Boxster piston ring end gaps?

[Homeoboxter]

Hi All,

I`m wondering if i should buy new rings for the pistons. Not sure if this has ever been released by Porsche, does anyone know the end gap tolerance values for the 2.5L engine?

Thanks!

[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 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!

[Smallblock454]

Check for 996 103 033 02

Mahle piston ring kit Mahle 504 40 N0
EAN 4009026929575

Contains:
Mahle 63504, Rechteckring, Nitriert, Heigth 1,2 mm
Mahle 63745, Nasenminutenring, Heigth 1,5 mm
Mahle 65959, Ölabstreifring (mehrteilig), Nitriert, Height 2,0 mm

https://catalog.mahle-aftermarket.com/eu/product.xhtml?eid=1195707#divider

Fits:
M 96.20, 85,50 Ø, 2.480 ccm
M 96.25, 85,50 Ø, 2.687 ccm
M 96.22, 85,50 Ø, 2.687 ccm
M 97.20, 85,50 Ø, 2.687 ccm
M 96.23, 85,50 Ø, 2.687 ccm

You'll find infos about correct gap in the workshop manual.

There are also piston ring sets for overbore pistons available:
Mahle 504 40 N1
Mahle 504 40 N2

Regards from Germany,
Markus

[Homeoboxter]

Originally Posted by Smallblock454

Check for 996 103 033 02

Mahle piston ring kit Mahle 504 40 N0
EAN 4009026929575

Contains:
Mahle 63504, Rechteckring, Nitriert, Heigth 1,2 mm
Mahle 63745, Nasenminutenring, Heigth 1,5 mm
Mahle 65959, Ölabstreifring (mehrteilig), Nitriert, Height 2,0 mm

https://catalog.mahle-aftermarket.com/eu/product.xhtml?eid=1195707#divider

Fits:
M 96.20, 85,50 Ø, 2.480 ccm
M 96.25, 85,50 Ø, 2.687 ccm
M 96.22, 85,50 Ø, 2.687 ccm
M 97.20, 85,50 Ø, 2.687 ccm
M 96.23, 85,50 Ø, 2.687 ccm

You'll find infos about correct gap in the workshop manual.

There are also piston ring sets for overbore pistons available:
Mahle 504 40 N1
Mahle 504 40 N2

Regards from Germany,
Markus

Thanks Markus,

This is helpful, seems the same ring set works for both 2.5 and 2.7 cars, as I thought. Unfortunately the Mahle sets are out of stock everywhere I looked at. Now I think I`m gonna go with this:

https://www.ebay.co.uk/itm/183341980498?ul_noapp=true

It`s an SPD product, which I`ve never heard about...

[Homeoboxter]

Originally Posted by Smallblock454

Check for 996 103 033 02

Mahle piston ring kit Mahle 504 40 N0
EAN 4009026929575

Contains:
Mahle 63504, Rechteckring, Nitriert, Heigth 1,2 mm
Mahle 63745, Nasenminutenring, Heigth 1,5 mm
Mahle 65959, Ölabstreifring (mehrteilig), Nitriert, Height 2,0 mm

https://catalog.mahle-aftermarket.com/eu/product.xhtml?eid=1195707#divider

Fits:
M 96.20, 85,50 Ø, 2.480 ccm
M 96.25, 85,50 Ø, 2.687 ccm
M 96.22, 85,50 Ø, 2.687 ccm
M 97.20, 85,50 Ø, 2.687 ccm
M 96.23, 85,50 Ø, 2.687 ccm

You'll find infos about correct gap in the workshop manual.

There are also piston ring sets for overbore pistons available:
Mahle 504 40 N1
Mahle 504 40 N2

Regards from Germany,
Markus

Workshop manual: does such thing really exist??

[JFP in PA]

Originally Posted by Homeoboxter

Workshop manual: does such thing really exist??

Yes, but it contains nothing about the engine internals. Porsche never intended techs in the field to work on these, so they never published anything.

[Homeoboxter]

Originally Posted by JFP in PA

Yes, but it contains nothing about the engine internals. Porsche never intended techs in the field to work on these, so they never published anything.

Yes, I have the Bentley workshop guide, which is useless for engine rebuild, Wayne`s book, and a parts list with diagrams I found on the web. That`s all I have.

[Smallblock454]

In the price range of the eBay ones i would go with OEM: https://www.********************************************** **************************************.com/oem-parts/porsche-piston-rings-99610303302/?c=bT0x

Edit: uhm - seems to be a competitor of pelicalparts.

Shure, an official pdf workshop manual in english language for the 2.5 exits.

[Homeoboxter]

Originally Posted by Smallblock454

In the price range of the eBay ones i would go with OEM: https://www.********************************************** **************************************.com/oem-parts/porsche-piston-rings-99610303302/?c=bT0x

Edit: uhm - seems to be a competitor of pelicalparts.

Shure, an official pdf workshop manual in english language for the 2.5 exits.

Markus, I`d go with that too if it was in the same price range, but that`s for one cylinder..

[Homeoboxter]

Originally Posted by Smallblock454

In the price range of the eBay ones i would go with OEM: https://www.********************************************** **************************************.com/oem-parts/porsche-piston-rings-99610303302/?c=bT0x

Edit: uhm - seems to be a competitor of pelicalparts.

Shure, an official pdf workshop manual in english language for the 2.5 exits.

Markus, I`d go with that too if it was in the same price range, but that`s for one cylinder..

[marsheng]

One of these will do, https://www.toolfactory.co.nz/products/ampro-3-jaw-engine-cylinder-hone-50-175mm-75mm?variant=39640318349&gclid=EAIaIQobChMIhN7U-pyL4AIVCSQrCh33Mg57EAYYAiABEgK7IPD_BwE

Quick hone (20-40 sec) with some cutting oil is normally fine. Just roughen up to help seal the rings.

Just think of it this way, take a sharp knife and draw it across and oil stone. Home many strokes does it need to sharpen, 6 or 12. Same with and engine, the stone tears the liner microscopically, a few slides of the piston rings beds them in .

Seen some aero engines documents where they 'lap' the rings in by hand with a piston lapping jig.

Have 2 CB125 twins and one is bored to 150 cc. I need to do my magic on the motor but that will be good for 14000+ .

[Homeoboxter]

Originally Posted by marsheng

One of these will do, https://www.toolfactory.co.nz/products/ampro-3-jaw-engine-cylinder-hone-50-175mm-75mm?variant=39640318349&gclid=EAIaIQobChMIhN7U-pyL4AIVCSQrCh33Mg57EAYYAiABEgK7IPD_BwE

Quick hone (20-40 sec) with some cutting oil is normally fine. Just roughen up to help seal the rings.

Just think of it this way, take a sharp knife and draw it across and oil stone. Home many strokes does it need to sharpen, 6 or 12. Same with and engine, the stone tears the liner microscopically, a few slides of the piston rings beds them in .

Seen some aero engines documents where they 'lap' the rings in by hand with a piston lapping jig.

Have 2 CB125 twins and one is bored to 150 cc. I need to do my magic on the motor but that will be good for 14000+ .

Will do. Honing will also help keep oil film on cylinder wall.
I also like to play with vintage Japanese bikes, I have a TX750 Yamaha and a CB750 K1.