Hillbert

I allowed a friend of mine to drive my S2000 a few weeks back. He missed a shift and likely over-revved the engine. I'm getting a P1399 (general misfire code), and sounds like its running on 3 cylinders. I tried putting new plugs and coils in it hoping that it was just coincidental that i'm getting a misfire after an engine overspeed, but No changes to CEL's or to to how the car is running. I did a compression test using a compression tester from autozone with psi readings of 90/90/90/0 in cylinders 1 through 4 respectively. I suspected the gauge was reading incorrectly because i could see the needle on the gauge spiking up considerably higher than 90 PSI (it would read higher and lose pressure down to 90 psi), so i went and exchanged the tester for another. I got new readings in the 150's for cylinders 1-3, and still zero compression in cylinder 4. At this point I don't trust the compression values for 1 through 3, but at least they are consistent and cylinder 4 is consistently at zero. I also added oil to each cylinder to see if compression rose, but no changes in compression noted.I think this rules out piston rings too.

I used a bore-scope to look into cylinder 4, looking for impacts of the valves on the pistons, however from the video it took, I cant tell if there was an impact or not. I've linked the video here: It looks like there might be a difference in the color of the metal where the valve could have struck, however i cant tell if this is just the lighting from the bore-scope. Any suggestions here? I don't really know what a healthy piston should look like.

At this point it seems like i'm dealing with a bent valve, so i've been prepping the vehicle to pull the head (removing intake box, heat shields, valve cover-). I went to check the valve clearances this evening and noticed that all of my clearances are very tight (considerably smaller gap than what is recommended).


Could my no compression issue be that valve clearances are just too far out of whack to build compression in cylinder 4? Or should i bite the bullet and pull the head?
Or is there any other way to test whether a valve is bent without pulling the head?

The car is a stock 2001, AP1 with 110,000 miles.

bgoetz

I don't see anything on the video but from what your describing it isn't good. You likely have some major bent valves and cracked retainers, the head will need rebuilt if it isn't damaged. I would be pissed at your ham fisted buddy.

Hillbert

He's a good friend of mine and has offered to cover the costs of any repairs. No hard feelings!

Halfassjack

Bent valve would have too much lash.....not tight. Burnt valve would be more in line with too little clearnce.

Billman250

Leakdown will tell it all.

If there was valve to piston contact, it will be near impossible to see. The contact area is so flat it barely leaves any impression.

Likely just head removal and lap in some new exhaust valves.

Be sure to un-torque the head incrementally, in sequence. And whatever you do, do not mill the head. No matter what any machine shop tells you.

kevinS2OOO

I happened to misshift the car at the track last year. My mechanic (Driving Ambition) did a compression test and a leak down test, he also mentioned there are a couple other signs to look for to diagnose whether it's bent valve. It has been a while and I don't remember.

But more than likely some of your retainers are cracked. Mine were. One of the valves was also bent, he pointed out to show me. Visually it is very difficult to tell, even if you had taken the valves out to compare.

Hillbert

I guess another basic question would be, can a bent/burnt valve cause zero compression in a cylinder? I can understand reduced or very low compression, but the compression tester didn't budge when cranking.

Billman250

Bent valve can surely cause 0 compression.

As mentioned above, you likely have fractured retainers as well as bent valves.

Where are you located?

Hillbert

Dayton Ohio

rmerchant3

Definitely do a leak down. Compression readings don't even tell half the story. But from your description, I'm leaning towards a bent valve as well.