Piston Carbon - Under Crown

[GeorgeP1111]

I'm refreshing my CA77 motor and have cleaned off the little bit of carbon that was on top of the pistons with a brass brush, but I do have carbon inside the piston under the crown as well. Is it necessary to remove this carbon (to prevent heat buildup maybe) and if so, is there any home recommendations for doing this? I am using a bio-degradable oil/grease solvent to clean all my parts, but it says that extended exposure to aluminum can interact with the aluminum so I am hesitant to just soak the pistons for a long period of time.

tnx
George

[48lesco]

I've used Kleanstrip Aircraft Paint Remover in the past. It softens up the carbon deposits in a few minutes to the point where you can use a toothbrush. Available at most auto parts stores. You have to wear good rubber gloves and have adequate ventilation - "Keep out of reach of children"

[cyclon36]

Maybe get a bottle of fuel system cleaner and brush it directly on? It's suppose to remove carbon deposits when in the fuel so I would imagine it would do wonders if applied directly. Never tried it before though. My go to cleaners in an engine are usually gas and/or carb cleaner.

[jensen]

Hi,

Are the pistons good enough to re-use ?
If not, it's a waist of time to clean them.

Check your pump for wear, normally the
oil from the big end keeps the piston crown clean.

How excessive is the carbon build up ?

Jensen

[GeorgeP1111]

48Lesco & cylon36 - Thanks for the carbon solvent suggestions.

Are the pistons good enough to re-use ?
Check your pump for wear, normally the oil from the big end keeps the piston crown clean.
How excessive is the carbon build up ?

-I checked the specs for my pistons in Bills's Dream Restore book and they are both Ok. There is some scoring (scratch)marks on the skirt but I cannot feel them with my fingernail.

-Yup, I intend to do this when I crack open the case after I get the top end done. What you mean "Big End"?

-It is not as much as I had on the top, but there is a coating of black when I look inside the piston. I don't know if it's excessive because I have nothing to compare it to, and the few pictures I have seen here were hard to tell (other than it's black) just how much carbon they had up there.

Because the underside of the crown looks like a tough place to clean out (other than chemical or ultrasonic cleaning maybe) I was wondering if it has to be carbon free there? I would think that the carbon would retain the heat and probably this is not a good thing, but maybe in the long run it's really no big deal.

Anyhow, just thought I'd ask.

tnx
George

[jensen]

Hi,

Big end is the bearing were the conrod meets the crank.
Small end is the bearing of the conrod were it meets the piston.

Jensen

[GeorgeP1111]

Big end is the bearing were the conrod meets the crank.

Ok, so the oil from the Big End is splashed (?) up to the piston keeping the crown underside/top (?) clean of carbon? Isn't the burnt on carbon a product of the oil and gas? I don't understand this.

Maybe this is a topic that should be taken up in another posting, but I have seen some folks say that carbon on the piston and in the head (valve chambers ) is due to a over rich fuel condition and others say it's due to poor oil rings/valve guides, or a combination of both.

I have refreshed a few auto engines in the past, but I just scraped off what ever carbon buildup there was on the top of the piston and never looked under it to see what there was there. These were "Shade Tree" refreshes, and when I was done there were no parts left over and the engines ran (I was Lucky). I'm on a real tight budget on this CA77 refresh so I'm trying to get by with what I can vs buying all new parts, but I'm also trying to learn as I go so I can make a wise decision on the parts I can clean and reuse and what I have to replace. I don't have the experience to know what is acceptable and what is not, so that is why I am and will be asking so many questions here.

tnx
George