DefSport

AP1 with 147k mi, I've owned for about 3k miles. Previous owner just daily drove it, never drove it hard at all. Over the past 5-6 months, I had gotten a few instances of misfires right after cranking the car. It would always clear within a few seconds, but twice it threw a CEL. One for multiple misfires and a bunch of cylinders - I thought it was due to the connectors for the cam sensors and coil packs being toast (falling apart), so I replaced all those and problem fixed. Then a few days ago I got another cyl 3 misfire code on start up. It's not a "everything misfiring" feeling, it's only a certain percentage of the combustion cycles usually, as it can be anything from a little rough after startup to really shaking the car around for a short while.

Plugs look good, but number 3 does have a little less carbon than the others... Gets my brain thinking. Compression results when stone cold - 232, 236, 240, 240 psi - obviously has good compression even accounting for me being at sea level (gauge is also reliable, reads spot on for other healthy engines).

I get a cheap borescope, and figure out the problem pretty quickly... (sorry for the glare, but I had to turn up the LEDs on the borescope to see anything, and they reflected off the mirror into the sensor a bit, but you still get the idea):

Cylinder 2 (looking towards cylinder 3's siamesed section)





Cylinder 3 (looking towards cyl 2, exhaust valve in shot)




A bit further forward in cyl 3






I've also seen a bit of smoke on a few start-ups, and honestly thought I'd be seeing the valve seals on the exhaust side leaking (I could only be so lucky right?). But it makes sense if there's a bit of coolant that has to burn off in the first few dozen combustion cycles which will cause a random misfire.


The pics of the piston tops show the same story, a little bit of carbon cleaned off close to the siamesed section of 2 and 3. Coolant consumption is roughly the Hi to Lo mark of the coolant overflow bottle in roughly 3k mi, so not a lot, and I think it only leaks after a hot shut down.



My question is where to go from here? I see 3 options really.

1. Take off head and throw on new headgasket and valve seals, AP2 intake retainers etc. and check valve guides for wear. Do NOT resurface head since some here such as Billman say not to. Leave block untouched.

2. Take off head and take it to a machine shop to resurface etc. Possibly try doing some resurfacing of block in-situ with a glass plate and sand paper.

3. Throw in a lower mileage engine, or maybe even an F24 build? I'd like to keep things somewhat on a budget, but I do have oil consumption on the high side of an AP1 (hard to get many street miles without track usage, seems to be ~1 qt/weekend of track usage, and about 1 qt per 700-900 miles give or take of street driving).


Thoughts? Head gasket failures don't seem too common on S2000, but they are out there. This seems like a pretty stable situation, and I have tracked it like this, so it'll probably get light usage before I tear her down for whatever I decide to do.

DefSport

Thoughts on where to go?

Reposting options as I see them...


1. Take off head and throw on new headgasket and valve seals, AP2 intake retainers etc. and check valve guides for wear. Do NOT resurface head since some here such as Billman say not to. Leave block untouched.

2. Take off head and take it to a machine shop to resurface etc. Possibly try doing some resurfacing of block in-situ with a glass plate and sand paper.

3. Throw in a lower mileage engine, or maybe even an F24 build? I'd like to keep things somewhat on a budget, but I do have oil consumption on the high side of an AP1 (hard to get many street miles without track usage, seems to be ~1 qt/weekend of track usage, and about 1 qt per 700-900 miles give or take of street driving).

Slowcrash_101

I'd go with option 1, maybe re-ring the pistons while you're at it if you want to lower oil consumption.

DefSport

I also will need to do the clutch at some point too, so I've honestly thought about going a bit further in depth on the engine.

Does a re-ring with no hone work if the cylinder bores are just slightly worn with no gouges? Or maybe just a nylon brush hone that I've seen some others talk about to smooth out the walls?

Slowcrash_101

Honing bores that aren't scratched up or in need of machining is pointless with the FRM bores IMO. If there's no scratches and the bores are not out of round, don't bother honing IMO. Under normal circumstances the bores will outlast the rings.

DefSport

There are some mild scratches in the bore according to the borescope, but it's difficult to tell if they're really minor or worrisome based on a low resolution pic.


I think the plan is to tear it down around Xmas time when I've got some more free time, and do the head gasket. If the oil consumption stays high, I might drop the whole engine and trans out when I do the clutch and will think about re-ringing it and doing bearings.

V6 Donut

Id pull it, go thru it and refreshen it up and slap it back in. Just what id do.

DefSport

I probably should just do that after COTA in Dec and do the clutch at the same time. What's the story if the bores have enough wear to be a concern? It seems forged oversized pistons + boring and honing an FRM block is such a crap shoot, plus an easy $1-1.5k cost depending on what else is freshened up at the time.


This has made me have crazy thoughts of J35/K24 swaps floating through my head though... trying to resist.

rpg51

I admire you for making the decision to refresh your engine when you could easily buy another low mileage S and be done with it.

Car Analogy

He's got a motor with great compression, some oil consumption, and a small head gasket leak. Buying a used motor is always a gamble, and is going to cost several grand. Doing the head gasket is a bit of work, but very little cost. He'd be ceazy imo to replace the motor.

I suggest:

Do just the head work now. Gasket, retainers seals.

While you have head off, inspect cyl walls. Decide is you just need rering, or more cyl work.

Buy parts needed for rering and plan for when you'll do the work, and arrange any machining (which I doubt you'll need since your compression is so good).

Meanwhile drive car with everything corrected except the oil consumption.