theMBV

My engine appears to have given up the ghost and I'm hoping to get some pointers on reasonable paths forwards. I know similar topics have been covered but I couldn't find answers to all my questions or up to date info.

Background info: 2003 AP1 stock powertrain, ~110k miles, I'm the second owner (bought at about 98k miles) and with me the car sees 50/50 track day/street use. A recent leakdown test showed ~10% across cylinders 1-3 and about 70% in cylinder 4 which appears to all be through the piston ring, honestly no idea what caused this.

Background info [updated]:

• Feedback from TrackSpec when changing intake keepers/retainers to AP2 "Cylinder 4 showed 70% leakage when pressurized at 100psi. Added a cap full of engine oil to cylinder and leakage improved by 10% indicating piston ring seal is not great"
• Was in process of moving at the time and wasn't able to deal with this. Car then threw a cylinder 4 misfire engine code. 2nd repair shop also diagnosed a bad piston seal through leak-down test.

Goals: Reliable track day car up and running sooner rather than later. No plans to ever go forced induction, maybe an intake/exhaust/tune to tweak the power-band at some point in the future. I have to use the brakes on the track so IMO stock power isn't a problem. For cost I'm willing to spend a bit more money now if it saves me money in the long run, I'd like to keep this car for a while.

To replace this I'm seeing a few options:

1. Gamble with an eBay engine. Long blocks seem to be in the $4-7k range with most over 100k miles.
   1. If I buy a used engine what do I need to know to minimize risk? Is leak-down enough info, or should I be requesting anything else?
   2. I've found some JDM engines (11.7:1 compression) for sale. From what I can gather these will work on 91 AKI but its not ideal. Not sure if these will pass smog. Would love confirmation.
2. Buy a new short block. Since all the pressure loss appears to be through the piston ring I assume replacing the short block and keeping my head should be ok?
   1. Spoon: The short blocks appear to be anywhere from $6500-$7800 new, but lead times are very long (I've been quotes up to 6 months). I like that its a brand new engine... if I can get one at all.
      1. Compression on Spoon short blocks is 11.8:1. Is that going to do anything for me in Cali on 91 AKI?
   2. Inline Pro: $2k for and FRM finish hone and Custom FRM piston set with rings and wrist pins.
      1. 1 year warranty if they do the whole long block for ~$4500, thoughts on if thats worth it?
      2. Reliability/experience with Inline Pro in general?
3. Re-sleeve current engine: From what I understand this isn't the best option for long term reliability.
4. Wild Card: get a stroker engine/short block from InlinePro/Spoon/anyone else. I don't need more power but if I'm doing all this anyway it might be nice. However, I assume none of the strokers are going to be as reliable as a stock spec engine.
5. other options? (I'm not putting an LS in the car lol)

engifineer

What do the cylinders look like? Any scoring and are they oval at all? Some light honing and re-ringing is possible on these I believe if it is done correctly. @Billman250 may see this and chime in.

If boring the cylinders is needed then yeah, the motor is pretty much done.

theMBV

Thats a good point, I haven't actually seen the cylinders. I received the diagnosis from a shop who said they couldn't do the work and put it all back together. Should I be pulling the head off and taking a look before doing anything else? For now I was hoping to leave the car intact so I can at least move in in my driveway or get it to a near-by shop.

engifineer

You could do an initial check for scoring by pulling plugs and using a bore scope (you can get fairly cheap flexible mini cams these days, good tool to have around for lots of purposes). That will at least give you an idea up front. If you see visible, bad scoring then you will know that the block is likely gone. If none or hard to see well, then you would want to pull the head. If no scoring is present, then to see the roundness of the bores, you may need to get it to a shop to properly measure.

Hopefully some others will chime in on their experiences on this motor, but I remember that others have done a light refresh (rings and bearings) prior to any engine damage. This motor is trickier than a lot of others in regards to rebuilding.

EffWun

Let us know what your decision ultimately comes down to.

I want to know more about inlinepro builds as well although there is someone on here with a 2.4 build from inlinepro seems to like it.

Slowcrash_101

Leak down is coming through the piston rings? Can you show us what the spark plug looks like at least? Passing a compression test and showing high leakdown numbers would indicate valves. If it's a top end issue, it's much cheaper to fix.

theMBV

I'm pretty sure I replaced the plugs during my ownership but can't find the maintenance record of it right now. This was initially noticed when I swapped my intake keepers/retainers to AP2, comment from the shop "VC gasket was leaking. Ordered replacement. Cylinder 4 showed 70% leakage when pressurized at 100psi. Added a cap full of engine oil to cylinder and leakage improved by 10% indicating piston ring seal is not great."

Slowcrash_101

Compression is going to increase if you add oil so that's not telling you much. It could be your valves are not adjusted properly? There's a lot of factors involved and a guessing game is just a way to waste money. Be sure of what is wrong first before you drop thousands of dollars..

Seeing the state of the spark plugs, boroscoping the cylinder, and checking valve lash are the cheapest most effective steps to determining how to proceed. If the spark plug is lose, if valve lash is too tight, that can affect compression.

When they did the leakdown test was air pressure escaping from the dip stick?

Remove the cylinder 4 plug from the car, take a pic and post it.

theMBV

Will post a pic of the plugs after work today and should have a scope to look at the cylinders by this weekend. These are from a leakdown, not a compression test, so I'm not sure I understand your comment "Compression is going to increase if you add oil so that's not telling you much".

Slowcrash_101

The reason you add oil to bump up compression is to see if the rings are sealing. You add it during a compression test, which involves cranking a warm car over. A leakdown test is different, you add air to the cylinder at TDC to a specified PSI, and the gauge tells you how much of that air pressure is being held by the combustion chamber. Adding oil while doing this will not increase compression, compression pressure on these engines is 220 psi, you're adding less than half that. When you crank the engine, the air pressure expands the piston rings creating a seal, putting 100psi in the engine isn't even tickling the internals, so adding oil is useless for a 100 psi leakdown test.

Much more useful is to note where the air is escaping from. If you hear it coming from the intake, it's intake valves, if you hear it from the exhaust(my money is here) then it's exhaust valves, if it's mainly the dipstick hole, then it's pistons because the air is going right into the crank case.

I hope this helps.