Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC - Chevelle Tech
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post #1 of 32 (permalink) Old Jun 19th, 16, 1:48 AM Thread Starter
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Question Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

Have a 350 SBC in the Chevelle that I just purchased. I need help with troubleshooting what is either a blown head gasket/gasket leak, intake gasket leak, or worn valve guide or all of the above? Here is everything I've done to try and troubleshoot and narrow it down:

Ran a compression test (WOT, dizzy disconnected, engine idled for a few minutes so not quite cold) and came up with:
1 - 130
2 - 145
3 - 140
4 - 146
5 - 140
6 - 137
7 - 150
8 - 135

Spark plug in #8 has some oil IN it (not on the threads) the rest look decent.

White smoke coming from the passenger side tail pipe, leaving black mark on the ground.

Vacuum test has it slightly fluctuating between 16-18hg.

Other basics:
-HEI distributor cap
-Timing is unknown but appears to be around 10-12BTDC @ idle.
-Replaced carb today with brand new Edelbrock w/manual choke (this helped eliminate a vacuum leak @ carb - it was a POS).
-Replaced fuel pump today (mechanical)
-New fuel line from fuel pump to carb

Also note, the vehicle does not yet have a water temperature gauge installed. I make note of this because the engine compartment feels overly hot... I'll hook up the gauge tomorrow to help narrow things down.

Vacuum test results confuse me based on the supplied diagram. Needle was rapid but then other times it was regular (Harbor Freight tool?) so looking at plugs and exhaust as to help further diagnose.
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post #2 of 32 (permalink) Old Jun 19th, 16, 2:30 AM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

A few squirts of oil in the low cyl's and a retest with better results would indicate ring wear, no change would indicate valve's.
The white smoke could be coolant or trans fluid (if auto).
A leaking head gasket coolant leak will usually clean the spark plug and combustion chamber, likely cause rapid and high coolant system pressure as well losing coolant level. A very small coolant leak may be hard to pinpoint, you can run the engine or pressure test the cooling system, after the engine has built up pressure you can remove the plugs, disconnect coil and wait 5-10 minutes,spin the engine over and check for coolant blown out of any holes. You can purchase a cooling system leak detector which will also detect combustion gas in the system.
BTW, How white is the smoke.
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post #3 of 32 (permalink) Old Jun 19th, 16, 2:40 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 slowmo55ss View Post
BTW, How white is the smoke.
Honestly, it's hard for me to tell how white it is. I also can't tell if it has a sweet smell/taste to it (I've combed the internet to try and figure out if its white or light blue and I've concluded white)...

Last edited by jaketoolson; Jun 19th, 16 at 2:56 AM.
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post #4 of 32 (permalink) Old Jun 19th, 16, 2:46 AM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

If it's hard to tell the color after it warms up, it's very small leak if any. Coolant is very obvious in the exhaust.
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post #5 of 32 (permalink) Old Jun 19th, 16, 2:53 AM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

Quote:
Originally Posted by slowmo55ss View Post
A few squirts of oil in the low cyl's and a retest with better results would indicate ring wear, no change would indicate valve's.
Going to have to wait until tomorrow actually. I'll report back on this then.

Quote:
Originally Posted by slowmo55ss View Post
If it's hard to tell the color after it warms up, it's very small leak if any. Coolant is very obvious in the exhaust.
When I mean its hard to tell the color, I mean, its clearly there and not faint. Its white and now that I've taken a step back from everything, I notice the coolant level is low (again). It's clearly a color -- it happens within minutes of startup and hasn't gone away after 10 minutes of idle. What has me confused are the black spots under the exhaust tips on the ground as well as the oil in the spark plug (I am assuming its oil though)
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post #6 of 32 (permalink) Old Jun 19th, 16, 3:14 AM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

The spots could just be carbon in the exhaust, mixing with condensation, or coolant?
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post #7 of 32 (permalink) Old Jun 20th, 16, 11:41 PM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

coolant in the cylinders confirmed - #7 and #8 cylinders. I dont notice any obvious breaks/wear in the head gaskets though. Perhaps warped but I honestly feel like someone forgot to torque these all down correctly -- you can see evidence on the gasket and corresponding head surface in the picture
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Last edited by jaketoolson; Jun 20th, 16 at 11:59 PM.
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post #8 of 32 (permalink) Old Jun 21st, 16, 3:41 AM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

did you break them loose by hand? even if you used an impact wrench you might be able to tell if a few are loose.

usually any SBC will look different/hot/burnt between the center two cylinders because of the two exhaust valves together.

Unfortunately, unless you drain the block you'll always have that anti-freeze at least in the two rear cylinders. it runs out of the head into the cylinders as soon as you break the head gasket seal.

What prompted this expedition to begin with? Was it in uncontrollable overheating? using water? making bad noises?

Looks like a 10.5:1 350, 492 heads and flattop pistons. that's not really a pump gas deal. That engine required premium fuel when premium was 97-100 octane.

Got a better pic of the #7 piston?

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post #9 of 32 (permalink) Old Jun 21st, 16, 4:19 AM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

Quote:
Originally Posted by Tom Mobley View Post
did you break them loose by hand? even if you used an impact wrench you might be able to tell if a few are loose.

Unfortunately, unless you drain the block you'll always have that anti-freeze at least in the two rear cylinders. it runs out of the head into the cylinders as soon as you break the head gasket seal.
White smoke from exhaust that wouldn't subside, vacuum gauge readings... Because I just purchased this and because its an SBC, I wasn't too worried about pulling things apart so hastily. It's easy

I did drain all the (remaining) coolant from the engine. Ask my wife, it's all over our garage floor lol... my bucket knocked over.

Last edited by jaketoolson; Jun 21st, 16 at 4:42 AM.
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post #10 of 32 (permalink) Old Jun 21st, 16, 4:40 AM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

Yes, 492's. I think Jan 1, 1972?

I wasn't really paying attention as I cracked the bolts off - again, just of the mindset that I'm going to be replacing gaskets and address anything I uncover. The PO didn't have a lot of information and based on some of my findings, was more of a fabricator and suspension guy as his knowledge on the engine and performance was limited.

I'm trying to get it back up and running without doing too much replacing. Obviously having the white smoke pouring out from the exhaust, my coolant disappearing, and it would bog down. Hoping to get away with not touching the pistons and just replace all the header/intake etc gaskets. Lifters all look fine, pushrods are all straight... so I'm hoping to put it back together shortly. I'll look at the timing chain and decide after evaluating the slop

Quote:
Looks like a 10.5:1 350, 492 heads and flattop pistons. that's not really a pump gas deal. That engine required premium fuel when premium was 97-100 octane
This is actually my first set of these heads - so I'm pretty novice when it comes to use/expectations on them (aside from loving the CC etc
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post #11 of 32 (permalink) Old Jun 21st, 16, 7:49 AM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

The casting date looks like A 12 6, which would be January 12th, 1966. Are there accessory bolt holes on the end of the heads?

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post #12 of 32 (permalink) Old Jun 21st, 16, 1:17 PM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

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Originally Posted by Steve R View Post
Are there accessory bolt holes on the end of the heads?

Steve R
Yup.
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post #13 of 32 (permalink) Old Jun 21st, 16, 2:21 PM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

Looks like a burnt exh. valve on #1?
Usually coolant will clean the cyl. head like new if it's ran long enough.
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post #14 of 32 (permalink) Old Jun 21st, 16, 10:16 PM
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

The casting number ends in 492, that's not a date code. It's like 3991492, a 4-bbl 350 head.

can't make any sense out of the casting date code. Those would be like a 1970 head. 1966 heads don't have the mounting pads and bolt holes on the ends.

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.

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post #15 of 32 (permalink) Old Jun 22nd, 16, 1:24 AM Thread Starter
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Re: Blown Head Gasket? Intake Gasket? Worn Valve Guide? 350 SBC

Quote:
Originally Posted by Tom Mobley View Post
can't make any sense out of the casting date code. Those would be like a 1970 head. 1966 heads don't have the mounting pads and bolt holes on the ends.
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.
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