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FJBen
06-12-2007, 03:18 PM
Chevy 350, 4 bolt main, RV cam...puff-o-bluish smoke on startup and then also right after idle. Sitting at a stoplight, when you take off, if puffs blue smoke.

I'm guessing it's valve stem seals....does that sound about right? I know the carb is running rich which adds to the smell, but any other ideas on the smoke?

Uncle Ben
06-12-2007, 03:42 PM
Chevy 350, 4 bolt main, RV cam...puff-o-bluish smoke on startup and then also right after idle. Sitting at a stoplight, when you take off, if puffs blue smoke.

I'm guessing it's valve stem seals....does that sound about right? I know the carb is running rich which adds to the smell, but any other ideas on the smoke?

How about sudden accell after long decell? If your running rich at idle you could be washing the cylinders which will cause some oil-bipass when throttle is cracked open. If it puffs blue after decelling down a hill right after you step back on the juice it's a good indicator of worn or rolled valve stem seals.

FJBen
06-12-2007, 03:50 PM
How about sudden accell after long decell? If your running rich at idle you could be washing the cylinders which will cause some oil-bipass when throttle is cracked open. If it puffs blue after decelling down a hill right after you step back on the juice it's a good indicator of worn or rolled valve stem seals.


The first sounds about right. It seems to do it more at the stoplights, at least thats when I notice it more.

The truck was in california for 4~5 years and I can't help but think he had it tuned for there. It' smells really strong which makes me believe it's really rich. On the other hand, it did basically sit for most of those years with very minimal usage so I'm wondering if it just dried up the seals???

The carb is a quadra-jet....carbs make me want to go TBI :)

SteveH
06-13-2007, 09:34 AM
I'd vote strongly for bad valve stem seals - typical Chevy problem. You can most easily replace them on the car using compressed air and a lever-type valve spring compressor. Not huge job, but acccess could be tight in some areas.

Uncle Ben
06-13-2007, 10:32 AM
I'd vote strongly for bad valve stem seals - typical Chevy problem. You can most easily replace them on the car using compressed air and a lever-type valve spring compressor. Not huge job, but acccess could be tight in some areas.


I totally agree that it's most likely GM's cheesy umbrella seals at fault. However, I have dealt with over carbed customer vehicles several times and the cylinder wash down can be a major player in blow-by. Need to diagnose and fix the problem first instead of just throwing money at it until it stops! BTW Ben, I have the air fitting for the spark plug hole, a spring compressor and the little oil control clips for the rockers that limit the amount of oil that will be running down your inner federwells :rolleyes: that you can borrow if you need them.

FJBen
06-13-2007, 10:43 AM
I totally agree that it's most likely GM's cheesy umbrella seals at fault. However, I have dealt with over carbed customer vehicles several times and the cylinder wash down can be a major player in blow-by. Need to diagnose and fix the problem first instead of just throwing money at it until it stops! BTW Ben, I have the air fitting for the spark plug hole, a spring compressor and the little oil control clips for the rockers that limit the amount of oil that will be running down your inner federwells :rolleyes: that you can borrow if you need them.


Very cool, thanks guys. I think we are going to try the easy path of tweaking the carb tonight. If that doesn't fix it, well then on to the next, although it's not major.

I have an ARB/longfield setup that needs to go in before that.:thumb:

Jenny Cruiser
06-13-2007, 02:52 PM
I vote seals & blowby. The seals in my 78K mile Scout leak (they're 41 years old) and it will smoke a bit at start up, but not after the engine is warm. No smoke at/after stoplights.

FJBen
06-14-2007, 10:34 AM
Toyed with the carb/timing/vacuum last night.

Best vacuum reading of 18 was at 35 degrees adavance:eek: but she really started smoking. We put her at 8 and could get a steady 15 with the same amound of smoke as I had before :rolleyes: So yeah. next test is compression to see if it's the rings or not.

The engine was rebuilt about ~5 years ago and literally has maybe 3,000 miles. New gaskets, rings, rebuilt heads and cylinder hone. It basically sat for many years which I think contributed to some dryness in the seals.

I guess if we have compression issues, or rings bad...I may just look at options of TBI swap from a junkyard truck. :rolleyes: the wife will love that :D

Uncle Ben
06-14-2007, 10:39 AM
Sorry to hear that Ben! There is still a slight (very slight) chance your cylinders were getting washed and driving it around with a better tune will reseat the rings. Strongest probability is the valve seals are cracked as everyone has suggested. I guess I will round up what your gonna need for umbrella deployment! ;) Be sure to do a dry and wet comp test so you know for sure it's valve stem leakdown and not scored cylinders.

Toyed with the carb/timing/vacuum last night.

Best vacuum reading of 18 was at 35 degrees adavance:eek: but she really started smoking. We put her at 8 and could get a steady 15 with the same amound of smoke as I had before :rolleyes: So yeah. next test is compression to see if it's the rings or not.

The engine was rebuilt about ~5 years ago and literally has maybe 3,000 miles. New gaskets, rings, rebuilt heads and cylinder hone. It basically sat for many years which I think contributed to some dryness in the seals.

I guess if we have compression issues, or rings bad...I may just look at options of TBI swap from a junkyard truck. :rolleyes: the wife will love that :D

FJBen
06-14-2007, 03:39 PM
Sorry to hear that Ben! There is still a slight (very slight) chance your cylinders were getting washed and driving it around with a better tune will reseat the rings. Strongest probability is the valve seals are cracked as everyone has suggested. I guess I will round up what your gonna need for umbrella deployment! ;) Be sure to do a dry and wet comp test so you know for sure it's valve stem leakdown and not scored cylinders.


Yeah it's a bit of a bummer...it's not smoking badly, but something seems amiss. The comp test shall tell all. Although i did find a 98 5.7 TBI with great compression and all harness for $800...hmmmmmmmmm:D

Uncle Ben
06-14-2007, 05:59 PM
Yeah it's a bit of a bummer...it's not smoking badly, but something seems amiss. The comp test shall tell all. Although i did find a 98 5.7 TBI with great compression and all harness for $800...hmmmmmmmmm:D


Last year of TBI was 95. TBI was OBD1 and Vortec, 96 up, is OBD2

FJBen
06-15-2007, 09:47 AM
Last year of TBI was 95. TBI was OBD1 and Vortec, 96 up, is OBD2

Thats what I was finding, they must have had the year wrong.

FJBen
06-25-2007, 09:51 AM
Did the compression test on sunday.

120
120
120
120
119
120
121
120

So I'd say I don't have a compression problem. We didn't do a "leak down" as we didn't have that tool, but we figured if the compression is that close to eachother there "probably" isn't anything major wrong....most likely just the valve seals.

Interesting notes:


My temp sender is in the side of the block, under the ramhorn manifolds. Now with the 195 thermostat, she raises up to 220 degrees and the "rockects" down when the thermo opens to 180...then climbs back to ~200 where it resides and the fan starts to work.

Could that sender on the side be getting heat from the manifolds showing it's hotter than it really is???

Uncle Ben
06-25-2007, 12:01 PM
Did the compression test on sunday.

120
120
120
120
119
120
121
120

So I'd say I don't have a compression problem. We didn't do a "leak down" as we didn't have that tool, but we figured if the compression is that close to eachother there "probably" isn't anything major wrong....most likely just the valve seals.

Interesting notes:


My temp sender is in the side of the block, under the ramhorn manifolds. Now with the 195 thermostat, she raises up to 220 degrees and the "rockects" down when the thermo opens to 180...then climbs back to ~200 where it resides and the fan starts to work.

Could that sender on the side be getting heat from the manifolds showing it's hotter than it really is???

It could....Rams Horns run hot so good possibility.

Do a wet comp test. Take a normal/dry test then add two squirts of motor oil into the cyl and recheck. If comp rises it shows loss if via cylinder damage/rings if it stays the same comp loss is valves. Your readings look great and consistent so I think the jugs are in good shape. I would say to the valve stem seals and run with it!