Time to clean the pistons...

[Oyster]

I am reconditioning my '89 900 N/A and took the head off this weekend to find that the piston crowns are "caked" in carbon...no surprise. My question is, what is the best way to clean the piston caps without removing them from the engine? I do not want to cause any harm while cleaning it, so I figured a wire brush might not be the best solution.



Any and all advice, good preferably, is appreciated.

[woywitka]

correct me if i'm worng please, but i have heard you can run atf in an engine to clean off all the carbon deposits, run for a short time, like a small drive around the block, then drain it out and fill it with engine oil. could you not just rub a little atf on the tops becuase it has detergents in it and shouldn't harm anything as it is still oil. don't do this unless someone else knows but i have just heard about its engine cleaning ablilities if used right!, or couldn't you also clean it using gasoline, that prob wouldn't do much harm, and it is one of the best cleaner/car polishes i have ever come across!anothe ropinon before you listen, but i jsut wanted to bring it up!

[MSOEMiller]

I scraped the piston heads with a razor blade. It was very time consuming, but they cleaned up.

[john-w]

The reccomended thing to use so you won't damage the pistond is a piece of hardwood. You should not go right to the edges as you will loose the natural seal between the piston & bore.

[REDTURBO84]

I was told by a old timer not to clean them .I trust him as he had a garage for years. After the valve job has been done they will clean themselves. So I never do or will .Never had a problem .Pat

[Maverick1970]

If it were me, i would scrape the large chunks off with a razor blade, use a couple of cans of carb cleaner, and finish everything off by wiping it down with ATF.

[Earth Brown]

use a spray carb or brake cleaner it will clean them as clean as a whistle.

[KevinC]

Classic German approach is to feed finely crushed walnut shells into the inlet manifold at medium and high rpms. They scrub all the carbon out and then exit via the exhaust.

Has worked on everything from ME-109's to M Power BMWs. And the Green Party approves!

[Carl Hernandez]

ive used a product called seafoam to great sucsess, just soak the piston crowns in it and when the engine is started it will blow all the carbon out of the exhaust.

[ejenner]

I agree with Pat. Don't clean them.

[Maverick1970]

Originally Posted by KevinC

Classic German approach is to feed finely crushed walnut shells into the inlet manifold at medium and high rpms. They scrub all the carbon out and then exit via the exhaust.

Has worked on everything from ME-109's to M Power BMWs. And the Green Party approves!

I've heard of that before, but i always worry about what it does to the catalytic converter and the valve seats

Seafoam is supposed to work pretty well too.

I wouldn't worry about the tops of the pistons though, just clean the cylinder walls off and vacuum out any big chunks of carbon, the rest can be left alone.

[Matthew]

I'd never feed any debris into the inlet of a running engine, whether it's organic or not. The ATF suggestion sounds like madness!

I used a non-abrasive pad to clean the pistons tops when I did the headgasket on my T16 a couple of years ago. However, although I think gentle and careful cleaning is unlikely to do harm, I now know better and would leave them be.

[CoastCard]

Depends how bad they are. Carbon deposits do retain heat and as such can ultimately cause problems. Seafoam works and is known as the 'dealer decoke', just don't stand behind the exhaust when you start it!!
Chipping it off (very carefully) with a non metallic instrument would be my preferred route then, if you feel the need, a very light rub with extra fine wet and dry dampened with petrol will finish the job off.
A handy hint is to put grease around the piston top to seal the bore (at tdc). This will catch the bits and can be wiped off afterwards preventing contamination of the bore.

Although not having tried it, I agree that chucking walnut shells in is likely to do more harm than good!!

[trackside]

"I agree that chucking walnut shells in is likely to do more harm than good!!" - perhaps you should inform the german car industry as they obviously don't know what they are doing.
Another method is to let the engine draw water in to itself at moderate revs - this steam cleans the valves as well. Use a thin tube on one of the vac connections connected to a water bottle - and I mean thin as too much with hydrolock your engine.

[CoastCard]

If it is so good, start a business:

How about 'Nut Blast' - use your empty nuts to clean your engine!
I am surprised we haven't seen them nationwide.

[KevinC]

While walnut shells sound tasty, I'm going to use Seafoam on my own car, screw the Greens!

[Matthew]

Can you wait until Kodak this Saturday before you use the Seafoam? It would be interesting (nay, amusing ) to see the results.

[Jeremy]

Latest build quality of some brands imported to the states suggests just that.

--Jeremy

Originally Posted by trackside

perhaps you should inform the german car industry as they obviously don't know what they are doing.

[KevinC]

Originally Posted by Matthew

Can you wait until Kodak this Saturday before you use the Seafoam? It would be interesting (nay, amusing ) to see the results.

As long as there is enough breeze so the cloud is not with us all day...