Piston Failure
I have a la 360, bored +0.060", kb pistons, Eagle H-beam rods, stock crank, retrofit roller cam, built Magnum heads, dual plane intake w/ holley 750, Fast E6 ignition. Timing set at 32 total. I've been tuning this setup for a few weeks now and took it to the dragstrip for the first time with everything last Friday. Runs mid 13.5's pretty repeatedly, with the best of the night being a 13.45. But I haven't touched the carb much and the secondaries are super rich it seems so it still has room to get better.
It's been running good so I decided to take it to see family on the 4th of July (the Thursday after the strip night). It's about an hour and a half drive down the interstate and if anything I could use the highway miles to figure out mpg (19.9 mpg, 93 octane pump gas!). The car cruised good, 3500 rpm @ 73 mph and the temp never went over 180* even with the 93+ degree day. The car cools down for a few hours and I drive another 45 minutes to visit with my friends and show off everything I've done to my car in the past few months. The car cools for about another hour and we decide to get fireworks (about a mile away). We take my car and I get on it pretty hard pulling out of the driveway, pulling trough the gears, shifting at ~6400 rpm. Start the car after buying a few snakes and sparklers and thought it was smoking, but it was a gravel parking lot so I figured it was gravel dust. We go to get ice cream (another mile away) and leaving from there there was definitely a smoke cloud following us, my heart immediately sank. I park the car and let it cool for a few hours while we shot fireworks and grilled and everything. Pulled it into their garage and pulled the plugs (#1,3,5,7- it was smoking from the drivers side exhaust):
Pulled the valve cover, valve seal is still there. Started the engine with breather off:
It ran good still and idled fine, so I swapped #5 spark plug into #7 and trailered it the 80 miles back home.
Pulled it off the trailer and let it warm up a bit, but the smoke didn't go away. Didn't seem to misfire or be down on power. In fact, laid some nice tracks pulling it from the trailer to my driveway :)
Pulled the #7 plug again (newish from cylinder 5) and this is what it looked like with the little time idling and pulling on/off the trailer:
I did a compression test and that cylinder is down 40 psi from what I measured a few weeks ago, but it held it there for 1+ hour. I din't pull any other pugs however. I'll try to get to that tomorrow if i get the time, was just trying to see if there was a hole in the piston.
What I'm thinking is that all of the driving I did got everything hot, and running it hard like I did caused the rings to butt up and crack/break a piston ring land. I have a picture of the exact piston I have in my engine I'll attach to give an idea of ring location. What gets me is how compression dropped 40 psi but holds it at that. Could something else make more sense? Idle has no noticeable change, no noticeable/significant power loss. Lots of blow-by, smoking from drivers-side bank, #7 plug is oil-fouled. Everything started occurring suddenly after hard acceleration after a day of driving.
I have a la 360, bored +0.060", kb pistons, Eagle H-beam rods, stock crank, retrofit roller cam, built Magnum heads, dual plane intake w/ holley 750, Fast E6 ignition. Timing set at 32 total. I've been tuning this setup for a few weeks now and took it to the dragstrip for the first time with everything last Friday. Runs mid 13.5's pretty repeatedly, with the best of the night being a 13.45. But I haven't touched the carb much and the secondaries are super rich it seems so it still has room to get better.
It's been running good so I decided to take it to see family on the 4th of July (the Thursday after the strip night). It's about an hour and a half drive down the interstate and if anything I could use the highway miles to figure out mpg (19.9 mpg, 93 octane pump gas!). The car cruised good, 3500 rpm @ 73 mph and the temp never went over 180* even with the 93+ degree day. The car cools down for a few hours and I drive another 45 minutes to visit with my friends and show off everything I've done to my car in the past few months. The car cools for about another hour and we decide to get fireworks (about a mile away). We take my car and I get on it pretty hard pulling out of the driveway, pulling trough the gears, shifting at ~6400 rpm. Start the car after buying a few snakes and sparklers and thought it was smoking, but it was a gravel parking lot so I figured it was gravel dust. We go to get ice cream (another mile away) and leaving from there there was definitely a smoke cloud following us, my heart immediately sank. I park the car and let it cool for a few hours while we shot fireworks and grilled and everything. Pulled it into their garage and pulled the plugs (#1,3,5,7- it was smoking from the drivers side exhaust):
Pulled the valve cover, valve seal is still there. Started the engine with breather off:
It ran good still and idled fine, so I swapped #5 spark plug into #7 and trailered it the 80 miles back home.
Pulled it off the trailer and let it warm up a bit, but the smoke didn't go away. Didn't seem to misfire or be down on power. In fact, laid some nice tracks pulling it from the trailer to my driveway :)
Pulled the #7 plug again (newish from cylinder 5) and this is what it looked like with the little time idling and pulling on/off the trailer:
I did a compression test and that cylinder is down 40 psi from what I measured a few weeks ago, but it held it there for 1+ hour. I din't pull any other pugs however. I'll try to get to that tomorrow if i get the time, was just trying to see if there was a hole in the piston.
What I'm thinking is that all of the driving I did got everything hot, and running it hard like I did caused the rings to butt up and crack/break a piston ring land. I have a picture of the exact piston I have in my engine I'll attach to give an idea of ring location. What gets me is how compression dropped 40 psi but holds it at that. Could something else make more sense? Idle has no noticeable change, no noticeable/significant power loss. Lots of blow-by, smoking from drivers-side bank, #7 plug is oil-fouled. Everything started occurring suddenly after hard acceleration after a day of driving.
