bombay digital > boxster > projects > engine rebuild/replace
For now, the following are my notes and research. I intend to edit some of the information down later.
If you have any info you would like to add, I'm all ears! Email me: trygve @ this domain
In the fall of 2010, my car started to emit oil smoke out the tailpipe under very specific circumstances on the track. The first occurrence was barely noticeable in my rearview mirror as I exited turns 6 and 11 at Thunderhill, and at the same time I developed a power steering leak that dripped onto the exhaust, creating a different kind of smoke that hid the oil problem.
I got the power steering leak fixed; it was a cracked / melted fitting where the return line meets the upper reservoir, which is common for tracked cars due to the heat involved in running the power steering pump at sustained high revs. The solution to that problem -- to prevent the leak from reoccuring -- is the underdrive crank pulley, which turns the pump at a slower, but still sufficient, speed.
But at the next track event, the final event of 2010, the smoke was still there, and worse. This time it was Infineon. Exiting the long left hand Turn 6 and upshifting from 3rd to 4th gear at redline, at giant oil cloud blew into the air from the tailpipe. Though the engine sounded perfectly normal, I immediately brought the car in and checked it over but found nothing visibly wrong. I went out for another session to carefully test the car and watch for any trouble; the problem happened again on the first hot lap, and then again as I crossed the start/finish line, which is a slight left turn redline 3rd-to-4th upshift. I parked the car and after asking around was advised that this was classic Air Oil Separator failure. Long left turns push the oil to the right side, where the AOS, if it breaks, can get overwhelmed and spew oil into the intake.
At first, it seemed that replacing the AOS might have solved the problem. The first two track days of 2011 were at Laguna Seca. The illusion provided was because for my gearing, Laguna Seca has no left hand turns that lead to a redline 3rd-to-4th upshift while still under a g-load. So the lack of noticeable smoke made me think that that new AOS had cured the problem, or that whatever the problem was, it must be due to oiling on the right side of the engine.
But the following event at Buttonwillow was the worst yet. On the advice (dubious in retrospect) from another Boxster racer, I let the oil get down towards the lower mark on the dipstick in an effort to reduce the amount of oil excessively pooling under g-load and causing the supposed AOS problem. But after the second session as I pulled off the track, there was noticeable "valve clatter" noise, worryingly a problem of a low oil level. So I topped up the oil to about the half-way mark, which took less than a quart. The result was indeed big clouds of smoke at the 3-4 upshift point on the main straight, until just enough oil had been lost into the air, at which point everything seemed fine. I was still concerned because the shift point is well down the straight when there is no more g-load, and on one occasion a cloud occurred exiting a tight right turn.
To narrow down the root cause by ruling out a possible defective AOS, I had it replaced again. We also uncovered and inspected the scavenge pumps to make sure they looked good, to be sure they were not allowing oil to pool in the cylinder head where it could overwhelm valve stem seals or something. But with the brand new AOS, on the first hot lap at the next event at Infineon, the giant clouds appeared at the same places as they had originally. I experimented with short-shifting there, and doing so avoided the smoke. But that's no real solution.
With the AOS ruled out, it was high time to isolate the root cause. None of the remaining possibilities were pleasant or inexpensive sounding. Oil had to be getting sucked into the combusion chamber at the moment of vaccuum change created by the 3rd-to-4th upshift off-throttle. If not via the AOS and intake, what's left were valve stem seals, pistons, or the crankcase walls.
A compression and leakdown test was performed to isolate what was allowing oil into the combusion chamber. The results exposed serious problems with two cylinders:
| Cylinder # | Compression | Leakdown |
| 1 | 170 (good) | 3% (good) |
| 2 | 165 (good) | 3-4% (good) |
| 3 | 130 (low) | 25-30% (bad) leaking to crankcase |
| 4 | 170 (good) | 3% (good) |
| 5 | 160 (good) | 4% (good) |
| 6 | 125 (low) | 25-30% (bad) leaking to crankcase |
So it is clear at this point. Cylinders #3 and #6 likely have a problem with their piston rings, or the cylinder bores. Lots of oil is getting past the cylinder and into the combustion chamber at certain moments. My 13-year old engine, with 138,000 miles, probably more than 20,000 of those on the track, requires a rebuild or replacement. I can't complain after all that time and good use in a racing environment. It runs fine on the street, but the blow-by, or whatever it is, is a no-go for track use. Not only is the tailpipe smoke intolerable on track, it risks running low on oil, and risks going boom if it suddenly worsens. Not to mention that the engine is surely down on power!
The following are, at this point, various notes as I try to figure out the cost of a new (remanufactured) factory crate engine, the cost of a junkyard engine, and the possibility and cost of rebuilding my engine or buying a rebuilt engine.
This is likely the cheapest option. But the health of these engines is a big question. Some are even labeled as damaged despite the same price as the others! In the best case scenario, a junkyard engine will have low miles and be in very good shape.
This is likely the most expensive option, or nearly so. Out of the crate this will be almost the best engine, and with application of the IMS/RMS fixes it should last for the practical future life of the car.
This would be a preferable path if the price is significantly less than a factory motor. The key is to find a reputable, experienced shop that knows how to refresh the M96 motor. There is one source that claims to put in several extra reliability items into the rebuild, but the cost is high. So far I am gathering links:
Vertex Auto (Miami, FL).... $5499 plus $4000 refundable core charge, estimated round trip shipping $550.
I asked what it does and doesn't include as far as what has been refreshed. Yes: bearings, gaskets, seals, valves, valve guides, rebuilt heads, sensors, internal drive shaft bearing, "everything on the long block". No: pistons, for example. What I forgot to ask about specifically was piston rings, since that is what my engine happens to need. Two-way shipping guesstimate is $550.