newbie with mysterious Cadillac 429 crankcase backfire

EZ

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The 769 is the one that goes into the rubber grommet on the valve cover of a late model small block Chevy.
Some of those were used in a rubber grommet in the intake manifold of a V-6 Buick, Pontiac, Olds motors as well back in the 1980's and 90's.
 

cedmac

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Just ordered 3 - CV 679 C's from RockAuto.com
we'll see if they are the right one when they get here
their picture of it looked correct - not that 'that' means anything

The local parts store guy has been 'checking with his ACDelco rep for two weeks now. :banghead:
Local dealership says 'their books don't go back that far' :yikes:
 

cedmac

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POR15 process photos

correct prep for this stuff is tedious and time consuming
glass bead, degrease-rince-dry, etch-rinse-dry, por15 prime, engine enamel

using a brush with this engine enamel is like spreading molassis on... never mind - very hard to keep it from running

low res pics

glass beaded
 

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cedmac

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POR15 process photos

degrease-rince-dry, etch-rinse-dry
 

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cedmac

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POR15 process photos

degrease-rince-dry, etch-rinse-dry
 

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cedmac

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POR15 process photos

por15 prime
 

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cedmac

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POR15 process photos

engine enamel
 

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cedmac

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POR15 process photos

engine enamel
 

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cedmac

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POR15 process photos

engine enamel

thats all for now ...
 

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EZ

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Lookin' good man!! That POR-15 stuff is great isn't it? I love Marine Clean and the Metal Ready is a great product too.
Keep the picture coming.
 

cedmac

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Thanks, yea, I think it's good / great stuff
but like I said - it's very hard not to get it running
actually, well, what I didnt show in the photos are all the runs
it's embarrassing !
I'm pretty finicky about things, well very finicky.

I followed instructions to the T

That engine enamel (80% solids) is sooooo thick,
no matter how thin you try to brush it, and I mean like almost slowly scrubbing it with the brush
it levels out beautifully and by the time your around the other side of the piece, the portion you just did has runs in it which are starting to dry already

it bothers me more than most probably
don't know if I'm gonna let it alone or not

If I let it dry good, flat sand the runs out and then recoat - I'm afraid it will just run again :censored:

mind you, I had 4 valve covers to change up how I did it.

the best was the last one where I thinned the paint by about 30% (10% more than recommended) brushed it on as thin as possible - hardly any runs but could use a second coat now in spots

I really think the engine enamel probably needs to be sprayed on something like a valve cover - anything that had a top AND sides - (of course, tops had no runs, just sides)
The galley pan looks great (nice and flat, no sides so no runs)

As for the intake, it's actually very nice that it's so thick - por15 AND engine enamel
there was some pretty deep pitting around the exhaust crossover (center portion, both sides)
which after the por15 prime coat and the thick brushed engine enamel, now is very smooth ! almost looks like molded out of plastic ???

But, all in all, I'm fairly pleased with it.
 

cedmac

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The por 15 brushes and levels real nice, no runs.

Think I'll level sand the runs on the valve covers, then spray a finish coat - to save doin all over again

When you spray the por15, do you use a air supplied resperator?

When you spray, how much do you thin

the por15?

the engine enamel?

Thanks
Ed
 

EZ

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I always use a resporator when spraying automotive finishes. Isocyanides will give you cancer. :yikes:
I'm not taking a chance even if I don't think a particular paint or primer has them.

I think the last time I sprayed POR-15 I thinned it about 10% or maybe a tad more. It seemed a bit
thick to me. Turned out real nice.

Their gas tank sealant works real well too. Use Marine Clean first, then etch with Metal Ready and then
pour the gas tank sealant in and roll it around. Looks like ceramic when it dries. Beautiful!
 

Matty

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What vehicle(s) do you drive?
66 Coupe Deville
Hello all out there,

I am a newbie here, and if I'm here typing online and not in the garage then I know I'm stumped.

Have a 66 Cadillac 429, completely rebuilt (freshened up is all she needed) 60,000 mile engine (that had sat too long)
anyways
fired her up two weeks ago
perfect !

put about 300 mile on her since
daily checking hoses, belts, bolts, etc. all the usual stuff that might need attention after a rebuild.

gettin cooler here in PA
went out to start her up last Wed and she wouldn't fire, right away
pumped it a few more times
then
B A N G
backfire - through the crankcase no less

smoke cleared
I calmed down
opened the hood, discovered the choke face plate was loose and choke out of adjustment (cold out, primary flapper open)

adjusted choke
turned the key
she fired right up

what I didnt notice before I closed the hood which caused lots of smoke after about 2 miles out was that the crankcase backfire blew the valve covers open between the bolts (both banks, top and bottom about an inch from face of heads) and also blew the valley cover pan open (also about an inch)

I am at a loss as to how this backfire got to the crankcase

I could go on but hope someone out there has had some experience with these 429's

thanks for your time
The most common cause for an engine backfire is a lean condition. Cold engines need more fuel and that's why they're more apt to backfire when they're cold. Make sure that your choke is operating properly along with checking the squirt from the accelerator pump nozzles in the front two barrels of the carburetor. If the squirt is late or weak then you will have an instant lean condition when the throttle plates are cracked open which would promote an engine back fire. This is even worse with supercharged engines.
 

Caddylackn

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The most common cause for an engine backfire is a lean condition. Cold engines need more fuel and that's why they're more apt to backfire when they're cold. Make sure that your choke is operating properly along with checking the squirt from the accelerator pump nozzles in the front two barrels of the carburetor. If the squirt is late or weak then you will have an instant lean condition when the throttle plates are cracked open which would promote an engine back fire. This is even worse with supercharged engines.
While I agree with everything you said, this example was a backfire through the crankcase (bent valve covers) and does not look like a lean condition in the combustion chamber.

I also think that maybe the q-jet plugs were leaking out the bottom of the carb causing the gas to get into the crankcase and was pressurized by a stuck pvc valve and eventually the gas fumes were ignited by blow by.
 

Darius

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In the, "For what its worth" category, I agree with Caddylackn that the backfire doesn't sound like a 'lean miss' backfire, so much as one involving a possible leak resulting in a backfire.

For the record, lean backfires normally occur through the top of the carb, while rich backfires are generally out the tailpipe.

Just a tidbit of experience - not that it helps.

Best of luck,

bro. d
 
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