So I had a new engine put into my S2000 after oil starvation ruined the rod bearings on my previous engine, I was told a valve adjustment was done and that the engine had good compression. I put the engine in along with an aftermarket clutch (big mistake) and it ran for about 1000 miles until the clutch blew and I replaced it with an OEM clutch and a lightweight flywheel. Sort of since then the idle on the car was a bit rough, just a slight shaking to the car at the lowest idle rpm I looked it up and it could have been due to the lightened flywheel. Another 1000 miles later, I notice a tapping to the engine coming from the front of the valve cover, on the same day after driving it more, the tapping gets louder and louder and scaled with the RPM, so I try to get the car home but on the way it starts misfiring, and then finally a flashing check engine light as soon as I'm almost home (i really should have got the car towed). The car gets parked up, as I start taking the valve cover to see what happened. Cylinder 2 (the misfiring one) had a completely mangled spark plug with bits coming off it and is slightly bent, as well as the ignition coil completely burnt. I suspect cylinder 2 was overheating, but I don't know why. The spark plugs on 1 and 4 were also very tight to take off and took off some of the thread with it. To solve the issue that caused this, I thought it might be TCT related as the tapping sound was directly from the front of the valve cover where the chain is, so the TCT was replaced, and a valve adjustment was done (nothing that they were pretty out of spec). Threads were damaged on 1, 2 and 4, 1 and 4 were fine after using a thread chaser, 2 was still an issue, but eventually resorted to a solid insert that was tapped and threaded in. I put everything back together, with a new ignition coil for cylinder 2 and new spark plugs and noted this:

The engine takes a long time to crank and actually turn on
There are noises but don't sound like misfiring
After a while of high idling, it drops all rpms, raises them and then drops them.
Check engine light P0335 something about a crank sensor

I haven't turned the car on since. I suspect it's something to do with the timing as I was manually cranking the engine during the valve adjustment, and may have done it with the bolts of the TCT not in, I also recall I put in two spark plugs, tried to crank by hand (I was using a vacuum to remove all material in the cylinder) and it felt like gears slipping and it was very difficult. I have also bore-scoped each cylinder, only 2 has a slight amount of scoring and damage to the top of the piston (probably from the spark plug tip that came off), the insides have been cleaned as much as I could. A compression test showed 200 175 149 175, so as result of the overheating a valve may be burnt, the head is going to need to get rebuilt, but I just want the car running somewhat for now. And while I was happy it even turned on, the erratic idle and check engine stopped me from continuing. I intend to check the cam timing next opportunity I get, but is there anything else I need to consider? I doubt it's the crank sensor itself.

 

Also to note the compression test was done on quite a weak battery so don't fully think it's accurate

 

I’d install a new crank sensor first. If it’s bad the ecu could be flooding that one cylinder with too much fuel or too little spark and washing down the bore.

 

Are they known to just fail randomly sometimes, any way I can verify it? Not a huge amount of info online about it but looks like it would be quite difficult

 

For anybody experiencing a similar issue, it was just a missing connector (the crank sensor). S2000 is running again with no shaking at idle, but the bog on set off is still present.

 

Is there still a check engine light?

Have you checked to see if your catalyst is broken?

Why did all that crazy stuff happen with the spark plugs? Did you torque them (24LB-FT) when you installed them?

I would have a competent S2000 specialist or shop take a look at the car to see if there are any other lurking issues.

 

Check engine light hasn't come on since i plugged the crank sensor back in, the car has been running just as it did before all the crazy cylinder 2 issues, minus the idle rumble. Have been driving it around for a few months, no check engine lights, only things to note maybe a slight loss of power in VTEC but I think that's down the slightly lower compression due to a burnt valve on cylinder 2. I also think the bog on idle is probably some sort of intake leak as I ran a smoke test and it was coming from the manifold, i tightened up a few of the bolts, no smoke but still acts the same, kind of feels like heat bog but definitely isn't. I will also say the car has been fairly consistently running rich for a while, it wasn't as bad after the valve adjustment, but definitely on the rich side (again potential intake leak)

I don't know how I would check if the cat is broken (other than taking it out) there's no engine lights or sounds or unusual smoke, but given pieces of metal could have gotten ejected out of cylinder 2 it's possible. As for the plugs I don't recall which torque spec I used, but I remember reading something about AP1 engines having an under torqued factory spec for plugs or something so I took which ever higher value I could find online, and then for cylinder 2 because it had an insert, gave it an extra half turn ish

My fatal mistake (which I regret now) I never got around to fitting new plugs or coils when I put the new engine in, it was whatever the previous owner did. The issue of the spark plug threads was really my own doing, I was too patient to let them soak in oil when they were getting tight to get out and damaged the thread, I'm guessing the overheating of that cylinder made that spark plug hard to get out. So I have a few theories on why this happened in the first place. My TCT was going, evident by slapping marks at the bottom of the timing chain and the ticking. This caused issues in timing/my valves, the valves also could have already tight and required a valve adjustment (the shaking at idle), the engine running rich due to potential leaks may have contributed, potentially didn't bleed my coolant correctly. I'm not entirely sure.

The car definitely needs to be checked over by an S2000 Specialist, which is seemingly hard to come by in the UK, if anything for the ongoing bog and overly rich mixture, but also for a head rebuild at some point. But I'm just waiting on the funds really from a new job really before I start treating the car. I put this engine in on a drive while at university, so it was a huge learning curve and it could have been done a bit more thoroughly, but I'm just glad it works (for now)

(Also attached


a pic of the mangled plug)

 

The bogging may just be from the vacuum leaks which you found.

The catalyst can be checked by taking it off and looking at the core of it. If its broken, shifted, or clogged, it will cause loss of power.

 

Holy Macaroni! Are those the spark plugs from the current engine in your car? Not only stripped threads, but I don't think I've ever seen one with that kind of insulation damage!

Was the engine making any knocking or other pre-ignition death rattles?

Thanks and good luck with the fix!

 

Your underlying cause was a loose spark plug.

It is imperative that the spark plugs are tight. Loose plugs will allow un-metered air into the cylinder, leaning the cylinder, overheating it, and melting the spark plug and the coil.

If you so much as touch the crankshaft without the tct in bolted place, you are guaranteed to jump the chain and cam timing will be off.