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Thread: MEP 831 FAQ for owners or potential buyers

  1. #11
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    Here is the Yanmar parts manual. This manual is specific to this exact engine model. It even includes the the correct grid heaters and the oil assist plug.
    Attached Files Attached Files

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  3. #12
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    Early production Mep831's had a Yanmar made in Japan later they went to Italy for production.
    The earlier ones had black plugs in the valve cover that were cut off and the plug was glued into the cover.
    Yes the sets will run without the battery it should run off the battery charger.
    No need to read the dip stick, look into the hole and the oil should be up to the bottom of the threads where the dip stick threads in.
    The engine doesn't hold a little over a gallon of oil it holds a little under a quart.

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  5. #13
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    Yea, I figured out about the oil today when I was filling it up. I had bought a gallon jug of only put in a quart.
    Chris Medico
    MEP-003a (sold), MEP-803a, MEP-802a, & MEP-831a

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    All of the 831a's I bought came with a piece of what looks like radiator hose in there - about 3 or 4 inches long. Loose and usually on the right side inside of the case. Anyone know what that is for? Also, what's the little shelf on the right side with the tie down strap for?

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    The little radiator hose looking thing goes on the intake of the engine. You can see if it looks like this one in the photo behind the fuel filter.

    20150130_171542a.jpg

    Can you take a photo of the shelf on the right? I don't seem to have that on mine.
    Last edited by DieselAddict; 01-30-2015 at 18:54.
    Chris Medico
    MEP-003a (sold), MEP-803a, MEP-802a, & MEP-831a

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    Got it. All of mine were sealed up with aluminum tape, so the hoses were removed. I'll snap a pic today.

  9. #17
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    The shelf on the right is for aux fuel hose storage, there should also be a black strap there.

  10. #18
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    So, whomever tried to work on my engine attempted to remove the oil filter without removing the retaining bolt. Doesn't surprise me because they made a mess of everything else they touched. When they did this they jacked up the oil filter so I decided to replace it. I didn't realize the replacement filter did not include the o-ring so I reused the old one until I could get a replacement. When I tried to start the engine it had no oil pressure. I confirmed this by removing the oil pressure sending unit and confirmed there was no oil flow. I called up Yanmar and they had no ideas why I wouldn't have pressure because the pump is driven right off the govenor. To access the oil pump I had to pull the enitire generator head apart. I'm happy to report that this isn't terribly difficult.

    The trick is that you CAN NOT remove the stator (the outer part) first. You must pull the armature first and then remove the stator. The armature magnets are so strong that it's litterally impossible to remove the stator. The moment you get it close to coming off a prybar will slip and the stator will magically reinstall it's self. The better way is to use a two jaw steering wheel puller and two 1/4"x2" grade 8 bolts. Thread the bolts in until they bottom out. I then used a 1/4" socket as a spacer to protect the bolt hole threads. It takes a fair amount of force to get the armature to break free, hence the grade 8 bolts. Even after the stator breaks free, you still have to keep turning the puller to extract the armature. Yes, the magnets are so strong you need to use the puller to remove the armature. Once the armature is out you can remove the stator retaining ring and the stator comes right off. Super easy. There is just enough wire length to lay the stator on top of the batteries. Just put something over the batteries so you don't short them out. I used a piece of packing foam for this.

    Now I had access to the oil pump. I tore the pump apart and couldn't find anything wrong with it. Totally stumped I decided to pull the oil filter and replace the o-ring before I turned in for the night. I noticed the original ring was very loose on the filter and had gotten pinched. I put the new ring on and had to tap on the filter to get it to fully seat. You really have to remove the electronic throttle control to see this. The throttle is only held on by two bolts and has a disconnect for the wiring so there is no reason to not remove it. By now I was totally stumped as to why the engine didn't have oil pressure. Desperate, I tried to start the engine again and got pressure! The problem must have been the pinched o-ring. I'm posting this as a warning for anybody who may be tempted to replace the oil filter. Plan on replacing the o-ring and make sure the filter is fully seated without pinching the o-ring.
    Last edited by Cord; 02-18-2015 at 00:11.

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  12. #19
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    Very strong magnets, Samarium cobalt, rare earth magnets.
    Have you attempted to re-assemble the PMA?
    When you go to put the rotor back inside the stator the magnets will pull it in and it will hit on one side.
    What you need to do is put a thin piece of plastic (mylar) inside the stator before you re-install the rotor. (Mylar like a drum head)
    Using the wheel puller to hold the rotor as you insert it into the stator
    Bolt the rotor back on to the engine shaft then pull out the plastic.
    If you don't do this the rotor will rub.
    When you finish bolting the stator and rotor you can push down and hold the decompression lever and rotate the engine by hand by pulling the rope start, the engine should turn over nice and easy.
    As far as the oil filter goes: there is suction at the filter and with a pinched o ring you cavitate the pump.
    When you re-install the filter line the holes up in the engine and filter, wiggle the filter back and forth while pushing the filter in, do not rotate the filter fully just back and forth, it should go in nice and easy.
    Those are washable filters they do not need to be replaced

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  14. #20
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    I have some thin plastic cutting boards I was thinking about using. They may be a little thicker than a drum head. How much gap do you think there is between the stator and rotor?
    Chris Medico
    MEP-003a (sold), MEP-803a, MEP-802a, & MEP-831a

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