Topic: Blue Smoke.....

[Pinhead]

My '79 650 has a little over 30k miles on it, and has recently begun to smoke a bit. It doesn't smoke at startup, or if I drive it aggressively down the road. It'll start smoking if I putt around (below 4k rpm) for an hour or so. If I rev the engine a couple of times pas 6k it'll completely clear out and won't smoke for a while again. I've heard that if it smokes at idle (it'll smoke a bit if it sits and idles for a while) than it's the valve guides and if it smokes more with more throttle it's the rings. Is this right? If it is the guides, what is involved (price and work) in changing them? It's kind of embarassing sitting at a stoplight with a fog machine dragging behind me...

[Gordon]

Have you done a compression test?

[Pinhead]

No, I only have basic tools. The bike runs great. Easily brings the front-end up in first and will bring it up in second with a little more throttle.

[Pinhead]

If the rings were bad, wouldn't the smoke get progressively worse with more throttle?

[400F_CaféKing]

What does your oil smell like? If it smells like gasoline your rings are bad.

[scunny]

it could be due to glazing of the bores, I recall you are running a bit rich at the moment.

[Pinhead]

No, not running rich anymore. I pulled the airbox cover and fixed that problem. I'll have to go smell my oil to see if it smells like gas. If not, that leaves the valve guides...

[nuke]

so how-to fix the valve guide problem cause I have a bit of blue smoke just when I start up for a few seconds. So does taking the air box just give more air= leaner? Shouldn't that be fixed some other way? Do you have to ride without it now? I feel like a kid......why? why? why? why?

[Pinhead]

so how-to fix the valve guide problem cause I have a bit of blue smoke just when I start up for a few seconds. So does taking the air box just give more air= leaner? Shouldn't that be fixed some other way? Do you have to ride without it now? I feel like a kid......why? why? why? why?

My bike was running rich with the airbox cover on because I re-jetted my bike from 90's to 102.5's. The normal change is 98's but I couldn't find any 98 mains.

A lot of the 650s suffered from choking out above 65mph because the stock air box was so restrictive and the engine couldn't get enough air. When I was running the stock 90's, if I took the airbox cover off my bike would just die because it would run lean. After I changed to the 102.5 mains, my exhaust stunk like gas. I pulled the cover and that problem went away. Horsepower also went through the roof. Just to be clear, I removed the airbox cover, not the entire airbox and filter unit.

-POWER LOSS:
Some people have complained about a general lack of power, usually problems revving past 5500 rpm or so under load.  I limited the options down to fuel delivery, air delivery, and timing. To make a long story short, it was air delivery - even with a new filter.  The inlet cover that holds the filter in place was restricting the airflow!  I discarded the cover and used washers to hold the filter in place. See picture below. Another idea mentioned to me was the gas cap vent becomming plugged, preventing adaquate fuel flow to the carbs at the higher rpm.  Hopefully one of these ideas will work for you.

[bryanj]

sounds like valve stem seals to me

[DammitDan]

Yup, it's not bad valve guides, it's bad valve stem seals.  They're much easier to replace than the guides, anyway.

However, do a compression check just in case.  You never know, it could be the rings.

[Pinhead]

Yup, it's not bad valve guides, it's bad valve stem seals.  They're much easier to replace than the guides, anyway.

However, do a compression check just in case.  You never know, it could be the rings.

Valve stem seals? What does changing seals involve? Would I have to pull the heads? I'm guessing if I pull the head, I'll need a completely new gasket set, right? Also, I'd have a little porting work done, getting rid of irregularities, etc. Keep in mind that I would have to do all of the work myself, would it be worth pulling the head (that is, if you have to) to just replace the seals?

[bryanj]

Not worth doing until smokes all the time and drinks oil. You will need to removed the head which means really the cylinders ought to come off and replace all the gaskets/o rings from the base upwards

[Jay B]

You can replace the valve guide seals without pulling the head. I did it on my 350f. I knocked the innards out of a spark plug and welded a short pipe nipple to it, with a quick disconnect air fitting on the other end. Put the piston at BDC and connect to compressed air. I was able to compress the valve spring by hand while my son took out the keepers. Worked like a charm. The 650 springs might be stiffer, but you should be able to come up with something to compress them. BTW, if anyone wants to borrow the spark plug thingie, you're welcome to it.

[SteveD CB500F]

So what stopped the valve dropping into the cylinder as soon as you remove the spring?

Oh - just reread the post.  Compressed air...

This must have worked or we'd have seen the post "dropped a valve into my engine..."   

[dusterdude]

ride the hell out of it until it oils the plugs so bad they wont fire.

[Pinhead]

Ok, I guess I'll wait until I need to pull the head for some reason. What about oil additives that might condition the seals? How about using ATF for a short while? Would that mess with the clutch?

[dusterdude]

none that i know that wont mess with the clutch

[Ibsen]

Ok, I guess I'll wait until I need to pull the head for some reason. What about oil additives that might condition the seals? How about using ATF for a short while? Would that mess with the clutch?

If you use oil additives that will tighten the leaking seals, you are also running the risk of clogging the oil ways.
Running a 20-50 oil might reduce the oil leak from the seals for a while, but in the end there is only one cure and that is to replace them.

[DammitDan]

I plan on pulling my head soon to do the same job you're going to be doing.  It will only take me about 4-5 hours total of labor for disassembly/assembly, and the gasket kit I bought was $75 for a full top end/bottom end kit (just in case I ever need to pull the clutch out again).  But then again, I've taken apart and put back together my top end 7 or 8 times now, and I hardly even need the manual anymore.  So if you've never done it before, expect to spend a weekend for the job.  I would recommend taking the head off, replacing the seals, and doing a thorough quality inspection on Saturday afternoon, then spending all day Sunday (8am to 8pm) reassembling it and going VERY SLOWLY and DELIBERATELY.  And be sure that when you take everthing apart, you log locations/immediately replace into the holes all the bolts you remove in the process.

Oh, and buy a torque wrench.  It's definitely a worthwhile investment.  Craftsman sells a decent one that goes from 10ft/lb to 85ft/lb for around $70.  You'd actually be surprised how much use it can be.

[Pinhead]

Does that top-end gasket kit include o-rings? I've also got a leak somewhere on the front of my motor that I'd like to eliminate if I were to take it apart.

What would be the "minimal" process?

[bryanj]

Gasket kit "should" include all the "O" rings but a couple of 750 sets i got recently for the F1 & 2 didnt have the oil feed to the head "O" rings( Yes i sourced some aftermarket "O" rings if people want them!) so best to get a genuine Honda set if you can (and afford it).
As I said previous, when you take the head off its the same bolts that hold down the barrel assembly so what usually happens (about 75% of the time) is if you dont pull the cylinders and change the base gasket and "O" rings a few weeks later you get a leak there, you may be one of the lucky ones BUT at the price of another head gasket is it worth the risk?
I dont think the Air Pressure idea will work too well on the 650 as the space round the valves is limited, its quite a common thing on cars, especially the old Ford Pinto engine but then the space is a lot more on those

[Ibsen]

Dismantling the top end isn't too hard to do since it can be done with the engine in the frame. But you will need a workshop manul. And you should follow all the steps regarding loosening and torquing down the cylinder and cylinder head bolts, and the rocker cover bolts. I also agree about replacing the base gasket and the o-rings for the oil ways. In the gasket set I bought from David Silver, the o-rings for the oil ways are made of nitrile rubber, and they are much better than the original rubber o-rings. But if you don't have any leaks from the top end, you might be able to replace the valve stem seals by using compressed air in the cylinders, but agree with bryanj, there isn't that much work space.
One thing that is very important to do when you are going to do a top end job on the 650 is to clean out the dirt around the two middle front cylinder/cylinder head bolts  beafore you start to loosen these bolts. Usually road dirt will be collected around the head of the bolt, making it difficult to fit a socket. And if you don't clean it out, the dirt will fall down into the bolt hole in the crankcase, contaminating the threads. It can be a bit tricky to get all the dirt out, but with some patience, it can be done.

And this slide shows what it is like to take off the cylinder head. I took these pictures when I had to replace the cam chain tensioner last spring.

http://smg.photobucket.com/albums/v291/ibsen22000/Cam%20chain%20tensioner/?action=view&current=RotationofDSCN1148.jpg&slideshow=true&interval=3

[Pinhead]

The work isn't necessarily the problem. I could tear the engine down to the last bolt if I needed to. However, the more work I do to the thing the more expensive it'll be to put it all back together. I don't think I want to risk dropping a valve into the engine, so when I do it I'll pull the head. This will give me the opportunity to have a little porting and combustion chamber work done, as well. Gasket sets, etc. cost money. I didn't want to have to pull the jugs, but while I'm there, might as well do some piston work. All of this would add up pretty quickly. Is there any other work that should be done while I have the head removed? Any "weak spots" in the 650 motor that should be checked/replaced?

[DammitDan]

Check your compression before you tear anything apart.

If you compression is still good, then you likely won't have to replace the rings.  However, be extremely careful putting the jugs back over the pistons (it's better if you have 2 people).  You won't need any special tools to compress the rings, a fingernail has always worked fine for me.

The only thing I must say be careful of is:  There are a lot of small bolts attached to this bike.  And they all like to fall down into the case.  I don't know how, but I think it's part of the same magical force that makes tools roll to a stop directly under the center of the car when you drop them.

So, cover all the holes as soon as you open them up.  You'd be surprised how a single nut can ruin your whole weekend.  (Mine managed to defy physics and drop straight into the crankcase after 3 or 4 bounces outside... I swear to god it completely changed direction mid-bounce!).