newbie with mysterious Cadillac 429 crankcase backfire

[cedmac]

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

 

[EZ]

Holy cow!! The back fire literally bent the valley cover and both valve covers? Wow!

Is there gas in your oil? Smell the dip stick. Is the oil level too high?

"EZ"

 

[mcdave71]

Sounds like the carb well plugs (quadrajet) are leaking to the point where enough fuel is is getting into the oil pan past the rings. Get enough fuel in there and the fumes can light off. Pull carb apart and clean off old seal on plugs and reseal with JB Weld. This is a know bad problem on the quads.
dave

 

[cedmac]

Thanks for responding all,

Had checked the oil just days before this happened - level fine - no gas smell
so I assume diaphram of new feul pump is ok

carb also was rebuilt before fired first time

what I have discovered since my original post is that the

PCV on these 429's is mounted horizontally

I have a 64' and 66' cadi shop manual
at the beginning of the section for feul and exhaust
it goes into a big schpeal about the PCV
quote
"The cadillac positive crankcase ventilator valve is not interchangable with those of other makes. Use of other than the proper valve may result in breather backflow and engine damage"

When I put this motor back together
all replacable parts, like PCV, were replaced with new of course
the PCV in it when this happened was a
FRAM Part # FV112 which cross reference's to

STANDARD MOTOR PRODUCTS Part # V112
AIRTEX / WELLS Part # 6P1022 {#6421971, 6421972, 6487503, PCV20}
ACDELCO Part # CV679C {#06421972}

upon further research - this PCV has a very wide range of applications - I'm assuming - NOT specific to this 429.

I think long ago, these manufacturers did away with the actual correct Cadi PCV because it had such a limited application Cadi 429, just 4 years production.
Don't know if the earlier 390's had the PCV mounted horizontally.?

If memory serves, most all PCV's on other carb'd cars I've had mounted vertically - even though these have a spring in them - the spring does not keep the valve closed preventing backflow when horizontal - but does when vertical.

This car ran great after firing it first time and driving it a couple weeks - had her up to 85 mph for very brief rpm range run throughs - flawless performance!
(ie: ruling out bad rings, pistons, etc.)

The cadi manuals also states,
"The ventilator valve is held nearly closed by spring pressure when the engine is not running. This prevents an accumulation of hydrocarbon laden fumes from collecting in the manifold when the engine is stopped, which could result in hard starting."

It then (if closed when not running) would also prevent vapors from carb manifold from backflowing through the pcv tube INTO the crankcase

So what I'm thinking now is that since this pcv is mounted horizontally and is not the correct one designed by GM for the motor (is not held closed by spring p[ressure when engine not running), the vapors from carb manifold are backflowing through the pcv tube INTO the crankcase when engine in stopped.

Does this make sense to anyone???

Thanks again

 

[EZ]

Makes all the sense in the world especially since the factory manual goes into such great detail about it but I never would have believed it in a million years! My suggestion is to find another PCV and try it. Get one that crosses over to the proper application if possible.

Oh and BTW...........let me know what you find! I'm sure I pitched the old PCV in the garbage when I tore down my engine. :cursing:

 

[cedmac]

OPGI (cadi, chevelle, pontiac etc web parts site) says they have the 'correct' ac delco pcv and lists year app 66 - 76
cannot give me the ac delco part no cross ref - they are lost it seems
as if it's good for a 66' 429 , then its good for say a 64' 429 too.
(I have both GM manuals - both say same thing)

I have looked anywhere I know and ordered and looked at all the cross ref pcv's,
they are all the same - not closed if in horizontal orientation - only when vertical

What I think I'm gonna do sinse it seems I will not be able to find the correct pcv
is modify the steel tube a bit so the pcv is mounted vertically.

I kind of hate doin that to a 61000 mile original car (paint and all) but...

 

[cedmac]

I'll let you know finally what I do,
I have a couple more old boxes to look through but pretty sure I DID NOT save the old (possibly original) pcv...

 

[Cadillac Kid 1]

Cedmac,
First of all the correct PCV is "ACDELCO Part # CV679C {#06421972}", and although they are getting rare, they are still around. I have run this one on my '66 (as well as everything up to '76), and my '66 has been horizontal in front of the carb, for over 15 years.
Not to look for trouble, but if your car drained enough gas back into the crankcase to cause that much damage when it backfired, I would also check your power brake booster diaphram and your distributor vacuum advance for damage. I'll also bet you find the hose connected to the transmission modulator has popped off as well.
The carburetor on your car is a Carter "AFB", which aren't known for leaking, and if the car ran okay with the exception of "a little oil leak", I might suggest a look at the fuel pump diaphram for a small leak into the crankcase that might be small enough not to effect engine operation (yet).
Greg.

 

[cedmac]

Thanks Greg,

The carb is actually a Rochester
Tranny vacum hose still connected
Brakes were fine for those few miles afterwards
I will check the vac adv too

even though because the choke was not adjusted and I probably flooded it trying to start it
I think the pcv I had on there (Fram FV112) didnt do it's job
but it as you suggest, might just be a slight leak at the feul pump diaphram
better safe than sorry so yes, I think I'll change that feul pump.

I'll track one of those acd CV679C's down and see if it's the same as the fram.

Ed

 

[EZ]

If you find someone selling the "correct" PCV please let me know where ya get yours. I need one too.
How does your oil level look now? Is it over full? Does it smell like gas? I just can't believe the damage that back fire caused!!! :yikes: Seems to me there would have to be a lot more than just some fumes to cause all that.

 

[cedmac]

If I can track one down I'll let you know.

Oil level was fine

Oil looked fresh (only 400 miles +/-)

Does not realy smell like gas (although my mind may be playin tricks on me at this point as everything 'could' smell like gas a little) Like lookin for a needle in a haystack that's not there

I cant believe it either, I've probably flooded a few carbs in my days and never such a thing.

I had a 64' for many years, never backfired, (however, you know how the glass gas filter bowl is so close to the distributer - I was sitting at a light one day in that 64' and K A B O O M , engine compartment exploded, by the time the fire co got there both front tires had exploded - the took axes to the front of the car to get the hood open - fire had gotten in behind dash by that point - car was a total loss.

Just imagine what was going through my mind when this 66' backfired so dramatically - smoke everywhere - at least no fire !

"WHERE THERE’S SMOKE----THERE’S NOT NECESSARILY FIRE"
hummm... maybe a new byline...

 

[Ted in Olympia]

I sure would replace that fuel pump; I'm sure this is what caused your problem.

Do you have the extra parts you need to fix this?

TED

 

[cedmac]

Thanks Ted,

You really think so?
Pump was new so I didnt consider it initially and just assumed with the choke (unkowingly out of adjstmnt) wide open I probably flooded it real good.
(Was in a hurry to go to a meeting, should have just taken the suburban or got out and took a peak under the hood - started well for two weeks before)

Fuel pump is ordered
Airtex, ACDelco twice the cost from restoration outlets and it's probably NOS (w/ possible dry rot diaphram) appears ACDelco is not producing these anymore as far as I have been able to find out.

Parts,
Actually had a spare set of Valve Covers for a 64' (don't have the dimples the 66' does)
After I found those, went down to the wood shop and made some forms for staightening the 66' VC's
Not too bad, actually now straighter than the 64's

No extra galley pan though
so
put some feelers out
got two responces initially
375.00 for the VC's and galley pan ( N O T )
and another for 200.00 - jumped on it
then, couple days latter - another guy finally got back to me
all 3 pieces for 130.00 - why not

so now,
I'll have 4 sets of valve covers and two good valley pans. (when they get here)

All will (some have) be glass beaded and done up with POR15 engine paint

If I don't need the extras after a year or so of driving it (this better not happen again - ugg.) I'll be trying to sell them.

Have you used this POR15 engine paint? or anyone else for that fact?

If used the none engine por15 stuff before and always sprayed it - finish like glass
They say if brushed it levels good...

I have so much to paint at this point, I'm wondering if I should brush it but concerned about the leveling / final finish ??? ?
Also want to be able to coat around the edges of valve covers, galley pan, and intake (thats where they start rusting)

Any por 15 por15 experts out there ?

thanks,
Ed

 

[Ted in Olympia]

Don't know about the POR15 paint but I wished I asked you about parts sooner.

I have seen lots for flooded engines and stuck floats but I have never seen one blow up a engine before. But I have seen lots of gas in the oil from a bad fuel pump.

Make sure you also change out the oil.

Good luck and have fun.

TED

 

[cedmac]

Why Ted, do you have lots of 429 parts layin around?

 

[Ted in Olympia]

I have a 67 Coupe and most of the engine is still there, including the parts you needed.

TED

 

[cedmac]

Ouch :censored:
Well, at least you know now about what they go for.

 

[cedmac]

Whats up with this message board?
last I looked I was termed a 'New Member'
now I see someone or something is terming me a backyard mechanic (under my avitar)
Not something to be known as where I come from... :no:

 

[Ted in Olympia]

It's a automatic thing based on the number of your posts.


New Member 0
Backyard Mechanic 10
Gearhead 100
Bleeds Caddy Blue 250
One Sick Caddy Freak 500

 

[cedmac]

oooOk.....
that's cool
(sort of can't wait to um ... Bleed Caddy Blue for some reason !......:cursing:............:screwy:...............:banghead:..................................................................:bolt:.
...........................................................................................................these thingies are too much fun too