Exhaust Valves
 

I decided to replace the valve springs on my 6x-4 heads to the comp cams recommended 988-16 springs. While I am doing this, I figured I might as well clean the carbon off of the chambers/valves and lap the valves, replace the seals, etc.

I noticed that the exhaust valves have some sort of ceramic material on their face that seems to be eroding off. Is these valves ok to re-use or do I need to buy new ones?

One piece stainless valves are never a bad idea. A lot of that white buildup will come off with a wire wheel.

+1 on wire wheel. I always guessed that stuff to be a cooked on lead compound? My mass spectrum analyzer is in the shop...;)

The ceramic stuff is call carbon. A wire brush will work, but I prefer bead blasting followed by polishing the head and stem of the valve. Since you've already have every thing apart, it would be a good time to check your valve stem clearances in the valve guides and touch up the valve seats and valve faces. This carbon buildup actually shows your engine is pretty much "on" as far as mixture setting goes. Tan is good; black and white aren't.

I also prefer to use the media blaster. Not only does a much better job, but a wire brush exposes you to all the dust flying off. Chances are good that the deeper layers are from leaded gas deposits.

Agree with others, but, will say, it's mostly additives in the gas, not lead.

Ways to combat the build up? There are, but, IMO, why bother. But just to say, occasional top end cleaning (seafoam, atf/water, meth/water injection, etc) is an option.

You could have the exhaust valves coated, there are coatings that combat the build up. But it's costly, time consuming, and doesn't last forever. I believe a number of new cars actually now come from the factory with coated valves.

I forget now, but it's either wider or narrower LSAs actually help with less build up on the exhaust valve (exhaust heat actually), I think wider, as well as more split in duration. Cam profiles can be used to help cool exhaust, know some turbo guys lean in that direction for turbo builds. Because of the back pressure on a turbo engine, they suffer from super heated exhaust valves.

Ok thanks. I just assumed it was supposed to be there because it was only on the exhaust valves and was underneath all of the carbon build up. I'll get them cleaned up.


Funny thing is that I soaked the valves in seafoam and nothing came off at all. Then I used brake cleaner and a small amount came off. the Wire wheel is about the only thing that works. I'm guessing those top end cleaners would never put a dent on something that is already caked on there. Especially the ones that just say to add it to the tank...

Anyway, thanks for everyone's help. I will feel better knowing that stuff is off of there.

I guess it would be a tight call on the Tetraethyllead lead (TEL). It's phase out of gasoline began sometime in the mid 1970's, and that's about the same time the 6X heads were introduced. So the initial layers on the valves might or might not contain THL. Most of the race gas is still leaded, although California has banned it.

Still nasty stuff, and best not to breath it.

Good points Mick.

Carbon and other deposits are tough to get off without being aggressive. I know what used to work for me, CRC gasket remover. Spray it on, let it set for about 15 or more mins, and wipe off. Sometimes took 2 applications, but it works.

Sea Foam really only works when the engine is running, just like atf/water trickled down the carb. Top End cleaner, same thing.

Ok, are these OE 2-piece valves, or stainless replacement ones? How are the guides? Have these been rebuilt within a reasonable amount of time/miles?

It may just be time to go through them and have them cleaned up. My one local machine shop charges $150 labor for disassembly, tank, check, valve job, and re-assembly. Add valves and seals, you would have fresh heads. if the guides are sloppy, it's probably another 150. Just to give you an idea. But you would be sure they're right.

Sounds like your doing a cam change, so now would be the time to do it. If the bottom end isn't high mile or is still in good operating condition, a fresh top end gives it a new life. I've had engines go into the 200k range with top end rebuilds.

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And the scope creep begins. :attention

Keep your budget and true intentions at the forefront.

With your time, materials, and proper tools ...a professional valve job seems the logical route to me too.

That white stuff on the Exhaust valves has all the traits of a ceramic oxide & occurs with Stainless & Stock Exhaust valves, and unleaded gasoline.

HIS, we used to remove the same stuff from the exhaust valves and ports on aircraft engines. 100LL is definitely NOT unleaded...

So the Exhaust valve ceramics from 100LL looks like 87 Octane unleaded?

I have scraped 100LL from the 2-Stroke exhaust PORTS; the LL residues appear to have more nodular texture (like 80 grit) with tans and browns, maybe reds & grays.

Whereas the 87 Octane ceramins is a uniform smooth (like 600 grit) having white with minor tans blended across.

To be honest, EVERY exhaust valve I've seen that burned 87 Unleaded had no or little buildup on them. You're leaving out one factor when comparing a 2 stroke exhaust port on 100LL to a 4 stroke port: oil consumption. I've cleaned hundreds of Lycoming, TCM, Franklin, P & W, Wright, Warner and Ranger cylinders with nearly identical buildups of this material. NONE were 2 stroke; all were air cooled and burned leaded fuel(most 100LL).