I understand the basics of lead as a lubricant. and zinc. my question is where do these metals end up as far as in the engine. I can t believe that they are all compounded and released thru the combustion process and thru oil changes. it seems to me that they must leave deposits in the engine. no?
Lead would leave some deposits on all the cooler surfaces in the combustion chamber, including valve seats, stems and spark plugs.
Spark plug life increased significantly when lead was left out.
Most of the lead went out of the exhaust, coating the exhaust system and into the environment as super fine particles.
These lead deposits were the basis for the old ‘rule of thumb’ that the engine wasn’t running too rich if the inside of the exhaust pipe outlet was near-white. Those near white deposits were the lead combustion products. Used to be, because lead oxide was so white it was used in paint (of course) but also in makeup. NOT good…
When metallic compounds (Zinc, Lead) were used as motor oil additives to provide extreme pressure protection, it was discovered they could slowly poison and destroy catalytic converters…Engines were modified and these compounds were removed from most automotive motor oil…To answer your question, they are drained out with the oil…In engines that burn considerable amounts of oil, these compounds tend to collect on the exhaust valve stems and ports and slowly strangle the engine…
A lot of those deposits stuck to the piston tops and valve heads. Tear apart an old engine that has run on leaded gas for 100k miles and compare it to a disassembled 100k miles unleaded gas engine. There’s a night and day difference in appearance and also a night and day difference in the amount of time needed to clean pistons and cylinder heads.
how would you go about cleaning the lead?
Cleaning piston tops, valves, combustion chambers, and ports was usually done by hand with a scraper and wire wheels. Bead blasting deposits off was also done; all depending.
There is an aerosol gasket remover that can be sprayed on and that will soften the deposits to some extent if left to soak for a while. Yes, it can be time consuming.
I did the water injection thing a few times back in the day. Not something I’d suggest for the novice or risk averse but it was pretty incredible how effective it was considering the alternative effort involved in mechanical removal…
“Back In The Day” car engines usually needed an overhaul at 70 to 100K miles…Overhauling car engines was an economically sound thing to do…But today, the engine is one of the longest-lasting parts of the car…Something else sends them to the bone-yard before the engine expires…Rebuilding today’s engines with the high costs and uncertain results is not done much anymore…
Lead and zinc were never the cause of heavy combustion chamber deposits…The other additives in motor oil, the detergents, dispersants and VIS, when burned, would leave major hard, crusty deposits…Todays oils are formulated to greatly reduce or eliminate these deposits…
water injection?
Yes, you carefully, slowly pour a very thin stream of water down the carb while the engine is running (not at idle), it converts to steam in the combustion chamber and removes deposits. Did I mention carefully? There may be equipment to ‘inject’ it, I haven’t seen that.
There are water/methanol injection systems being sold as intake air charge coolers. Not really a “cleaning” tool. Spray bottle into the intake while running should work pretty well.
Just any FYI experience. I had a failed head gasket that leaked coolant into the cylinder. When I pulled the head, the piston top on the leaking cylinder was very clean. Noticeably cleaner than the other 3.
The key to cleaning with water is that liquid water needs to hit the dirty surfaces.
The water flashes to steam with explosive force, ripping away the deposits.
With the charge cooling injection the water has vaporized by the time it reaches the combustion chamber.
That’s an age old verification method for a coolant breach. Pull plugs, if any look like they’ve been sandblasted clean and white, it doesn’t bode well.
Yes Caddyman, we’re talking about vintage problems by and large. I’ve never found any of my more modern engines with lead deposits in them 
or high volumes of carbonization for that matter…
I had an old lawn mower back in the late 60’s that was getting hard to start almost pulling my arm off…I pulled the head and nothing but caked white stuff on the piston and on the valves. This was run on leaded fuel as non leaded did not exist…I scraped all this stuff off the piston, then used sandpaper to clean up the valves and the seats, carefully not to damage anything, and had everything down to metal. I put the head back on using the same gasket and gave it 2 pulls and it started…After this it always started on the 1st or 2nd pull…I know it was a bad seal with the valves due to this “lead residue” on them…Engine seemed to have twice the power now. I used it for another 4 or 5 years after that, until I hit something and bent the crank.
While water, and anti-freeze, can certainly remove some deposits in the combustion chamber it can also cause a few problems.
One is the possibility of hydro-lock and the other is that water/anti-freeze can be very corrosive in the combustion process which can lead to piston and/or valve failures.
I rigged a water injection system on my old air-cooled VW. It involved a 2 gallon reservoir made of thick plastic, vacuum line, and a cheap brass valve. I teed the vacuum line to a manifold source and made sure it ran to the bottom of the tank. The other trick was to adjust the valve to prevent too much water from getting sucked in that it would choke out the engine. I was refilling that tank every other day, but the engine ran much better at highway speeds.