Curlybandit

Hey everyone.

I went to the track today to take my '93 del Sol Si for a spin. It has (or had...) a built NA d16z6. During the last Dyno tuning I made 158whp. I love this little SOHC but today something happened....

I came around a corner at the track, tried to downshift and it felt like I missed the gate. I can't recall if I over-revved the engine (I'll have to watch the video) but I heard a noise. I pulled off the track and tried to start but all I got was a CLUNK.

I had it towed home. I pulled the plugs to try to move the engine at the crank. I noticed plug #1 had what looked like some markings on the base of the plug around the electrode. Then plug #2...

Trying to take #2 was much harder than it should have been. When I finally got it out I could see that the electrode end looked entirely smashed in. I pulled the valve cover off and everything there seems ok. Doesn't look like a valve dropped (I can see all 16 shafts and the connections to the springs).

What could it have been!? Did I actually drop a valve? Valve float (I'm using the Rocket Motorsports valve springs and Ti retainers with the stage 4 re-grind camshaft)? Detonation?

The timing belt still looks good (I have the cover off to access the adjustable camshaft gear) and the camshaft gear is still sitting at 1* advanced.

I've attached pics.

Plug from cylinder 2:


Plug from cylinder 1 (much less damage but still evidence of something contacting the plug):

JRCivic1

You have eaten a valve... or obliterated a piston. Either way, time to tear down. The plug pics you have posted indicate flying metal striking the spark plugs... the question is where did the metal come from ???

Curlybandit

i definitely looks like metal has been impacted onto the plug. I would be surprised if it were a valve since I'm using aftermarket springs and retainers, but I suppose anything is possible. I won't know for certain until I tear it down.

it's a high compression build using P29's and an aggressive camshaft. The block was decked and the head resurfaced during the build. The compression calculator suggested near 13:1. It was advanced only 1* but there would have been very narrow tolerances. I wonder if even the slightest amount of valve float, in spite of the springs, could have resulted in this...