Identifying cavitation with heads off? Now with PICS!

[volvo 4 life]

Hello! I'm new to the forum and recently picked up a 94 7.3 idi that was listed as a factory turbo engine. Turns out that based on the harmonic balancer and exhaust valves, it actually appears to be a naturally aspirated motor and one that was beaten pretty hard. All 8 pistons are cracked and all 8 prechambers are cracked beyond the fire ring. The heads believe it or not do not seem to have any visible cracks. My plan was to buy new pre chambers and a set of pistons and run it but the very first cylinder on the driver's side has pitting in it and it concerns me. I was wondering if there's a way to determine whether or not the pitting occurred from water in the cylinder at some point or if it's cavitation. I filled the water jacket with water and let it sit over night and there was no water in the cylinder the next day. Also I took a sharp pick to the pitting and could not push it through no matter how hard I tried. Any thoughts? Thanks for any advice and sorry for the long first post!!

 

[Thewespaul]

Welcome to the forum, when I build these engines I pressurize the cooling system to check for cavitation while the pistons are out, generally though it will show as soon as you fill the cooling system up. The pitting is probably from the engine sitting with water in it and the cylinder walls rusting. You will need to bore the cylinders out to get rid of the putting and have a good piston ring seal, but if pitting is more than 20 thou I would either get a different block or sleeve all eight holes. Can you post pictures of the cracked pistons? It is extremely rare to see the pistons cracking in these engines, and it’s possible the engine may have been rebuilt already with oversized pistons. Make sure to magnaflux the heads and check for cracks, even if it’s not visible it’s likely those heads are cracked if the prechambers are all toast.

 

[volvo 4 life]

I'm trying to get my photobucket account email figured out, I haven't used it in years so until then I guess I can't post pictures but they are cracked in multiple spots. I don't know what this engine went through but it definitely got hot. If the block is deemed to be useable by the fact that the pits in the cylinder don't leak water then I was halfway considering just putting some pre chambers in and running it even with the cracked pistons. I don't think this engine is worth putting a bunch of money into and if I can get a little time out of it while I search for a better core at least I'll be able to use the truck.

 

[nostrokes]

Welcome to the forum.

Sounds like it had a bad head gasket and the PO parked it.

IMHO.. I'd boat anchor that engine and find a good running one or a builder core instead of sinking a ton of money into it. Like Wes said if the prechambers are cracked it's likely the heads are too. If the Pistons are cracked there was some serious issues somewhere, over fueling extreme heat....

 

[volvo 4 life]

Yeah I agree, it had to be abused pretty badly. It supposedly had an 093 turbo on it that the kid removed and used on his own truck so it was probably turned up without an egt gauge and ran hard. Sucks to spend money and end up with a piece of junk

 

[icanfixall]

As already posted. Welcome to the forum. Now please clean off any piston top and see if it tells you20 or 30 or 40 on the top. Then look at the block serial number located to the drivers side of the injection pump gear housing. Its right by the corner of the aluminum bracket.If it has the letter K then this is the turbo block.Also in the numbers will be either 6.9 or 7.3. Basically all idi block appear to be the same externally.
Now for the cavitation issues.Pressure testing the block is the only way to know if this is a problem. If the head gaskets are not too damaged just install the heads and plug up any other coolant flow paths. Do not use more than 25 to 30 lbs of water air pressure. That can blow out any freeze plug. With the heads in place any coolant or water flows out the bare block. Hopefully this engine is out and on a quality engine stand.Its so much easier to work on them that way.

 

[IDIBRONCO]

If it has the letter K then this is the turbo block.

You mean the letter "T". The number will start "7.3TU2U" while the N/A blocks start as "7.3DU2U".

 

[Thewespaul]

That’s right, K is referring to the vin code for the turbo models, the engine serial won’t have a K in it

 

[volvo 4 life]

I looked at the pictures I have of the pistons and the number stamped in the top is 1816562c1 and there is an uppercase A stamped just outside of the bowl cutout. It is a serpentine belt engine so it's at least a 1992 and from what I can tell it is definitely an NA engine. There are no dimples in the valves as there would be if they were sodium filled and the harmonic balancer weight is offset like the NA engines. Also there is no sign of anodizing on the pistons either so everything visually points to it being naturally aspirated. I don't have any of the lower end taken apart and honestly at this point I probably won't bother. I think I'm going to put some prechambers in the heads and try running it. If it runs and doesn't use coolant then eventually I'll rebuild it but for now I need to put something together and the budget is tight. I have a 95' F350 dump truck with a 460 and an auto and the engine needs to come out before spring as the oil pan is leaking and the freeze plugs are starting to weep so I'd rather take the gas engine out and put the diesel and my rebuilt ZF5 in there and get 15 mpg instead of 6.5 mpg. That's the plan at least!

 

[volvo 4 life]

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Here's the pictures! And those are the worst of the 8 pistons, the other 5 are cracked but not as noticeably.

 

[IDIBRONCO]

Those are definitely N/A pistons. I'm also fairly sure that they are the factory pistons and are standard sized.

 

[Thewespaul]

Those are ****** bore na pistons, looks like some glow plugs have gone through that engine too. Check the valve guides and make sure they aren’t shot. A lot of run hard 7.3s I see worn valve guides that end up getting the engine pulled. Engine runs fine but eats as much oil as it does diesel

 

[IDIBRONCO]

Between the precups and the cracked pistons, I wonder if somebody got a little bit too anxious with the Bill Cosby in a can?

 

[Oledirtypearl86]

It's not as bad as I imagined I'd magnaflux the block and heads and rebuild it with new pistions I bet those pits would hone out and it looks like they are from water sitting in the chamber also I wonder if it came from a bad cowl gasket leaking water in the air cleaner

 

[volvo 4 life]

So with cracks like those, how nervous should i be if I run it NA? It seems that these pistons can take a serious amount of abuse and rarely if ever, suffer catastrophic failure. A friend of mine just did head gaskets on his 6.9 and the tops of a couple pistons looked like they got shot with bird shot from glow plugs being ingested and it still runs great. They definitely seem robust.