XuTVJet

I constantly read posts on this forum, other forums, and YT videos saying that bore scoring is a non-issue issue on the base model 987.1 and 987.2 motors. The reason most note for this claim is because of the smaller displacement of these motors (2.7 to 2.9 liters) with little to no scientific explanation to back up the claim. I find this rather hard to understand/believe as both motors have the same problematic cylinder liner coatings as their S car 3.2 and 3.4 motors counterparts. I have a hard time buying the smaller displacement rationale, especially given that the 987.2 base and S model motors are closed deck (i.e., thermal expansion should be better managed).

We all know the 987.1 S motors can and do get bore scoring and we're also seeing it in the DFI 3.4 motors. I do have wonder if the reason why don't see much, if any bore scoring in the base motors is because:

1) Fewer of them were sold thus less reported issues with bore scoring
2) Fewer are presumably competitively driven.
3) Perhaps owners of the base model cars tend to drive less aggressively.

Am I off my rocker

hueyhoolihan

i think you're right. it's #4 "all of the above". they sold a gazillion of those 2006 "S" models AFAIK and if know my porsche "S" type owners, they were slavering at the mouth to get them out on a track.

and just because i agree doesn't necessarily mean you're ON your rocker.

sectachrome

5) Base models are God's favorite. The meek shall inherit the earth etc.

McSwine

His will be done (‘09 2.9 here).

Glue Guy

Been thinking the same. There doesn’t seem to be any real data, meaning numbers, behind the complaints of bore scoring. Fewer cars, fewer complaints with the base model.

Mike Murphy

Similar reason Hartec explained in the 996 world when comparing the 3.4 versus 3.6. The smaller engines produce less horsepower, less heat, and have different rod ratios. The smaller engines also need more revs to get similar torque output, so less lugging and better oil circulation at higher revs. But scoring can still happen on the smaller engines, just less prevalent.

ZuffenZeus

With the M9X generation of Boxster/Cayman, one of the biggest differences between the base vs. the S model engines is piston composition. The base engines used cast pistons, and like the Carrera M9X engines, the S model Boxster/Cayman engines used forged pistons. Again, 986/987 Boxster/Cayman base engines with cast pistons are LESS prone to cylinder bore scoring. As Jake Raby has mentioned many times, the borescoring problem is an equation of many variables that leads to the problem. The 9A1 is a totally different beast of an engine and yes, there are reports of borescoring primarily on cylinder #1.

Read this from LN Engineering:

Jump to the 10 min. mark:

bredward

Mostly true, with one exception. The 3.2L used in Boxster S in 2005-2006 are cast, not forged, if I am not mistaken.

Raudona

I believe the 987.2 base engine (2.9 liter) has port fuel injection whereas the S models have direct fuel injection. In the direct injection configuration, there could be conditions where the fuel spray impinges on the cylinder wall and washes some lubricant away, leading to bore scoring. For the port injection engine, there is less of a tendency for wall wetting since the fuel and air are partly premixed before they get into the combustion chamber. In other words, there is no fuel jet spraying directly inside the combustion chamber. My guess is that this is a big factor in why base engines don't get as much bore scoring as the the S engines.

ZuffenZeus

Thank you for that clarity. Basically, the general rule is the Boxster/Cayman engines that have cast pistons are less prone to scoring. The M96.26 in the S model is less prone to the problem and one of the biggest differences is piston composition.

When the Boxster got the M97.22 and M97.21 in 2007, the problem really showed it's ***.

ZuffenZeus

I think this list will help those worrying about the problem:

Raudona

So what is scraping up against the cylinder wall in order to create the bore scoring? Is it the piston ring, the piston itself, or some debris (chunk of dirt or metal particle)?

hueyhoolihan

rings are designed to scrap up against the cylinder walls, AFAIK. that's there purpose. without it there will be a lack of compression. but without proper lubrication there will be excessive heat, galling and consequently damage.

Raudona

Maybe I should clarify my question. Under normal operation, there should be a thin film of lubricant between the cylinder wall and the piston rings, and there should not be any metal-on-metal scraping or scoring happening. I was wondering about what's changed when bore scoring happens. Do we think the lubricant film failed, allowing the piston rings to gouge the cylinder walls via abnormal metal-on-metal contact? Has the piston itself contacted the cylinder walls (for example if it was tilted slightly with respect to the cylinder walls)? Or is there some debris (dirt or small bits of metal) that got in there?

Mike Murphy

Read this: https://www.hartech.org/images/downl...0(interim).pdf