What's this hard, white crap on my exhaust valve?

[stinkwheel]

Pulled the cylinder head off the Enfield Bullet yesterday to see if I can see why it's burning so much oil. (30 minute job)

There is a plaque of hard, white material in the middle of the exhaust valve. It looks a bit like plaster but it's hard as nails, I had to literally chisel it off.

I have no idea what it is. Could it be sulphates or something from the unleaded petrol?

That valve was polished (like mirror polished on a buffer) 10k miles ago. The soot I can explain, it's venting more oil into the environment than BP. The white crap, I have no idea about.
https://i48.photobucket.com/albums/f216/stinkwheel/enfield%20head%20231010/head.png
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Blue_SV650S]

Nothing unusual here ... its all quite normal .... you have already said its burning oil ... move along!
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The purpose of life is to fight maturity.

[LongJohn22]

Carbon deposit from the burnt oil passing out of the engine through the exhaust port. It's white from the extreme temperature of the combustion process.

In the sixties when I did my apprenticeship, it was quite common to remove the head every 20-30 thousand miles to carry out a "de-coke", and that is the coke that was being referred to. valves were also lapped in, new head gasket fitted, job done. Heads were generally cast iron in those days so they were seldom skimmed for no good reason. The job took around 5-6 hours graft. Hope this helps.

[tatters]

Had the same white deposites on my R100GSPD after 50,000 miles of the crank case breather venting oil into the air box.
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[el_oso]

i believe it is baked on carbon. i've found that it dissolves easily with caustic soda/oven cleaner/strong alkali

p.s. men in black is an awesome film
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Duke 390
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Car: Jeep Wrangler 4.0L

[Teflon-Mike]

I'd SO like to say that its calcium deposits from the tap water used in the cooling jacket, denoting water getting into the cylinder due to head-gasket failure..... but I think that jest would last about as long as it took for you to say 'But its air-cooled'... occassionally works though!

Yup. Tis normal depositation, and entirely usual, especially if the bikes been burning oil.
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[stinkwheel]

Cheers guys.

The more observant of you may have noticed where the head gasket appears to have failed to seal properly between the cylinder and the exhaust pushrod tunnel.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Walloper]

It's a carbon/combustion deposit which, contrary to what's been said, doesn't dissolve as easily in Caustic Soda.
It needs scraping, chipping or sand blasting/glass beading to remove it. (Or several dunks in the bath)
It is/can be also a cause of pre-ignition as a 'hotspot'. Stores the heat of combustion and ignites next charge early.
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W-ireless A-rtificial L-ifeform L-imited to O-bservation P-eacekeeping and E-fficient R-epair

[weasley]

I'll give the chemistry lesson!

It is not 'coke', but 'ash'. Coke is carbon-based deposits, like soot and so on - these will burn off if hot enough. However there are metallic compounds in engine oil that, when burnt, form oxides (eg calcium oxide, magnesium oxide, zinc oxide) - these will never burn off and are, as you have discovered, quite hard to remove. An acidic substance may help remove them, but then this could attack your valve too, so maybe not!

[Chalky.]

Remember that time when you got "close" to your bike?

The aftermath




/\ what they said.

[stinkwheel]

It's off ok. I chiselled the worst of it off with an old screwdriver then scraped the remnants away with a 2p.

I was just wondering if it was indicative of some other problem other than the oil leak, which hopefully a different type of head gasket and some new, all-singing, all-dancing flange sealant should fix.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[tahrey]

Used wire wool and "cream cleaner" bathroom enamel polish to shift the most tenacious bits of black & white clag off my pistons and cylinder head when I overhauled the car some years back. Fairy and a nylon brush got rid of the worst, and caustic oven cleaner the rest, but what was left just needed abrasives and elbow grease...