350 engine rebuild numbers

[Blind Old Coot]

Just pulled a 2007 MCI 350 that smokes a little. Want to try yo rebuild myself, first time .
The top ring has a "25" on it. Still has visible cross hatches in both cylinders.
Top ring has a .010 end gap.
Cylinder bore is 2.648
Piston skirt is 2.644

Seems the "25" translated to .25mm... that's less than .001
So the 50 oversized is about .002

Crank looks good...no aluminum traces...

Do I need the 50mm piston and rings or can I just do a quick hone and drop in the 50 oversize rings.? Or is the 50 over piston needed?

Are the pistons really bigger ?

Excited to at least try this. An excuse to buy a torque wrench and hone. Good winter project for northern Illinois.

Added sheets from manual.
Thank you

[Timberwolflt]

You still have crosshatching and I’m sure machining marks on the pistons... you’re good to go... You just need standard piston rings... no oversizing necessary. Do take the time to check the ring gaps in the cylinders that they will be installed in... make sure you push em down about an inch... you can use the piston for that...probably won’t matter which but keep them separate Because insufficient end gaps will cause nearly immediate catastrophic failure in your new motor. The rings heat up and expand sooner than the cylinder and they will bind up if the gap is too narrow. I’m plenty happy with .010 even though that’s the upper end of the specs

You were probably gettin your smoke from worn valve seals... ida done the valve job and saved the rebuild for later but since you’re in there... I’d still replace both rods if you can find oem or quality rods... they surely have some wear at the crank end and I believe metal fatigue is an issue with these aluminum rods

Definitely follow the torque specs... these aluminum blocks will strip and the torque specs on these motors seem low even for aluminum

If you haven’t already found this... it will be very helpful to you
http://products.jacobsen.com/img/manuals/27615-g01.pdf

[Blind Old Coot]

Hi Timberwolflt,
No oversize necessary...is good with me. I ordered a standard complete kit with pistons, rings,rod and gaskets. Should be here this week.
My concern was when I saw the "25" on the rings. I will measure ring end gap with the new rings and use the piston to lower them about one inch.

Finally washed all the muck off the engine.

Thank you for the manual, that's how I took it apart. Step by step, verse by verse.

Watched a couple of videos on valve lapping so I do this correctly. They all mention filling the combustion chamber with a solution and blow compressed air into intake and exhaust to check for valve seal....what kind of solution.... water.?

Torque specifications (wet). Book says 80% because they are lubricated...I did get lubes to assemble with, so stick with the 80% ?

How did you make out with the clutches on yours?

[Timberwolflt]

Not sure about filling the combustion chamber but they’re checking the seal at the valve seat. Truth is... when you lap the valves with the compound, you’ll be able to feel, see and hear the seal. But if you want to check it after you’ve installed the valve springs, the easiest way is to squirt some WD40, or diesel fuel (which is what I use for cleaning solvent), or penetrating oil into the intake and exhaust ports... let it set a couple minutes, then flip the head over and check for seepage. Make sure you’ve cleaned all the lapping compound off of everything real well first. You don’t want to leave any of the compound anywhere in the motor... not the slightest trace.

I wouldn’t spend too much time doing the guzintas on the torque specs... when you’re talkin 12, 16 or 19 ft lbs... 80% - 100% ... ain’t much difference. Mine are always ‘wet’ with diesel fuel and I usually just go 100%... it’s really just a budge further

Haven’t done anything with my clutch or belt... I’m really diggin the way it’s working right now... I’ve got 15mph and a smooth start...I don’t need a bunch more speed for bumping around my fields on these stiff springs... it foams my coffee

[Timberwolflt]

That .25 may indicate that you already have oversized pistons which means someone may have put oversized pistons in there... if that’s the case... you’ll need to go back with .25 oversized pistons/rings

[Blind Old Coot]

So I'll wait till kit shows up and see if it doesn't cost to much to return . It's just paying for a learning curve that I need to do. I expected surprises but I really want to learn this.

Plan B... if the cost is too much to return... can I order first oversize rings and use the pistons that came out of it.? They do look good to me.

Sounds like diesel is also a good assembly lube too.

In the mean time, I was able to go thru the clutches....super smooth now.
All the stray wiring has found a home and everything electrical works.
Recovered the seats....
Cleaned and put new brushes in starter/generator...
Took the big ugly ball picker frame off her face.. the ugly duckling is looking pretty good.

[Timberwolflt]

There’s no reason you can’t reuse the pistons... check the skirts for wear... the whole piston for any hairline cracks and clean em up... they’ll work just fine... the rods will be the same so do use the new ones

Where did you wind up getting the parts?

And quit being so stingy with the pictures. We like pictures

[Blind Old Coot]

I finally was able to print the manual you sent my way verses on the tablet ...that was good.

Speaking of pictures, I showed a coworker the tilt bed on your buggy ,with the radius how to do , and you got a standing applause. He is the go to person to get things welded. We talked about them for a while.

The parts... found a cart store with online store, thru Ebay...$289

The pistons still look usable.

Here's how I hinged the tilt bed on mine. Easier to get the alignment I needed.

So plan B is a go. I'll order rings for .25 over and install on original pistons. The book/manual shows a one piece bottom oil ring to replaced the original 3 piece. Have not seen any for sale. Is it worth going to EZGO for new rings.?

The manual does have a number 72544-g01 for 25 over...

[Timberwolflt]

You shouldn’t be having any trouble with that hinge... looks pretty stout

My oil rings came in three pieces... I think every one of the oil rings that I’ve ever installed have been three pieces... the corrugated center goes in first