Vacume leaks

Recently on my TWM 8 stack I noticed a strange sound on deceleration. It was a ppssst type of sound and was like a backfire without the popup through the injectors on the front left injector. In searching for the source, I would put my hand over each injector to feel for anything unusual. What I found was that all the cylinders but one, would pull your hand down on the bell and if you had a rubber glove on it would make a screeching sound as the air went by the glove. On the left front cylinder there was little if any vacuum. As I woud pull the throttle linkage barely open I was seeing fire just beneath the throttle valve on this one cylinder. I pulled everything down on the intake and noticed a black soot mark on the outside bottom of that very cylinder. Looking down into the port you could see the edge of the gasket(felpro) which had ben trimmed on installation. The AFR 205 heads have a very large pasageway and I had to grind away a lot of the intake runner to get a match. Looking at the the outside edge of the intake and head joint it looked like the gasket was installed a tad low. On the opposite head, the gasket is showing across the mating line. In looking at the front of the engine I used RTV sealant for the mating surface around the distributor. This area looked like it had dried out and may not be sealing the corner of the block/head/intake. Taking off the intake is going to be a major headache. I have tried a novel approach to seal these areas. I used hot glue to seal all of these surfaces. Will be firing the engine up soon. Just have to finish reinstalling the parts. This is one of the hardest installs there is. Most of the interior nuts bolts and things have little to no room to install them. You have to use a magnet wand to install the washers and nuts and bolts. Then a standard socket can tighten them down.
What I am worried about is that the leak may be on the inside runner of the intake, which would involve removing the intake. Does anyone have any suggestions on a way to seal that part of the intake runner without removing the manifold?? I envision gluing some sort of rubber liner to the runner to seal it. Any thoughs along those lines?? Appreciate any help possible.

Bill
 
Sounds like an intake valve not closing/sealing. Even if the gasket was leaking there should be some vacuum, I would think. Do a cylinder leak down.
 
Hi Bill,
Reading your post, I realised that I’d had exactly the same problem as you on my engine, which has an 8-stack injection system. I hadn’t actually spotted the issue when the engine was running, but it was evident when I stripped the engine to resolve other issues (I’ll post on this when I get a bit more time)<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com<img src=" /><o:p></o:p>
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The attached is the view I had looking down the inlet manifold after removing the throttles and the state of the gasket when removed. The issue was caused by the cork gasket between the block and the manifold being too thick, preventing sufficient clamping force between the manifold and heads. A dry build confirmed this and it was rebuilt with o-ring cord between the manifold & block (the manifold has a channel to take this) and a small amount of sealant on the gasket to cyl head to prevent any movement<o:p></o:p>
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To do the job properly, unfortunately you’re going to have to remove the manifold, which as you’ve pointed is a PITA! I found using a crow’s foot spanner is really useful for the fixings underneath the throttle flanges<o:p></o:p>
Hope this helps<o:p></o:p>
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Rgds,<o:p></o:p>
Andy<o:p></o:p>
 

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Andy,
Just a note to you about the removal of the intake gasket. I was not looking forward to trying to pry the intake off the engine. So I took Plan B approach. The intake manifold has a water exit/neck at the front of the engine that sticks out from the block I was trying to find a way to lever on this piece. My rear motor panel support is too high to get anything under this piece or any other part for that matter. I remembered that I had several ring gears for the Porsche left over from my teeth breaking incidents. So I took one and put it around the water neck on the intake and used the engine hoist to gently pull the manifold away from the block, which it did. What it showed was the gasket on the #5 port(left front) had slipped down into the lifter galley. Air and some oil was being sucked into the cylinder.
P6240130_zpshh9z0ujd.jpg


The O2 sensor is on that bank and it evidently was reading lean as all the plugs were black, which says the computer was trying to pump more gas in to the mix. Explains that when I would race the engine without load there was a lot of soot coming out the exhaust and a lot of backfiring on deceleration along with flames shooting out the back. Will have to re phase the distributor as well since there was fire seen under the throttle plate on that cylinder as well(phasing a distributor is for electronic ignitions that incorporate a distributor to "distribute" the spark to the various cylinders).
The bolt openings are too big for the bolts to hold the gasket in place, so some sealant/gasket maker will have to be used to hold them in place while slipping the manifold back on.I will use some bolts with the heads cut off as guides for the manifold. That way i will know they are sliding down straight to the heads.

Bill
 
Hi Bill,

Glad to hear that you’ve managed to get it to bits and the problems is what we’d diagnosed. A simple fix and you’ll soon be up and running again<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com<img src=" /><o:p></o:p>

Rgds,<o:p></o:p>
Andy<o:p></o:p>
 
Bill,

For what it's worth (prob not much) I was having sealing problems at the manifold to head gasket....went through two gasket sets before I figured out what was going on - the heads weren't square to the manifold face. I had to "ease" the head bolts a bit as I recall to get the manifold on square to the mating surface of the heads. Then, basically, torqued everything down to the right setting progressively. This worked well and solved the sealing issues.

Good to hear you discovered the source of the leak.
 

Randy V

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Bill,

For what it's worth (prob not much) I was having sealing problems at the manifold to head gasket....went through two gasket sets before I figured out what was going on - the heads weren't square to the manifold face. I had to "ease" the head bolts a bit as I recall to get the manifold on square to the mating surface of the heads. Then, basically, torqued everything down to the right setting progressively. This worked well and solved the sealing issues.

Good to hear you discovered the source of the leak.

This type of issue is generally caused by the decking (milling) of the cylinder block along with the milling of the heads. When both are done, it will almost always manifest itself in a poor fit of the intake manifold to the cylinder heads.
The correct fix is to have the intake manifold milled to fit properly. I have also heard of one machine shop here that mills the intake surface of the cylinder head rather than requiring the intake to be resurfaced.

One other point to note - for the Ford 302 almost all cylinder head manufacturers are recommending a torque increase for the top row of bolts/studs by 10 ft lbs. This is to counteract the pull of the intake bolts which has been shown to reduce the clamping force of the head bolts.
So, that is 80 ft lbs on the top and 70 ft lbs on the bottom.

Good move on the alignment dowels Bill..
 
Have any of you guys had to add sealant around the water inlets to the intake?? The only water lines on the TWM manifold is at the front passage for the 351W. The rears are absent/blocked off. Would that be a good idea to hold the gasket in place particularly at the base as it is only about 1/4" of gasket material?

Bill
 

Randy V

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I do... Permatex's Right Stuff - I use it on thr block rails front and rear, the also around the water ports both front and rear..
 
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