not a good sign.

KD7CAO said:

I most definitely have a valve issue. Got the exhaust off and the center caps over each cylinder off. From the front of the engine (fan end) the second rocker, the fourth rocker, and the sixth rocker are all loose. But the 2nd takes the cake. I can pull the push rod completely off to the side of the rocker. I bumped the starter over a little at a time and I can see all of them move the valves except the second. The push rod goes up and down, but there is so much sloppiness it doesn't try to move the valve. I am going to try and tap it with a rubber mallet and see if it bumps. I have a feeling every valve needs to be adjusted so going to be opening the book and reading up.

Okay. I may be in over my head. I can not find a way to adjust the valves in the manual. In TM 9-2815-253-23 in Section X 3-26 it begins talking about the Rocker Lever how to remove and how to inspect the push rods. It does say to tighten the nut to 25 ft-lbs. But, there is no instruction on how to actually adjust clearance from the rocker to the valve. I downloaded an actual Lister Peter LPW4 manual and it has a little more information, but still does not tell me how to actually adjust it. One YouTube video I found that looks like it was made with a 1999 flip phone says that you file down ears to adjust. However that is not written anywhere that I can find. I am searching the forum, but what I seek does not seem to be jumping out at me. Any recommendations?

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If I understand this correctly, then there is no clearance to be checked

KD7CAO said:

Well this is not a good sign. View attachment 948094

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This rod has seen better days

peapvp said:

If I understand this correctly, then there is no clearance to be checked


This rod has seen better days

View attachment 948095

View attachment 948096

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Yup that is what I saw. I pulled the offending rod and my heart sunk. I guess I have no choice now but to tear all the way into this engine. Now I definitely want it out of the bed of my truck.

Serious question though. I have never done more than replace a water pump or alternator and change fluids on diesels. Is this too steep of a learning curve? I have a large Craftsman mechanics tool set. I know I will need some more tools like torque wrenches.

Thoughts? Anyone in the DFW area that could help me if I get really stuck?

Ok, so here's the thing.... on that motor, after touching the rocker arm nuts you're supposed to tighten them and wait like 1/2 hour for the lifters to bleed down, otherwise they will hang open and hit the pistons slightly when you crank it AND bend the pushrods.
Good news is this motor has the valves 90* to the flat top of the piston, so quite often you can bend a pushrod and not damage the valves.
BUT I really think the root of your problem was carbon buildup in the exhaust ports holding the valves open and causing the pushrods to appear loose.
You now have 2 choices, pull the head and inspect the valves and clean the carbon or you can 1 by 1 put each piston at TDC, remove the valve keepers and spring, then attach a drill to each valve stem, spin the valve while pulling it up against the head. Do all 4 exhaust valves, reassemble and start it. if you have compression and it starts. run it really hard and try to burn all that carbon out.
Personally I would suggest pulling the head off to inspect the valves and clean everything manually.
R&R on the head is really only a 1 hour job and the head gaskets are available for $30
This was such a problem back in the day that Onan actually sells a "Decarboning" gasket kit, which contains everything needed to disassemble the top end to clean out the carbon. You don't really need everything in this kit, but it should still be available. You can also find a complete gasket kit for under $100 if I recall.
I say dig into the ENGINE TM, read up, ask us questions then DIG IN! It's not that bad.