Scored Cylinder Wall

[Gonekuku]

99 Deville, 108K miles, drove it into the garage with a suspected blown head gasket. It sure was. Cylinders 1 and 3 had obvious signs of water in the cylinder etc. The piston in cylinder 1 has little dings as if something small and sharp tumbled inside for a second. Head has a few similar dings. Valves are fine. The cylinder wall has several scores / gouges that are easy to detect with the fingernail (see attached image). With a feeler gauge, it appears that the top piston ring is fully intact. Is this block trash? If I hone this out and still feel the grooves, would it be foolish to re-assemble this? Should I pull this piston and see if the ring lands are in tact? Get another block?

[hjb981]

Welcome to the forum! I do not know enough to answer your question (surely some others will chime in with some opinions on your picture), but I have one thought: could such scores and pits have been caused by a platinum electrode that came loose (from the spark plug)? Or are they to small to cause that? Have you checked the spark plug to see if both platinum electrodes are there? They are the very tiny little pellets at the ends of the electrodes. Of course that does not change the way the cylinder looks, I was just wondering if a detached platinum electrode could cause something like that, since I have heard that they sometimes do detach (it was also the cause some years ago when I had a miss-fire situation; one platinum piece was missing, and changing to new plugs cured the miss-fire).

[BodybyFisher]

I once asked the guru that very question and after he stopped laughing he said that its so tiny that it would be blown out of the cylinder. It is not likely that it could cause ANY marks on the top of the cylinder and dome as was described above.

Something must have gotten into the cylinder to cause this a nut or small bolt, grit, rocks

I did a search and many have said if you can feel it with your fingernail you should hone it out. its a shame you didnt check the compression before removing the head but that probably would have been useless due to the blown head gasket anyway, see this for additional thought

http://forums.rennlist.com/rennforums/944-turbo-and-turbo-s-forum/266916-what-do-you-think-cylinder-scoring.html

[Cadillac Jim]

I suggest that you look at the head for combustion chamber damage too. I once saw damage like that on a 3.5 liter BOP aluminum V8 that had been sleeved down to 3.0 liters for racing in the SCCA in a 3 liter class. It had not been sleeved properly and after one lap, just a minute or two of running full tilt, one sleeve moved down and caught a ring and shattered it. The piston and head had damage similar to what you show on the piston crown.

It's quite clear that some significantly large metal part came in the intake, was hammered for several seconds, then washed out the exhaust, where it probably still lies in the cat. The engine would have made a noise and behaved like it was clearing its throat, then been OK. Old MG TC/TD/A four-cylinders sometimes ate a ring and did that. It could have been some time ago, but the damage does look fresh, so it could have been part of the event that resulted in head gasket damage, although I don't know how no 3 could have been affected unless it pulled a head bolt.

I know someone who hydrolocked his LS-1 in a Chevrolet truck driving through deep water. He insists that he was running with an air cleaner element, but it's plain to me that if splashed water hydrolocked his V8 he was running with an unrestricted intake that caught a wave. Once my wife's maintenance mechanic removed her air cleaner as part of a check-up. Check and see if someone removed your air cleaner element. If so, check your MAF for damaged wires.

[JohnnyG]

You really need to know how deep the scores are before you can decide on honing the cylinder. One unavoidable side effect of honing is that material is removed from the entire circumference of the cylinder, so take the depth of the scratch and multiply it by two. That's how much larger the cylinder will be after honing.....once that number exceeds maximum tolerances, the block is trash. Going beyond tolerance will cause piston slap and premature wear. Given how common these engines are, and the number of man hours to rebuild, plus parts....all to end up with a stock block, I'd replace the engine now before you dump any more cash into it.

[JohnnyG]

If you don't want to replace the block, I'd replace the head gaskets and button it up. Those scored marks don't look too deep and would likely not result in any loss of performance. To put a bunch of money into a 13 year old car isn't realistic. This opinion ignores any other problems that the engine might have, such as burning large amounts of oil.

[airmike]

I would not reuse that block with standard bore. It looks like the piston was trying to seize to me. I would suspect piston and ring damage, and would definitely take it apart to check before putting it back together. As JohnnyG said about them being plentiful.

[Gonekuku]

Thanks everybody for the feedback. Great forum by the way!

With the combination of replies, I am paranoid about piston and/or ring damage. I'm not in a big hurry to bolt the motor together and end up pulling it out again in 0-10,000 miles. I'll pull the piston. Let's see what we have.

The rest of this Deville is almost flawless. Black on black. Maybe two wrinkles in the driver's seat. I plan to keep it for several years (I say it now). Starting fresh knowing the bottom end is solid and zero oil leaks will yield a nice new old car.

[BodybyFisher]

Let us know how we can help and welcome aboard. Keep us up to date if you tear the engine apart, this will be very interesting

[rockfangd]

Thanks everybody for the feedback. Great forum by the way!

With the combination of replies, I am paranoid about piston and/or ring damage. I'm not in a big hurry to bolt the motor together and end up pulling it out again in 0-10,000 miles. I'll pull the piston. Let's see what we have.

The rest of this Deville is almost flawless. Black on black. Maybe two wrinkles in the driver's seat. I plan to keep it for several years (I say it now). Starting fresh knowing the bottom end is solid and zero oil leaks will yield a nice new old car.

now thats what I love to hear from a caddy owner. I love the triple black Cadillacs. does it have a landau also? If it were mine I would get a donor engine, pull the heads and timesert it. then reseal the crankcase. install it and enjoy another 300000 miles. Welcome to caddyinfo. Definately curious what caused that scoring. Very rarely do I ever see anything like that even under the worst conditions

[KHE]

It is important that the rod bearings and the rod cap bolts be replaced when they are taken apart. There is a high degree of crush during assembly. If you do not replace the bearings, they will spin causing damage to the crankshaft.

I would think a CNC hone would clean up the bores in the block and restore the crosshatch pattern in the block without removing too much material from the bore. There is a specific Ra (roughness average) specification fot the Northstar engine that must be followed. Do not let some moron use a "dingleberry" hone and a drill to hone it. It must be done on a machine where the rate of feed can be controlled to get the proper crosshatch angle.

If you're going to use a junkyard engine, I would replace the piston rings since they may be stuck and cause oil burning. Also, be sure to use your existing intake manifold and fuel rail. Many times, junkyards pull engines and cut the fuel lines and leave the fuel system exposed while the engine is on a rack. The moisture will eventually damage the fuel injectors.

I would also replace the rod bearings and main bearings as long as the engine is apart. Replacing the main bearings probably wouldn't be necessary but since you'll have the case separated to re-seal it anyway, an extra $40 to replace the bearings is not a big deal in my opinion.

Use the GM engine sealant (there is NO aftermarket equivalent) and follow the service bulletins when re-sealing the crankcase. Post back with any questions along the way.

[Gonekuku]

Nothing catastrophic, but it's not pretty. The edge of the piston is a bit rough, and almost appears as if another metal melted into it? The piston is scored on the same side only and 2/3 of the lower portion. I'm still thinking something took a tumble inside, and as another event maybe the engine overheated real well to have the piston score the walls. What do you guys think? Roll the dice and buy a another engine to tear down.

I've worked on my own cars about 20 years. Maybe rebuilt about 8 non-aluminum engines. This Northstar engine is for sure a new experience. This 99 Deville has been in my home garage for 1.5 years now (Wife's BMW already got nailed by one hailstorm in the driveway). I have the 99 shop manuals, and I'm constantly finding new info, like the GM block sealer. Initially I was thinking semi-difficult head gasket job, then noticed the half block leak, and now the rod bearing and bolt requirements. I already have the heads clean and reassembled with new valve stem seals. I admit, I didn't discover these score marks until I was doing a final clean in preparation for assembly. I hadn't rotated the crank enough. Oh and... I've already installed the Huhn thread inserts into this block with red thread lock (Torch them out for my next block?). I'm making rookie mistakes, but hey, I'm catching them all! This engine reminds me of the Tom Hank movie: Money Pit.

[Gonekuku]

Scored piston...

[Gonekuku]

The cylinder wall has the score marks / scrapes, and the top 1/4" of the cylinder wall (above piston ring contact) at the gravity side of the cylinder is a bit corroded. That about summs it up.

[rockfangd]

I still suggest same as above. use the current engine for core or parts

[KHE]

I doubt you'd be able to save the inserts byt you may be able to heat them up enough to break the loctite bond.

Replacing the valve satm seals wasn't really necessary - the originals are viton and will last virtually forever. Hopefully, the replacements you bought are Viton or you may be replacing the valve stem seals again in the near future.

Keep in mind that this engine is not a small block Chevy engine - the repair techniques are vastly differend. The service manual must be followed to the letter.