Topic: Trust my tach?

[Untold]

My '76 CB550 is my first and only motorcycle I've owned, so I don't have a reference point. I just am not sure if my tach reads accurately.  It looks like the correct stock tach for the bike, based on what I've seen.

The engine seems happiest around 5k rpm, but I see people talking about revving way higher than that.  Occasionally I'll open it up to (what reads to be) around 7k, and it just seems like I'm putting a lot of stress on the engine.  Around 5500 rpm in 3rd gear, I'm at around 45mph.  Does that sound right?  I know there's math that can tell me, with wheel size and gearing and whatnot, but I wouldn't really know where to start.
Am I just playing it too safe? Should I trust the tach and feel ok as long as I'm under the redline?  Or should I go by feel, which I have nothing to compare it to? 

The bike runs strong, never had any real issues, and am meticulous about valves, carb sync, cam chain tension, oil changes, etc. 

[Xnavylfr]

These bikes use that RPM to their advantage, 5000 in 3rd for a short shot is not bad get the bike up in 5th out on the hiway and running about 65 your RPMs should be about 5K, If it is buzzing a LOT higher that, your gearing needs changed. The engines are happy on the Hiway running 5k.



Xnavylfr(CHUCK)

[bjbuchanan]

Just remember it is not a stock car engine, old one at that, that isn't meant to eclipse 6200rpm ever. This is a motorcycle engine that revs.

You can wind it out to 9500 without hurting it. 5k is a happy cruise, don't lug them because then you won't be in your powerband to get away from the crazies/texters/talkers/clowns out there.

[Untold]

That's what I mean, though.  I know I should be able to get up to 9k, but when the tach reads 7k, it SOUNDS like it's really screaming. So I don't know if my tach is reading correctly. 5k on the tach feels like 7k. 
I just swapped tach and speedo for another set I had off of a bike that i KNOW was a 550 (my bike had been lightly modified by the PO, so I'm not 100% sure these are 550 gauges). 

It does seem to feel more accurate now, although it was tough to see because the gauge lights don't work on the new set. I think I wired them up wrong, or knocked a connection loose in the headlight cluster, because my turn signal lights used to stay lit when running, but now they don't (blinkers still work).  I only unplugged 4 wires from the old gauges and then re-plugged 4 wires from the new gauges, so I don't know wtf happened.  Time to study the wiring diagram. Ugh

[w1sa]

These tachs usually over-read (up to 10%), and rarely/almost never under-read.....standard drive sprockets are 17F, 37R.....therefore (from oem data), true revs at about a true 45 mph in 3rd is 5000rpm.....so, for me the other important thing is to also understand how accurate my speedos read....I usually calibrate speedos against portable GPS.

[Untold]

My speedo seemed to be dead on, checked against those construction zone Speed Limit signs.  I think maybe my tach wasn't lubed or the needle was dragging or something.  New one seems better. 

[Chachi]

It's possible that you had a 750 tach on there which is a different ratio than the 500/550s. Just a thought.

[Bankerdanny]

If you are used to the sound of a car engine then 7k is screaming. However there is still lots of revs left. it takes a while to get comfortable with the sound of the kind of revs a Japanese 4cyl can generate. Try a modern 13k RPM sport bike some time. The shriek of the engine is an unforgettable sound.

[bollingball]

These bikes use that RPM to their advantage, 5000 in 3rd for a short shot is not bad get the bike up in 5th out on the hiway and running about 65 your RPMs should be about 5K, If it is buzzing a LOT higher that, your gearing needs changed. The engines are happy on the Hiway running 5k.



Xnavylfr(CHUCK)

Have you tried this yet? Post back after you try this to help others
Thanks
Ken

[trueblue]

If the engine is a long way out of tune then it will sound like it is screaming at higher revs.  When I got my 650 I had a hell of a time getting it to rev, it sounded like it was all done at 6k but I found a PO fix from hell, corrected that and now it revs cleanly all the way to 10k, and sounds like it has less strain on it doing so than it did before revving to 6k.

[bollingball]

If the engine is a long way out of tune then it will sound like it is screaming at higher revs.  When I got my 650 I had a hell of a time getting it to rev, it sounded like it was all done at 6k but I found a PO fix from hell, corrected that and now it revs cleanly all the way to 10k, and sounds like it has less strain on it doing so than it did before revving to 6k.

Trueblue OK I haven't had my 2nd cup of coffee yet and don't know what the photo is for and what happened to those 3 links?

[trueblue]

Just to show it could always be worse .  That was a 113 link cam chain, where there was supposed to be a 112 link chain, the PO didn't back the cam chain tensioner off before fitting a new cam chain, that was his "fix".  He joined 2 inside links together and the couple that are chewed up is where the chain was trying to part company with the gears .  I was just lucky that it didn't.

[MCRider]

Untold: The bike should pull cleanly and smoothly to redline in each gear. IF the tach were reading slow, your engine would run out of pulling power beofre the tach reads redline. That's the tell.

ITs pretty hard to over rev the engine as the valves wilil float and it self limits.  If it reads 7000, but you think its revved out, it simply won't accelerate more and you know the tach is off.

An old tach (or speedo) can dry out, (especially if it were ever stored upside down) and the needle will drag, not keeping up with the spinning drum that is trying to move it, so you have a legitimate question. Such a situation will require disassembly of the insrtument and replenish of the lubricant.

Also in 5th gear, the tach should read about half of its range (o to redline) at half of its top speed (about 100) half being about 50.

Generally speaking.

[Untold]

Thanks all. After swapping tachs, it seems like the problem was with the original tach itself. The new one seems to read more accurately, and the needle doesn't bounce around at higher rpms like the old one did.
The engine itself had always felt great and pulled strong. Just didn't match up to what the tach was telling me. I have this pesky problem of trusting myself over the instruments, so I knew something was off. Appreciate all the insights

[MCRider]

Thanks all. After swapping tachs, it seems like the problem was with the original tach itself. The new one seems to read more accurately, and the needle doesn't bounce around at higher rpms like the old one did.
The engine itself had always felt great and pulled strong. Just didn't match up to what the tach was telling me. I have this pesky problem of trusting myself over the instruments, so I knew something was off. Appreciate all the insights

That goes to my comment about old instruments. They dry out. Dragging and needle bounce are the symptoms. For many years I was raised with the idea that they were not salvageable. Since getting into the restoration crowd, this forum, etc. I've learned that they can be dissassembled and cleaned, relubed and reassembled, good as new. Many here have done it, and I have sent a few to ForeignSpeedo in SanDiego. They will do it all for $85 per.