Engine Rebuild & White Smoke out of the Breather Tube

[cgguy09]

Knights of the SOHV...Heed my call,
What's up, sailors? I've been out of the game for a while, but I'm back. Way back in November I had some issues with oil not getting to my cam shaft. I was able to blow it out. But I'm going to build the engine just to be safe. However, something that has been plaguing me is white smoke out the breather tube. When I first got the bike the rings were worn, I replaced them & rebuilt the engine. She ran perfect, minus the smoke out the tube. Then my bolts holding the Cam sprocket sheered off...(never forget to use a solvent on those bad boys). So I'm about to do another rebuild and I'm trying to avoid the breather tube smoke again.

Any ideas what could be causing it? I put too many miles & road it too hard to be residual in the top of the engine after the rebuilds. I'm thinking maybe blow by in the rings? The compression tests were always spot on. I inspected the rings & they looked perfect. I honed the inside of the cylinders each time. Would oversized rings be a solution?

My engine oil level was always within spec. An old timer told me not too long ago to keep it at the half way point that the high oil mark was too high & caused too much oil up in the fly wheel. (I think he just liked to talk though)

I want to be clear, this was't soft gentle puffs of smoke, when I was at a stop light or stop sign, I would notice the smoke bellowing up around me as if Santan were ready to pull me into the depths of hell.

Anyway boys, its good to be back. Thanks in advance for the help.

 

[ApriliaBill]

On this bike do you have a di stick or window? If it's a dip stick do you know for a fact that is the correct stick? It does sound to me you have too much oil. How much oil did you put in it? If everything is spec, and your not losing oil, It doesn't make much sense.... Maybe valve guides didn't seat...

 

[cgguy09]

On this bike do you have a di stick or window? If it's a dip stick do you know for a fact that is the correct stick? It does sound to me you have too much oil. How much oil did you put in it? If everything is spec, and your not losing oil, It doesn't make much sense.... Maybe valve guides didn't seat...

I have a stick...and I guess I can't be sure if its the right one. The bikes been through so many hands over the years. It fits in to the engine case just fine and showed the shame dull finish as the rest of the engine before I shined it up. The valve guides should be set, especially after the last rebuild...when those bolts on the Cam sheered I bent two valves & just replaced everything.

That's why I think it may be ring issue? I know some people always go with a larger size.

 

[mydlyfkryzis]

White smoke is usually water vapor.....I put a clear tube on my CB360, and it too has white smoke...The water condenses quite a bit on the inside surface too. Once run for a while, most of the moisture is out of the engine, and the smoke is very little...

The NORMAL product of good combustion is water. The reason cars blow white smoke out the muffler in the winter...Once fully warmed, the hot exhaust doesn't allow condensation and the vapor remains clear.

The bike is pretty hot, but the tube is not...the water vapor (from a little blowby) condenses and becomes visible on the exit of the tube.

If it looks like a low pressure steam leak, you may have an issue, but a little vapor released from the tube is normal.

 

[rockcitycafe]

sounds like excessive blowby, even though the cylinders were honed, it doesn't mean they are round or straight, I'd have it bored first over

 

[cgguy09]

White smoke is usually water vapor.....I put a clear tube on my CB360, and it too has white smoke...The water condenses quite a bit on the inside surface too. Once run for a while, most of the moisture is out of the engine, and the smoke is very little...

The NORMAL product of good combustion is water. The reason cars blow white smoke out the muffler in the winter...Once fully warmed, the hot exhaust doesn't allow condensation and the vapor remains clear.

The bike is pretty hot, but the tube is not...the water vapor (from a little blowby) condenses and becomes visible on the exit of the tube.

If it looks like a low pressure steam leak, you may have an issue, but a little vapor released from the tube is normal.

Yes, unfortunately it is the later, the low pressure steam leak. After another rebuild I noticed it & it went away after a few good hard rides. This one lingered for a good while and got worse as I rode and the harder I rode it... Insert Sad Face

 

[cgguy09]

sounds like excessive blowby, even though the cylinders were honed, it doesn't mean they are round or straight, I'd have it bored first over

Thanks for the reply,
Damn, I'll take it to my local shop and see if they'll measure the bore for me. I know bore-tech does this, but I know its pricey. Money, as always is an issue. Any recommendations on the way I should proceed forward? Or should I just get ready to spend a ton of cash?

-cFogs

 

[rockcitycafe]

about $50 a hole and $75 for a set of first over pistons

 

[Tim]

Is this the 1971 CB350 K3 you have in your profile?

Definitely invest in some 0.25 or 0.50 pistons and rings (I've always skipped the 0.25 just to be sure I'm getting into fresh meat on the cylinders). They seem to be all over eBay for the $100 range for a set.

Like Sean says, $50 a hole is the right price for a bore/hone. So $100 for machine work and $100 for parts and you have a new motor.

 

[cgguy09]

Is this the 1971 CB350 K3 you have in your profile?

Definitely invest in some 0.25 or 0.50 pistons and rings (I've always skipped the 0.25 just to be sure I'm getting into fresh meat on the cylinders). They seem to be all over eBay for the $100 range for a set.

Like Sean says, $50 a hole is the right price for a bore/hone. So $100 for machine work and $100 for parts and you have a new motor.

Roc & Tim,
Thanks for the advice, boys. As always, I appreciate it. I'll be breaking it down this week & visiting Flying Tiger to see if they'll hook me up.

Take care,
cFogs