Exhaust smoke - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Sonicman · 08-23-2010, 08:36 PM

Just rebuilt my 250 L6. Started up great BUT.......now there is white/blue smoke coming out the tail pipe. This was not there before. This was my first rebuild. Does this mean my head gasket is bad and the smoke is from burning oil? I torqued the head bolts to 95 ft-lbs as my Haynes book told me. I have no leaks any where. Need advice before I pull the head off again.

71meangreenc10 · 08-23-2010, 09:15 PM

Go back through and check the basics, do a compression test if you have the tools, check the fluids for mixing. White usually means antifreeze is burning and blue is oil. Something is mixing somewhere....

How much of a rebuild did you do? Full with piston rings or just the top end?

Smitty

Davetopay · 08-23-2010, 09:47 PM

Yeah, we need to know how in depth the rebuild was. Was it a hone and ring job with some new bearings, or was it a full machine shop job?

Sonicman · 08-23-2010, 10:06 PM

New pistons and rings, and rod bearings, cleaned build up on all valves. And all new gaskets. No machine work. Also I noticed the oil gauge reading very very low.

Davetopay · 08-24-2010, 06:34 AM

Quote:

Originally Posted by Sonicman

New pistons and rings, and rod bearings, cleaned build up on all valves. And all new gaskets. No machine work. Also I noticed the oil gauge reading very very low.

Ok, did you at least hone the cylinders? If not the rings won't seat and you will burn oil.

cam.man67 · 08-24-2010, 07:09 AM

Quote:

Originally Posted by Sonicman

Just rebuilt my 250 L6. Started up great BUT.......now there is white/blue smoke coming out the tail pipe. This was not there before. This was my first rebuild. Does this mean my head gasket is bad and the smoke is from burning oil? I torqued the head bolts to 95 ft-lbs as my Haynes book told me. I have no leaks any where. Need advice before I pull the head off again.

Valve guides, perhaps? The same thing happens to me on startup, and I know my guides are getting worn. I doubt the head gasket is the problem.

Sonicman · 08-24-2010, 09:16 AM

Did not hone the cylinders. They seems very smooth. I did clean everything with brake parts cleaner.

68gmsee · 08-24-2010, 10:04 AM

Quote:

Originally Posted by Sonicman

Did not hone the cylinders. They seems very smooth. I did clean everything with brake parts cleaner.

You may have to redo the whole thing again...

Tkmadone · 08-24-2010, 12:00 PM

I disagree with the honing, unless there was cylinder damage.

http://www.snowvalley.20m.com/bikes/dnthone.htm

Did you get the head, specifically valve guides and seals looked at?

cdowns · 08-24-2010, 12:19 PM

did you measure the ring gap b4 installation?

68gmsee · 08-24-2010, 04:25 PM

Re. honing: Yes, it definitely helps to seal the rings. Old engines that have a lot of miles on them have an uneven surface that doesn't excactly match the circumference of the new rings.

I've heard of some saying it's not necessary, but 100 yrs of machinists, mechanics and engineers saying it does is enough to convince me.

Reason for machine work on an old engine is wear on the cylinders may be uneven or you could have cylinders that are not perfectly round requiring reboring.

raycow · 08-24-2010, 04:51 PM

How much cylinder ridge did you have? Did you remove the ridge before installing new parts?

Ray

hotrod100 · 08-24-2010, 06:02 PM

Another question is did you stagger the ring gaps on the piston?

08-23-2010, 08:36 PM	#1
Sonicman Registered User Join Date: Jul 2010 Location: Denton, TX Posts: 155	Exhaust smoke Just rebuilt my 250 L6. Started up great BUT.......now there is white/blue smoke coming out the tail pipe. This was not there before. This was my first rebuild. Does this mean my head gasket is bad and the smoke is from burning oil? I torqued the head bolts to 95 ft-lbs as my Haynes book told me. I have no leaks any where. Need advice before I pull the head off again. Last edited by Sonicman; 08-23-2010 at 08:49 PM.

08-23-2010, 09:15 PM	#2
71meangreenc10 Its a Truck Thing...... Join Date: Dec 2004 Location: Sierra Vista, Arizona Posts: 3,159	Re: Exhaust smoke Go back through and check the basics, do a compression test if you have the tools, check the fluids for mixing. White usually means antifreeze is burning and blue is oil. Something is mixing somewhere.... How much of a rebuild did you do? Full with piston rings or just the top end? Smitty __________________ 71 C10 283/3SPD Full Resto 71 GMC 1500 Sierra Grande http://67-72chevytrucks.com/vboard/s...d.php?t=518599 70 C10 Suburban Former military GSA truck. 72 Chevy Blazer 4X4, Sloppy Jo, Mountain Climber. Wife says no more trucks. http://67-72chevytrucks.com/vboard/s...d.php?t=707378 72 GMC 1 Ton Motor Home, wife said no more trucks until she saw this one. Gen 3 6.0/4L80E 4.10 http://67-72chevytrucks.com/vboard/s...d.php?t=761110 68 GMC Suburban was 3/4 ton, now 1/2.Wife shook her head 71 C30 Wrecker 71 C20 Scott-Bilt As weird as it gets..BB Cheyenne AC Truck 68 GMC Long Stepside. They keep following me home 71 C20 Longhorn/Ole Yellor 69 C30 Former Motor Home, Flat Bed time

08-23-2010, 09:47 PM	#3
Davetopay Registered User Join Date: Oct 2009 Location: Leesburg, VA Posts: 424	Re: Exhaust smoke Yeah, we need to know how in depth the rebuild was. Was it a hone and ring job with some new bearings, or was it a full machine shop job?

08-23-2010, 10:06 PM	#4
Sonicman Registered User Join Date: Jul 2010 Location: Denton, TX Posts: 155	Re: Exhaust smoke New pistons and rings, and rod bearings, cleaned build up on all valves. And all new gaskets. No machine work. Also I noticed the oil gauge reading very very low. Last edited by Sonicman; 08-23-2010 at 10:08 PM.

08-24-2010, 09:16 AM	#7
Sonicman Registered User Join Date: Jul 2010 Location: Denton, TX Posts: 155	Re: Exhaust smoke Did not hone the cylinders. They seems very smooth. I did clean everything with brake parts cleaner.

08-24-2010, 12:00 PM	#9
Tkmadone Registered User Join Date: Aug 2009 Location: Simi Valley, CA Posts: 193	Re: Exhaust smoke I disagree with the honing, unless there was cylinder damage. http://www.snowvalley.20m.com/bikes/dnthone.htm Did you get the head, specifically valve guides and seals looked at?

08-24-2010, 12:19 PM	#10
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Exhaust smoke did you measure the ring gap b4 installation? __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

08-24-2010, 04:25 PM	#11
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Exhaust smoke Re. honing: Yes, it definitely helps to seal the rings. Old engines that have a lot of miles on them have an uneven surface that doesn't excactly match the circumference of the new rings. I've heard of some saying it's not necessary, but 100 yrs of machinists, mechanics and engineers saying it does is enough to convince me. Reason for machine work on an old engine is wear on the cylinders may be uneven or you could have cylinders that are not perfectly round requiring reboring.

08-24-2010, 04:51 PM	#12
raycow Registered User Join Date: Mar 2003 Location: San Francisco, CA USA Posts: 2,454	Re: Exhaust smoke How much cylinder ridge did you have? Did you remove the ridge before installing new parts? Ray

08-24-2010, 06:02 PM	#13
hotrod100 Registered User Join Date: Aug 2009 Location: Bullhead City, AZ. Posts: 88	Re: Exhaust smoke Another question is did you stagger the ring gaps on the piston? __________________ My build thread.



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