Mahle Pistons and correct installation

[Porboy911]

I'm in the middle of the rebuild and just got my pistons and cylinders back and wouldn't you know it I can not find anything on the direction the pistons need to go in. I have a 50/50 chance of getting right however... So these are Mahle 90L58 pistons (see photos). They were probably a mid year change by Porsche but I have not seen any others around on any videos only on here have I see n mention. So i really hope I get a quick return on this message. Everything being equal and the excellent engineering of this engine it would stand to reason that the writing on the cylinder would be in the same direction as the writing on the piston. Anyhow please assistance is required. Thanks.

[Zuffenwerker]

2.7 CIS pistons?
Usually on the drivers side of the engine the bump on the piston goes towards flywheel
Passenger side of the engine bump goes towards the crank pulley

If you put them in wrong pretty sure you’ll find out pretty quickl after you install your rocker arms because the there will be some “piston stops”

[Flat6pac]

My train is the concave side is toward the spark plug
Bruce

[john walker's workshop]

Just remember, lump to the left. Nothing to do with the flywheel on CIS pistons. The top of that cylinder looks bad, btw.

[Porboy911]

Originally Posted by john walker's workshop

Just remember, lump to the left. Nothing to do with the flywheel on CIS pistons. The top of that cylinder looks bad, btw.

I had my local Porsche guy refinish the cylinders they said it looks bad but should still be ok. Thanks for the info

[Porboy911]

Originally Posted by Zuffenwerker

2.7 CIS pistons?
Usually on the drivers side of the engine the bump on the piston goes towards flywheel
Passenger side of the engine bump goes towards the crank pulley

If you put them in wrong pretty sure you’ll find out pretty quickl after you install your rocker arms because the there will be some “piston stops”

Yup they are CIS. Thanks.

[Porboy911]

Originally Posted by john walker's workshop

Just remember, lump to the left. Nothing to do with the flywheel on CIS pistons. The top of that cylinder looks bad, btw.

So basically the way I have them placed in the photo is correct. I had assumed that this is correct but better to check with others.

[E Sully]

This side Up.

Down

[john walker's workshop]

Originally Posted by Porboy911

I had my local Porsche guy refinish the cylinders they said it looks bad but should still be ok. Thanks for the info

I wouldn't use it.

[AlKidd]

Is your opinion based on building an engine for a customer, that you have to warranty? Someone tackling their own rebuild / reseal may have to make some choices for economic reasons.

Originally Posted by john walker's workshop

I wouldn't use it.

[john walker's workshop]

Usually when you find junk, you trash it. I don't see why anybody would use that.

[AlKidd]

How do you determine "junk" from a photo? Wouldnt depth of pitting, degredation of the seating area only be known by having it on hand?

[dannobee]

We can see the pitting/fretting/degradation of the fire ring (worst on the right side of the barrel). Where the "head gasket" goes. I'm in the same camp as John; no, I would not run it like that.

You should be able to locate one cylinder to replace it. John might actually have one. If not, Henry likely does. Or post a WTB ad in the classifieds.

[pocv0]

"I had my local Porsche guy refinish the cylinders they said it looks bad but should still be ok. Thanks for the info"

Get a new local Porsche guy. lol Don't use it .

[boyt911sc]

Originally Posted by AlKidd

How do you determine "junk" from a photo? Wouldnt depth of pitting, degredation of the seating area only be known by having it on hand?

Al,

Listen to John W. You and I or most of the people in this forum will not have enough experience to even come closer for comparison. Take a good look at the top of the cylinder shown in the picture. It is heavily pitted. I personally will not use or recommend this cylinder for use. It is a bad cylinder and should be discarded and replaced. An experienced and knowledgeable engine rebuilder would never even think of using it.

Tony

[brighton911]

Not much chance of that sealing properly for long or more likely, at all. Chuck it and get a replacement. And make sure all the corresponding head surfaces are OK. No sense doing the job twice.

[Dpmulvan]

Looks like the victim of a broken case stud. Using that would make me lose sleep.

[harrydarwen]

If you put them in wrong pretty sure you’ll find out pretty quickl after you install your rocker arms because the there will be some “piston stops”
Speed Test