Britbike forum Forums Thread Like Summary - De-coking pistons

I thought that soaking in kerosene would soften the carbon enough to brush it off, but I've been soaking these pistons for weeks and the carbon still won't come off, even with a brass wire brush. Is there another solvent that would work better, or should I blast them? (We have a blaster at work with glass bead medium.)

Note: Not in a hurry; machinist is not available until May.

"Back in the day" the way to get rid of excessive carbon build up on piston tops was to do an "Italian decoke"
This involved taking the bike to the nearest longest straightest stretch of deserted road and running the bike flat out for as far and as long as you could.
Recommended!

If the engine is apart and won’t be assembled until spring, take all the alloy bits to a place that does “soda blasting”. Won’t harm the alloy, no media left behind, and removes carbon and oil with ease. Any soda residue can be removed with a little water on a rag.

Steve

^^^ i attest to the utility of the italian tuneup.

the black cloud in the rear view mirror is eminently satisfying.

I wasn't planning on de-coking my pistons but while my head was out for a valve job I dampened a couple rags with Marvel Mystery Oil, rubbed 'em around the cylinder walls then stuffed 'em in the cylinders on top of the pistons. When the head was ready to go back on I pulled the rags out and the carbon was flaking up. I was worried about some of the carbon getting down into the rings so I shop vac'd up what was loose then carefully scraped the rest of the carbon off with a wood stick- working from the outside in- picking up the loose bits with the shop vac then rubbing it down with a damp Mystery oil rag. In the end the pistons were so clean I could read the "20" (thousand over) on the top of the pistons. That was a thousand miles ago and no problems. Just my two cents.

I've found methylene chloride paint stripper to work well. Another remedy suggested 50:50 ATF:brake fluid, but paint stripper works better. Great for cylinder heads where you dont want to risking scratching the combustion chanber by using hard and sharp objects.

Ray

Don't be fooled by the term Vapour (Vapor) Blasting, It is exactly the same media as bead blasting but with water added.
If bead blasting will fukc up an engine vapour blasting will too.

The only way is to thoroughly wash in hot soapy water, poke through all holes, blow out with an air line, rinse and repeat another half a dozen times. Then when you are sure it is clean wash again

4" wire brush in a high speed drill works great for me , just on the crown, doesn't hurt it if you don't go mad.
I clamp my drill in a vice, hit the side button to keep it spinning and use like an improvised bench grinder, that way you can control the piston in your hands.
Bit of 500 wet n dry / WD40 after to polish it nicely.

My tuppence worth, Oxalic acid ( make your own from rhubarb leaves) softens piston crown carbon, finish with fine steel wool.