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szielinski · Joined: 13 Jul 2003 Posts: 94 Location: Canberra, Australia

Can someone with a bit of technical clout clear this up for me.
Does TEL lubricate exhaust valves or is it dibromo-ethane (or neither) ?
If TEL is, was this originally intended with the choice of TEL as an anti-knock additive or was it serendipity ?

rwahlgren · Joined: 15 Aug 2003 Posts: 324

Just an observation. If the melting point of TEL is anything like lead. It would not be present on any of the surfaces. (valve face or valve seat)
And with the added scavengers that are to rid the combustion chamber of it. I would doubt there is much left to do much lubricating. But what it does do very good. And have had it proven to me. It cools the combustion process. I do not remember the figures. But in a VW engine with a cylinder head temperature gauge, leaded gasoline burns much cooler than nonleaded does. (At least I think that is why the cylinder head temperatures are much lower with leaded gasoline. )And since an exhaust valve lives in such high temperatures anyway. I would say any amount of cooling is good. Thus reduces chemical and heat erosion of the seat and faces. It seems the cure for valve burning problems when going to nonleaded gasoline, was to use stainless steel type valves. Stainless steel would have a much higher resistance to chemical attack. It does not lubricate it self. It is going to feel the same affect when closing that the original valve would. And if it were a softer material, then it would deform much easier. So it most likely is more a cooling thing. Cam design is what will keep from hammering the valve to the seat. If you have ever seen a cam ring from an R-2800 you would see P & W Opens and closes those valves pretty gently. The ramps are pretty long. It would be nice to see a study on this topic. And if there is any such depositing of tel on the faces and seats. And if a nano film would really make a difference.

szielinski · Joined: 13 Jul 2003 Posts: 94 Location: Canberra, Australia

http://www.answers.com/topic/tetra-ethyl-lead

tmcdaid · Joined: 03 Feb 2004 Posts: 9

Lots of good info in the answers.com link. Thanks!

I recall from the leaded gas days that spark plugs would acquire white or gray deposits, presumably largely lead oxide which we don't see in engines using unleaded gas. I once pulled the cylinder heads from a leaded gas burning '68 Oldsmobile V-8 that had, it turned out, a warped intake valve. All the exhaust valves had deposits on them that looked similar to spark plug deposits. The bad intake valve, which was surely running hot because it was leaking, also had such deposits. The other intake valves were much cleaner looking. I gathered that heat, or maybe the flow of exhaust gas was part of the process of forming those deposits. I'd be very interested to know more about the actual deposition process.

I also recall that the big thing manufacturers talked about doing to make engines live with unleaded gas was to put in harder valve seat inserts.
_________________
Tim McDaid

hholzer · Joined: 13 Jul 2003 Posts: 4

Spend some time with torch in hand welding up auto body parts and sooner or later you run into something that has already been patched or filled with lead based solder or worse yet brazing rod. Getting these involved in your weld contaminates it and weakens it severely. The brass is much worse than the lead but not present in TEL so forget it for now.
It was often possible to "burn out" the lead sufficiently to permit completing a weld where it was essentially non structural but if not "burnt out" sufficiently even this weld would come "unstuck" or crack. This was a dead certain result where brass was involved.
I've read and can certainly believe that TEL simply contaminated or poisoned the potential high temp "hammer weld" that could occur between a hot valve and a hot "soft" seat and result in fragments of valve and/or seat being pulled out upon subsequent opening. Said pits and debris soon lead to burnt valves. The "hard" seats are apparently not weld compatible with valve material at the temps involved.

pshort · Posted: Sun Dec 31, 2006 20:40 Post subject:

I was just reading a bit from the RRHT book "Rolls-Royce Piston Aero-Engines - a Designer Remebers" by A A Rubbra. On page 130, when discussing the Eagle 22 sleeve valve engine and the reasons for using sleeve valves in this 3000+ hp design, he says

"It was well recognised that at long lives the exhaust valve seats in poppet valve engines suffered from the effects of highly leaded fuels".

rwahlgren · Joined: 15 Aug 2003 Posts: 324

Sites like answers.com can have information from average joes, passing on the normal stories or wivetails, just because information is obtained on some site on the internet, that does not mean it is fact, or the final answer. It would be better to hunt for information from engine manufactures, or SAE reports than look on the net.