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Author Topic: Help my CB350F is spewing white smoke on one of it's exhaust!  (Read 3099 times)

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Offline fastlee84

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Help my CB350F is spewing white smoke on one of it's exhaust!
« on: December 17, 2010, 12:56:52 AM »
Hi guys, I acquired a cb350four. I managed to start the engine after changing the battery as well as the rectifier as I found out that it is not charging the battery.

After that managed to get it running. But as I travel on the road, I responses that it could only reach to 90km/hr and not more. I also notice white smoke coming out of one of my right side exhaust.

When I took out the right side exhausts, I saw lots of engine oil in the second last piston.

The bike had it's pistons changed before.
I suspect it might be the piston ring or one of the valve that is causing the leak or engine oil. Can anyone suggest what could I do to stop the leak and get it to go faster?
Forgive me if i ask too much! I just wanna learn.

Offline Terry in Australia

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #1 on: December 17, 2010, 01:37:29 AM »
Buy a compression gauge mate, you just warm the engine up, then (carefully) remove all of the spark plugs. Screw the gauge into each spark plug hole, then crank the engine for a few seconds (5 should do) with the throttle held wide open. Check the reading and write it down for each cylinder.

Compression pressure should be 140-170 psi for your bike mate, but I'm guessing that your #3 cylinder will be way below this. The fact that your bike has had new pistons installed doesn't mean much mate, unless it was done properly, and new pistons won't fix worn out cylinders. Do the compression test and get back to us. Have fun!

BTW, my stock CB350F would do a genuine 155 KPH after I rebuilt it mate, and that's plenty fast for a 350F! Cheers, Terry. ;D   
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Offline Sam Green Racing

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #2 on: December 17, 2010, 01:49:40 AM »
Despite what Terry said, a compression test won't fix it. It will have to have the top end off at least to find out the problem.
Problem could be, 1 worn valve guide (causes smoke) 2 cylinder worn, rings not fitted correctly, rings broken, piston cracked, piston holed. (would cause lack of power due to no compression)

Sam. :(
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Offline Terry in Australia

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #3 on: December 17, 2010, 01:57:39 AM »
So you don't think a compression test is a good place to start Sammy?  ???
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Offline fastlee84

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #4 on: December 17, 2010, 02:01:33 AM »
I think a compression test is needed so we can pin point the location or cause of it. Once we know which valve is low we can focus on it. Then I could open up the top to view exactly the cause of the leak. Correct me if I'm wrong.

Very likely it's my valve guide that is loose or worn out. I will check it out soon. Let u Gus know.

But another question is, if it IS my valve guide, what should I do?
Forgive me if i ask too much! I just wanna learn.

Offline Sam Green Racing

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #5 on: December 17, 2010, 02:17:52 AM »
So you don't think a compression test is a good place to start Sammy?  ???

Well he knows it's smoking and down on power plus he knows which cylinder is causing the problem, all a compression test will confirm is what is known all ready. So he spends money on a compression tester and still has to strip it down.
Chances are it won't be the guide as that wouldn't affect the performance, just make it smoke.

Sam. ;)
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Offline Terry in Australia

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #6 on: December 17, 2010, 04:15:51 AM »
Yep, agreed Sammy, however all he knows at this stage is that there is smoke coming out of his pipes and there's oil in one cylinder. A compression test will tell him the condition of all 4 cylinders, and if it's only one cylinder that is causing the problem, then he can concentrate on that one.

It could be a knackered piston and/or rings, or a burned valve, and once again, there are tests that he can do to determine which problem he is likely facing. A worn valve guide will make a bit of smoke, (moreso when he backs off than on accelleration) but I doubt that's going to reduce the power to almost nothing.

I bought a compression gauge on EBay for under 20 bucks, and there are plenty available on EBay now for that kind of money, so it's no great expense, and a great diagnostic tool. If his engine needs a complete top end rebuild, it won't add a great deal to the overall cost. Also, it'll be very handy for him to take with him next time he goes to look at a bike that he's thinking of buying. It'll probably save him a lot more than it's purchase price. ;) 
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Offline fastlee84

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #7 on: December 17, 2010, 07:21:56 AM »
Thank you for your detailed advice. Really appreciate. I will open up the top block soon to check out the extend of the damage.

By the way, let say it might be a busted piston ring, could I just change a single piston (.50) with the same size to fit into the cylinder without boring to the next size?
Or just get a replacement ring. I tried to contact the website I bought it from(Cmsnl.com), but they don't ship it to my country anymore. :(
Could I just get a piston ring from any company with the same size meant for CB350f?
Forgive me if i ask too much! I just wanna learn.

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #8 on: December 17, 2010, 07:37:42 AM »
If you go in to fix the problem, a complete new top end gasket set is in order, 4 new pistons, and a fresh set of rings.  The head can be measured and examined for damage, parts replaced, and a complete valve grind done.  The cylinder bores will need honed at the minimum.  Do it right if you have the parts off anyway. A compression test is also a good idea.  Borrow a tester if necessary.

Offline MoMo

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #9 on: December 17, 2010, 07:50:25 AM »
 

By the way, let say it might be a busted piston ring, could I just change a single piston (.50) with the same size to fit into the cylinder without boring to the next size?
Or just get a replacement ring. I tried to contact the website I bought it from(Cmsnl.com), but they don't ship it to my country anymore. :(
Could I just get a piston ring from any company with the same size meant for CB350f?
[/quote]

Kind of premature speculation,  better to ask the questions when you determine what you need.. A compression test is the start, a leak down test is better but not necessary, then tear down and find the damage,  and then ask while all is fresh in your mind.  BTW,  all can be done with the motor in the frame...Larry
Present: 1975 CB750, 1974 CB750, 1975 CB400 four,  1966 Suzuki S32 150cc , 1984 Honda Sabre, 1998 Pacific Coast (my daily rider) ,  ALL FOR SALE EXCEPT THE SUZUKI!

Past: Two Honda XL125s )(I rode one in enduros), Honda XL175, Yamaha DT1, MZ 250 ISDT, Harley Hummer, 1969 Honda CB350, 125 Sachs/DKW, 250 Ossa Pioneer, 1968 250 Montesa La Cross, Yamaha RD350, two Yamaha TX500, eight Honda CB450 dohc, 250 KTM, 1982 Yamaha 650 four(worst bike ever owned), seven Honda CB400f's, 1983 Honda VF750F Interceptor, 1981 CB650, 1973 CB350G, two 1973 CB750s, mint 1975 Honda CB550F, two 1977 CB750K7s , two GL500I Silverwings, 1973 Jawa 175 Trailmaster, SL350 K2, 1970 CB750K0, 1972 CB350, 1974 CZ 250 Enduro, and  probably others long forgotten.

Offline camelman

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #10 on: December 17, 2010, 09:29:20 AM »
It might not be piston rings at all.  The engine might be completely sound.  That "oil" could just be raw fuel mixed with carbon in the exhaust, and the white smoke coming out the exhaust could be more raw fuel coming through a cylinder that isn't firing.  There are a wide variety of issues that could cause that, one of which being a stuck carb float.  If a float is stuck, then too much fuel will enter the related cylinder for it to fire, and the engine won't make much power.  Or, it could be bad rings and valves.

What I am saying is that before speculating too much and worrying yourself, you should diagnose.

FYI, you cannot remove the cylinder head on a 350F while it is in the frame.  You can with a 400F (very similar bike), but that is because it has a lower overall engine height.

Camelman
1972 350f rider: sold
1972 350f/466f cafe: for sale
1977 CB400f cafe:sold
1975 CB400f rider: sold
1970 CB750 K0 complete bike: sold
2005 Triumph Sprint ST 1050 rider

We've got to cut it off... and then come down on rockets.  (quoted from: seven minutes of terror)

Offline MoMo

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #11 on: December 17, 2010, 10:16:06 AM »
Camelman,  thanks for the correction.  It has been awhile(about 30 years) since I worked on a 350f and naturally I assumed(you know what happens when once does that :D) the process was the same as the 400...Larry
Present: 1975 CB750, 1974 CB750, 1975 CB400 four,  1966 Suzuki S32 150cc , 1984 Honda Sabre, 1998 Pacific Coast (my daily rider) ,  ALL FOR SALE EXCEPT THE SUZUKI!

Past: Two Honda XL125s )(I rode one in enduros), Honda XL175, Yamaha DT1, MZ 250 ISDT, Harley Hummer, 1969 Honda CB350, 125 Sachs/DKW, 250 Ossa Pioneer, 1968 250 Montesa La Cross, Yamaha RD350, two Yamaha TX500, eight Honda CB450 dohc, 250 KTM, 1982 Yamaha 650 four(worst bike ever owned), seven Honda CB400f's, 1983 Honda VF750F Interceptor, 1981 CB650, 1973 CB350G, two 1973 CB750s, mint 1975 Honda CB550F, two 1977 CB750K7s , two GL500I Silverwings, 1973 Jawa 175 Trailmaster, SL350 K2, 1970 CB750K0, 1972 CB350, 1974 CZ 250 Enduro, and  probably others long forgotten.

Offline TwoTired

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #12 on: December 17, 2010, 10:32:40 AM »
It might not be piston rings at all.  The engine might be completely sound.  That "oil" could just be raw fuel mixed with carbon in the exhaust, and the white smoke coming out the exhaust could be more raw fuel coming through a cylinder that isn't firing.  There are a wide variety of issues that could cause that, one of which being a stuck carb float.  If a float is stuck, then too much fuel will enter the related cylinder for it to fire, and the engine won't make much power.  Or, it could be bad rings and valves.

What I am saying is that before speculating too much and worrying yourself, you should diagnose.

FYI, you cannot remove the cylinder head on a 350F while it is in the frame.  You can with a 400F (very similar bike), but that is because it has a lower overall engine height.

+1 on the analysis point.

A cylinder will oil up if it simply doesn't fire for a while.   Look at the spark plug tip.  Is it fouled or sparking?  Does swapping plugs move the problem?  Is the spark lead reliable for the dead cylinder?

It sure won't hurt to do a compression test.  But, there are also carburetion issues that can prevent the cylinder from firing and becoming an oil pump.

Cheers,

Lloyd... (SOHC4 #11 Original Mail List)
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Offline phil71

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #13 on: December 17, 2010, 10:59:15 AM »
stuck float is a good tip if the smoke is white,and not blue. a quick check would be to sample the oil and see if it smells heavily of fuel, or is very diluted. If it is, a compression check with the fuel drained and off would let you know if there's any permanent damage to the rings.

Online faux fiddy

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #14 on: December 19, 2010, 12:31:25 AM »
It might not be piston rings at all.  The engine might be completely sound.  That "oil" could just be raw fuel mixed with carbon in the exhaust, and the white smoke coming out the exhaust could be more raw fuel coming through a cylinder that isn't firing.  There are a wide variety of issues that could cause that, one of which being a stuck carb float.  If a float is stuck, then too much fuel will enter the related cylinder for it to fire, and the engine won't make much power.  Or, it could be bad rings and valves.

What I am saying is that before speculating too much and worrying yourself, you should diagnose.

FYI, you cannot remove the cylinder head on a 350F while it is in the frame.  You can with a 400F (very similar bike), but that is because it has a lower overall engine height.

Camelman

My head and bores came off with the engine mounted in the frame.

If you go in to fix the problem, a complete new top end gasket set is in order, 4 new pistons, and a fresh set of rings.  The head can be measured and examined for damage, parts replaced, and a complete valve grind done.  The cylinder bores will need honed at the minimum.  Do it right if you have the parts off anyway. A compression test is also a good idea.  Borrow a tester if necessary.

Absent real serious problems, a hone, and just lapping the valves can do wonders.  Just depends on how you want to use the bike, and what you want to spend. Re-using pistons is fine  if the rings are or can be made  free in their grooves and not stuck,  and the bores measure out okay without grooves or pitting..
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Offline camelman

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #15 on: December 19, 2010, 02:46:40 PM »
Poor Boi said:  My head and bores came off with the engine mounted in the frame.

Camelman says:  ARGH!  I'm very jealous.  Mine won't.  I doubt there are any frame differences, so I'm just going to have to try mine again.  Heck, it needs to be rebuilt again anyway.

Camelman
1972 350f rider: sold
1972 350f/466f cafe: for sale
1977 CB400f cafe:sold
1975 CB400f rider: sold
1970 CB750 K0 complete bike: sold
2005 Triumph Sprint ST 1050 rider

We've got to cut it off... and then come down on rockets.  (quoted from: seven minutes of terror)

Offline Terry in Australia

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #16 on: December 19, 2010, 03:03:25 PM »
If you've ever tried to do a top end rebuild with your engine in the frame mate, you'll know that it's no fun at all, it's hard enough to compress piston rings and feeding pistons into cylinders on a bench, let alone in a bike frame. If you're a contortionist, or perhaps a masochist, my apologies, please ignore.  ;D
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Online faux fiddy

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #17 on: December 19, 2010, 03:34:21 PM »
I don't see that it should be any mounted  harder in the bike. Of course the tank and intake stuff was removed, and I pulled the coils up and used the rear skewer bolt across the to hold them out of the way, and tucked the coil wires out of the way.

Other than that it wasn't that hard, can't remember for sure, but I probably first fit the bores through behind where the carbs would be, alligned them port/starbord to the studs and set them on from behind.  I know that's how the valve cover went on best.

And squeezing the new rings into the bores took about an hour of figiting, but seems no more effort than if it were  out of the bike or a stand.


EDIT:
I didn't realize that doing this in the bike was not so common or I would have done some more meticulous notes of how I did it. I think I used the manuals in the FAQ's here. Here are the pics I took:


http://forums.sohc4.net/index.php?topic=58702.msg686630#msg686630
« Last Edit: December 19, 2010, 03:44:09 PM by poor boi »
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Offline MoMo

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #18 on: December 19, 2010, 04:09:07 PM »
If you've ever tried to do a top end rebuild with your engine in the frame mate, you'll know that it's no fun at all, it's hard enough to compress piston rings and feeding pistons into cylinders on a bench, let alone in a bike frame. If you're a contortionist, or perhaps a masochist, my apologies, please ignore.  ;D

Terry,  the 400f is really very easy to do in the frame-I've done three in the past year-mostly because everything is light and the chamfer of the cylinder allows the rings to slide in with only finger pressure....Larry
Present: 1975 CB750, 1974 CB750, 1975 CB400 four,  1966 Suzuki S32 150cc , 1984 Honda Sabre, 1998 Pacific Coast (my daily rider) ,  ALL FOR SALE EXCEPT THE SUZUKI!

Past: Two Honda XL125s )(I rode one in enduros), Honda XL175, Yamaha DT1, MZ 250 ISDT, Harley Hummer, 1969 Honda CB350, 125 Sachs/DKW, 250 Ossa Pioneer, 1968 250 Montesa La Cross, Yamaha RD350, two Yamaha TX500, eight Honda CB450 dohc, 250 KTM, 1982 Yamaha 650 four(worst bike ever owned), seven Honda CB400f's, 1983 Honda VF750F Interceptor, 1981 CB650, 1973 CB350G, two 1973 CB750s, mint 1975 Honda CB550F, two 1977 CB750K7s , two GL500I Silverwings, 1973 Jawa 175 Trailmaster, SL350 K2, 1970 CB750K0, 1972 CB350, 1974 CZ 250 Enduro, and  probably others long forgotten.

Offline Terry in Australia

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #19 on: December 19, 2010, 09:56:51 PM »
Well done guys, I did a top end rebuild on a Suzuki GS1000S with a new set of Yoshimura 1085cc pistons (no chamfer left after reboring the cylinders) and it was a pain in the butt. I've built penty of engines on the bench, and they were much easier, particularly when working at a comfortable height. Cheers, Terry. ;D
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Offline camelman

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Re: Help my CB350F is spewing white smoke on one of it's exhaust!
« Reply #20 on: December 19, 2010, 11:55:37 PM »
Yeah, I'm on the same page with Terry on this one.  I just built up a 466 (400f), and it wasn't chamfered.  I'm pretty sure I would have pulled my teeth out in frustration if it was in the frame.

However,  I think we are off topic.  Isn't there supposed to be more news on this spewing 350F?  I'd like to hear what happened with it.

Camelman
1972 350f rider: sold
1972 350f/466f cafe: for sale
1977 CB400f cafe:sold
1975 CB400f rider: sold
1970 CB750 K0 complete bike: sold
2005 Triumph Sprint ST 1050 rider

We've got to cut it off... and then come down on rockets.  (quoted from: seven minutes of terror)

 

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