Gs550 rpm

[Guest]

I just rebuilt engine of a 1980 GS550E and things are mostly great. I was never able to ride it before the rebuilt. It seems to idle at 1100 - 1200 rpm and at 55mph its at 5000 rpm. Is this normal? I have no clue but 5000 rpm seems alittle high for that speed. Im about 225lbs if that helps.

Also I seem to get a loud vibration around the top of the head at the 5000 rpm. Less than 4800 and more than 5200 it sounds great. Any ideas?!

[Stahlgrau333]

Speed vs. RPM is going to be set mechanically. Disregarding clutch and tire slippage (which should be inconsequential), your engine is going to turn at the same rpm at a given speed regardless of engine performance...it just may use more or less fuel to reach that speed/rpm, or in the case of a performance issue, not reach it at all.

Did you change sprocket gearing when you did your rebuild? That's about the only thing that would change your RPM/Speed ratio.

[tkent02]

The 550s love to spin. Wind it out.

[ndbaker]

I did not change the gearing.

[mike_of_bbg]

I just rebuilt engine of a 1980 GS550E and things are mostly great. I was never able to ride it before the rebuilt. It seems to idle at 1100 - 1200 rpm and at 55mph its at 5000 rpm. Is this normal? I have no clue but 5000 rpm seems alittle high for that speed. Im about 225lbs if that helps.

That idle is right where it was supposed to be: 1100+/-100.

I personally have 16/50 gearing (so a bit taller than stock) and the bike spins around 5200 @ 65 MPH.

Also I seem to get a loud vibration around the top of the head at the 5000 rpm. Less than 4800 and more than 5200 it sounds great. Any ideas?!

Watch the cam chain tensioner knob and see if you see it shaking around that speed. You might need to rebuild it or at least add some more tension. Don't touch it while the motor is running of course.

[cowboyup3371]

I'm running 6000 in 6th gear at 70 mph so yea, you're fine.

[ndbaker]

Has anyone changed the gear ratio for the 550? I believe its stock 15T front, 50T back. Just looking to lower the RPM at highway speeds, and I dont know much about gear ratios.

[BassCliff]

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[tkent02]

Worse gas mileage, sluggish acceleration, lower top speed, shorter engine life.
This is what you get when you change sprockets to lower highway RPM on a 550.
It is designed to turn very high RPM, with it's itty bitty pistons that move up and down about an inch, valve timing, carburetion and everything else is intended to have the snot wound out of it. It won't hurt the engine at all.

Go listen to a F1 race with the volume turned very high, then go ride the crap out of the 550. It's a good sound.

If you don't like high RPM engines buy a Herdley.

[mike_of_bbg]

Figure on dropping about 300 RPM @ 55MPH by adding a tooth in the front, or about 100 RPM @ 55 MPH for each tooth dropped in the back. Naturally this comes at the expense of torque. 16T in front is the max recommended on a 550 because of the clutch push rod. The front sprocket is easier to change and cheaper - and also easier/cheaper to change back if you don't like the change. If your chain is stretched wait until replacement as the sprockets and chain tend to wear together.

[ndbaker]

So youd only change sprockets if you had one of the bigger engines?

[ndbaker]

mike_of_bbg, did you experience any of the issues tkent02 mentioned below?

[mike_of_bbg]

Not badly, though I think I'm lingering a bit longer before up-shifting because it takes a little torque away. But my current ratio is only about 4% off from stock. Stock on my bike was 15/49 but 49T sprockets are not available any longer, so I'm up one in front but up one in the rear as well. If you change the ratio much you'll see tkent02's symptoms - lack of power at the wheel for sure.

Stock = 3.267
Now = 3.125

It takes a bit of the edge off at highway speed, but little more than that. Sounds like you'd be better served by finding out what's unnerving @ 5k.

[tkent02]

So youd only change sprockets if you had one of the bigger engines?

I change sprockets all the time, depending on what I'm doing with the bike, and which bike it is. With the 550, they just about nailed the ratios for all around use, including highways. I tried several different ratios during the 100,000 plus miles I rode the bike. Anything lower ratio and it was a real dog, anything higher ratio it just got better for acceleration, blasting the mountain roads, just about anything fun. Yes, even cruising, as with the higher ratios you don't have to downshift three times to accelerate when traffic dictates. With a stock engine, used for highway riding, the stock ratios are about as low as it makes sense to go. If you go much lower, you will rarely be able to pull sixth gear.

[ndbaker]

Worse gas mileage, sluggish acceleration, lower top speed, shorter engine life.
This is what you get when you change sprockets to lower highway RPM on a 550.

Same issue if I were to decrease the rear sprocket on the 550?