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.

Pressurizing the entire manifold won't show which port is leaking internally. Now if you put the same engine on a scope, won't the spark line be affected by one leaky port? Hank

No, it won't isolate one particular port, but wouldn't it show whether or not the manifold is sealed up to the heads?

I don't know about the scope. Never used one.

I suppose you could check for a lean cylinder with a heat gun,works pretty good on diesels.Hank

I know they make engine dyes,colored dyes, for the cooling system,to check for leaks.m
Maybe they have a dye for the oil ,you can see on the plugs ?

With the advent of the smoke machines used in auto repair shops today the easiest solution would be to fashion a plate for the carb mount, loosen all the intake rockers to close the intake valves and inject the smoke into the manifold thru the carb plate. Leave the oil filler off and watch for smoke out of the crankcase..

Originally Posted by HWORRELL

With the advent of the smoke machines used in auto repair shops today the easiest solution would be to fashion a plate for the carb mount, loosen all the intake rockers to close the intake valves and inject the smoke into the manifold thru the carb plate. Leave the oil filler off and watch for smoke out of the crankcase..

Thanks, that's more of what I had in mind, except allowing Joe Scratchrubber to check it at his house with simple tools. Maybe he doesn't even have shop air. If he installed a Schrader valve and a 0-15 psi gauge in the carb plate, then he could attempt to air up the intake volume with something as simple as a bicycle tire pump. If he couldn't get any pressure going, wouldn't that be proof positive that the intake wasn't sealed on the inner side? This would be, as you said, with all intake rockers loosened. I'm just trying to find a cheap way for any backyard hot rodder to do this operation.

Has anyone been able to find a carb plate with a hook on it used to remove the motor from the car? If they are available commercially, that would allow purchasing everything by mail. I made one years ago from scrap metal and an old u-bolt welded to it.

Back in the 70's I designed a plate to attach to Vega cylinder head, that you could pressure up with an air hose 1/4 inch nipple. It had a shut off valve with a pressure gauge. Then you put it in a pan of hot water to see any bubbles or lost pressure you know the head was cracked. If you use the same idea of lost pressure, you could talcum powder and repressure then tear down to see if the leak was gasket or valve seat. You know if you have lost pressure your going to tear down. You could even let it set over night for any pressure lost. Can't think of any other way to find the leak. I used foot powder spray on trans or oil pan gaskets to find leaks. Clean area spray powder on watch for leak.
Brad

You can get those plates, I'm sure speedway sells them & I am pretty sure Harbor Freight & Northern Tool sell them fairly priced.. You can build your own smoke preasureizer my favorite way "CHEAP"
1. 12 volt soccer ball pump.....$10 -$15 bucks
2. clean 1 gallon paint can
3.handfull of steel wool
4. couple 5/16 brass hose barbs
5 3-4 feet 5/16 hose
6. a diesel glow plug
7. turn signal flasher
8.14 guage wire & alligator clips
9.transmission fluid or fog juice [ cheap @ any party store]
install the house barbs into the upper edge of the paint can "solder,braze weld,etc."... obtain a nut or fitting for your glow plug to screw into and weld.braze or solder this nut to the paint can approximatley 2-3 inches up from the bottom edge of the can. install your glow plug and wire it up using the turn signal flasher to blink it on & off... add the steel wool to the paint can,fill it to about 2 inches above the glow plug..sprinkle your smoke juice over the steel wool ,install the paint can lid, hook the soccer ball pump to a hose barb,connect your pump & glow plug leads to a 12 volt power source and you should start getting preasurized smoke from the other hose barb..
you can use the hose to connect to vacume hose fittings and vacume hoses to find leaks. Denny can probally draw up a wiring diagram as I don't nave any way to do it..... Now for the lawyers.... If you burn your car,garage,house or yourself up.it's your own dang fault so don't come lookin for me............

But this does work,I've seen it in action..it's not as effective as the commercial units costing $1,100 bucks,but it is effective. you absolutley gotta be sure and use a low preasure pump as you don't wanna blow the lid.. off your can..........