Author Topic: 1956 dual four intake leaking at the heads UPDATE 10/17  (Read 335 times)

Offline cadman56

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1956 dual four intake leaking at the heads UPDATE 10/17
« on: October 08, 2017, 08:26:38 AM »
About a month ago my engine got to running poorly with no power.  Dwell and timing are fine.  Manifold vacuum was low but steady at 13-15" Hg.  When spraying Brakleen along the manifold to head connection the vacuum and rpm increased dramatically.  So, I replaced the intake to head gaskets.  All is together but the problem is still there.
I torqued the bolts per manual specs but I started in the middle.  Should I have torqued the corners first?
Could the manifold be cracked?
I have rebuilt many 56 engines with the single carb and this is my first dual carb setup.
Any tips or suggestions welcome as I will start to tear it down on Monday.
She was running so good before this happened.
Thanks in advance.
Larry
email:  lblanchard6@cox.net    cell:  316-617-7328 if you wish to call

10/17
i hand wrenched the entinge to get play out of timing chain.  Then I marked the harmonic balancer at the timing pointer.  Then I reverse wrenched the engine until the distributor rotor budged in a backward rotation.  After remarking the harmonic balancer I obseerved a distance between the markds of at least 1/2".  The distributor is already rotated in advanced position to where the vacuum advance unit almost touches the firewall.
Compression does show between 150-170.  I am thinking the cam timing is off.  Thoughts?
Thanks.
« Last Edit: October 17, 2017, 10:19:18 AM by cadman56 »
Larry Blanchard CLC#5820
1956 Cadillac Coupe deVille (sold)
1956 Cadillac convertible (sold)
1956 Cadillac Eldorado Seville
1967 Cadillac Eldorado (sold)
1968 Cadillac convertible
1991 Cadillac Fleetwood Brougham dElegance

Offline Lexi

Re: 1956 dual four intake leaking at the heads
« Reply #1 on: October 08, 2017, 09:05:08 AM »
Larry I will send you an email. Clay/Lexi

Online South_paw

Re: 1956 dual four intake leaking at the heads
« Reply #2 on: October 08, 2017, 12:42:03 PM »
Yes it is possible that the manifold is cracked. But a couple of questions for you. When you pulled the manifold off, was there any sign of leaks on the intake gaskets? Is your heat riser valve operational?

Offline cadman56

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Re: 1956 dual four intake leaking at the heads
« Reply #3 on: October 08, 2017, 03:02:23 PM »
No sign of leaks on the gaskets, heads or intake.  The heat riser is stuck wide open.  Intake was tight to.  I at first thought the timing had slipped but it was where I had put it 2 yrs. ago, 8-10 deg. advanced.  Vac advance works fine and so do the mechanical advance units.  Dwell right on 30 deg. No misfiring on the plugs so it is definitely a fuel delivery problem. 
Fuel pump is fine too. 
This happened with in about 3 hrs. time.  We drove it to where we volunteer, parked it and 3 hrs. later got in it to go back home.  It was hard to start and problematic all the way home.  I finally told the wife to shift it down and let it rev up between gears just to get it home.
Hope it isn't cracked.  Will find out this week when I tear it down again and get it magnafluxed.
Larry
Larry Blanchard CLC#5820
1956 Cadillac Coupe deVille (sold)
1956 Cadillac convertible (sold)
1956 Cadillac Eldorado Seville
1967 Cadillac Eldorado (sold)
1968 Cadillac convertible
1991 Cadillac Fleetwood Brougham dElegance

Offline Eldovert

Re: 1956 dual four intake leaking at the heads
« Reply #4 on: October 08, 2017, 04:16:19 PM »
Larry,
Try sitting the manifold on the heads without gaskets and seeing if you can slide a feeler gauge in around the mating surface. The head or block might have been shaved during a rebuild and changed the relationship between the two.
Cheers,Pat

Offline cadman56

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Re: 1956 dual four intake leaking at the heads
« Reply #5 on: October 08, 2017, 06:07:29 PM »
I will do that Pat.  With 62K showing on the clock I would hope the engine is non molested but who knows.
Thanks.  I will keep all posted.  Larry
Larry Blanchard CLC#5820
1956 Cadillac Coupe deVille (sold)
1956 Cadillac convertible (sold)
1956 Cadillac Eldorado Seville
1967 Cadillac Eldorado (sold)
1968 Cadillac convertible
1991 Cadillac Fleetwood Brougham dElegance

Online South_paw

Re: 1956 dual four intake leaking at the heads
« Reply #6 on: October 08, 2017, 06:27:28 PM »
I knew something bothered me about this post but I couldn't think of why until now.  Don't use brake cleaner. When heated up, the gas fumes from it can kill you. The intake manifold cross over can definitely get hot enough to burn that stuff off. 
 
http://www.brewracingframes.com/safety-alert-brake-cleaner--phosgene-gas.html

Offline Lexi

Re: 1956 dual four intake leaking at the heads
« Reply #7 on: October 09, 2017, 12:41:37 AM »
Lou is right. Frightening stuff when heated. That link Lou posted should be mandatory reading for all. I first read that a while back and it gave me a new outlook and respect for that product. Clay/Lexi

Offline Roger Zimmermann

Re: 1956 dual four intake leaking at the heads
« Reply #8 on: October 09, 2017, 01:55:32 AM »
Years ago, I had the same problem on my '56 Biarritz. Once warm, it would barely run in the 700-1200 rpms. I was thinking the problem was vapor lock, but it was not. When I reassembled the engine, I checked if the manifold would "dance" on the heads (without gaskets of course); obviously, I was not careful enough: when the manifold was removed again, some gaps were found by checking with a feeler gage. I reworked the manifold with a long file until the gaps were acceptable.

Offline PHIL WHYTE CLC 14192

Re: 1956 dual four intake leaking at the heads
« Reply #9 on: October 09, 2017, 03:39:44 AM »
Which type of gasket did you use? The originals are pressed tin and there are various new ones that are a thick compressible material that should stop any leaks. Phil