Ok here is the deal.A few weeks ago my car developed a miss which was bad enough for me to think it could be driveline related.Never any noise from motor,oil pressure was good,no coolant usage, and car did not overheat.Did notice oil leaking from the header from cylinder 7.Also the car has been using more oil than normal.A friend was a big help and rode with me to determine it was definally a miss and not driveline related,which between my flexplate issues with this car and having driveshaft issues before i wasnt sure. came home and pulled the plugs to find the plug to cylinder 7 black and crusty,all others were fine.At this point we did a compression test which showed only 70 psi to cylinder 7 while being in the 190 range for the others. I added oil into the spark plug hole to cylinder 7 to see if pressure would increase which it did not, stayed at 70psi.Yesterday we pulled to head to look for answers which are unclear to me and the friend i had helping out. I am posting pics to see if anyone can help figure out what went wrong.?Things that we noticed is pison has no eyelash or obvious contact with valves but if you can see in the pics the bottom of the piston is smooth with no carbon as is the bottom of the head in the same spot. Again there was no drivetrain noise noticed and we manually turned the motor over and the piston does not appear to be coming up higher than the block to contact the head so we dont know if this a contact point or what would cause this lack of carbon buildup.The piston and valves have extreme buildup of a black crusty material much more so than other valves and pistons.No obvious signs of a head gasket leak but these were mls gm gaskets and messy when the head was removed.The header from the exhaust of cylinder 7 is nasty, a heavy black crusty buildup. We sprayed brake parts cleaner on both the exhaust and intake ports of the valves and did not notice any coming through to combustion side, i am not sure if this is the proper way to check for a bad valve, would putting the solvent on the combustion side and pressurizing the intake and exhaust ports be better?Also there is a pic of the spark plug to this cylinder.I have no experience diagnosing internal engine problems and would be really appreciative if someone can give me their opinion on what the fix will be for this. Spun bearing may be what happened but it is my understanding that this causes engine knock which i had none and the car actually idled pretty good to have been obviously been running on 7 cylinders for awhile.Also, why would the wear only be at the bottom of the cylinder and head. If you look closely at the shiny spots it doesnt actually look like a point of contact, no scarring or anything.I dont have a clue here,hoping for the best though.I was layed off this week and a new motor is not in the budget...Forgot to add these are patriot heads milled to 59CC.

 

How is the cylinder wall in that hole? Have you noticed any oil consumption leading up to this?

 

Looks like oil blow-by cause by a bad ring land on the piston. The ring land is likely either broken or damaged in some way. You can replace the rings by pulling the oil pan off & then removing the rod from the bottom & then the piston the from the top. You can buy a ring kit & them do them all while you're in there. Don't know if you can buy rings for just one piston, but it's a big job, so why not do them all while you're in there?

Sorry, to hear about the job. Best wishes on finding a new one.

 

How many miles have you put on it since the miss fire started? Im curious to know if you changed the spark plug in that cylinder before ripping your heads off? It honestly looks like you have been driving around with just no spark in that cylinder, it would explain the mass amounts of carbon build it.

 

The cylinder wall is smooth with no scratches or gouges.I have noticed more oil consumpion but i also went to 0w30 mobil one due to getting a coulpe free cases from a friend.

 

could a ringland be damaged and the cylinder wall be smooth with no gouging or scoring?Thanks for the opinion.

 

The reason i pulled the head was the loss of compression for that cylinder. I was hoping to find a slightly bent valve or something to that nature.

 

Yes, i had extreme detonation on my stock pistons and completely took part of my pistons clean off..... it still have full compression and the sleeve didnt have a mark on it. But i did have a a bad ticking sound. Did you notice that cylinder making any noises? Typically if you do break a ring landing or ring, you will hear it. It will be loud and obvious something isnt right. Did you ever try just switching a spark plug?

 

Thats indeed oil deposits.Not too quick to jump the gun but id say rings.Also what does the intake and exhaust runner look like on that cyl?

 

It could also be PCV or valve guides. What does the back of the exhaust valve look like?

Shane

 

The intake runner is actually cleaner than the ones for the other cylinders.That was one thing odd that i noticed,not as much oil buildup.

 

the rings are a possibility, but you sould have done a leak down test before you pulled the head off.

 

The intake runner is cleaner than the others while the exhaust runner looks about the same maybe a little more buildup but there is a nasty oil like buildup in the header for that cylinder compared to the others.

 

No ticking or anything just down on power with vibration felt in the car due to the dead cylinder.I didnt try changing spark plugs ,due to the loss of compression we decided to pull the head

 

He did.......


jhall,

Did you happen to notice if there was oil air coming out of the oil filler cap, with the car running & cap open? It still looks like a ringland to me.

 

I am going to pull the valves in the next few days but what i can see is a black carbon buildup like the other valves, definally a little more buildup in this port than the others.

 

Givin your info id have to agree with Ls1-450 on this one b/c,of the compression issue along with the oil deposits.

 

Did not check this.We did pressureize the cylinder with the rockers off and noticed that there was air coming from the oil tube but also checked other cylinders with good compression and they did the same thing so did not take this as meaning anything.I should of bought a leakdown tester but was hoping to see evidence with the head removed.It appears that i made a mistake here.

 

I would pull the valves out of the head and check the seals, I would also want to pull the moter and get the pistons out of the holes. I'm guessing rings or ring lands as well.

 

Is it just me or the exhaust valve looks burnt?

It seem like a piston ring/landing problem. It's acting and looks just like mine did when I blew off my top piston landing. Yet it still looked perfect from the top. The piston ring was holding the piston together.

Any metal in the oil?

Here is mine.