Piston Cleaning - My Method

[TCarlisle]

From time to time, threads pop up with people who are changing head gaskets and such asking for advice on how to clean the pistons and cylinders. I often give the advice "leave it alone". The reason for this advice is because of the risk of cleaning the carbon off and having chunks drop into the crevice between the piston and the cylinder wall not being worth the reward of not having carbon on the pistons. Also, the items most people are tempted to use to clean leave behind microscopic particles that are very abrasive (3M Scothbrite pads as an example) and have been know to ruin engines as those particle find their way into the clearances between moving parts and bearings.

So I recently (like right now) had to do a head gasket, and at first I was going to heed my own advice and leave it alone. But I admit, it is tough to go through all the work of removing a cylinder head and not address the carbon. So I looked at it and thought about it, and here is what I determined as a way to get this done.

First, I tried to scrape the carbon with a putty knife, and yes, it broke off in chunks and I wasn't liking that. So what I did was get some brake cleaner and sprayed it on the areas of carbon buildup, as little as possible to minimize run off going down the cylinder, and then when I scraped with the putty knife, the carbon just turned to very fine dust as it came off.

Here is the method I used:

1) Do all the scraping of the gasket surface first, with towels in the cylinders to minimze the amount of crap that is dropped into the cylinders. Once you are done prepping the deck surface, then address the pistons and cylinders.

2) Pick a cylinder, and rotate the engine until that piston is TDC. Please note throughout this procedure, when I say rotate the engine that means to turn the engine in the clockwise direction from the crank, and don't forget to hold tension on the timing chain as you don't want it to come off the crank sprocket.

The reaon we start with brining the piston to TDC, is so that when we spray the brake cleaner, no matter how careful we are or how little we use, there will be some run-off that runs down the cylinder wall. If the piston is at TDC, the run-off has a lot longer to travel before dumping into the crankcase.

So, with the piston TDC, spray the brake cleaner on the carbon, and then use a paper towel to douse up the excess, and then somewhat quickly rotate the engine to move the piston down the cylinder and wipe the run-off from the cylinder wall. This is simply to minimize the amount of brake cleaner that ends up in the crankcase.

3) Now, bring that piston TDC again and use a small (I used a 1 and 1/4 inch) putty knife at about a 30 degree angle to scape the carbon off. It works best to use small and fast and many strokes rather than less strokes with more force. You may be tempted to bear down harder on areas with more buildup, but don't. Use minimal force but just scrape that area for a longer amount of time.
As you see carbon dust building up as you scrap, wipe it up with a towel.

Do this until the carbon build is gone from the piston head. Then spray a little more brake cleaner and wipe with a towel to get all the carbon dust out.

4) Repeat until all pistons are done.

5) Now about the cylinder wall. You won't have carbon buildup on the cylinder walls in the area the piston rings make contact, as the rings pretty much wipe the cylinder wall clean each stroke. But about the top 1/2 inch of each cylinder wall will have build-up because the piston rings don't go higher than that. What we will do is clean that top 1/2 invh, being very careful not to touch, and especially scratch, the area of the cylinder bore that the piston rings contact. Leave that area lone.

6) Pick a cylinder, and turn the engine until that piston is at the bottom of the stroke and just starts to come on it's upstroke. we do this because as we scrape the carbon off that cylinder wall, it is going to drop down onto the piston, and some will drop between teh piston and the cylinder wall. We want the piston on it's upstroke so that after we clean the cylinder wall, we wipe the piston head clean of the dust that fell on it, and then bring the piston TDC and as the piston travels upward to TDC, the rings push that dust up to the top of the cylinder wall. If the piston was situated so that piston was on it's downstroke, as we turn the engine that dust woudl go lower down the cylinder wall and depper into the cylinder. With the piston on it's upstroke, the piston delivers the dust to the top of the cylinder for us.

7) So with the piston at the bottom but on it's upstroke, spray the top 1/2 inch with brake cleaner and then turn the putty knife and use the sides of it to lightly and carefully scrape the carbon off the top 1/2 of the bore.

Run your finger over the area, and only scrape the areas where you can feel buildup. If it is brown colored but you can't feel buildup with your finger, then don't worry about it.

8) Wipe the piston to get the dust off it, then bring the piston upwards and keep rotating the engine so the piston goes on it's downstroke and goes down about an inch. Notcie the piston rings delivered that dust to the area to you can just wipe it off.

9) Now turn the engine until the piston is at the bottom of it's stroke, and wipe the cylinder again. Turn it more to bring the piston up and then down, and clean the bore again. Each time the piston goes through a stroke, it will leave some dust and carbon particles behind. Wipe it off and bring teh piston through another stroke, wipe, and repeat until the cylinder stays clean through an entire stroke. This will take about 10 strokes and wipes.

10) Repeat for the rest of the cylinders.

11) Once done, rotate the engine and watch to see if any pistons are "leaving dust or debris as they start their downstroke (like in step 9) and wipe that dust and debris. Keep turning the engine and wiping until all cylinders no longer leave dust and debris.

12) When you aseemble the engine, don't use the best oil money can buy because you really should change the oil after the first 50-100 miles since you used a solvent. No matter how careful you were, some of that solvent got past the rings and into the oil. It is inevitable. LIkewise some of that carbon dust inevitably got into the oil also. But if this contamination is minimal, it is no big deal. But change the oil very soon after you are running again to get the contaminated oil out and replace with good oil.

That is it. This is a method to clean your pistons without using any abrasive tool like a 3M wheel which probably creates twice the amount of dust & debris that you woudl have to worry about contaminating your engine.

NOTE: Your pistons won't come clean like new. They will still be discolored where the carbon buildup was. This is because the piston head is grooved, and there will still be carbon down in that groove. I say don't worry about it. Sure, a brush might get the carbon out of those grooves, but the brush may also leave behind particles that you don't want in your engine. Also, you may wear down those groves if you hit them with a tool.

[Meatball546]

Nice article. Does anyone know how well Seafoam works for doing that? I doubt it does as thorough of a job as doing it by hand, but just how good of a job does it do?

[TCarlisle]

I seafomed the engine about a year ago. When I took the head off I didn't see as much carbon as I expected for an engine with 225K miles. The intake valves were pretty clean on the underside and the the ports were pretty clean too. I think seafoam had something to do with that.