Intake manifold leak
#3138076
04/14/23 11:35 PM
04/14/23 11:35 PM
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Joined: Apr 2006
Posts: 4,220 West Plains, MO
DrCharles
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West Plains, MO
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As posted previously, I finally put my PRH-ported Speedmasters on my 451 Dart, and drove it to the first-of-the-season West Plains Car Club cruise-in at Steak & Shake! It seems I have a little work to do - the (Performer RPM) intake manifold must not be sealed properly so it idled rougher, less vacuum, and AFR leaner, and when I let off the gas on the highway and hit it again, a puff of blue smoke comes out the tailpipes. All of those are classic symptoms of intake leaks sucking oil from the valley. I re-used the valley pan (once) and brushed on Permatex #2 for the sealant on both sides of the pan (Ultra Black on the ends). The manifold feels just a little too high in the V and the bolts wouldn't start. I rat-tailed the holes in the intake just a few thousandths (barely removed the paint) and then all eight would go in. (The heads were cut .055 I think, but obviously Dwayne knows how much to cut the intake surface) Also retightened the bolts. Another variable is the lash on my lightly-reground Mini-Express. Schneider recommends .018", so I set them to .012" cold, expecting the typical .006 growth of the aluminum head on iron block. Previously with the iron heads, I'd set the lash "a little" looser than the usual +.002 for break-in, but don't remember how loose, and never got around to readjusting the valves in, now 1370 miles. So I'd expect some vacuum drop at least until the engine warms up, and maybe even a leaner AFR due to the increased overlap (charge dilution) with tighter lash? But valve timing wouldn't cause the puff of oil smoke... that has to be oil getting sucked in to one or more ports since the guides and seals are all brand-new... also, when I abruptly let off the gas after accelerating to 5200 rpm, I could actually hear an intake sucking sound... My plan is to experiment with propane or carb cleaner. Luckily the big-block is an easy manifold removal. I'll get a new valley pan, and use a thicker sealant. Probably Ultra Black unless everyone says to use something else thanks for any tips. -Charles
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Re: Intake manifold leak
[Re: DrCharles]
#3138082
04/15/23 12:46 AM
04/15/23 12:46 AM
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Joined: Feb 2003
Posts: 10,215 Someplace you aren't
SomeCarGuy
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I Live Here
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Posts: 10,215
Someplace you aren't
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Should be a streak on the surface where it is leaking. Pull it and see where it is and work on a solution from there.
I want my fair share
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Re: Intake manifold leak
[Re: DrCharles]
#3138118
04/15/23 02:57 AM
04/15/23 02:57 AM
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Joined: Aug 2003
Posts: 43,204 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,204
Bend,OR USA
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Last edited by Cab_Burge; 04/15/23 03:03 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Intake manifold leak
[Re: DrCharles]
#3138173
04/15/23 10:54 AM
04/15/23 10:54 AM
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Joined: Jan 2003
Posts: 75,020 U.S.S.A.
JohnRR
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I Win
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U.S.S.A.
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Did you have to rat tail the holes upward or downward to get the bolts in ? If downward a THICKER sealant is only going to make matter worse , you intake needs to be cut because it's not fitting properly , which is why you had to file the bolt holes.
If you had to rat tail them upwards then adding the thin paper gaskets between the pan and the manifold would have been the proper solution ... maybe on both sides of the valley pan if it was really low ...
Filing the intake bolt holes is not the right way to fit the intake.
running up my post count some more .
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Re: Intake manifold leak
[Re: JohnRR]
#3138193
04/15/23 12:25 PM
04/15/23 12:25 PM
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Joined: Apr 2006
Posts: 4,220 West Plains, MO
DrCharles
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West Plains, MO
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Did you have to rat tail the holes upward or downward to get the bolts in ? If downward a THICKER sealant is only going to make matter worse , you intake needs to be cut because it's not fitting properly , which is why you had to file the bolt holes. Downward - but the sealant will band-aid the problem if the gap is bigger at the bottom than the top (i.e. the angle of the manifold face does not match the angle of the head intake face). As already pointed out here, I need to take everything off and use feeler gauges to see where it's not mating properly. Filing the intake bolt holes is not the right way to fit the intake. Yeah, no [censored] Sherlock but I don't have a Bridgeport mill handy, nor a nearby automotive machine shop I can trust! And I wanted to get the car running again while the weather is nice and cruise-ins are frequent
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Re: Intake manifold leak
[Re: topside]
#3138516
04/16/23 05:10 PM
04/16/23 05:10 PM
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Joined: Sep 2003
Posts: 19,421 north of coder
moparx
"Butt Crack Bob"
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"Butt Crack Bob"
Joined: Sep 2003
Posts: 19,421
north of coder
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i check the intake as Cab and others have said, and also use a smear of grease on the head side, and silly-cone one the china walls, big and small block alike. when using the silly-cone of your choice on a small block, make sure the wall "guide pins" for the gasket are removed, as this will make sure your intake doesn't bottom out on the ends, thus not allowing it to fully seal on the heads. just an old geezer spilling his experience with a small block intake leak he couldn't find. ............. [as my old man uset'a say : Back up to an A$$kickin' machine with a bag full'a quarters and start shovelin' 'em in !" ]
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Re: Intake manifold leak
[Re: moparx]
#3138585
04/16/23 09:19 PM
04/16/23 09:19 PM
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Joined: Apr 2006
Posts: 4,220 West Plains, MO
DrCharles
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West Plains, MO
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Interesting you should say that... earlier this afternoon I discovered what I think is the problem. I pulled the carb and manifold and the only unusual thing I saw was a puddle of oil on top the valley pan. No oil in the ports. Pulled the valley pan and it looked like some of the sealant had run down the pan, confirming a big gap. I set the manifold directly on the heads and I immediately found that the "tips" were hanging up on the Chinese wall and I couldn't slide the manifold back and forth to line up the bolt holes without one end or the other hitting the wall. And when I had torqued it down previously, it deformed the valley pan there too like a sheet metal brake! This is one of those "I shoulda thought of that"... with .055 milled from the heads, and my block has not been decked (it was really close when I built the short block a long time ago). A couple minutes work with a die grinder and it then sat on the heads perfectly... So I put the valley pan back on with the bolt holes centered, and sealed the corners and the end rails. I also cleaned the Permatex #2 from the valley pan, as many people don't use sealant around the ports at all. Intake back on - only had to wiggle it a little to get all the bolts in and torqued to 25 ft-lb. HOWEVER. It still is running leaner and with lower vacuum, even after warmup. At least it will now idle without having to tickle the gas pedal, so that is an improvement. I waved an unlit propane torch around all the ports, especially underneath, but there was no effect on the idle at all. I didn't get a chance to see if the puff of oil smoke after decel is gone tonight. Is it possible that my new, much better-breathing heads (made that much difference to the carb tune? I figure at idle, the throttle butterflies are the most important airflow limitation Also the lash is tighter (set .006 tight for aluminum since the hot spec is .018), so maybe more overlap. That could definitely make vacuum drop, but from 8-9" Hg. down to 6-7"? I'll need to check one hot and see if it actually loosens up .006, as every engine is different. Edited to add: I've been reading on other forums and it does indeed appear that it can make that much difference! I'll check one hot, but I think I'm going to run them again at .003 or .004 looser and see if my already-borderline idle manners come back Any more thoughts? thanks.
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