Topic: Further Adventures of the Missing 6th Gear

[phil71]

why waste your time speculating? He already knows everything, and perhaps is content getting passed by vespas.

[trueblue]

sounds to me like he is only running on two cylinders since the racing gearset for the 550 in 74 was a 16 front 34 rear only running on two cylinders you can open the throttle wide open and only go 70 mph

Danno are you talking about the bike or the rider only running on 2 cylinders

[Stev-o]

C'mon man! Someone needs to go over there and show him only two cylinders have spark

[dave500]

itll be running on four,its just down on power for what ever reason and cant pull the taller gear ratio hes using.

[breezy]

After just reading this entire POST I thought I was completely exhausted.
But no,  I had some energy left, so I went out to my 1978 CB550 K  with a cloth tape measure.

My non stock Bridgestone 110 / 90  /  18 inch tire has a circumfrence of about  80.5 inches.

Many thanks for the measurement.  Mine is 79.5", hardly enough to make for the difference in gearing that I'm getting.  The next step is to suss the wear on the front sprocket. 

[breezy]

1. I'm on the highway with a speed limit of 55mph, keeping up with traffic.  I have maybe an eighth inch of throttle left, the engine is screaming, I'm in 5th gear searching for a needed 6th gear.  5mph plus or minus is not going to effect the gross results.  With that data set, my tach reading is simply not necessary. 

Yes it is.  "Engine is screaming" isn't usable data.  A number indicating the engine revolutions per minute is.  If you think the tach reading is irrelevant, then what difference does it make if you post it?

You forgot the 1/8" of throttle left part.

[breezy]

Screaming is not a number, you need to find out exactly what the revs are and tell us, its not that big of a secret, it sounds like it is out of tune.  Unless you put the rear tyre from a 50cc scoot on the back it wouldn't have made that much difference to the top speed.  If you think these engines are a carnot heat engine then you obviously don't know what you are on about, they are an internal combustion engine, the basic principal is the same as any other engine in any other bike/car/truck, but they are far and away different from the old english bikes and lightyears ahead of a vw.  Have fun ruining your bike because you are too pig headed to listen.  I'm off to ride my 650 which runs like a top because I listened to the people on this board who had been around these bikes for a long time, even though I am a diesel mechanic by trade and work on engines for a living.

I don't want to add to the opinionated piss-headedness you seem to evidence when people think for themselves.  I can't tell you how much crap info I've gotten off forums comprised of "experts".   An internal combustion engine IS a Carnot heat engine, which also includes steam engines in the category.  If the SOHC motors had torsion bar valve springs like the older Hondas, desmodromic valves, 4 poppet valves per cylinder, dual spark plugs, electronic ignition, fuel injection, roller crank, tuned exhaust, and a compression ratio of 11:1, it would be "far and away different".  As it is, it's a pretty standard motorbike mill with zero mystery for anyone trained on Brit bikes or aircooled VW's.  I want to know who put a 34 tooth final drive sprocket on my 550 that came stock with a 37 tooth sprocket and why.

[jneuf]

*edit*

Removed my own post..

[Gordon]

1. I'm on the highway with a speed limit of 55mph, keeping up with traffic.  I have maybe an eighth inch of throttle left, the engine is screaming, I'm in 5th gear searching for a needed 6th gear.  5mph plus or minus is not going to effect the gross results.  With that data set, my tach reading is simply not necessary. 

Yes it is.  "Engine is screaming" isn't usable data.  A number indicating the engine revolutions per minute is.  If you think the tach reading is irrelevant, then what difference does it make if you post it?

You forgot the 1/8" of throttle left part.

No I didn't.  That bit of info could be helpful, but only in conjunction with the tachometer reading.  I'm not really holding out hope that you'll post it, though, because it's become apparent that you either don't actually want any help or you already discovered days ago that the problem was due to an obvious oversight on your part and don't want to admit it.

Either way, I have no reason to be upset about it and neither does anybody else, to be honest.  I hope you get it worked out.   

[breezy]

I only live about 10 miles away.  I thought of making an offer to go help.  But, I'm now convinced breezy just wants to position everyone else wrong and him right, and most importantly doesn't want to post information that will confirm his ignorance.  He is determined to grind up the cases for yet another failed attempt at fixing something beyond his comprehension and capability, and follow his own misdiagnosis.

Some people have to learn their own hard way.  It's a shame that another bike will suffer from the ignorant.  I pity the Craig's list, ebay, or other buyer that pays him for screwing up yet another vehicle.

A litany of assumptions that don't apply.  I don't position myself as wanting anything other than a solution.  Show me where I'm not being logical.  Which point is that does not follow an efficient course of action.

1. I'm on the highway with a speed limit of 55mph, keeping up with traffic.  I have maybe an eighth inch of throttle left, the engine is screaming.

This is indicative of cylinders not firing, and YOU being totally unknowledgable about what this bike sounds like at 9000 RPM. I speculate you f'd the carb rebuild. 

A cylinder not firing, you must be kidding.  If that happens on my VW, I know it immediately.  Go ahead, pull a plug cap off one of your cylinders and tell me the bike sounds normal.

And your high speed circuits are failing in one or more cylinders.   Probably left some parts out, or didn't clean bits that take extra effort to remove and clean (Emulsion tubes, and or the main's spring retention clips.)  These are mechanical slide carbs, but throttle position does not directly indicate the engine RPM, only rider demand.

C'mon guy, what parts could be left out and not be noticeable?  A loose main jet because the retention clip was not put back.  Gimme a break.   You are making #$%* up and using your fantasy to paint me as a mechanical dweeb.  You think I can't tell the difference between a motor out of tune and a motor at near max revs that is geared wrong.  You think I'm on this forum because I hadn't thought of every observation so far posted.  That's why I thought there was a missing 6th gear.  I've been around motors all my life.  You think I can't tell when a motor is working extremely hard at supposed cruising speeds?!

You don't have to get insulting just because I thought there might be some variations in internal gearing that a mechanic might have #$%*ed with.  I already posted that this 550 has a 34 tooth rear sprocket.  Nobody thought that was odd even tho the 550 comes with a stock 37 tooth sprocket.  Not one person here sussed that there may have been a former problem with gearing that necessitated swapping a 34 tooth rear sprocket for the stock 37 tooth one, and this fact even tho we're talking about gear ratio problems.

2. My buddy who I got the bike from said it was riding fine, he could do a ton, barely- it's an old bike. 

...And the carb got f'd up the carbs since he did that.  Old bike has absolutely nothing to do with it.  The machine runs as good as it's mechanic.  It would do near 100 when new, it will do that now if the right person fixes the accumulated abuse it has received.

Since you won't tell us the tach indication, I suppose it is too much to ask what the spark plug deposits look like after that 55mph dash with near wide open throttle.

The tach cable had a broken valve cover mount casting.  It worked the first time I took it out on a short ride.  During the second longer ride the cable broke.  I have a new one on the way and will give you the reading when it's installed.

But, that wouldn't matter anyway, as you are right and 1000 people with far more experience and knowledge about this bike must certainly be wrong.  I don't need to travel and go out of my way so you can tell me that in person.

Go ahead, hack up the engine case, put a bigger front sprocket on it, and watch your top end speed get lower.  I dare you!

Oh stop.  How many cafe'd CB's have had the holy crap hacked out of them.  Your call to purism is basically luddite.

[breezy]

Breezy:
  If your bike is topping out at only 65 mph there are really only 3 things that can be happening. (1) The engine is not pulling the rpm you think it is due to a mechanical or tune problem. (2) The engine rpm is high and the speed is low because of slippage in the drive train. (3) The rpm is high and you are going a lot faster than you think you are because the speedo reading is wrong. I don't think they make an 18" tire that would fit your rim and be small enough to cause the gear ratio change that would be as drastic as what you are describing.

Thanks for working on the actual problem, Bob.  1. The bike's tach cable broke and I have a new one on the way.  I'll give the reading soon as I get it installed.  I've ridden older 500 and 600 cc bikes for years and know what to expect when I crack the throttle wide.  This bike had good accelleration, it wasn't acting like a sick puppy.  2. Slippage might be a problem, but I've never had a clutch slip, and I've experienced that in bikes, cars and scooters, that slipped only at the top end of the rpm range.  A slipping clutch can be broken loose with full throttle at any point in the acceleration range, most easily in the power band.  3. I'm on a 55mph highway where cars normally travel 60-65.  I'm keeping up with traffic and the motor is working very hard at near full throttle.

If this problem was easy or obvious, I'd have it fixed by now and spared you good folks all the eyeball rolling fun. 

[trueblue]

An internal combustion engine is a heat engine not a Carnot heat engine.

A Carnot heat engine[2] is a hypothetical engine that operates on the reversible Carnot cycle. The basic model for this engine was developed by Nicolas Léonard Sadi Carnot in 1824. The Carnot engine model was graphically expanded upon by Benoît Paul Émile Clapeyron in 1834 and mathematically elaborated upon by Rudolf Clausius in the 1850s and 60s from which the concept of entropy emerged.

So you are saying all the engines you have worked on are hypothetical, because it is not actually possible to build a carnot heat engine.  Throttle position doesn't indicate rpm btw, only load, a poorly tuned engine can be on WOT yet only be doing 3-4k, so that means jack, everything you have said points to a poorly tuned motor which is running out of power as the load comes on, it may have plenty of power down low but is probably dropping a cylinder or 2 as the revs come up.  I would like to see one of your POS veedubs doing 9000rpm, these engines can do it with ease, providing they are tuned right, but seeing as you have it figured out and know exactly what you are doing carve into the engine cases chuck a bigger gear on the front and see if you can even get it to move, let alone improve the top speed.   And on that note I'm out, enjoy destroying your bike

[breezy]

It could well be Breezy that trusting your friends workmanship may be holding your bike back.
He had the carbs apart and may as TT said have missed something that on the surface looks minor but in these engines is significant.

I appreciate your helpfulness.  When I do carbs, I use an egg carton or ice cube tray to keep the bits organized in.  They went back together with no pieces left out our incorrectly installed

TT mentione dthe emulsion tubes, TT has taught many of us on here about these little suckers, cleaning them out to make the petrol froth up is vital, if you just clean out the main hole down the throat of this brass tower the bike may run but not perform.

I have a collection of syringes with needles to use on cleaning carb passages.  Before anyone jumps down my throat about sticking wires or whatever into jets, don't.  The needle tips have been ground flat, they don't go inside the jet, they but up against it and I look to see if there is a healthy piss stream from all the holes, including the emulsifier holes.  I blow the jets dry and inspect the holes against a light.

The minute holes in the sides need to be clean as otherwise it's no dice for the mechanical carbs of the old bikes.
Please listen with an open mind to the suggestions, I'm picking you will have (like many of us have) a EUREKA moment when the penny drops.

I do listen with an open mind, I'm looking for answers.  I'll get the speed and tach data posted soon as I get the tach working.

Insults are a dime a dozen on the internet where we don't need to face each other but are not much help to a person seeking a solution.

Thanks, people can get huffy if you don't fall in lock step with their every utterance.  As I've previously said, there is a lot of iffy advice out there on forums and I have to run it all past my experience and logic circuits.

[Rigid]

Your right, it's not a car engine, carnot. get it?  Anyway, I just read the entire 6 pages cause it is cold and rainy here and my roast isn't quite done.  Personally, I say let him grind away the case.  Maybe swap in a set of gears out of a Suzuki? I will take offense to one statement however: "I tend to be logical and not follow the dictates of churchmen unless they are using logic as well" at the end of the day, your logic will fail, and the wise will be made foolish.  That being said, he lives 10 miles from a foremost expert in the SOHC, TT.  The irony is palpable.

[breezy]

Truly, this must be a joke, and the TS is trolling everyone here on the forum...I asked for rpm readings in the first thread on this, and he refused. If he REALLY wanted help, he would have provided some of the info that was requested...

Any guy who claims that sort of prior bike and engine experience surely knows that the tire, of all things, is not making a 40 mph difference in top speed. And please don't grind the cases for a 21 tooth front sprocket...

If you are serious, and are just being stubborn, give us some tach readings and make sure you are firing on all cylinders.

I'll get the instrument readings soon as I get a new tach cable.  It's on its way.  As I previously posted, take a plug cap off one of your cylinders and see if that's going to be hard to notice.  I'm being serious, am not a troll, actually do have a lifetime of experience around motors, bikes in particular.  Yes, a 40 mph difference is a real head scratcher.  Nobody seems to take any of the data I offer seriously.   People need to read the posts for content and not interpolate their own predispositions. 

I've had a number of suggestions that the clutch might be slipping.  In order for clutch slip to be a factor in this case, the clutch would have to slip at 55-60mph, consistently. but nowhere else.   If clutch slippage were the issue, particularly the kind that would be evident only at 55-65mph, with that factor of wind resistance load, he clutch would break loose on full throttle anywhere in the power band, Particularly in 1st or 2nd.  I can't make the clutch slip, and can bring the front wheel off the ground in 1st.  Contributors to this forum who overlook these obvious trouble shooting details are not reading for content and thinking analytically and I have a right to not snap off a salute and leap out of the foxhole.

[breezy]

Oh man this is great. I think your problems started here...
How do I know the timing mark is on the firing stroke rather than the exhaust stroke on #1?

I had the cam out when I posted that.  What's point you are making?  A helpful post noted that it doesn't matter, that the cam can be 360 out and it will just move the firing stroke on all the cylinders.  At what point are you trying to be helpful?

[Duke McDukiedook]

Num, Num, Popcorn is goo-ood. 

[breezy]

6.  If necessary, the front sprocket will be sized according to the percentage difference computed according to the difference in my top speed vs. the stock top speed, with a little subtracted to compensate for the age of the bike.  If the sprocket I end up with is too big for the housing, I'll remove metal from the housing, far cheaper than getting an 18" rear tire with a fatter profile and setting the tire I bought on fire at the next Occupy (city of your choice) protest.

This would have to be one of the most stupid posts i have ever read on this forum....

How would you compute gear ratios then?  Giving me that data would be helpful.  Acting like an arrogant snot is not helpful.

You are aware that there are thousands of your model bike on this forum ..? And we are aware that you are not listening to people who Obviously {well obvious to us} know more than you do about these bikes....  If you think that a fatter profile tyre will find your missing 50MPH then you are delusional....... 

No a fatter tire won't find the missing 40mph unless it's a lot fatter.  Why do you suppose the bike has a 34 tooth rear sprocket?  Not one person on this thread has touched on that anomaly in the bike's setup. 

I wish TT would go round to this guys house, we all need a good laugh.....

Feel superior now?

[breezy]

I almost didn't do this, but come on
Can I get banned for this? Just askin.....

I'm an idiot song

Thanks, man, keep the rubber side down.

[Bob3050]

[quote  I want to know who put a 34 tooth final drive sprocket on my 550 that came stock with a 37 tooth sprocket and why.

  Breezy:
    There could be any number of reasons a PO changed the rear sprocket from 37 to 34. Possibly they were trying to lower cruise rpm at freeway speeds or they may have gotten a sprocket given to them or they simply made a mistake when they replaced it. A three tooth difference is not a drastic change. You are looking for something that has made a major change in the performance of your bike and I don't believe your sprockets are your problem. I think you are going to find that the engine is not pulling the rpm to reach the speed that it should. I hope you're able to find the trouble. Good luck.
 Bob
 

[breezy]

TT and Dave, You both put it far more sucintley and politely than i can be arsed to any more for this particular deaf idiot

"Deaf idiot". 

Kay, you arrogant self righteous approval junkie keyboard wanker, I'll be sure and post the YouTube of me doing a donut on your skanky bits with the completed bike.  In the mean time, grab a beer and enjoy the circus.

[breezy]

sounds to me like he is only running on two cylinders since the racing gearset for the 550 in 74 was a 16 front 34 rear only running on two cylinders you can open the throttle wide open and only go 70 mph

This bike had a 74 tooth rear sprocket and a 17 tooth front sprocket.  What is your guess at why someone would put a 34 tooth sprocket on the back of a stock (non racing) setup?

[phil71]

There's one question no one has asked. What does the rider weigh?

[Tews19]

He does look about 6'4-6'6 280. I'm so lost with this thread. What is the original concern? Topping out at 55 or 65?

[Rigid]

He does look about 6'4-6'6 280. I'm so lost with this thread. What is the original concern? Topping out at 55 or 65?

Just read it all, yes, "topped out" at 65 mph with throttle to the stop and apparently NO clutch slippage. That is what I gathered?