Hi guys, I work on weekends to get my miata turbocharged. This weekend, I remove the head to replace the headgasket and headbolts in a preventive measure and to check the general condition of the pistons surface, carbon buildup and valves condition.

While being gentle, I removed a millimeter!!! of carbon on the pistons with a soft metal scrapper, I saw a carbon buildup between the cylinder bores and the pistons circumference.

Is there any way not to damage and remove that carbon efficiently?? I thought about a product called combustion chamber cleaner and the finest metal sandpaper I can find and be patient not to score the surface in any way.

Any suggestion is welcomed, i dont want to remove the pistons and get the stones in the bores.

 

Sea Foam, but carbon isn't necessarily a bad thing. Just knock them down with a scouring pad and move on to something more productive.

 

I have always used a wire brush on a drill to buff the tops of the pistons. You can use sea foam to loosen the crud.


Once the engine is running again....

Mixing 3 oz of acetone with every 10 gallons of gasoline will keep the combustion chamber from building up carbon deposits. The spark plugs will always appear fresh.

Using acetone with your fuel is a controversial subject. The Miata fuel system can handle it without any ill effect.... however I'm not sure about a turbo charged engine.

I did an experiment years ago on my lawn mower and found acetone truly does keep the combustion chamber clean.

 

DIY race gas = pump premium + acetone + toluene.

 

Carbon is not that big of a deal, the minute you crank the car, carbon lays down on everything...and supposedly it's a good insulator.

 

thanks for the advices, but it looks like buildup is cruddy and has a certain texture, like sandy asphalt for 3mm on the top of the bore.

 

I use those round brown velcro backed disks on stuck on head gaskets,works amazingly fast and does not affect the head or deck. use a die grinder and not a electric drill it'll probably work just as well on carbon.
Nick

 

3mm of carbon buildup is pretty serious. Seafoam or water injection will blast it out, but I'd worry about what's going to happen to it when you're done with it.

My shop mate is obsessive about carbon buildup on teh pistons, and in teh combustion chambers, and he'll get all OCD on it with a toothbrush and Awesome/ Simple Green. A little elbow grease and Awesome will knock enough of it down that i wouldn't sweat it, but the Awesome will get past the rings and drain down into the crank case, and you'll need to change the oil before you drive the car.

 

its not 3mm thick, its 2-3mm in height at the top of the bore but .5mm thick AT MOST...
ill sand it down with smooth sanding paper and combustion chamber cleaner.

thanks guys, your reassured me. Ill get the valve stem seals replaced in the head to eliminate variables also.

 

So you just mean the ring of carbon that the top ring doesn't hit? If so, just ignore it, lol.

 

exact, in other words, that what I meant...

 

We call this a carbon "ridge." When rebuilding an engine, we use a ridge-reamer to scrape it off so we can push the pistons out.

You've got to be careful with this ridge. You don't want to dig into the cylinder wall metal at all. That's the top-most travel of your compression ring, and it is mated to the cylinder wall at that point.

Honestly, unless you're tearing down and plan on honing the cylinders, you shouldn't touch it. It does no harm. Rather, it helps the seal at TDC.

 

Awesome waste of time.

 

+1 on the SeaFoam. I do this every time I change my oil: get the stuff in the can with the long straw and give it about 3-4 second blast down the spark plug holes on a hot engine. Let it sit for 10 minutes or so then change my oil. Be prepared for smoke when you fire it up that first time. Piston tops stay relatively clean.

I really should have taken pics of the bores of the 73' Ford FE390 v8 I pulled the heads off last week. Emissions era, low compression, zero quench carb'd v8 with about 8.5:1 comp ratio and 38 year old valve stem seals = carbon like 10 ****'s. The ridge was epic.

Or: Leave the carbon, helps increase the comp ratio

 

Doesn't mopar make a combustion chamber cleaner or something similarly named? I think a guy on m.net used it and it literally was a soak, wait, and wipe deal. I'd say search for it but I think they're still down.

 

The Mopar (or was it GM?) labeled stuff... I remember reading that thread on m.net, then reading elsewhere (google) about piston and cylinder wall etching if it was not completely cleaned out of the engine? Might be a different product but it sounded too aggressive to me.

 

found it. I wouldn't use it. But if he's hell bent on scraping his cylinder bores, I'm sure this is a safer alternative.

http://forum.miata.net/vb/showpost.p...42&postcount=9

 

let some ATF soak on top of the pistons.

 

I bought ford cc cleaner and let it soaked to remove carbon deposit on the rings and ridge. Will wait for it to drip down in the oil and flush before starting the engine. I need to replace the oil pan anyway...

 

Just leave it be before you **** up and score your cylinder walls and bust your rings or some stupid ****. Who gives a **** about some carbon on pistons. The cylinder is full of FIRE what do you expect