One of the virtues of owning and running Japanese machinery is the total assurance that anything built post 1970 will happily run unleaded.

Apparently not so BMW, it seems that my recently acquired early K100 VIN number 0004979 is only happy on a diet of lead. Do other owners use additives or have had their valve seats replaced. Any advice.

Cheers



fent

The well known BMW Guru Robert Fleischer says on his page about K's http://bmwmotorcycletech.info/K-hints.htm Note the cut and paste below is of his copyright information and I urge you to read that page because there is a HUGE (yes I am shouting) amount of information on that page and on the remainder of his site.
Regards,
K-BIKE

Gasoline's: A
little-known fact about Classic K bikes, is that very early ones were designed
for
LEADED fuels. If you do NOT use leaded fuels
in these
bikes, then do keep an eye on the valve
clearances more often
than usually done. BMW modified the bikes so they are
OK on UNleaded
fuels.

The modifications occurred at:

K75: no information, does not apply.

K100: at serial number 0007291

K100RT: at serial number 0024999

K100RS: at serial number 081107

Hi K-bike

Honestly no need to shout, aside from some residual heavy metal concert damage, my hearing is fairly adequate

As new to the world of BMW this was simply an issue I hadn't anticipated and hence my reference to Japanese machinery with which I am more familiar.

Despite having read a lot of articles about buying a K100 and what to look for, I recall no mentions, in anything I read, on the requirement for leaded petrol on early bikes.

The previous owner of my 84 K100 stated that in 10 years and 20K he never used leaded petrol and that in the regular valve clearance checks he states he undertook, was never required to change any shims. Its possible the head has been changed for a later one but not within the knowledge of the PO or file of receipts that came with the bike.

I don't have a significant issue with running an additive, but was primarily after some real world experiences from out there owners rather than information which confirms my biks requirement to run leaded petrol. Its likely I may seek a later head at some point but only after I have undertaken a full engine health check.

Cheers

Fent

210,000 miles on a very early production K100RS with European cams on a diet of exclusively unleaded gas, even when touring in Mexico and Europe, and no problems. Any claim that any year of the K bike needs leaded fuel is pure bovine excrement (kuh scheisse?). This engine would routinely go in excess of 50K miles before any valve would need adjusting. I retired it because the rings were finally starting to go and compression was down to around 140 psi per hole.
The early Ks with their three row radiators and fairly rich state of tune do not have problems with valves and valve seats. None whatsoever. These are the most durable of the Ks. Where you see problems are the later four valve bikes, twins and Ks with lean tuning and very hot combustion for emissions. Those start to pit the seating face of the valves. There can also be hot spots in the Nikasil near the exhaust valves that you do not find in the earlier two valve bikes that have so much more coolant in the head and a big three row radiator.

Hi Fent,

I've been running my '84 RS on un-leaded without any additive for the last 27 years and no problems. If ever I do have a problem, then I'll consider changing the head, but until then I'll just keep riding.

Paul.

Hi TM and SCP, thanks for that input, it kind of justifies my 'no need to worry.........just yet' approach that I hoped would result from this purchase. As I say I've yet to get the bike into my garage/workshop/refuge after which Ive got some time to give it a full stem to stern checkout before the first touring event of the year in May.

Cheers

Fent

I have run my 1984 K100RT on unleaded fuel since I have owned the bike and never had any problems. I did a 4500 mile Europe tour 3 years ago on this lovely old bike and she has never really let me down. I did have to replace the fuel pump and fuel pressure regulator last year (search my other posts) but other than that I have had no major issues (107,000 miles on the clock now and running sweetly)

when i rebuilt the engine on my 1986 k100, i noticed that the exhaust ports have a groove machined into them just upstream of the valve seat. this denotes a hardened seat for unleaded fuel. I then managed to ruin this head when opening up the ports, by cutting through into the water jacket, and had to use a spare, ungrooved head, made in 1984. i'm not too concerned about this, as i read that the valve seat regression problem only affects iron heads,the theory being that during combustion, microscopic particles of iron are shed from the combustion chamber and stick to the almost red hot exhaust valve seat. the valve then shuts and the 2 surfaces become slightly welded together. valve then opens and the weld is torn off, taking some valve seat with it. This does not happen with an alloy head as the metals do'nt weld. Have done 6,000 miles so far on this engine. will report any future unusual shimming !.