Pitted heads and pitted cylinder

[Rob4]

I tore down a military engine that was locked up and found that antifreeze had worked its way into most of the cylinders. With a little work I was able to get the crank to move and checked out the cylinders and all looked good except one. It has a small pit about 0.030 deep on the wall. I'm not sure if the wall around the pit is still strong and can be trusted even though it looks good. Also, each head has one cylinder area that has perhaps a dozen very small pits about 0.010 deep where it was exposed to the moisture of that cylinder. The bottom of the block is sound with no cracks. My thoughts are to use this block but maybe I should go look for another one.
Should all the cylinders be bored to be on the safe side after being exposed to antifreeze or can they be trusted? Can just one cylinder be bored out for a larger piston without causing a vibration (or worse) problem? Can a 6.2 be sleeved? What problems if any will the pitting in the heads cause? Would it be wise to shave the heads? Thanks for any help.

[rustyk]

I can't speak specifically (my experience with coolant intrusion was as a Navy ship's engineer, and in labs), but this sounds like "erosion corrosion" caused by coolant droplets that were turned into superheated steam that eroded the cylinder wall.

In the cases in which I got involved, the damage was all local, meaning that there were no issues with the remaining material. Apparently in your case, the leakage was confined to the head area, because ethylene glycol in the lubricant is generally a death warrant.

I'm sure others can tell you if it can be bored out to remove the pits. At the least the heads should be checked for warpage. If it were I, I'd opt for a new/used head, as the pits could cause problems with the combustion process (probably minor, but best avoided).

[john8662]

The heads I wouldn't worry about, as long as any pits won't affect sealing rings on the head gaskets (surface).

For the bore, we'll need to see a picture. Is this pit on a location where the rings ride, or above? If above, again I wouldn't worry about it. If it's where the rings ride on the bore, then yes, it would be a problem because it would be the same as a score in the bore, a source for loss of compression.

Yes, these engine can be sleeved, with mixed results. If I had the option of boring all 8 and installing OS pistons, or just sleeving the one hole, I would opt for boring all 8. The possibility of having issues with the sleeve is high, I've seen them move in the bore, cause sealing issues with the head gasket, etc. Not to mention, that after sleeving, you have to slightly deck the block, the side that got sleeved, and the other side to match deck height.

Good to hear that there are no cracks in the bottom end. Do not discard this block due to the issues mentioned. If you're looking for an easier engine to fix to use, then yes you could do that, but keep or sell the crackless bottomed block...

J

[Rob4]

Thanks guys for the input. it sounds like going over size with all the pistons is the way to go. I'll go with the pitted cylinder first and see how much is needed to clean it up. Is there any advice on how much standard OS to go once the bore is clean? Since I am replacing the pistons should I just go with an os as needed or perhaps look at a larger bore to gain more power? I plan to add a turbo down the line. Thanks again.

[rustyk]

I would certainly encourage considering the offerings by TDP sponsors, including the possibility of ~18:1 compression ratio pistons. If it were I, I certainly would not want to depend on an auto-parts store.

[john8662]

There is NO noteable increase in power with the OS bore on these diesels. I consider it better to have a thicker cylinder wall than to have a bigger bore size.

Just bore it as large as necessary to clean things up, this will take some measuring experience by a machinist that normally runs the boring bar.

For piston brands, I suggest either Federal Mogul, or Mahle (Clevite). Never Silvolite.

J

[Rob4]

Thanks again for the input. I really appreciate it. It's my understanding that going with the 18:1 pistons may cause a slightly harder starting condition but this is far outweighed by greater engine longevity. In Oklahoma, really cold weather is usually not a problem plus I am using a manual start switch/relay with "60" glow plugs so I'm not too worried about that. I will go with a much greater Engine life (Hopefully).
I have another military engine that from the outside anyway looks to be a good engine so far. By that I mean it turns over freely and has all the openings capped off with plastic caps. I am going out in a few minutes and pull the pan and look around and see if it looks good inside (no cracks,etc.).
From previous threads it's my understanding that some military surplus Silovite pistons were available on eBay. Can anybody tell me if the Silovite pistons were used as original pistons in all 6.2 military engines when they were first built or were they put in the military engines when they were remaned? Can I tell by looking at the bottom of the piston who manufactured them? The pistons on the engine with the antifreeze problems had a number inside the piston that started with 140 followed by 777 later in the number, I think. When I pull the pan I'll look closer on this engine.

[john8662]

Stock pistons were normally Zollner, or Bohn.

If it had Silvolites in it, it's been remaned, if it's been remanned (has OS pistons in it) then there is a chance .

The 140 part number etc pretty much gives it away as a stock piston.

I would seriously think about the lower compression thing, if this isn't going to be a top notch high performance engine, then I'd stay away from it.

Stick to stock compression ratio or at the most one point lower for a non-turbo and for Banks/ATS turbo engines running stock hardware.

6.2's last a long time when rebuilt properly, they lasted a long time in civilan installations going down the highway and performing the duty of a light duty diesel engine.

Just put a stud-girdle in the bottom end to keep the block more rigid.

J