cleaning carbon from pistons

This works well for removing carbon...

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I think it's a good idea to remove the carbon. If you have an engine that working perfectly they don't carbon up at all, but that doesn't happen often. Scrape the stuff off, try to get it out of the ring margin, don't worry about tiny scratches on the pistons. Clean off the top of the bore as well. I use a scraper made out of an old wood chisel with the sharp corners rounded off to smooth out the tops of pistons if they have eaten a stone or something, you could do the same with your coolant leak pits.

Brian

It sounds like you are only cleaning piston tops. Not much of a problem here. You should not be able to get to the piston sides/walls, the area were the ring grooves are without removing pistons. Yeah, scratches on piston walls are bad- minor scratches on top/dome are not much worry.

Ryan Underwood wrote:

couldn't stand looking at them.

I normally clean them before removing the head. I pour a pint of ATF slowly down the intake while keeping the engine running. This puts off a large cloud of smoke. I have been told a pint of water will do the same job without the smoke.

When I open them up after this, the tops of the pistons and the chamber look just like new.

I sure wouldn't clean them in place. The carbon will get down the edge of the piston which can ruin rings. I would wait and do the liquid shock/burn method after putting it back together.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Ryan Underwood wrote:

couldn't stand looking at them.

If you've got accumulated and hardened carbon in one particular cylinder, that cylinder's probably burning oil.

Removing the carbon from the piston tops and combustion chambers is a good idea, as long as it is done properly.

"the rings digging into what they are seated in" does not parse. Whatever you read, this isn't it.

Some say waving your arms in figure-8s for an hour each day keeps pink alligators away. No, there is no reason to leave a ring, 1/4" or other size, of carbon.

No, and there's no reason to leave the carbon -- if present -- on the cylinder wall.

Do not worry about scratches on the piston head.

Leave them alone.

Pock marks are pits. You can't fill 'em; they'll fill with carbon soon enough, so leave them alone.

No.

It's completely safe and much more effective than brake cleaner.

Neither ammonia nor lye is appropriate for this task.

Horseshit. Moly rings have been around for decades, number one, and it is not "way harder" to get a good ring seal with non-moly rings.

You are, but it doesn't involve carbon removal. You've got an engine with

200,000 miles on it. There's already evidence that some cylinders are pulling oil. You're about to put a nice, new/rebuilt cylinder head on it. The increased cylinder vacuum and pressure from the nice, tight cylinder head is going to finish-off the bottom end of your engine in a hurry. It is very common to do a head swap on an old engine like this and have it become an oil burner deluxe in very short order.

Scrap it or rebuild it, but you'll regret a halfway job.

On a fuel injected engine it doesn't seem like ATF would work too well because the intake is sideways. I heard about the water trick too but some said that it sometimes takes aluminum with the vaporized carbon (kinda like how a piston in a HG-leaking cylinder gets all pock marked). Then you have the problem of accidentally using too much and getting hydraulic lock.

Two of them I was able to simply wipe clean with B-12. The other two were pretty caked with hard carbon, so I used a gasket scraper (shaped like a screwdriver, with a wide flat tip). I tried to pick up the biggest pieces with masking tape and blow the smaller ones off with compressed air, then afterwards went around the top piston edge with a piece of paper to try to knock any bits that fell back onto the top. Then I turned the motor over a few times and when each piston was at BDC, I wiped off any carbon that was left/streaked on the cylinder wall. Now I can rotate the motor and there is no carbon.

Potentional problem: some B-12 got down the sides of the cylinder. I hope that doesn't ruin the ring seal, i.e. does a carbon film along the piston travel contribute to the seal? Because if there was one, the B-12 ate it.

Yup.

I can't find what I read, but it indicated that any horizontal force on the piston is bad for the ring seal, including that of scraping or rubbing carbon off on the top.

Thank you, this certainly sounded like a myth.

At the top, or anywhere on the cylinder? I asked in another post if cylinder carbon film contributes to the ring seal at all. I cleaned all the carbon off the very top where the piston would be at TDC, but only accidentally cleaned the wall of one cylinder.

Yes, I bought a can and saved myself several hours as well as effort which would have amounted to more scratches on the piston. I love this stuff!

I'm not an engine tech. All I know is that the credit Japanese short blocks are given for lasting so long tends to be for moly rings. And people in this NG have claimed that blowby after a top-end swap is rarely an issue with moly rings.

I'd love for people to debunk, disprove, etc this because it certainly sounds like handwaving or product promotion to me, but I don't have any reason to believe it to be false (yet).

Why would it become an oil burner? If anything, it would just increase blowby. If the excessive blowby ends up blowing oil into the intake, then the PCV system can be modified to accomodate it. I guess the biggest risk here is losing seals from the increased crankcase pressure if the PCV is too restrictive, but I don't see where oil burning necessarily comes into it unless the oil ring seal was disturbed.

The oil that fouled the cylinders may have come from the old valve guides or from the valve cover or HG leak dripping down through the spark plugs. A good dry/wet compression test should provide assurance that the rings were okay, at least as far as I know about testing rings.

The notion of ATF removing carbon is a myth anyhow.

There is no means by which B12 down the cylinder could "ruin" (or affect at all) the ring seal. The ring seal is dynamic, not static.

Er...no. Where do you get these imaginative ideas of how engines work?

Incorrect.

Yes, and I asked (in so many words) where you got that notion.

...or "superior" Japanese engineering, or "superior" Japanese alloys, or any of many other guesses and assumptions that have nothing to do with reality.

That's known as the "I've never seen it, therefore it doesn't exist so I'll post to Usenet authoritatively saying it doesn't exist" effect.

Er...let's try again:

The increased cylinder vacuum and pressure from the nice, tight cylinder head is going to finish-off the bottom end of your engine in a hurry. It is very common to do a head swap on an old engine like this and have it become an oil burner deluxe in very short order.

Which part do you not understand?

Blowby is when cylinder pressure overcomes the ring seal. Oil burning happens when cylinder vacuum overcomes the ring seal. Same phenomenon; the only difference is the direction of the unwanted flow. That's why engines that burn a lot of oil due to poor ring seal also tend to have a lot of blowby due to poor ring seal. It is relatively scarce to find the one without the other.

Er...no, it can't.

The same place such ideas are debunked, right here on rec.autos.tech. Google groups goes back a long way.

From some search I was doing on the subject. I'd prefer to throw it out there and have someone like yourself hammer on me for mentioning it than to be overlooking something important. Then the rebuttal is in the archives for posterity.

The part where the rings are necessarily weak, the ring seal is weak, or both. A properly maintained motor can't have a close-enough-to-new bottom end to accomodate a rebuilt head? What about just using a HG shim if it was a questionable situation?

Thanks for the explanation. I've seen more jap engines burning oil from valve guides than from oil rings, but it sounds like you have a broader background than I.

Well, this job really needs to stay manageable, so if the rings are doomed, then so be it. Cross that bridge when I come to it and all. Just means I'll be losing another weekend and head gasket if I'm not sick of the car by that time. I don't have enough experience to be trying to install new rings - no idea what hone to use, whether a rebore and/or oversize parts are necessary, or how to correctly break the new rings in, among other things I'm certainly overlooking.

Drill bigger hole in valve cover and intake, install bigger hose. Or use some fix-it product to alleviate the crankcase pressure that I can't remember the name of. I wouldn't recommend relying on such measures, but that doesn't mean that it can't be done when push comes to shove.

Bullshit Daniel.

The pint of ATF or water slowly poured into a hot running engine removes all the carbon and cleans the inside of the combustion chamber like new.

This method was used for years on city driven carb engines that developed a ping and run on (dieseling) from carbon build up as well as a treatment before a head gasket or valve job to clean everything for easy inspection and working conditions.

I have a photo of my engine just after I opened it up to do a head gasket. I cleaned it first and you can see some of the large chunks of carbon that didn't get all blown out because I just cleaned it and shut it down rather than the usual drive after.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

I just thought of something related to the use of water to remove carbon.

Isn't that the same reaction used long ago to create "producer gas" from coal? React steam with coal at very high temperature- converts carbon to carbon monoxide, and reduces some of the steam to elemental hydrogen.

To the first part, no the ring seal isn't "necessarily" weak. And even if it is getting weak, putting a fresh head on it won't do any damage to the engine (the phrase "finish off the bottom end" is one that I disagree with). It MAY lead to an increase in oil consumption, but it won't do damage. I've put fresh heads on a 150,000 mile engine, and had the oil consumption go from a quart/2000 miles to about a quart in 1500 miles. Said engine lived until 270,000 miles before the oil consumption and loss of compression got extreme, so it was well worth the investment in fresh heads.

How well maintained was your 150k engine? Obviously, this is exactly the result I would hope for - as opposed to the hellfire-and-damnation predictions - but we'll see how it looks once I get it started tomorrow (and hopefully didn't leave any tools inside the engine).

As far as cylinder wear goes, there is a visible ridge at the top of each cylinder if you angle the light at it, but I can't feel the ridge with my fingernail. That's as precise a measurement as I got before the new head went on.

Hopefully I'll get a couple more years without a bottom end or transmission failure before it's time to tear it down for rings and bearings. By that time it should be my second car, so the time crunch and learning curve would not be an issue (i.e. I could actually remove the motor at that time). And everything I've done to this point is now a known quantity.

Or someone might total my car. Do insurance companies adjust for new parts and maintenance? :-P