R80G/S (4) 633CSi with 450K mile
'68 R60/2 '88 K100RS Special Edition
Phil Hawksley's site lists quite a few serial numbers of R100s that were 1985 and 1986 models. These are the months of build:
R100RT - 7/87 and 8/87 ('86 models) <--- Edit: These are '87 models; my bad ---
R100CS - 9/84 and 10/84 ('85 models)
R100TIC - 9/84 ('85 model)
R100 - 9/84 and 10/84 ('85 models)
R100RS - 9/84 thru 12/84 ('85 models)
R100RS Mono - 7/86 and 8/86 ('85 models)
R100RT Mono - 11/84 thru 2/85 ('85 models)
Last edited by 20774; 10-19-2008 at 03:37 PM.
The essense of the situation is that if/when your bike built in the 1980s needs frequent valve adjustments to maintain the gap it is time to take the heads off and examine them. You will either find deformed valve heads, or worn heads or seats. In either case you should replace the seats - even if they look good-as-new.
I have replaced the valve seats, guides, and valves in many air cooled BMW cylinder heads, /2 through /7. And never used the OE BMW parts unless insisted on. I use standard automotive hard seats, after market one piece valves, better quality, less money, and Ampco 45 valve guides. These parts have been stone relible over the years. I know the thread is over whitch years the probblem exsisted, that I can't say excatly, late 70's early 80's were the ones I saw most. Other air cooled motorcycles had the same issues when the lead was removed from fuel.
I'm a little confused. I thought the change-over for model years happened after the August "vacation". Thus a bike built in September 1985 would be a 1986 model. That's the case with my September 1977 built '78 R100/7. So then, why isn't a bike built in July or August 1987 not called a 1986 model???
September 1986 through August 1987 = 1987 model, not 1986 model
And just to confound things a bit - Voni's R1100RS was built in March of 1993, purchased in May of 1993 ("Beta Bike") and still titled as a 1994 model. You should have seen the puzzled folks at the DMV over that one.
The 1984s were indeed the "Last Edition" R100s.
R100GS appeared in 1987 and R100RT and R100RS reappeared in 1988.
There were no 1985-1987 RS or RT.
'12 R1200RT, '02 R1100S, '84 R80G/S
One way to get longer life out of your valves and seats from post '80 heads is to get rid of the ' air inpulse system'. This devise has caused as much damage as mismatched seats and valves. Having excess combustion happening at the exhaust port burns up the valves and seats at a much faster rate than normal. This devise does nothing to improve the performance, reliability,better fuel economy, or long life of the engine. It's a hindrance. I recommend a total removal of the whole system. It's like an iceberg, hidden; most of it inside the airbox. Probably 1/3 of the airbox is taken up by this hideous devise. It's an obstruction to the airflow, which is vital to your engine's performance. By now most airheads are do a topend anyway, some are on their 2nd or 3rd rebuild.With the head off it's a good time to remove the system. Even heads with mismatched seats/valves are usually good for 100,000 and believe me someone will pipe in they got 150,000 plus and their bikes are running better than ever. Good for you continue on.
Isn't there a lead additive that could be used in the pre 1980 models that could delay the onset of the vavle recession problem?
How does one go about finding a cylinder head rebuilder that has the good experience to do the valve work on the 80's model airheads. And how do I go about being sure that the best seats for the job are selected.
BMW does not sell the seats do they????
Anyone know of a competent machine shop in the southwest USA that is fully qualified to perform this upgrade?
I had Tom Cutter at Rubber Chicken Racing Garage do mine and I was very happy with the results. It's about $40 to ship them out.
FWIW I'd use someone who knows airheads as you read horror stories about the guys who used Bubba's machine shop.
Just my .02
Have a good one,