Piston Cleaning and Coating

9FF · 09-20-2011, 05:46 PM

Hi, I'm new here, long time poster on RL but sometimes you need a change. Will do a formal intro later with pics etc, etc as I know everyone likes that on forums. Meanwhile I need some advise about my pistons and I hope you kind folks will help me out.

These are KS (Alusil) pistons, standard spec, tolerance group 1.

1. What is the best/safest way to clean up the carbon off piston tops, above the top ring and the brown spots on the skirts?

2. Anyone have the specs for these pistons so I can check the measurements?

3. There are a few scratches on the skirts, some down to the aluminum. I've used Swain coating in the past, it's alusil compatible correct?

Any other advise appreciated -Mike

AA_Ezra · 09-20-2011, 10:35 PM

Welcome to the board im sure others will chime in later and do the same.

As far as the top of the pistons go i can tell you what i used to cleaned the top of them while they were in the car to get rid of all and any carbon. CRC Gasket Remover I used it the same way you would wood stripper, Put a nice layer of the stuff on it and let it sit for about 10 min and use a non marring gasket scraper to help get crud off. Clean and repeat, and soon you will be at a point were all you need is a rag to clean it off and it comes out very clean.

If i had taken my pistons out I would have thrown them in an ultrasonic cleaner with either just Distilled wattter or a combonation of distilled water and an aluminum safe cleaner at 10% and work my way up. But if you dont have an ultrasonic cleaner that I dont have a clue,

Arizona_928 · 09-21-2011, 10:45 PM

+1 on the CRC. It's safe on aluminum.
I would be careful with the piston though. I have seen alot of builds go up in smoke because the lining decided to flake off the piston.

Cocacolakidd · Cocacolakidd's Garage

I would chime in to say be very careful with the piston skirts as they are coated with an iron coating (Ferrous Oxide) to make them compatible with the Alusil Cylinder. They would other wise wear out quickly if the coating is disturbed. The pistons would be ruined or you would have to have them re-coated, and that could be expensive...

When cleaning pistons in the block if any debris or non-compatible solutions get between the cylinder and piston it could only take turning the crank/piston assembly a few revolutions by hand even to ruin the block or pistons...One fellow on the boards here let a very small piece of hard carbon get between the piston and cylinder bore. That small piece of carbon ruined many hours and allot of expense he had in the block because he had to scrap it.

Cleanliness is next to Porscheness...er, how did that go.

John_AZ · 09-22-2011, 10:47 AM

Quote:

Originally Posted by AA_Ezra

As far as the top of the pistons go i can tell you what i used to cleaned the top of them while they were in the car to get rid of all and any carbon.

CRC Gasket Remover I used it the same way you would wood stripper, Put a nice layer of the stuff on it and let it sit for about 10 min and use a non marring gasket scraper to help get crud off. Clean and repeat, and soon you will be at a point were all you need is a rag to clean it off and it comes out very clean.

If the pistons are still in the car, normal for just a HG change,
be careful you do not let the carbon on top of the piston fall between the piston and cylinder wall.

Some do not touch the top of the pistons.

If you do, put the piston at the top of the block. Put thick grease around the outer edge of the piston top and clean away. The grease will prevent carbon falling down the cylinder walls. Lower the piston and wipe grease away. Repeat.

Also, do not clean the top cylinder ridge or use a ridge scraper. This ridge improves combustion.

Never scratch the top of the block.

GL
John

whalebird · 09-23-2011, 12:17 PM

Fuzzy pics, but they don't look that bad. I soaked mine in Carb cleaner for a little while, and rinsed them off with brake clean/compressed air. The carbon on top was a little more stubborn. I used a soft roloc pad on a die-grinder for that. You'll want to prep the cylinders with the sunnen an-30 paste to insure good ring seating.
Piston survey is in the workshop manual and spec book. I'll see if I can find mine.

9FF · 09-23-2011, 03:28 PM

Quote:

Fuzzy pics, but they don't look that bad. I soaked mine in Carb cleaner for a little while, and rinsed them off with brake clean/compressed air. The carbon on top was a little more stubborn. I used a soft roloc pad on a die-grinder for that. You'll want to prep the cylinders with the sunnen an-30 paste to insure good ring seating.

Piston survey is in the workshop manual and spec book. I'll see if I can find mine.

Sorry about the iPhone pics, but they look quite good. There are a few scratches down to aluminum on the skirts only but I think a swain coating will sort them out. Tops are fine, just some discoloration so I might swain coat the tops too. Just getting them measured up to see if they are in spec.

BTW no one noticed, these are the 10.6cr Euro pistons

cjpacitto · 09-24-2011, 04:31 AM

The pistons themselves are not alusil. Only the block is alusil.

As stated above, there is an iron oxide coating on the skirts to protect them from the silicon in the block.

I had my pistons done by Swain Tech. When I got my pistons back the additional thickness from the coating made them too large to fit into the cylinders. Yes, it's only a few thousandths thick, but the piston to cylinder clearance on these engines is very small to begin with. I had to hone my cylinders out a couple thousandths to get the proper clearance then finish with the Sunnen compound. After all that was done I discovered that standard piston rings were too small and had way to big of an end gap. Luckilly Lindsey Racing makes oversized rings for exactly this purpose.

BTW, both Swain Tech and Lindsey say coatings are compatible with Alusil blocks.

9FF · 09-24-2011, 06:18 AM

Quote:

The pistons themselves are not alusil. Only the block is alusil.

As stated above, there is an iron oxide coating on the skirts to protect them from the silicon in the block.

I had my pistons done by Swain Tech. When I got my pistons back the additional thickness from the coating made them too large to fit into the cylinders. Yes, it's only a few thousandths thick, but the piston to cylinder clearance on these engines is very small to begin with. I had to hone my cylinders out a couple thousandths to get the proper clearance then finish with the Sunnen compound. After all that was done I discovered that standard piston rings were too small and had way to big of an end gap. Luckilly Lindsey Racing makes oversized rings for exactly this purpose.

BTW, both Swain Tech and Lindsey say coatings are compatible with Alusil blocks.

Thanks cjpacitto. Yes I know about them not being Alusil, these are KS pistons so they are for alusil blocks unlike the factory Mahle pistons which are for nickasil blocks. I'll be doing the swain coating on the tops and skirts, they recommended their PC9 coating for the skirts and TBC for the tops, both are Alusil compatible. I read the an-30 honing thread, good info there and good to know about the Lindsey oversize rings. Will post pics when done.