Blown intake/exhaust manifold gasket?

christian

christian

Senior Member
My idle has been getting progressively worse, where as anything off idle everything is perfect. I switched out several carbs all showed the same symptoms, which leads me to believe its the motor not the carb. Checked timing , ignition everything is good. Hooked up my vacuum gauge to the wiper plug and got quick fluctuating readings from 16 to 23, very rhythmic, bouncing between the two like a super fast metronome. Got out my les Andrews and the only think that fit was his condition for sticky valve. So I dumped about a quart of MMO in my crankcase, 4oz in my fuel ( oops, turns out I only had a half tank, so I double dosed it I guess) and hooked my vac line to a Dixie cup of MMO. Pretty much have MMO in every orifice of the engine :eek:

Started it up, High Idle, and it drew in the MMO out of the cup faster than I would have every imagined!

Next thing I know my engine is shooting out MMO from the intake and exhaust manifold gasket. I guess that means my gasket is no good? It's a one piece thick paper type gasket, which has been crumbling to pieces as of late.

After about 20 mins of thick clouds of white smoke took it for a ride seemed to run and idle great, some hesitation right off idle, but I'm thinking that may be from the double dose of MMO I added to the gas.
 
Hi Christian,

Humble opinion:

Tight fitting joints at manifold gaskets are almost as important to an engine as one's lungs or one's heart to a human being; however, for many, they are considered about as important for health as toe nails.

Remove intake/exhaust manifold, check for flatness, correct if necessary, install new "copper" clad gasket, & drive off into the sunset with a smile like a 1950's western cowboy hero.

Hope this helps.
 
Spray some WD40 [ I use ether] around the intake flanges and see if the idle changes. If it does, you have a leak. If you change the gasket, lay a straight edge along both manifolds[ while still bolted together] and see how big/thick of a feeler strip will fit between manifold and straight edge. If a .010" strip fits, they need to be cut.
 
christian said:
Right before the vacuum test I was thinking vacuum leak, I sprayed the gasket area to no effect.
Click to expand...

Well, it doesn't appear as though you have a leak [depending on what you sprayed]. You sprayed around all 3 flange areas and that would probably get into the throttle shaft bushings also as they should be checked too.
So, if its idling that badly, have you tried disconnecting/shorting cylinders just see if its isolated to specific holes ? If thats not it, maybe there is a low circuit carburetor issue. What carburetor are you using ?
 
Well, after the MMO into the vacuum port and driving it around I'm not having any idle issue anymore. Just a little hesitation off idle, which I'm assuming is due to putting so much MMO in the fuel. Right now I'm just concerned about all the MMO that was gushing out of the intake and exhaust ports while it was being sucked in...... I expected it to just come out the exhaust in plumes of smoke ( which it did). Not out between the ports which it did also.
 
For what it's going to cost and for how long it's going to take and the fact you say the gasket is falling apart already. REPLACE it with the late 31 copper ones. FWIW
Paul in CT
 
Times 4 and check the manifolds for level across the ports. Don't torque the manifold bolts. I just tighten firmly with a socket and 1/2 inch drive ratchet. after running a few cycles I retighten. If over tightened it mashes all the give out of the gasket and warps the front and rear inner ears of the exhaust manifold.
 
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