Topic: High altitude 73 CB500 daily driver ( 5/20/17 update )

[riverfever]

Dan I did mine without splitting cases. It was a little tricky to get out but various picks finally did it.

[Desert Dan]

^Thanks for the info Chris, I left well enough alone with mine as it isn't leaking but it's good to know it's an easy replacement.^
    So over the past thousand miles Ive developed a new problem, the engine has started to burn oil. Its not a huge amount and it's very sporadic when it does but I can see smoke coming from the tailpipes. Im leaning toward valve seals on this one but its a very strange the way its burning oil.
    On the first start of the day the 1/2 pipe blows out clouds of white smoke for about 5 min then stops, the engine will then run fine for about 100 miles not burning any oil then after 100 miles the 2/3 tailpipe begins to blow small amounts of white smoke at idle and a steady stream of smoke on acceleration. When the 2/3 pipe starts blowing smoke I can feel the engine lose a little power and start to run hotter and rougher and it will sound louder, but sometimes if I stop and turn off the engine for a moment it will magically stop smoking and run smooth again.
    For instance yesterday I rode the bike up to Fort Collins where I do my flight training which is about 100 miles one way and it ran great all the way up there not burning any oil, I stopped for 2 hours while I did some flying then on the way home it ran rough and was smoking out of the 2/3 exhaust. I stopped after 15 miles to let it cool and see if it would behave itself but it persisted in running rough almost all the way home. When I was about 15 miles out from my house I stopped to throw on my jacket and when I turned the bike back on it was running nice and smooth again, I had only turned it off for maybe a minute  .    When I first noticed it beginning to smoke I first checked and re-adjusted the valve lash and reset the timing, I also checked compression and got just about 165 on all four cylinders plus or minus 1 or 2psi. At this point I think it's valve seals maybe a couple didn't seat right or maybe some of the guides are worn and are damaging the seals. When I check the spark plugs all 4 look decent with 2 and 3 being a little iffy but none caked in oil deposits 1/4 look really good and so do the tops of their pistons while the tops of 2/3 look a bit carbon fouled.
Number 1 spark plug

Number 2 spark plug

Number 3 spark plug

Number 4 spark plug

    My game plan at this point is sometime in the near future Ill pop the valve cover off and replace the valve guide seals on cylinders 2 and 3 since they are more suspect then 1 and 4, and while Im in there I will also re-torque the head. Beyond that the only thing I can think of is it's a problem with the oil rings on the 2 and 3 pistons, the oil consumption isn't excessive maybe a 1/16nth of a quart every 200 miles. If any one has any ideas as to the oil burning issue Im all ears at this point.

[Desert Dan]

After 200 miles the oil level dropped maybe an 8th of an inch from the full mark on the dipstick. I have been having a stuck float issue on the #2 carb but the smoke comes from the 3 and 4 muffler on my 4into2 exhaust. I used the clear tube method to set all my float heights and the over flow tubes are all clear and working properly. I did think it was strange none of the plugs showed oil consumption.

[HondaMan]

When these bikes burn oil, it also usually shows up at the header pipes on the front of the engine as a light greasy smear, as they don't seal 100% like modern designs.
More likely: the float level(s) are sticking, like CalJ suggests. This makes the pipe(s) slowly load up with unburned fuel until enough of it lights off to either smoke (white), or lightly pop (like a real mild backfire).

I think you already have new seals on those valves?

[Desert Dan]

I picked up a rack of 550 carbs today from the motorcycle salvage yard for 30 bucks, they're pretty nasty but full of good parts and good floats, Ill use one of the new salvaged floats on my #2 carb to fix it's sticking float issue and while Im at it Ill recheck the float levels of the other 3 carbs. When I was on my ride yesterday and it was running rough there was no sign of fuel coming out the overflow tubes when I was idling at stop lights. I did a pretty thorough job of cleaning the engine the other day after replacing some leaky oil seals and I saw no evidence of oil on the headers. The head does have new vesrah valve guide seals installed back when you ported the head, before all of this summer's rain flooded your garage. When the bike is running correctly it runs extremely well and when its acting up it still runs pretty well. It very well could be a float issue, when the bike is running well it's gas millage is in the high 40's low 50's and when its running rough it drops down in to the low 40's.

[Jerry Rxman Griffin aka MuthaF'er]

Sticky float = suspect pin.

[riverfever]

Jerry...just out of ignorance...what are you talking about here? The brass pin that the float pivots on?

[Desert Dan]

All the float pins in the spare rack of carbs I bought were suspect, I had to cut a few of them to get the floats out. The float pins in my good set of carbs are in good order I can easily remove them and the floats actuate freely, my #2 float is suspect because the brass tab that limits how far it can drop in the bowl is missing and I think it's causing the float to get hung up when the fuel gets low in the bowl.

[Desert Dan]

    Long time no post everyone! Ive been pretty busy since the last time I posted with school starting back up, but I have still been riding and working on the good old 500. Not long after my last post I put in a "new" float and float pin in to the #2 carb from the spare rack of carbs I picked up at the junkyard and for the last 1,600 miles I have not had an issue with it over flowing, that is untill this afternoon. I drove the bike to school this morning with no issue but later in the day when I rode it out to the airport it was running rough and bogging down in the mid rpm range, sure enough when I parked it the #2 carb was pissing fuel out of the over flow again. I plan on putting a new float valve in there as soon as possible to fix this recurring issue as I enjoy riding the 500 far too much to let it sit around unused.

Here is a picture of where I had the float level set in #2 and the other 3 carbs, which was working well for the last 1,600 miles.

   
Last time I updated the 500's progress we collectively thought that the smoke was unburnt fuel from improper float heights, but it has continued to smoke and burn oil since I fixed the float issue. Im burning about 1qt of oil every 1000 miles. From what I can tell it only burns oil once the engine has gotten good and hot and the oil has gotten thinner, usually this is about 80 miles of highway riding or 30 minutes of city traffic riding. There is no smoke coming out of the exhaust while the engine and oil are still cool but once everything has heated up i get a steady stream of smoke from both sides of the 4 into 2 exhaust and from the valve cover vent tube. Im 95% sure that cylinders 2 and 3 are the culprits because their pistons are oily and black while pistons 1 and 4 are a dark brown color. When the engine begins burning oil I don't feel any loss in power and it is not burning enough oil to fowl the plugs or leave much in the way of residue on the plugs, which I find very odd. My best guess is that for some reason the oil rings on 2 and 3 never fully broke in and oil is being burnt off the cylinder walls, but the last time I did a compression check I got the same reading +- 1psi on all four cylinders ( I believe it was either 165psi or 160psi on all 4, I don't remember which.)
    Besides the oil burning issue and the #2 carb acting up on me again everything is going great on the 500, Ive put 5,200 miles on it since I finished the engine rebuild in March. One of the best things about riding the 500 is all of my riding buddies get floored when every one at gas stations and restaurants come up to talk about and admire the little CB and ignore the big, new, and chromed out V-twins that my buddies ride.

And a few humble pictures of the CB500 in it's natural environment.

[Desert Dan]

My money is on the valve seals as the cause of oil entering the cylinders.

I'd be pretty happy if it were just valve seals, Ive got a set of new Vesrah valve seals sitting on my work bench at home. I could slap those puppies in the bike over a weekend.

[HondaMan]

Maybe check for a cracked or chipped valve guide? Or, check to see if the intake valve in the cylinder(s) of question now have excess clearance on their stems (i.e., if you pull the head off, try the 'wiggle test' of the valve with it lifted about 6mm off the seat). If the [new] engine (head) was last run on normal gas and now has suffered the ethanol solvent having washed out the valve guides, the once burned-on oil film may have washed away, leaving too much clearance on the valve stems. I see this happen with the 750 heads pretty often. Since the guides were not changed in the head (just the valves and head cleaned, new seats ground on both), this clearance may have increased. If so, you will have better luck sealing the guides with the Buna valve seals than with the Viton type: the Viton ones are orange color and the Buna are charcoal. Viton is stiffer.

[Desert Dan]

Worn valve guides were another suspicion of mine, especially since the head received new valve seals when I sent it off to you. Im not overly concerned with the oil burning issue at the moment because the bike runs the same whether it's burning oil or not, and it has yet to foul a plug or have any detrimental side effects. Ill try those Buna valve seals you describe, any idea where I can order such a part? At the current moment Im off at school so I don't have a garage to do major repairs in so Im just going to fix the leaking #2 carb and continue to feed it's oil burning habit, as I plan to keep riding the 500 up to the very last minute of the riding season. Worst case scenario in my mind is once theres snow on the ground and riding season is solidly over I can pull the head and and see if new guides are in order, and if Im in that deep there might be room for improvement as I have been eye balling that cruzin image big bore kit for a while. 

[Desert Dan]

   So I have re-fixed the leaking #2 carb issue, I pulled the float needle valve out and polished the end of the needle that blocks off the brass portion of the inlet valve as it had developed a ridge on the end of the needle seat. So far the fix has worked so Im crossing my fingers that the problem wont resurface for another few thousand miles.
   

HP loss of these carb'd engines is about -1% of total output per 1000 feet altitude, all else being equal. So, by 8000 feet, the 500 is typically running about 32-ish HP at 7000 RPM. Higher-compression pistons (if they are NOT forged pistons) will reduce this effect by about 50%, as the efficiency stays higher. This is why the "Gentleman's Express" version of these bikes (590cc, made with 750 pistons) has been popular for many years. Way back when, Action Fours used to make some 1mm oversize 10.5:1 pistons for these bikes, and if the owner stayed with the stock cam this made for a mighty torquey 500, indeed! Then, the rear sprockets would lose a few teeth to make them smoother 80 MPH tourers, too. But, those who decided they wanted a "big cam" to go with the pistons discovered the efficiency was very low until 7000 RPM, so the bikes became a nuisance to ride. (Something to ponder...).

   Mark, Im intrigued by the " gentleman's express" modifications you described in an earlier post, could you elaborate on what modifications have to be done in order to fit the 750 pistons and make the engine a 590cc. Boring the cylinders out on the 500 from 56mm to 61mm seems like a lot would it be better and or possible to get my hands on a 550 cylinder block and do the boring on that?
   And my last question pertains to ride-ability, right now I believe Im running the stock sprocket combo but I was wondering if there is a better sprocket combo that would be more efficient on the little four. Right now in 5th gear at 65mph the bike runs at 5400rpm and at 80mph it is screaming at 7000rpm.

[Desert Dan]

7,000 is not screaming with a redline of 9,500. These are small motors with tiny pistons that require revving to extract power from them. If you want a lower torque band, you'll need to move up to a much larger displacement motor that reclines closer to 6,000.

I figured the torque of the engine would be the primary limiting factor, I just feel a bit guilty when I hold the engine in the higher rpm band for extended periods of time.

[HondaMan]

7,000 is not screaming with a redline of 9,500. These are small motors with tiny pistons that require revving to extract power from them. If you want a lower torque band, you'll need to move up to a much larger displacement motor that reclines closer to 6,000.

I figured the torque of the engine would be the primary limiting factor, I just feel a bit guilty when I hold the engine in the higher rpm band for extended periods of time.

Don't feel quilty about that: this is exactly what Sochiro and Company had in mind for this bike. When it came out, the US speed limits were 70-75 MPH, and the tires and gearing it came with put it right into the upper RPM powerband these engines have. My brother toured next to my 750 for 8 years with his, and it never missed a beat, nor cared. The top speed of his grew from 102 MPH when it had 1000 miles on it to a little over 112 MPH when we last 'played' together when it had about 28k on it. (On that trip, it blew the whole core of the #2 muffler out onto the hiway near Fort Collins!)

[SOHC4 Cafe Racer Fan]

From the mouth of Hondaman -- so it is written, so shall it be done!

Yes, 7K is not that high on the revs, even for sustained periods/miles. 

[Desert Dan]

Well if Hondaman and two other really old timers say so, it must be true. My guilt has been abolished, I was just worried I was over working the bike holding 7k rpm for sustained periods.

[SOHC4 Cafe Racer Fan]

Yeah, Dan. Ride it like you stole it! Wring its neck a little!

[RAFster122s]

Just don't take it up to redline in 1st gear, that could be a very hard shift...
Going up to 8800 and above is going to take you to some fun speeds so, exercise judgement to gauge police presence.
David

[Desert Dan]

For the most part I keep the rpm's right around 4k but Ive been known to get it right up to the red line on occasion. On a related topic thats out of purely academic curiosity is it possible to do a wheely on a 500 or does it lack the required torque?

[SOHC4 Cafe Racer Fan]

For the most part I keep the rpm's right around 4k but Ive been known to get it right up to the red line on occasion. On a related topic thats out of purely academic curiosity is it possible to do a wheely on a 500 or does it lack the required torque?

You can do a wheelie on a 50cc bike.  A stock CB500 will not generally power wheelie.  With a big bore kit, cam, ported head and CRs you can get the front end to lift using a 1/4 turn throttle.  If you know how to wheelie, you can get a stocker to do it.  I'm not really a wheelie kind of guy.  I've power wheelied powering out of turns on my modern bikes, but I don't try to wheelie.

[Desert Dan]

You can do a wheelie on a 50cc bike.  A stock CB500 will not generally power wheelie.  With a big bore kit, cam, ported head and CRs you can get the front end to lift using a 1/4 turn throttle.  If you know how to wheelie, you can get a stocker to do it.  I'm not really a wheelie kind of guy.  I've power wheelied powering out of turns on my modern bikes, but I don't try to wheelie.

Thanks for the wheelie education, what sparked my interest was I'd notice the front end would get light on hard  acceleration which seems to me to be the first step to doing a wheelie. I think Ill hold off on doing wheelies on the cb500 and practice on a dirt bike or something in the meantime.

[RAFster122s]

Being a little rough on the shifting of my CX500, I have been able to lift the front wheel on shifts but, not wheelie. My CB550 is still a project on hold.

David

[HondaMan]

Hey Dan: (or anyone else with 550 parts?)
Do you happen to have a leftover 550 set of cylinders? I need some for one of our members who's engine took a terrible hit in shipping here from NY. And, I need a tach drive for the head as well: his is broken in two.

Anyone?

[HondaMan]

Hey Dan: (or anyone else with 550 parts?)
Do you happen to have a leftover 550 set of cylinders? I need some for one of our members who's engine took a terrible hit in shipping here from NY. And, I need a tach drive for the head as well: his is broken in two.

Anyone?

Just the gear? I am pretty sure I have that. Sorry, no extra jugs though. Send me a PM with an address and I'll ship that off.

Thanks for the reply, Cal!
This one's gear is OK, it is the housing on the outside of the head that got hit in transit, broke it right in two!  The tach cable is still screwed onto it, so it acted like a lever on the housing.