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Discussion Starter #1
I'm in the process of cleaning up my pistons from naturally aspirated 98 block with mechanical Injection pump. Noticing what appears to be some melting on pistons 8, 6 and 5 I attached a picture of #8 because it seems to be the worst one. Any ideas about the cause of this damage? I was hoping to re use the pistons with new rings if they are in spec but I guess I will replace these three.
 

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Any other damage to the rods, skirts bores, etc?
 

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Discussion Starter #3
I used a ridge reamer to clean bore ridges but I didn't see anything out of the ordinary. The block is in the machine shop now getting magnafluxed and hot tanked. Skirts seem to be ok with light scuffing. Need to buy a bigger micrometer to measure skirt diameter to check against specification. Just waiting to hear back from shop to make sure block isn't cracked. Noticed I had a lower output stock waterpump so if all goes well I will upgrade to 130 GPM and duramax fan
 

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I used a ridge reamer to clean bore ridges but I didn't see anything out of the ordinary. The block is in the machine shop now getting magnafluxed and hot tanked. Skirts seem to be ok with light scuffing. Need to buy a bigger micrometer to measure skirt diameter to check against specification. Just waiting to hear back from shop to make sure block isn't cracked. Noticed I had a lower output stock waterpump so if all goes well I will upgrade to 130 GPM and duramax fan
The other things to look for are cracks in the mains and webs ( which you have in the shop being tested)....and the crankshaft.
Hard to say with those pics. ingestion of foreign material would have produced more dings on the pistons
 

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Double check your turbo impeller to make sure you have no missing pieces, Scoring on the housing, etc
scratch that I forgot you have a N/A motor
 

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Discussion Starter #7
The engine is out of a 1986 Chevrolet c20 I thought I was buying a 6.2 but when I tore the block down the casting said it was 98 506 block The main bearings also had 98 stamped on them So I didn't get it with a turbo, not to say it never had one at some point. It has DB2 pump This is my first rebuild so it's been a learning process
 

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The mark on the piston almost seems like someting hit it. Does the head have a mark on the same spot?
 

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Discussion Starter #11
I didn't see any indentations on the head but the precups have a lot of carbon build up below the precup port. Soaking them with some oven cleaner so I might discover something when I clean them up a bit + inspect them for cracks
 

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The #8 piston you posted looks kind of like coolant erosion from a bad head gasket. That can happen If the engine was ran a long time with the HG bad.
Maybe,a long ago someone repaired the HG and just ran it the way it was.
 
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