leaded fuel

[schrader7032]

Marshall -

I'd suggest in the short term you give up the use of lead. It's actually illegal to use aviation gas for road use. If you're doing something like that, it's really better to do it in small doses per tank, rather than to put it all in there at once, IMO. And the lead is not for the pistons but for the valve seats.

Other options could be use of lead substitutes. I've used a product called ValvTect VT-6000 in my /7 for a number of years. Not sure if it's really doing anything, but I do have about 93K miles on the bike and the valve clearances are remaining steady. I probably need a top end overhaul anyway, so the issue is probably moot. I will convert to unleaded internals when I do the top end.

With about 28K miles, you are beginning to get to a point where you should consider having the slingers cleaned, if it hasn't been done already. This involves complete disassembly of the engine. The crankshaft has to come out of the bike. Unless you're mechanically inclined and know how to read things inside the engine, it's best to have a qualified mechanic do this job.

While you're at it, you could install new valve seats which are compatible with unleaded gas. Probably the intake valves will be fine, but the exhaust valves will need to be replaced at some point. New valve guides might be in order...maybe even new valves. This is where the experienced mechanic can make recommendations.

But since you will need to have the slingers cleaned in the next 5-10K miles...maybe 15K..., just ride it, use pump gas (probably the high octane stuff), watch the valve clearances, and get some peace of mind with a slinger cleaning/top end overhaul down the road.

My 0.02...

Kurt in S.A.

[Allan.Atherton]

The /2s do not need lead, or a mechanical valve conversion to use unleaded gas. Valve seat recession due to lack of lead is not a problem these days. It might be if the old valve seats were subjected to long periods of high rpms as in extended high speeds or racing, but the seats are fine in the use that they get today.

There were a few years in the early 1980s when the airheads suffered fast valve seat recession, evidently due to introduction of air injection which leaned the mix and cause more heat for the seat material. Those bikes had air tubes leading into their intakes.

Valve seat recession occurs in two ways. One way is when the valve lip pulls molecules of metal off the valve seats, causing pits which interfer with good valve sealing and hence compression.

The other way is when these pits are remedied by lapping the valves, which is rotating the valves against the seats with an abrasive compound, making a perfectly smooth and tight seal. Each time this is done, some material is lost from the seat and the seating surface recesses back up into the head. Eventually so little seat can remain that this ring of hard metal can just fall out of the soft aluminum head, causing damage.

Lead deposits on the seats acted as a lube and slowed this process, but also built up on piston crowns and spark plugs. Recession is not a problem with the use we give the bikes these days, so you don't need to do use lead or substitutes. Substitutes are undesirable because they cause heavy deposits. If you have access to leaded gas, it takes very little of it to lube the seats -- far, far less than to raise the octane. Just a pint in the tank every few tankfuls will do the job.

If and when you need the heads overhauled, you can have a so-called "unleaded conversion" done. There is no question that the AMPCO-45 bronze guides in these conversions are good, and everybody uses that material for all guides. The so-called unleaded valve seats may be mis-nomer, as one cannot buy any other kind these days. And finally, the Black Diamond stainless steel valves popular in these conversions are controversial. They are stainless steel, blackened by hardening, descendants of valves developed by Kibblewhite for racing decades ago. Some say stainless steel is not a good valve material, that BMW's own plain steel valves are better. And in an Iron Butt vintage bike that Bench Mark Works built for a customer, a Black Diamond valve broke after two days. The main value of Black Diamond valves may be that they cost 1/2 that of BMW valves. I have had heads on my bikes done both with Black Diamond and BMW valves, and all I can say is the BDs were cheaper but I hope they don't break.

[MarshallF]

Kurt and Allan, thanks for your replies. I knew about the slingers and had them cleaned at a dealership last year but probably wouldn't have sprung for new valve seats at the time given the $$. It's worse than taking the cats to the vet! You've given me a ton of useful information and I really appreciate knowing what's behind "you should or shouldn't do this". Glad to know that I won't be screwing up the environment or the bike.

Hoping for one more weekend day that's warm enough and dry enough before the salt gets spread.
Thanks, again. Marshall

[schrader7032]

There were a few years in the early 1980s when the airheads suffered fast valve seat recession, evidently due to introduction of air injection which leaned the mix and cause more heat for the seat material. Those bikes had air tubes leading into their intakes.


Allan -

It's been written quite a bit about the '81-'84 bikes that had the problems. It wasn't valve seat recession...you gave a good description of how bits and pieces of a seat can become dislodged, eventually reducing the metal in the seat. However, for these first bikes in the '80s, BMW opted for a metallurgy in the seats that was supposed to help with the transition to unleaded fuel. They got the metallurgy wrong and it didn't conduct heat from the valve back into the head. In addition, some of the bikes had bad grind angles/dimensions on the seats resulting in reduced contact between seat and valve face. The result was retention of heat in the valve itself. Over time, the edge of the valve tuliped and the valve dropped into the seat. Same result...loss of valve clearance. This was deemed valve face plastic deformation, not valve seat recession. Beginning with the 1985 models, BMW finally got the parts right.

It is my understanding that bikes before 1981 will eventually have a top end problem. As you indicate, it depends on how the bike is treated and the sustained temps that the parts see.

Face it, the engine can't last forever and parts will have to be replaced. The great thing about these bikes is that is easy enough to do and there are good parts for replacement. Not many marques can claim that.

Kurt in S.A.

[Allan.Atherton]

[... the '81-'84 bikes that had the problems... BMW opted for a metallurgy in the seats that was supposed to help with the transition to unleaded fuel. They got the metallurgy wrong and it didn't conduct heat from the valve back into the head. In addition, some of the bikes had bad grind angles/dimensions on the seats resulting in reduced contact between seat and valve face. The result was retention of heat in the valve itself. Over time, the edge of the valve tuliped and the valve dropped into the seat. Same result...loss of valve clearance. This was deemed valve face plastic deformation, not valve seat recession. Beginning with the 1985 models, BMW finally got the parts right....
Good to know - I had not heard of the plastic deformation and tuliping.

[VBMWMO]

I bought my R69/R69S from a guy last summer (07) who said that every fall, before he put the bike down for the winter, he would run a tank of AV fuel through it so that he could get some lead back on the pistons. Last fall, I met him at his hanger and he generously provided me with a tankful, but I didn't get the feeling that he was interested in doing this again. So, should I be seeking out a local airport to get a few gal. of AV or finding an additive to dump in the tank with the premium unleaded that's in there? Or should I do nothing?
By its serial #, the engine is a 1960 R69. The frame, by it's serial number, is an R69S (with telescoping forks). The odometer's around 28K.

Thanks for your help
Marshall