Guys,

Im about to pull my intake manifold to check for an internal vacuum leak. Will there be any evidence of the leak? will the gasket not be compressed as much in sports? Will there be a coolant trail or oil trail anywhere?

thanks guys

jeff

You may be able to see an "unsealed" area in the gasket. Also look for "trails" of dark down the intake ports.

Think about this , I have never done it but someone posted a note saying they were looking for a vacumn leak... They took the carb off and put a motor lift plate and added a tire valve stem to the plate.. Then plugged off all vac lines and rolled motor over until all intake valves were closed. He said he pressure up manifold and heads to check for leak. Did not find any.
He got away from takeing off manifold to check seals.

Sounds silly . I have never tried this but would really like to know if this is works. My guess is , if you hear something leaking it could be either a valve or gasket.

well, i pulled the intake and i noticed a few things.

1) the valves have a bunch of crud on them. maybe this is totally normal.

2) just about all the intake passages on the head on both sides were shiny. they looked like the bottom of the engine valley where the push rods sit on the lifters. where the oil flows freely.... almost all of my intake passages looked like that. does that mean that oil was going down the intakes? does anyone have a color picture of what the head intakes should look like???

3) there was some shiney liquid on some of the valves that were closed. im assuming that this is oil, not gas... as gas would have evaporated. i dont think its coolant.

4) there was some dark spots of something on one of the valve guides (do they hang into the intake a little?)

5) there were some tears in the blue material around the ports, but this could have been me moving it around before i pulled it up.

there were no obvious teats or anything in the gaskets on around the end walls.

what do you guys think? do i have an oil problem somewhere? last year, i did a compression test and they were all 190-200. could this be bad valve guides?

also, is it ok to bump the motor over to watch the valves go up and down? its much easier to stand back and watch now without the intake. coolant is drained.

thanks guys

anyone?

thanks

Can you post pictures? I went down that road and found out my guides were bad and my carburetor idle circuit was plugged. Everyone was telling me vacuum leak. Turning the motor over now won't hurt a thing. Jjust don't let it start.:)

well, i coulda posted pics but my wife stole HER digital camera from me :) so i have to wait till tuesday for pics

i know my carb was fine. i put a friends holley on and the car acted the same way. got everything dialed in as best i could and the vac gauge was all over the place.

ill turn motor over today to watch things. but after that, my starters getting disconnected cause im pulling the motor to rebuild it. :)

finally gonna build this motor right....myself. my previous build was hardly a victory ;) the guy that built mine has screwed up quite a few motors from what i hear.

I would pull all the spark plugs and look for misted oil on the threads.This usually is a good indicator for a big time intake leak combined with low manifold vacuum.This assumes that you have have a good ring seal and have not over revved the engine so the valve retainers did not damage your seals.I would do a leak down test and rule out rings.You may have to slot your intake manifold holes if the heads or the block have been shaved.The angle will not change but the depth will.A starting point only,let us know

leak down test was good last year. all mid-upper 90s (93-97%). ive never taken the thing over 6K. i do have oil on all the plug threads. i dont buy that oil on the plug threads is a valve cover leak. the threads are after the seal (taper or gasket) to the head... and i have no oil train down the side of my engine...even a light one.

I don't know about big blocks, but my small block heads have the intake rocker studs threaded through into the intake ports. Oil was working its way down the threads and depositing on the back sides of the intake valves. Sealant on the intake rocker stud threads cured the problem.

Al,

my heads seem to have the open stud holes to the intake ports too.

What kind of sealant did you use?

One trick a friend of mine showed me was to take a can of carburetor cleaner and spray it around the base of the carburetor where it seals with the gasket. If you can hear the rpm's jump up slightly, there's a leak. Not sure if you want to attempt that but just a suggestion. I know you don't have a leak around the carburetor but something you could consider.

They took the carb off and put a motor lift plate and added a tire valve stem to the plate.. Then plugged off all vac lines and rolled motor over until all intake valves were closed.

What crank position has all the intake valves closed??

maybe you could just take all the rockers off...

Al,

my heads seem to have the open stud holes to the intake ports too.

What kind of sealant did you use?

I used permatex liquid. The kind with the brush built into the cap. "Aviation Form-a-Gasket" item #80019.

Jeff - when you were leaving the house last weekend I noticed blue smoke when you fired the engine up that I had never seen from your car before. It seemed fine as you drove away, how is it at shift points or when you are getting on it? Do you have a PCV valve on the engine, I remember just breathers before you moved east and back.

Hey Dennis,

nah, always ran pvc in the passenger side and breather in the drivers side.

it pulled nice...not as hard as i thought it should, but nice. no hesitation at all. just idled like crap and used oil from day one. and the vacuum gauge has always been wild too...

the carb once dialed in, the mighty demon 750, was real nice. i hear they make blow through carbs, but i know C/S Specialities (I think thats their name) is all over blow throughs.

the rocker sealing thing that Al told me about is definitely something that ill do to these heads or to the AFRs im thinking about getting. The valve guides apper to be bronze.. i have no idea what kind of prep went into the heads. ill play detective though and i might be able to use them with the procharger.

it might be coming out tonight. :)

What crank position has all the intake valves closed??

Is ther such a position? Seems at least one must be open since 2 have to be opening and closing each rev.

no hesitation at all. just idled like crap and used oil from day one. and the vacuum gauge has always been wild too...

the rocker sealing thing that Al told me about is definitely something that ill do to these heads or to the AFRs im thinking about getting. The valve guides apper to be bronze.. i have no idea what kind of prep went into the heads. ill play detective though and i might be able to use them with the procharger.

it might be coming out tonight. :)A wild vacuum gauge shows either a stuck/slow/low lift valve. Oil on the valve head shows worn guides and/or faulty stem seals.

I would like to see multi-cylinder engine being rotated to close all the intake valves at the same time.