Double Intake Gaskets????
Thread Starter
Le Mans Master
Joined: Jan 2002
Posts: 8,913
Likes: 283
Double Intake Gaskets????
My intake is decked, how much I am not sure. I had it decked .015 a few years ago.
I did an intake gasket job in June, and I think I have an intake leak to the inside. It is going lean at high RPM, and when I free rev the motor, it takes a few seconds to return to normal idle.
I am wondering if it had been decked before, and is not seating correctly. It sits so low on the heads, the block rails are so close, that the cork gasket will not fit.
Put my new fuel pump on today, and that made no difference. Something is just night right above 4000 RPM. I have not ruled out ignition, but my hunch is and intake leak.
After three years of trouble free service, I guess it is my turn.
Mark
I did an intake gasket job in June, and I think I have an intake leak to the inside. It is going lean at high RPM, and when I free rev the motor, it takes a few seconds to return to normal idle.
I am wondering if it had been decked before, and is not seating correctly. It sits so low on the heads, the block rails are so close, that the cork gasket will not fit.
Put my new fuel pump on today, and that made no difference. Something is just night right above 4000 RPM. I have not ruled out ignition, but my hunch is and intake leak.
After three years of trouble free service, I guess it is my turn.
Mark
Race Director
Joined: Feb 2004
Posts: 11,039
Likes: 2,592
From: Del Boca Vista FL
If it idles normally I would not usually suspect vacum leak at the intake, or anywhere else. I am not an expert on this but in my experience vacum leaks wreak havoc at idle and are overcome when engine rpm is increased.
Why was your intake manifold machined in the first place? If it was to match heads that were significantly machined to increase compression are you still using the same heads?
While you have the engine at idle you can spray some carb cleaner or similar product around the area where the manifold meets the heads and see if you detect any vacum leak by observing change in engine speed.
Rich
Why was your intake manifold machined in the first place? If it was to match heads that were significantly machined to increase compression are you still using the same heads?
While you have the engine at idle you can spray some carb cleaner or similar product around the area where the manifold meets the heads and see if you detect any vacum leak by observing change in engine speed.
Rich
Pro
Joined: Oct 2004
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From: Terre Haute Indiana
Wounded Warrior Escort '11
St. Jude Donor '05
Intake Leaks
If you are looking for Vac. leaks use Propane. You can get a kit at NAPA that uses a small Propane torch bottle. This saves a mess on the Carb. and intake. 
Firedog
Firedog
Burning Brakes
Joined: Aug 2001
Posts: 1,104
Likes: 1
From: Frederick Md
Originally Posted by ghostrider20
My intake is decked, how much I am not sure. I had it decked .015 a few years ago.
I did an intake gasket job in June, and I think I have an intake leak to the inside. It is going lean at high RPM, and when I free rev the motor, it takes a few seconds to return to normal idle.
I am wondering if it had been decked before, and is not seating correctly. It sits so low on the heads, the block rails are so close, that the cork gasket will not fit.
Put my new fuel pump on today, and that made no difference. Something is just night right above 4000 RPM. I have not ruled out ignition, but my hunch is and intake leak.
After three years of trouble free service, I guess it is my turn.
Mark
I did an intake gasket job in June, and I think I have an intake leak to the inside. It is going lean at high RPM, and when I free rev the motor, it takes a few seconds to return to normal idle.
I am wondering if it had been decked before, and is not seating correctly. It sits so low on the heads, the block rails are so close, that the cork gasket will not fit.
Put my new fuel pump on today, and that made no difference. Something is just night right above 4000 RPM. I have not ruled out ignition, but my hunch is and intake leak.
After three years of trouble free service, I guess it is my turn.
Mark
I never surface the intake, it renders it a one motor intake, the one it's bolted on.
You can get thick intake gaskets, don't do the double intake it will leak for sure. I wonder if the plugs are getting any oil on them?? The intake can seal on the top and leak on the bottom sucking oil into the combustion chambers.
Don't use a end rail gasket, use a nice thick bead of silicone sealer as the end rail gasket.
The .015 that was machined off the intake is not enough to make a difference.
In extreme cases when heads are machined say .200, the intake side needs to be corrected and once in a while the end rails of the block will need machining.
Thread Starter
Le Mans Master
Joined: Jan 2002
Posts: 8,913
Likes: 283
Thanks for the help.
Not sure what has been done to the heads, or how many times the intake was decked.
It is an Al intake, and was out enough to require being decked.
Thanks
Mark
Muncie Man, could you PM me your price on M-21 Rebuilds?
Thanks
Mark
Not sure what has been done to the heads, or how many times the intake was decked.
It is an Al intake, and was out enough to require being decked.
Thanks
Mark
Muncie Man, could you PM me your price on M-21 Rebuilds?
Thanks
Mark
Le Mans Master
Joined: Apr 2000
Posts: 5,104
Likes: 1,362
From: New York New York
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If you suspect a vacuum leak under the intake, just cap off the oil fill and any other holes that are for the crankcase, remove the dipstick and install a vacuum gauge on the tube. Now start the engine. If after a few minutes you see a vacuum of any kind you have a problem with the intake gaskets. It should register a slight pressure.
Safety Car
Joined: Feb 2003
Posts: 4,068
Likes: 27
From: St. Joseph Mo
If you suspect a vacuum leak under the intake, just cap off the oil fill and any other holes that are for the crankcase, remove the dipstick and install a vacuum gauge on the tube. Now start the engine. If after a few minutes you see a vacuum of any kind you have a problem with the intake gaskets. It should register a slight pressure.
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