R80 RT purchase help

I'm shopping and found 2 R80 RT Airheads near me. A 1983 low miles excellent shape and a 1985 50,000 miles good shape with 1,000 cc heads, cyclinders, etc (previus post). Same price. Push me in one direction, or not. I have a 77 RS and a Oilhead RT so this is just a "I need another Airhead" purchase. Sorry if I have already posted this but I didn't find it when searching this forum. Mono vs Twin shock, valve recession vs circlip, tube vs tubeless tires.....i know Airheads reasonably well I'm mostly curious what the herd intuits. Thanks

I think I'd favor the '83 model just because it is unmolested. I'm not sure of the true benefits of putting 1000cc stuff on the R80...sounds nice but not sure it lives up to the hype.

84 versus 85

Having had a chance to ride both the 84 R80RT and the 85 side by side in 85, My take is the 85 is a bit quicker handling the 84 more stable due to the smaller front wheel of the 85. And to be honest, it was not a huge difference in handling. Other than that, the big difference is a lot of of the electrical connections on the 84 and older bikes was moved out of the headlight shell to under the gas tank. This makes things a bit easier to work on but again not. by a great amount.

I am sorry I don't remember if the 85 bikes had tubeless rims or not. The 84 calls for tube type tires.

After I compared the bikes and rode them, I ended up with the 84. I liked the styling better and the tiny bit more stability when cruising, I don't live in an area with a lot of twisty turns roads so quicker handling is not high on my list of things to have.

I also wondered about some of the electrical stuff moved out of the shell to under the tank, and how would it do in the exposed area under the tank. Inside the headlight shell, it was dry.

As far as the 1000cc jugs on a R80RT, I have been thinking of doing the same thing myself. I haven't yet because one or two people who I know did have not yet given me their opinion as to the pros and cons. You have to understand the final gearing for the 80 engine makes it rev about 1K more RPM at a given speed. This was done to make up a bit for the HP difference between the 1000 and 800 engines. I have no first hand knowledge of how the engine will perform with the engine modifications. Theory has it, a 1000cc bike with the 800cc final drive would be quick for acceleration than a stock 1000cc bike, but, I don't know how the power band will change with the jump from 1000 to 800.

To be honest, if you want a 1000cc airhead, buy a 1000cc airhead. Unless you have the money to experiment with the 800cc conversion, it may not be worth it or may be a headache. Of course, as long as the conversion was done properly, using one of the kits available with the stock 800cc heads, the bike can always be changed back to 800cc from the 1000cc. St.

Go with the 83 as it sounds like a good bike and is original. You may have to do some work on the heads ( or maybe that has already been done ). Yes there are some benefits to the newer model but once you start down the path of modifying a stock bike, adding heads etc, it tends to go down in value and you can be getting yourself into a can of worms. Not all additions are well done and they alone can cause you some issues.

So I vote for the 83 R80.

I own an 83 R80 and my FIL owned an 85 R80RT. I would opt for the 85 bike. The 81-84 airheads had very deficient front forks along with valve deformation issues. The 85 models fixed both of those issues and added a rear suspension upgrade as well. 50k is not a lot of miles and if the 1000cc conversion was done properly the only real downside comes in a slight increase in engine vibration at some speeds.

Or, just buy the red one...


Best,
DeVern

If you're going to fit R100 cylinders to an R80, you should for sure fit the rear drive ratio from an R100.

Went for a ride once where two of us were on R100RS and one was on an R80RT ... the R80 was out of gas first. This is because the engine was spinning nearly 1000 rpm faster than the R100s at any and all road speeds. The R80 engine is pretty smooth at any rpm, the R100 less so. My R1100S has an even rougher engine and my R1200RT has a balancer shaft and feels wonderful.

BMW did produce R100s with the smaller 32 mm cylinder heads, same as fitted to R80, this on '77-'78 R100/7 and on all R100s post 1984, and of course these all had the same 32 mm carbs, although not necessarily the same jetting. If you fit the large valve (40mm) R100 heads in your conversion, you ought also to fit 40mm carbs. Throttle cables aren't the same between 32 and 40mm carbs. Bikes with the large valve heads really ought to have an oil cooler.

There's more to the story ... although one thing is always the same: BMW engineers get it right, shade tree mechanics seldom do.

Go with the 83. I just bought my second one. Wish I kept my first one. After 23 years I still wanted to replace my 83. Just liked the ride.