30 vs 45 degree exhaust valves

[jforgo]

OK, my 1980RT's will be needing headwork. Guides are dying. Bike has 90K miles. I do not want pics such as in this recent post as a result:

http://www.bmwmoa.org/forum/showthread.php?t=33909

So, then, what is the deal with 11 341 257 837 45-degree exhaust valve vs the 30 degree 11 341 338 285 part?
or does Black Diamond have any advantages?

Thanks!

[PHMarvin]

Hi,
The later airheads used 30 degree valves. Your 1980 has 45 degree valves. I have read the 30 degree valves are harder on valve guides. Were it me, I would make sure the heads, as rebuilt, would have the latest unleaded 45 degree valve seats, new guides, and BMW (NOT Black Diamond) 45 degree valves. I know BMW valves are more expensive, but those are what I would use.

[brickrider]

Hi,
The later airheads used 30 degree valves. Your 1980 has 45 degree valves. I have read the 30 degree valves are harder on valve guides. Were it me, I would make sure the heads, as rebuilt, would have the latest unleaded 45 degree valve seats, new guides, and BMW (NOT Black Diamond) 45 degree valves. I know BMW valves are more expensive, but those are what I would use.

Ditto.

You stand only to lose time and money by trying to change the original engineering of this engine. Yup, the parts are pricey, but -- how many 29-year-old rice burners do you see being used as a primary motorcycle?

Ride Safely,
BrickRider

[jforgo]

What about the valve seats? Are there BMW unleaded valev seats?
Those pix on the post I referenced are not where I want to be.........

[PHMarvin]

Hi,
The valve seats (on the airheads) starting with the 1981 model year were for unleaded fuel. Unfortunately, BMW got the metallurgy wrong and the valve seats did not permit sufficient cooling of the valves. This was corrected. The '85-later model years did not exhibit the problem and, although BMW never admitted the error, the current valve seats (if you purchase them through the BMW parts system) are not the same as those in the '81-'84 airheads. The current ones do permit sufficient cooling and seem to work fine, if they are installed correctly. All the USA K-bikes had unleaded-compatible valve seats. The earliest K100 bikes when they were first sold ('83-'84) in Europe required leaded fuel, but the USA bikes don't have that problem.