Finally bought a MEP-831a

[AfghanVeteran2010]

Is it normal for the exhaust rocker arm to move around like this(side to side)? The Intake rocker is solid as a rock(side to side movement), I have looked at engine TM and yanmar manual and could not find any remarks on this.
View attachment 689927View attachment 689928

Opps my bad the intake rocker also moves too, it was under tension. Engine was TDC. I did the leakdown test, there is a loss of pressure some where. I could not hear any air threw air intake(filter removed) or the exhaust. I can hear hissing threw top oil cap, this is also close to the air flow might be mistaking that for sign of leak. While oil fill cap was removed I placed my hand on top and observed gauge for change, there was no change. I replace cap allowed 5 mins to pass no change either. Injector area tested for leaks none observed, tested with soapy water. Back to rockers the rocker cover cap holds them in place.

 

[AfghanVeteran2010]

Just finished watching some YouTube videos about doing a leakdown test. 0%-10% is Good -- 20%+ is questionable. Its almost on 20%, looks like the rings are leaking too much. Cant hear any thing threw exhaust or intake, I can hear air in valve cover when I take oil cap off it.


Leak through gasket

1. Cylinder head improperly tightened. - Think I would noticed it leaking, than again.

2. Broken cylinder head gasket. - same as #1



Leak in crankcase - Flow chart


1. Poor quality lubricating oil - been using brand name 10W30 looking in yanmar manual I should be using 20W40 15F - 100F it gets warm where I live. 10w-30 is good for -10F-85F. Can improper oil grade cause a leak like this?

2. Piston Ring Sticking - No way of telling until it pulled that I know of.

3. Broken/worn piston ring - same as #2

4. Broken piston ring lands, Worn ring groove - same as #2


Even if proper grade of oil fixed this which at this point I think wouldn't help much, the cylinder walls are probably built up with carbon and the piston rings and maybe the piston its self bit the dust.

 

[DieselAddict]

Bad rings would explain both the smoke and the low power. I think you are at the decision point to tear it down or not.

 

[AfghanVeteran2010]

I want to get this machine working like it should, Ive been looking threw on how to replace rings. The only thing that has me wondering is what size/style puller do I need for the alternator.

Edit: found post taking about pulling alternator going to order this on amazon

 

[AfghanVeteran2010]

I pulled the head today, the rust on piston is from head stud. I removed the head gasket also. Going to pick up puller from auto store tomorrow and proceed further. Thanks

 

[rustystud]

It's hard to tell from your pictures, but it looks like you have some cylinder "glazing" going on there. It would be a good idea to remove the piston and run a good ball hone down there. Clean-up the piston and check for "glazing" on the sides of it. Then some new rings and bearings and your golden ! Also maybe a valve job since your there.

 

[AfghanVeteran2010]

What kind of cleaner degreaser should I use to clean engine parts? Probably going to soak the parts for awhile once i get it apart.

I am going to be pulling the engine completely apart, as for honing the cylinder what size hone do I need piston is 78mm.

Thanks

 

[DieselAddict]

I personally like to use a pretty strong solvent like kerosene mixed with a bit of acetone with a stiff brush. You should know the risks of this concoction - This is flammable. You'll need to do it in a well ventilated area. Its not kind to your skin. It is however very effective. You'll need to dispose of any left over chemical properly. I keep a quart of this stuff made up and in a metal pain can.

For lower volatility you can go with a water based concentrate available at auto parts stores. It will take more work but its much safer to use. I keep a jug of concentrate for rough cleaning.

If I'm doing a small job a can of carb cleaner is tough to beat. Read the label. It may be just as noxious as my custom mix.

 

[rustystud]

What kind of cleaner degreaser should I use to clean engine parts? Probably going to soak the parts for awhile once i get it apart.

I am going to be pulling the engine completely apart, as for honing the cylinder what size hone do I need piston is 78mm.

Thanks

If you have no ridge at the top of the bore then a good "ball" hone will do just fine. Just get a ball home that is larger then 78mm. Use a good honing oil and keep a steady up and down motion going. Once you see a good crosshatch pattern emerge then stop honing.

 

[AfghanVeteran2010]

I pulled PMA today, bolts that attach to stator are 1/4-20 by 2" use grade 8 it takes some serious force to initially break lose. I had to have some one put a wrench on fly wheel nut to prevent engine from turning. On the second picture it looks like the stator may have rubbed the side of rotor at one time, or it may be from previous tech installing it.

 

[AfghanVeteran2010]

Piston pulled, rings move around freely side to side. Piston took a lot of force to pull out of cylinder. Does the rings look bad?








https://youtu.be/C0d5smI8uGY

https://youtu.be/sg73m6ZFG14

 

[DieselAddict]

Its hard to tell in the photos if the rings are ok. Being loose is at least a good sign.

Can you carefully remove the top ring and push it down into the cylinder? Then measure the gap. That will let you know how much wear you have between the cylinder and ring.

 

[AfghanVeteran2010]

Ok, the gap is .025 inch or .635mm

 

[DieselAddict]

Per the manual your gap is (Edit) NOT beyond the service limit.

Do do you have a copy of the Yanmar L70 manual?

 

[AfghanVeteran2010]

I have the Service Manual


Am I looking for end gap ?

 

[DieselAddict]

Exactly. That is end gap. You'll see in the manual to check it at the top, middle, and bottom of the cylinder. That will show you how much taper it has.

 

[DieselAddict]

I looked in the wrong column. Your gap isn't outside the service limit. Just more than standard.

 

[AfghanVeteran2010]

so i should rehone, new rings and, valve job. am i missing any thing

Sent from my SM-G935P using Tapatalk

 

[rustystud]

It is hard to judge the condition of your piston rings and piston. You need to totally clean it, and then check for "scuffing" marks. The bore has signs of scuffing and needs a good honing. I'm pretty sure you don't need a rebore, just new rings and a good honing and you will be back up and producing power in no time !

 

[rustystud]

I forgot to add. Don't use "synthetic" oil until your new rings are broken in. Us a good 5-30W standard oil. Also when you first start-up, load the generator to at least 80% . Keep it at this for at least two hours. Four hours would be better if you can. Then shut-off the unit and drain the oil and replace the filter. For the next twenty hours keep the standard oil in it. Then you can drain the oil and replace the filter and install a good synthetic oil. These "Yanmar" engines are fantastic little power houses, and with just normal maintenance can last years. I really love them !