I have to do a head gasket repair on my 2001 4 cyl accord ex. I Notice carbon deposits on the top of the pistons while doing a piston soak in the hopes of slowing my oil consumption. Is there any way I can clean the carbon off the piston top and piston rings while I have the head off?

 

what's a "piston soak" and why do you think it will help with oil consumption? how many miles on the engine? you may want to get a valve job done while you have the head off.

go to your local chebby dealer and get a can of "goodwrench top engine cleaner", pour that in the cylinders and it will loosen up all the carbon so you can clean the tops of the pistons. make sure you change the oil after you get it all back together.

 

Two comments:

1. Carbon on the top of the piston (or the lack thereof) will not affect oil consumption one way or another.
2. The carbon left behind by modern fuel burned in modern engines is rather thin and, for all intents and purposes, benign. Said another way, there will be no benefit to cleaning up the tops of the pistons, and if you do, they'll just carbon right back up.

 

Do the soak with the head off. MMO or whatever you're using should loosen the carbon on the top of the pistons enough that it can be wiped away with a rag. For the piston rings, since you can't get to them with just the head off, the longer the soak the better; two or three days min, a week is even better. Just turn the crank to reposition the pistons every day and keep the cylinders filled with fluid.

 

1. you are correct shipo
2. not quite. carboned up pistons cause an increase in compression and the more likely there will be detonation (especially if the EGR system is marginal). in addition, higher cylinder pressures will increase the level of NOX produced and may cause emissions failure (if applicable to the state he lives in). carbon is also like a sponge for fuel, it loves to absorb fuel and will decrease engine performance and increase the amount of fuel it takes to do the same work with a clean engine (reduced fuel economy).

 

My problem is the guy that owned it before me clearly neglected it with long OCI and cheap oil so there is carbon caked on the pistons. The compression is fine and the car drives ok but there is excessive oil consumption burning a quart every 500-600 miles. Being that compression is good and i can see compression on the top of the piston, I came to the conclusion that it must be carbed up oil control rings.

 

I really wouldn't bet the ranch on that.

Have you ruled out the valve guides? I'd be far more inclined to suspect them than the piston rings.

As for the carbon, changing the oil really won't affect that, ALL engines develop deposits on the piston crowns, combustion chamber roof and valve faces; it's normal and removing it won't help anything.

 

The carbon build up is excessive for a car with only 105000 miles. Right after i bought the car i did an oil change and it looked like it hadn't been done in 20,000 miles. I pretty sure it was neglected. Also I have no smoke at start up or idle so i don't believe it valve stems.

 

A couple of easy ways to tell the difference. Bad valve guide seals will usually result in a puff of blue smoke out of the exhaust after the car sits overnight whereas rings won't. Bad rings will usually show blue smoke while accelerating at higher speeds whereas valve guides won't. The biggest clue in my experience: Coked-up rings caused the engine oil to get very dirty, very soon after an oil change. By-products of combustion getting past the rings. The MMO soaks halved the consumption from 1qt/400 miles to 1qt/800 miles. Not great but not bad. Use a turkey baster to save the MMO (or whatever you're using) when turning the crank with the head off.

 

The increase in compression you are talking about is only from a static position, but what about total swept volume? That would decrease your compression.