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MG TD TF 1500 - Decoking pistons

Help, Has anyone come up with a means of removing carbon from the top of pistons without scratching the surface. I have tried a small area with a scraper but it tends to leave small marks on the surface. The scraper has a clean edge but the carbon particles are leaving marks on the piston. Any suggestions would be appreciated.
George TD4224
G. L. Raham

Varsol? Heavy Duty Oven Cleaner?
gblawson (gordon)- TD#27667

Hi George,

You've raised a classic query - I assume you want to do this with pistons still in the block. I always use the end of an old 6" metal rule but as you say small scratches result. These can then be cleaned up with fine steel wool and I wouldn't be too worried about them. If you ever have to take a head of soon after a decoke you'll be amazed how much carbon has gone back on no matter how polished the piston was!

The trouble is much of the 'assumed wisdom' goes back to a time when a decoke was done every few thousand miles, not needed with today's fuels and oils. You'll even see nonsense like using a sharpened flat stick of solder! - try it and you'll see what I mean! Certain oils like Redex can help if left on overnight, as can carbon removal chemicals but it's probably better to stick to carefull scraping in my opinion.

Cheers, John.

J.C Mitchell

Have any of you tried the process of metered water injection? I've not tried it but have seen it done and it really cleans the chambers right up. Just need to keep the engine running at a high idle and slowly meter water into the carb. I have a Triumph motorcycle I'm going to try this on. It is recommended that you do an oil change after this is finished.

I've not done a lot of research on it yet so I don't know how long you have to do it. My understanding is to meter the water in with the engine on high idle and keep feeding it in to the point the engine falters but does not die. You will see quite the cloud coming from the exhaust as it does it's work.

In the states I hear either water or a product called Sea Foam works.
l rutt

Carbon isn't nearly as problem on the crown of a piston as it is in the rings, where it can cause them to stick, rock and snap. This is much more prevelent on two cycle engines. John is right, it is much less of a problem with modern fuels. On two cycle engines we run a decarbon process using Seafoam, which is essentinally naptha in a can. Seafoam also makes a good fuel stabilizer, and can be added safely to the fuel tank in a boat, car, or yard appliance to prevent excessive carbon buildup.

Steam cleaning is good, I've seen it a few times when the head gasket on a boat has failed and water fromt he jacket migrates into the combustion area. It gets things very clean! Of course the resulting loss of compression due to the head gasket failure is noticible, so I tend to repair that straight away! One of the major clues of a bad head gasket is a shiny spark plug.

My take would be to run the engine with some Seafoam and not to worry about the scraping and stuff falling in the engine as a result. If you have actual pinging from hot spots on the piston igniting the fuel mix, that's different. But as John said, with our fuels and the relatively low compression of even a modified head, no problems.

Dave Braun

I'll second Dave's advice on Seafoam, a great product. I had a sticking valce and ran 2 cans through the gas and no more sticking valve.
R Dougherty

Thank you, Gordon,John,Irutt,Dave & R. Dougherty, As I have the pistons on my workbench I will not be in a position to run the motor. My apology for not mentioning this in my thread. I thank you one and all for your responses. I follow this forum every day and am crusing through the archives in absolute amazment at the help that is available to those of us that enjoy these wonderful cars. I hope that in the future I will be able to help as I have helped. Thank you all again,
George TD4224
G. L. Raham

I use a very soft wire brush on a drill motor. With the pistons out, the oven cleaner may be the easiest.


I used a homemade hardwood scraper on the pistons in situ. Would work on the bench too?
Willem van der Veer

This thread was discussed between 28/01/2008 and 30/01/2008

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