Way to go. Rooting for you. Keep the updates coming.

 

Where are you guys getting your engine parts from? Ebay rebuild kits? Rock Auto? OEM parts from mitsuibishi dealers on line? Any brand to stay away from? I see vendors such as DNJ, ITM, King, etc

 

Continued with the tear down..

Upper main bearings found to be good with no distortion in the shells and were still held tight to the block. Lower front and rear main bearings were also found to be good with no distortion in the shells and were still held tight to the girdle. However, the middle lower two main bearings showed extreme damage and were distorted; note copper layer is fully exposed and the backing is starting to break.

The crank main journals show markings which cannot be felt with a finger nail, so I am optimistic about regrinding.

I hope to take the block, crank, rods & pistons to machine shop this week.

 

The engine block rail has these stampings on it. I assume this means something regarding the bearing and/or piston sizes that were used during original assembly.

Anyone know what these marks mean and how to decode?

Edit - found this detail in the manual. If shows the piston sizes used in each bore during original manufacture. Piston sizes are labeled by Class A, B or C.

Anyone know what these Classifications stand for relative to aftermarket pistons?

 

Went to the machine shop last night.

Rod journal for the 1/2 throw is worn excessively and cannot be reground to a factory undersize. So I need to find a remanufactured crank.

Anyone had any experience using the cranks from Rock Auto? Rock Auto lists a reman crank for $345 (after core) with rod and crank bearings. Looks like Rock Auto Gets the cranks from these folks:
Crankshaft Supply, Inc. -- Crankshaft Kits

These folks list a crank for $225 after core (not sure if they have inventory):
Crankshaft Kit 94-02 MITSUBISHI 3496/3.5L V6 ENGINE #6G74; MONTERO

Machine shop also recommended that I replace the #1 and #2 rods due to heat distortion concerns of the big end. He said that I should be able to buy two OEM rods and that the gram weight will be dead on due factory tolerances and would not need to rebalance. Likewise, the #1 and #2 pistons need to be replaced due to the scoring and they said that I can swap out the pistons with OEM ones without creating an imbalance.

Cylinder walls of the block all look good and the machine shop said to use a dingle berry type hone to remove the glaze and stick with the factory bore.

Am open to suggestions regarding parts suppliers.

 

Using the engine block decoding in Post 14, my scored pistons from cylinders 1&2 are Class B.

What does this Classification mean?

I can order OEM pistons that are Class B, but they do not come with piston rings. So when I order rings, do I order standard or some oversize?

The block stampings indicate that all of my pistons are Class B with the exception of cylinder 6 which is Class A. What does this mean regarding rings?

Piston rings come in a set for 6 pistons. How do I address that 5 are Class B while one is Class A?

Lastly, fyi Mitsubishi uses unusual "Left/Right" nomenclature. The "Left" bank is the passenger side and the "Right" bank is the driver side. Mitsubishi defines left/right from the front looking at the engine. Note the factory labeling on the camshaft timing gears.

Edit 5/12/16

The above information regarding left/right is not correct. Left/right is defined by looking forward from the passenger compartment, not from looking at the front of the engine. The left/right labeling on my cam gears I'm assuming is from the grease monkey at the hack garage that did the prior head gasket replacement (I now think the head gasket had failed again letting coolant into the oil, thinning the oil, and roaching the two con rod bearings).

Also, I have since found a good diagram for labeling of the cylinders, firing order, and the plug wire order on the coil packs.

 

I called Crankshaft Supply Inc. and they confirmed they supply to Rock Auto. Their price direct ($357) was $12 more than Rock Auto which is odd. Rock Auto discount codes of 5% can be found so looks like I will go thru Rock Auto for the reman crank. With the discount code, the savings is $29.25.

Will also bundle the order with Rock Auto for the various gaskets, timing belt, oil and water pumps, head bolts, etc.

Need to figure out the piston and ring issue first before I order any parts.

 

I believe the class A and class B pistons refers to the size difference (piston diameter). B class is slightly smaller (normal size) and A is larger one. The sizes are determined by the size of the bore into which they will be fitted to. When the engine was manufactured, they determined that one bore was larger than the others and it should take the A size piston. Look into information regarding specifications for the engine. There should be tolerance numbers for bore size and piston sizes. You calculate the differences between specific pair of bore and piston and based on that determine if you need a replacement piston of size B or size A . Not sure about the piston rings. I'd guess that unless the bore is very much out of spec you will need a standard set of rings. If the the engine had all bores re-ground, you will then need oversized rings. I do not know if you can put an oversized rings on a single cylinder. I'd think this is not recommended. My guess would be that this will create and imbalance in power production (one piston being larger and thus produce more power).

 

Thank you hunter. I get the concept of "select fit" at assembly due production tolerances. I need to translate this into useful information for parts ordering.

 

I will try to stop by a Mitsubishi dealer this week and talk to a parts guy and maybe a service tech to see if they can shed some light on this Class A/B crap. I'm not real optimistic. Hard to believe this information is not out there.

The OEM manual has a section for the engine block about honing and reboring. It says that the final piston to bore clearance after honing should be 0.0008 - 0.0015 inch (0.02 - 0.04 mm) and that all cylinders should be the same size.

Found the attached info for a Mitsubishi F8QT Diesel Engine regarding Class A and Class B cylinder/bore combinations. Doing the math shows that for that engine, the classes differ by 0.25 mm (0.0098"). Also the Class A is the smaller of the two. So it appears that at time of manufacture, they built that engine with differing bore sizes in spite of the manual telling us not to do so. I assume this is similar practice to the gasoline 3.5L 6G74 engine?