Boxster piston ring end gaps?

[marsheng]

Generic answer.

Is there pressure buildup from the engine case breather, if not, rings are probably fine.
If the car is for high RPM, a slightly larger gap is ok as very little gas/air gets through the gap a such a short time.
Hasting Rings says 0.014 " per inch of bore.

I'm sure there will be after market rings for sale. Most ring widths today are roughly the same for similar size pistons. I haven't stripped a 986 motor but I presume they are nikasiled, so get compatible rings. Ie not for cast iron.

I have a 2.7 motor in the shed just waiting for some spare time to give it a full overhaul.

[Homeoboxter]

Originally Posted by marsheng

Generic answer.

Is there pressure buildup from the engine case breather, if not, rings are probably fine.
If the car is for high RPM, a slightly larger gap is ok as very little gas/air gets through the gap a such a short time.
Hasting Rings says 0.014 " per inch of bore.

I'm sure there will be after market rings for sale. Most ring widths today are roughly the same for similar size pistons. I haven't stripped a 986 motor but I presume they are nikasiled, so get compatible rings. Ie not for cast iron.

I have a 2.7 motor in the shed just waiting for some spare time to give it a full overhaul.

Hi,

Thanks for the answer. Unfortunately I know nothing about the pressure buildup bc I`ve never seen this engine run. I looked at a Haynes manual for my SAAB 900, based on that values the second ring is out of spec (SAAB uses Mahle pistons and rings as well, the bores are larger though, so I don`t know how accurate that is for a Porsche). Based on what you are saying it really depends on the bore size so it still might be good, I`ll check that out. My worry is mostly about the side rails for the oil ring, if I place them into the bore I can see through the ring and the bore.
Interestingly, you can buy aftermarket rings for all the other engines but not for the 2.5L. For my car the only option I found is to buy the originals, that cost around 2K so it`s out of the equation. I did some research and found that certain BMW rings are the same in size, I`m not sure those are good for Nicasil though..

[356Guy]

Originally Posted by marsheng

...Hasting Rings says 0.014 " per inch of bore...

Are you sure they don't say 0.004" per inch of bore? I think 0.014" would be the total end gap

[marsheng]

Originally Posted by 356Guy

Are you sure they don't say 0.004" per inch of bore? I think 0.014" would be the total end gap

Sorry you are correct, from the web Example: 4" (bore) x .0035 = .0 14 minimum gap. I work in mm so I didn't click that .014 was wrong figure.

I understand the 2.5 and 2.7 are basically the same motor. The 2.7 has a 6 mm longer stroke and the pistons are 3mm lower to fit.

My guess is the rings are the same if you can get 2.7s.

I'm sure there are aftermarket ones available for a few $100. Rings aren't rocket science.

[Homeoboxter]

Originally Posted by marsheng

Sorry you are correct, from the web Example: 4" (bore) x .0035 = .0 14 minimum gap. I work in mm so I didn't click that .014 was wrong figure.

I understand the 2.5 and 2.7 are basically the same motor. The 2.7 has a 6 mm longer stroke and the pistons are 3mm lower to fit.

My guess is the rings are the same if you can get 2.7s.

I'm sure there are aftermarket ones available for a few $100. Rings aren't rocket science.

I`m not sure about the bore, the ring sets for the 2.7 are listed as 86.5 mm standard size. In my 2.5 I measured roughly 85 mm. But here for instance they claim the two engines are the same bore-wise:
https://www.auto-data.net/en/porsche-boxster-986-2.7-boxter-24v-228hp-6710
I`ll check what the manual says about this.

[Homeoboxter]

Originally Posted by Homeoboxter

I`m not sure about the bore, the ring sets for the 2.7 are listed as 86.5 mm standard size. In my 2.5 I measured roughly 85 mm. But here for instance they claim the two engines are the same bore-wise:
https://www.auto-data.net/en/porsche-boxster-986-2.7-boxter-24v-228hp-6710
I`ll check what the manual says about this.

Yes, the bore size both for the 2.7 and the 2.5 should be 85.5 mm, so rings listed for the 2.7L should be ok for the 2.5L, unless I`m missing something else.

[BYprodriver]

Originally Posted by Homeoboxter

Yes, the bore size both for the 2.7 and the 2.5 should be 85.5 mm, so rings listed for the 2.7L should be ok for the 2.5L, unless I`m missing something else.

You should measure the cylinder bore's for wear, if they are worn beyond spec you should probably reinstall the original conforming rings in their original positions.

[Homeoboxter]

Originally Posted by BYprodriver

You should measure the cylinder bore's for wear, if they are worn beyond spec you should probably reinstall the original conforming rings in their original positions.

Well, I don`t know the specs and I don`t have precise tools to measure the wear. The bores show no sign of wear by feel and the ring gaps do not change much when I slide the ring all the way down the bore, and there`s no difference if I place the ring to the top of the bore (the area that the ring normally does not reach) vs. if I slide it down. So I assume the wear is not substantial. I think the compression rings could be reused, my worry is about the oil rings, the side rails seem deteriorated, I can see through between the cylinder wall and the side rail when I place them into the bore.

[BYprodriver]

Originally Posted by marsheng

Generic answer.

Is there pressure buildup from the engine case breather, if not, rings are probably fine.
If the car is for high RPM, a slightly larger gap is ok as very little gas/air gets through the gap a such a short time.
Hasting Rings says 0.014 " per inch of bore.

I'm sure there will be after market rings for sale. Most ring widths today are roughly the same for similar size pistons. I haven't stripped a 986 motor but I presume they are nikasiled, so get compatible rings. Ie not for cast iron.

I have a 2.7 motor in the shed just waiting for some spare time to give it a full overhaul.

There is no nikasil in any 986 engine.

[Homeoboxter]

Originally Posted by BYprodriver

There is no nikasil in any 986 engine.

Thanks for elaborating on that!