Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC - Page 2 - Chevelle Tech
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post #16 of 32 (permalink) Old Jun 22nd, 16, 2:06 AM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

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Originally Posted by Tom Mobley View Post
That piston doesn't look to have been run with water in the cylinder. Any of the pistons clean? running with water sort of steam blasts the carbon off the piston and out of the chamber. usually one of two are much cleaner than the other. 3 & 5 would be clean if the head gasket was bad between those two.
This engine was re-purposed (I would say rebuilt but there's no way) about a month or two ago. He pulled it from one car and transplanted it to the Chevelle. I'm convinced that during this transplant and "re-purposing", he failed to correctly torque a head down. I'm also going to assume the reason the piston isn't as clean as you would expect it to look having had coolant running into it is because the engine has barely been run.... but who knows

At this point, I'm going to be replacing the gaskets after I clean the surface of the block. I've taken the heads apart and so far haven't found any sign of worn valve guide seals.
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post #17 of 32 (permalink) Old Jun 22nd, 16, 9:28 AM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

What do you mean coolant is dissipating? Does the car have an overflow tank? Maybe the white smoke and residue on pavement are an idle miss in the low compression cylinder(s)?
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post #18 of 32 (permalink) Old Jun 22nd, 16, 4:49 PM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

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What do you mean coolant is dissipating? Does the car have an overflow tank? Maybe the white smoke and residue on pavement are an idle miss in the low compression cylinder(s)?
Sorry, "disappears" would be more appropriate. No, its not in the reservoir, it's just gone. I filled up the radiator when I bought the car and after 2 days of tinkering on the engine realized in addition to the other symptoms, the coolant was about 1/2 gone.
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post #19 of 32 (permalink) Old Jun 22nd, 16, 5:50 PM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

What he said. does the car have a coolant recovery bottle? If it just has an overflow hose running down the side of the radiator it will dump water out everytime you fill the radiator to the top.

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post #20 of 32 (permalink) Old Jun 22nd, 16, 6:13 PM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

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What he said. does the car have a coolant recovery bottle? If it just has an overflow hose running down the side of the radiator it will dump water out everytime you fill the radiator to the top.
I appreciate everyone's input and remarks. I should have been clearer in my last comment - it does have a reservoir, and no, it is not leaking onto the ground straight from the radiator nor is it going back into the reservoir. There's clearly a crack or blown head gasket causing the coolant to be burned off.
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post #21 of 32 (permalink) Old Jun 23rd, 16, 2:12 AM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

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I appreciate everyone's input and remarks. I should have been clearer in my last comment - it does have a reservoir, and no, it is not leaking onto the ground straight from the radiator nor is it going back into the reservoir. There's clearly a crack or blown head gasket causing the coolant to be burned off.
What the guys have been trying to tell you here, although not getting the point across is "The Coolant Does Not Burn". It turns to "Steam" so any place you had a "Coolant Leak" would be so clean it cannot be mistaken. The point is you have Coolant going someplace other than the combustion chambers in your engine. The "Inside" is really clean and no evidence of Coolant running into the oil. SOOOOOO how about a leaking "Heater Core". It won't take you a minute to find the area that is damp if that's where its going. Incidentally I had a small block 400 in my truck. It started with a low speed miss that went away after startup, but would return when shutoff(hot or cold). When I finally pulled the heads, I had two cracked Cylinder Heads,#2,#5 Cylinders......they were so clean, both Cylinder Head and Piston that they looked like they were brand new, except for the crack in the heads. No telltale smoke, and the only coolant I lost was negligible. When I had a Heater Core Leak, I had to disconnect the hoses because the leak was that bad. I hope this helps.
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post #22 of 32 (permalink) Old Jun 23rd, 16, 4:06 AM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

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What the guys have been trying to tell you here, although not getting the point across is "The Coolant Does Not Burn". It turns to "Steam" so any place you had a "Coolant Leak" would be so clean it cannot be mistaken.
Ha! Well, it wasn't obvious enough because the questions being asked over and over, I had already answered multiple times... but it makes sense now Just needed someone to yell lol.

I've brain dumped as much info as possible. The white smoke, disappearing coolant, lower compression in #8, wet spark plug in #8, vacuum tests... it felt obvious. But then again, as a software engineer, the easy bugs always turn into the hard ones to find because I spend time looking for complex errors in my algorithms when it turns out the problem was simply a missing comma......

I'll check the heater core tomorrow. But now that it's long blocked, I have had some busy nights with my son cleaning and rebuilding the cylinder heads hah.
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post #23 of 32 (permalink) Old Jun 23rd, 16, 4:33 PM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

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Originally Posted by jaketoolson View Post
Yah, I read A12 which I thought was "January 1, 1972" but I was unsure. I'm not overly concerned about the date either

To reiterate my original comments -- smoke coming from exhaust, vacuum readings fluctuate, coolant dissipating... this is why I've concluded head gasket, but also come here for help narrowing things down.
Engine oil usually looks like chocolate milk too.... Easy diagnosis when you see that.
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post #24 of 32 (permalink) Old Jun 29th, 16, 11:54 PM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

Update:

First off, no heater core... all deleted.

After cleaning all surfaces, I replaced the head/intake/exhaust gaskets etc; Replaced spark plugs. Cleaned the heads and valves -- the exhaust valves ALL seem to have not been seated or lapped. If you look at the pictures from before, note the exhaust valves don't line up evenly with the intake valves. I lapped everything by hand and although I noticed a slight difference in the seat of the exhaust valves, clearly an issue.

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post #25 of 32 (permalink) Old Jun 30th, 16, 3:58 PM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

I'm still getting smoke from both tailpipes. I'm going to try and move it out of the garage so I can film it and show the color.

I installed gauges - volt/temp/oil. Let it idle for 10 minutes and the temp climbed to 250 (it has 190 tstat). I also unplugged the vacuum line going to the transmission modulator ruling out ATF.

Once I pull it out, I'll have to borrow a floor jack as its pretty low to the ground and I can't easily get to the oil pan and filter to check for milky color etc;

To take the heads to a machinist and have them rebuilt costs about $550. I'd rather pull the engine and just throw a cheap 350 crate in and get the rest going.


Last edited by jaketoolson; Jun 30th, 16 at 4:13 PM.
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post #26 of 32 (permalink) Old Jun 30th, 16, 9:28 PM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

may as well pull the cam and see what you got in there before deciding to rebuild the heads or drop in a short block. are alum heads out of the question?

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post #27 of 32 (permalink) Old Jul 2nd, 16, 1:58 AM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

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are alum heads out of the question?
I did another compression test. For brevity, everything is looking to be around 150lbs. Squirted some oil in the cylinders and the numbers really didn't change... so no, Aluminum heads are not out of the question!
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post #28 of 32 (permalink) Old Jul 3rd, 16, 1:29 AM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

Just another thought here, Is the smoke you are getting constant and an extremely large amount, or is it more of puffs on startup and sort of smoky deceleration....????? Good bet that your intake valve guides are allowing oil to get buy. You can try to install some umbrella seals since you already have the motor back together. If this fixes it..... they lasted a really long time on an old 56 Chevy I had. They were a pain in the ass to install(serious sludge)but they lasted until I changed the powerglide to a 3-speed and blew the motor up. I hope this helps.
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post #29 of 32 (permalink) Old Jul 3rd, 16, 2:52 AM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

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Originally Posted by langss View Post
Just another thought here, Is the smoke you are getting constant and an extremely large amount, or is it more of puffs on startup and sort of smoky deceleration....????? Good bet that your intake valve guides are allowing oil to get buy. You can try to install some umbrella seals since you already have the motor back together. If this fixes it..... they lasted a really long time on an old 56 Chevy I had. They were a pain in the ass to install(serious sludge)but they lasted until I changed the powerglide to a 3-speed and blew the motor up. I hope this helps.
I did install valve umbrella seals including the o-rings. The smoke was constant.

Today I did wet compression tests and the readings were not greater than a 5% increase from dry readings in any cylinders (averages). So the rings are good and the heads need to be machined.
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post #30 of 32 (permalink) Old Jul 3rd, 16, 3:12 PM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

Well I was hoping.........

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