Thread: Intake manifold leak

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This seems to be an ongoing problem with "V" motors. It's been the same since I was a kid and nobody has a good solution to finding the problem. Finding an external leak is pretty straight forward with using propane or some other combustible material, but finding an internal leak has escaped a solution. With the help of other board members input, I'd like to find that solution. What I'm thinking is to find a way to pressurize the manifold/head ports and maybe do a leak-down test on it to determine if there is a good seal there or not without having to remove the intake and inspect the gaskets for "pinch" and then you still don't know for sure.

What if you were to use a flat plate and gasket in place of the carb (or throttle body), drill a 0.453" hole and install a tubeless tire valve.

You could also drill, thread and install a low pressure gauge (maybe 0-15 lbs) to see if the system would hold pressure.

A more sophisticated approach would be a leakdown tester with shop air and the air pressure adjusted down to whatever the intake gaskets would take without blowing out. That's what I don't know. How much do you think they'd take without throwing in the towel?

I was thinkin' maybe an engine lift hook plate that is bolted to the carb base on the intake manifold could be pressed into service for such a tool.

Help me out here fellows and let's see if we can find a solution with the motor buttoned up.

I've figured out how to do it when building the motor. Here's my solution to that......
Measure the thickness of a new intake manifold gasket. Get flat washers or shims that will measure that thickness. With the manifold off and the mating surface on the cylinder heads de-greased, put a dab of RTV on the washers/shims and stick them on each corner bolt hole on the cylinder heads. Let the RTV set up. Stuff paper towels into the ports to keep debris out. Make up 16 pea-sized balls of modeling clay. De-grease the intake manifold at the ports. Place the balls of clay on the top and bottom of each port of the manifold, squishing them down well so they stay in place. You want them to be thicker than the shims/washers that are RTV'd to the heads. With your fingers, coat a little oil on the heads where the clay will meet the heads to keep it from sticking to the heads. Now carefully place the manifold into place on the heads and use bolts on the four corners to just snug the manifold down until you feel resistance against the shims/washers. Remove the manifold carefully and measure the thickness of the clay at all 16 positions with the depth function end of your 6" dial caliper. You'll know pretty quickly if the manifold/head interface is square. Record the measurements on the manifold with a permanent marker like a Sharpie. The widest measurement will be the standard to which you will want your machinist to cut the other positions on the manifold to make it square with the heads, thusly sealing up the motor.