Scored Sixes: Porsche 9A1 Bore Scoring Explained

When Porsche rolled out the 9A1 flat-six in 2009 (you'll also see it called the MA1), it threw out a lot of what made the M96/M97 famous for the wrong reasons. No intermediate shaft. A closed-deck block. A much better oiling system. Bore scoring didn't go away completely, though. From everything the specialists have published, it's a lot rarer on the 9A1, and when it does show up it often isn't the same failure the M96 crowd knows by heart.

Scope disclaimer: this is a roundup of what the shops who've opened a lot of these engines have published, plus what we've seen on our own bench. Nobody has published real failure-rate numbers for the 9A1, so you won't find any here. If you're already past the reading stage and need it fixed, here's how we do it: Porsche Bore Scoring & Block Repair in Colorado.

Which Engines We're Talking About

The 9A1 showed up in the 987.2 Boxster & Cayman and the 997.2 911, then carried on into the 981 Boxster & Cayman and the 991.1 911. It's a closed-deck Alusil block with direct injection, with one exception worth knowing: the base-model 987.2 Boxster and Cayman still used port fuel injection. That matters later when we get to the fuel arguments. If you want more on what closed deck actually means, we cover it on the Subaru side in Closed Deck vs. Sleeved Blocks: What Your EJ257 Actually Needs.

Car	Main 9A1 engines (base, S & Carrera)
987.2 Boxster / Cayman	2.9 (base), 3.4 (S)
981 Boxster / Cayman	2.7 (base), 3.4 (S)
997.2 911	3.6 (Carrera), 3.8 (Carrera S)
991.1 911	3.4 (Carrera), 3.8 (Carrera S)

The 991.2, the 992 and the 718 moved to a different, coated bore, so they're a different story. That's where this article stops.

Which 9A1s Actually Get Reported

LN Engineering, a big US Porsche engine specialist, lists scoring in the 987.2 Boxster & Cayman 3.4, the 997.2 3.6 & 3.8, the 981 Boxster & Cayman 3.4, and the 991.1 3.4, 3.8 & 4.0. It also says it has never seen a case in the base-model 987.2 and 981, even though they share similar Alusil blocks.

Hartech in the UK calls 9A1 scoring "much more infrequent" than the M96/M97 kind, and says the failures it has dealt with were very small in number, every one a seizure, every one in cold weather, with the driver admitting to driving hard very soon after setting off.

Then there are single documented cases. A UK write-up (published by JZM, 2018) covers a partial seizure in a 2009 997 Carrera S, and a 2010 997 Turbo with 23,000 miles, a loud knock after cold starts, more than 60,000 misfires logged on cylinder four and scoring found in that same cylinder.

That's one big specialist's list, one shop's handful of failures and a couple of individual engines. It's not a statistic, and we're not going to pretend it is.

Lokasil vs. Alusil: What Changed From the M96/M97

Neither engine family runs iron liners or a plated bore from the factory. Both run the piston and rings directly on aluminum-silicon, and both rely on a coated piston skirt to keep aluminum off aluminum. The difference is where the silicon comes from.

1. Lokasil (M96/M97, 1997–2008). A porous preform full of silicon particles is cast into the block at each bore, so only the bore area is high-silicon. There was more than one version of it. Verdict: the famous one, for the wrong reasons.
2. Alusil (9A1, 2009 on). The whole block is cast from a hypereutectic alloy around 17% silicon, and the bores are finished to expose the silicon particles. Porsche had used Alusil before, in the 924S, 944 and 968. Verdict: a much better track record, but not a perfect one.

On the M96/M97, Hartech describes classic scoring: one side of the piston and bore damaged, the other side clean, from coating wear or loose silicon particles on the thrust side. On the 9A1, the reports point somewhere else.

Failure Mode #1: Clearance & Cold Seizure

This is the one that's specific to the 9A1, and it's about clearance. The piston heats up first because it's sitting right under the fire. The bore has to catch up. If the clearance is already tight and you lean on it before the block is warm, the piston can take up the room before the cylinder grows to match it.

Hartech's take, paraphrased: the 9A1 block is closed at the top and the bottom, with solid casting sections tying the lower bore to the outside of the block where the main bearings sit. Those are the last parts of the engine to warm up, especially in freezing weather. When Hartech measured failed engines, it found some bores had shrunk at the bottom in the thrust direction, mostly cylinders 1 or 4 and sometimes 2 or 5, while the far end of the same bank was still round. It also says the 9A1's cold piston clearances were tighter than earlier engines.

The US specialist whose list we used above separately describes shrinkage in the bores closest to the main bearing saddles causing piston seizure at the bottom of the bore, with factory piston-to-cylinder clearances under .001".

Two shops that have measured a lot of these blocks landing on the same area of the bore is worth paying attention to. Why it shrinks is still an open question. Hartech suggests casting stresses relaxing over time but doesn't claim to have proven it.

Failure Mode #2: When the Al-Si System Breaks Down

The second mechanism is the classic one, and it applies to any Al-Si bore. The exposed silicon particles carry the load on a thin oil film. As the bores wear, those particles fracture, and once there aren't enough left (or the piston skirt coating wears through), you get aluminum rubbing on aluminum: galling, metal transfer and scoring. Hartech puts classic scoring on the thrust side, and Flat 6 Innovations, writing about the M96/M97, says early scoring starts at the bottom of the cylinder.

Hartech also notes the 9A1 couldn't use quite the same hard piston skirt coating that worked so well in the older Alusil engines, and thinks the replacement may be less durable. We're leaving the coating trade names out of it.

Cold Starts & Short Trips

Cold keeps coming up. Every 9A1 seizure Hartech has dealt with happened in cold weather, and Hartech says the lower bore is the last part of the engine to warm up, lagging behind even the oil temperature, and slower still when freezing air is flowing over the block. Flat 6 Innovations goes as far as telling M96/M97 owners with symptoms that they most likely live, or their car once lived, in Canada or the northern US.

Short trips are the other suspect. The JZM write-up suggests not using these cars for two-mile runs to the shops, and points at stop-start city driving. That's one writer's view, not a measured result.

A Colorado winter with a lot of short trips is about the worst case on paper. On paper is as far as anybody's proven it.

Fuel Washdown & Direct Injection: The Contested One

This is where the arguments start.

• The US specialist above: fuel getting past the rings is common on direct-injected engines and dilutes the oil, which it says is easily handled with shorter oil changes. (Worth knowing: it also sells the oil and fuel additive it recommends.)
• The JZM case: the injector specialist on that 997 Turbo blamed the injectors and bore washdown. JZM's own technician agreed the injectors were probably involved but doubted the washdown theory, because the scoring wasn't in quite the right place for it.
• Hartech: writing mostly about the M96/M97, Hartech rejects fuel and injectors as the cause, partly because the damage initially shows up on one bank.

And remember the base 987.2: it's port-injected, so it isn't part of any direct-injection argument at all. Our read: keep the injectors healthy because it's good practice, but nobody has proven washdown is what scores a 9A1.

Spotting It (and What a Scored Engine Turns Up)

Here's what we see, and what to watch for. These are signs that can point to bore scoring, not proof of it:

1. Oil use that keeps climbing.
2. Noise. A tick that sounds like a lifter, or a knock that's worst from cold. Often that's piston slap from the extra clearance the scoring has opened up.
3. Misfires or a check engine light.
4. One tailpipe sootier than the other.
5. Shiny aluminum debris in the oil filter.

A borescope through the spark plug hole is a good next step, but it can miss damage low in the bore. Add a leak-down test and/or a compression test, coupled with a used oil analysis, and together those can help diagnose an issue. They point to it; they don't prove it. The only way to know for sure is to inspect it. The JZM 997 Turbo above fits the picture: a knock after cold starts and misfires logged on the scored cylinder.

Here's what we've seen once they're apart: I've yet to tear one down that didn't also have other issues like a broken rod or a bad rod bearing. We're not saying which came first. We're saying a scored engine deserves a full teardown & inspection, not just a bore repair.

Prevention: Warm It Up

Our own advice comes first, and it's simple: It's always best to let oil temp reach 155-160° F before you apply any throttle more than ambulation requires. Translation: just enough throttle to get the car moving gently until the oil is up to temperature. Watch the oil temperature, not just the coolant gauge.

Hartech's work backs that up: the lower bore lags behind the oil temperature, so a warm oil gauge is the minimum, not a green light for full throttle. The US specialist above adds two maintenance items:

1. Shorter oil change intervals. No more than 6 months or 5,000 miles.
2. Keep the injectors clean. Top Tier fuel and a fuel additive with polyetheramine (PEA).

Repair Options

Once a 9A1 is scored, it's coming out and coming apart. There are a few honest ways to fix the bores:

1. Overbore & plate. Bore the original Alusil block oversize and Nikasil-plate it. The US specialist above offers this and says most 9A1 blocks don't need sleeving at all.
2. Replacement alloy cylinders. Hartech fits complete replacement alloy cylinders.
3. Ductile iron liners. An established option for these blocks, sold by Design911 for the 991 Carrera S 3.8.

Here's ours: a flanged ductile iron liner, fitted at a slight interference, with a special chemical compound between the liner and the parent bore for heat transfer. It's still a dry liner. The sleeving, boring and block indexing are done on a CNC. A 3.4 can be made into a 3.8, and into a 4.0 with a crank change. Either way, it needs a tune after.

Hartech and Flat 6 Innovations, both respected Porsche shops, aren't fans of iron liners, mostly because an iron bore needs more cold clearance than an aluminum one. We respect that. Our view: "There's nothing wrong with fitting a forged piston at .003" piston to cylinder wall, yes it will make little bit of noise when cold but if it uses an offset wrist, that often quiets the assembly down."

The Bottom Line

The 9A1 isn't an M96 with a new badge. It's a better engine that scores less often, and when it does, the published accounts point more at seizure low in the bore, tight clearances and a hard drive on a cold engine than at the one-sided scoring the earlier engines are known for. The fuel side of the story is still an argument, not an answer.

So warm it up, change the oil, and if the signs show up, get it looked at early. If your 9A1 is already making noise, start with our Porsche bore scoring & block repair page.

Sources

• LN Engineering, 9A1 2009 Boxster Cayman 911 Nickies
• Hartech, 4 Main Problems with Porsche Engines, pp. 13–14 & 124–137
• JZM Porsche, "Gen 2 Bore Scoring: The Smoking Gun?"
• Flat 6 Innovations, Cylinder Bore Scoring
• Design911, 991 Carrera S 3.8 engine rebuild cylinder liners