speed rII

Ok, now that I have my engine taken apart, I think that I might have my pistons coated. Ceramic top and moly skirts.

So, is there some reason why the skirts should not be coated?
Will the coatings work with alusil?

logray

I'm not sure about doing that with the stock pistons and stock lokasil lining.

But at least for the JE pistons and nikasil lining LNE offers, coating their pistons is one option.

From http://www.lnengineering.com/boxster.html

speed rII

Thank's logray, I think that I have only the top of the pistons coated.
Not sure thou that it makes eny difference in NA engines...

Byprodriver

I like the skirt coating, it helps prevent scuffing, reduces friction, & can reduce extra clearance from wear (about .0005)

nick49

We were coating pistons used in high performance motorcycles with a black friction reducing coating in the '70s and '80s. It was made by Kalgard and called Piston Kote. It was supposed to keep the skirts happy and aid in redcing friction in that area. Once a piston skirt starts to kiss the cylinder from excessive heat and expansion the damage is already done. Added heat from friction causes more heat and more expansion until the piston will start dragging and metal transfer will result. When the piston finally cools it will often collapse.

I believe the new teflons and moly coatings are a replacement for tin that pistons have been coated with for years. The tin was a sacrificial and friction reducing coating. In a properly engineered and tuned motor the piston should not touch the cylinder but glide on a thin oil film. Fits at room temp are as close as .0005" in a 3.5" bore. That's really close.

Decide for yourself if coating is necessary. Many factory pistons now use it. Talk to your machinist. If you are thinking of coating your used pistons, I would not. Changing their characteristics regarding expansion and heat holding/shedding abilities is something you don't want to experiment with. I build high performance motors in my line of work and my advice is based on experience.

Macster

The stock pistons come with an coating of iron (I forget the name) on their skirts to guard against similar metals (alum. piston and alum. cylinder bore) from making contact.

AFAIK, the piston tops are not breaking down from the heat of combustion or you would not be re-using the pistons.

The pistons are oil cooled (from underneath) by oil jets (one per piston) that according to Porsche's literature help cut the piston's temp by 50C.

I'd say if it ain't broke don 't fix it.

Sincerely,

Macster.

logray

"...with optional thermal barrier coating and hard anodized top ring land for superior durability..."

Supercharged application.

Shown in the above pictures (second post).

365dan

Macster,
Do the splash valves need to face a paticular direction and do they need to be glued in ?

Thank you for you posts they are quite helpful.

Byprodriver

The piston oil squirters should point to the underside of the pistons & be inserted in the crank carrier housing with loctite 640 bearing retainer.

Flat6 Innovations

I love piston coatings, when properly coupled to other coatings. I have had bad situations when using coatings on piston crowns, without addressing the ring lands. The heat thats reflected created micro welding of the rings to the lands. When coating piston tops, I also coat combustion chamber, and valve faces.

Skirt coatings are safe, and I use them in most every Performer build. Running clearance can be effected by the thickness of the coating, so always consider that during assembly.

365dan

Byprodriver,

Thank you for your reply. My question was not clear. The bottom end of the splash valve has 2 outlets, do they need to be in line with the crankshaft or at 90 degree angle or does it not matter ? Thank you in advance it has been difficult to get the detail info to rebuild a 996 3.4, the forums are a great help.

Flat6 Innovations

The spray of oil is delivered evenly, pretty much no matter the direction of the squirter installation.

These are the things that I cover in my 4 day, hands on, M96/ M97 engine rebuild school.

365dan

Flat 6

Thank you for the help. I would really love to take your class. But living & working in SF bay area it's tough to get free time. I am using this rebuild as a stress relief, with the promise of future enjoyable spirited drives. Thank for all the work and comments you arever greatly appreciated. Wish your book was out. I am sure it will be a best seller in the 996 community.

Flat6 Innovations

The book will be released at the 2016 Porsche Literature Meet, in March. Thats been my goal for the last year, and it will happen.

That said, I just finished two books. One for the 996 and one for the 997. I have the 997 boos in stock, and the 996 are set to be delivered by the print shop in two weeks.

These are fastener torque specs books for the entire car.. They extensively cover every engine fastener as well, and even our aftermarket components from LN Engineering are specified in the book. The 997 book is 189 pages, the 996 book is 150 pages.

This makes your rebuild easy, as the specs are laid out in the order of engine assembly with illustrated parts breakdowns.

365dan

Flat 6

Looking forward to the release.
Any hope of getting a draft copy of the 996 torque specs, as I am currently in a build?? As you can tell I was raised if you don't ask you don't get, or learn.