1978 R80/7 with 37:11 final drive

[georgej]

I'm sorry for raising tis topic again.Previous owner said it came this way from the factory.I bought the bike last fall,I've been riding to work almost daily.He told me she revs high,great for two up riding.My question is this.Am I hurting the engine or shortening its life?At 60 mph she's turning a little over 5000 rpm's in 5th gear.I don't mind it so much I'm getting used to it.I generally don't ride much faster than 60-65MPH I'm almost never on the interstate. So for now I'll leave it as is and in the future I'll change the final drive.
George

 

[krehmkej]

George,

This is my second R80. It also came with 37:11 gearing. On the first one, I was always wanting to gab another gear, so I am changing this one to a 32:10. Will see how that goes, I can always swap back. As far as damaging the engine, that never came into the equation. They were designed that way, and I ran my first one really fast while living in Germany

 

[rocketman]

on my 78 R100 her sweet spot is between 4-5K and I Never run her below 3K and hardly ever use 5th unless its open flat slab; so I don't see running it at 5-5.5k is gonna hurt it in the least, all airheads I've owned love rpms, that's when they run the smoothest. As long she' running at a good speed and getting plenty of airflow you should be good.

RM

 

[bikerfish1100]

the owner's manual for my '78 R100RS listed a "maximum sustained rpm" that was only 250 rpm below that of the "maximum rpm". they like to run fast.

 

[BUBBAZANETTI]

i rode a beat up 84 R100 at an average of 6000 rpm for almost 2 months on end. never lost a drop of oil. can't say the same about my current bike.

 

[r60us]

If your bike has a 37:11 final drive (3.36:1), the engine turns about 4000 rpm at 60 mph, not 5000 rpm. Perhaps your tach is inaccurate??? I have found 4000 rpm to be the sweet spot on every post 1970 boxer I have owned.

mph = rpm / (gearbox ratio X final drive ratio) X wheel diameter* / 1056
mph = 4000 / (1.5 X 3.36) X 81.68 / 1056
= 61.4 mph

* wheel diameter = 81.68 inches for 400 X 18 Metzler ME77 tire

This matches the values on the road speed vs rpm graphs for the 3.36 ratio final drive in the /5 owners handbook.

 

[rocketman]

The tach on the 78 is an electronic (first year I Think) so can't see how it could be off, but the speedo certainly could be as they were mechanical and notoriously inaccurate, my is off by a good 10 mph at 60 compared to what my gps says, (on the low side) but I've others that were way above actual speed.

RM