some news on no power saga.

[mtdave2]

http://67-72chevytrucks.com/vboard/s...d.php?t=365777

that’s the first post..

i pulled off the timing chain cover with great hopes of seeing dots not lined up, but knowing they were.. what did i find?



so i started taking the intake off to prep pulling the cam... i have argued a few times with people far more knowledgeable than me with motors that i thought the problem was a vacuum leak. i always got a..no no no,, wouldn’t cause that..


i did have one friend of mine, a lonnnnnng time race guy motor head say he thought i was what he called a flapper. that is a intake gasket that was not sat right and was hanging in side of the motor. at an idle there was no leak, but under power the extra vacuum would pull the gasket away from the metal causing a massive leak. (the crack is in the paint)




i think he may be right. these a photos of the front of the motor, intake gasket. the end twisted up, and was hanging inside. on the underside of the intake there is grease/dirt streaks (i did rub some away when i touched it)



soooo i guess i go buy a gasket set, and pull all this back together and see what happens..

if its not the problem, still an interesting education.

[69GMCLonghorn]

Is that a crack in the block right under the gasket???

[mtdave2]

Originally Posted by 69GMCLonghorn

Is that a crack in the block right under the gasket???

no, its in the paint as far as i can tell. it freaked me out when i saw the photo too

[Jim_PA]

turn it over by hand, and watch all the lifters. See if they are all moving up the same amount.

[chevy_mike]

Looks like someone used a cork seal AND RTV. If you use the cork, use gasket tack to hold it, not RTV since it will allow the cork gasket to move when squished down.

I have always used RTV only, a 1/4" thick bead, let it skin over and then set the manifold on squarely.

Again, RTV or cork (or rubber) not both.

[mtdave2]

think everyone has missed the point.

[chevy_mike]

Originally Posted by mtdave2

think everyone has missed the point.

And what point it that???

You said you think you had a vacuum leak that would happen under load. Since your timing chain looks good, looking at your pics of the intake gasket, it looks like a major vacuum leak would have been happening.

I offered info about what I thought was wrong, using RTV and the cork gasket, which would definitely cause the gasket to slip, possibly causing the afore mentioned problem.

If I am missing the point, you need to tell us what the real point is then???

[Jim_PA]

Originally Posted by mtdave2

think everyone has missed the point.

I think so too.

Do you think it's lacking power because of an oil leak?

[Jim_PA]

Originally Posted by chevy_mike

Looks like someone used a cork seal AND RTV. If you use the cork, use gasket tack to hold it, not RTV since it will allow the cork gasket to move when squished down.

I have always used RTV only, a 1/4" thick bead, let it skin over and then set the manifold on squarely.

Again, RTV or cork (or rubber) not both.

I used the self-adhesive cork, and a THIN coat of RTV ontop of the cork after un-successfully using straight-up RTV twice. No leaks yet! knocking on wood....

[Jim_PA]

Originally Posted by chevy_mike

And what point it that???

You said you think you had a vacuum leak that would happen under load. Since your timing chain looks good, looking at your pics of the intake gasket, it looks like a major vacuum leak would have been happening.

I offered info about what I thought was wrong, using RTV and the cork gasket, which would definitely cause the gasket to slip, possibly causing the afore mentioned problem.

If I am missing the point, you need to tell us what the real point is then???

There's no vacuum leak to be had from his leaky china-wall seal.

That's like saying you have a vacuum leak from your dipstick.

[Jim_PA]

I always like to keep things basic... so I'll throw this out there anyway

From your first pic -- you do realize with the dots in that position that you are at TDC of #6, not #1, right?

[Jim_PA]

Ok, one last post, sorry for all these ideas coming to me in spurts...

Get a new balancer, turn crank one full turn (so both dots are pointing straight up, putting you at TDC #1...). Use a piston stop or some other method of verifying your timing marks. Drop in the dist, so the rotor is aiming towards the #1 cylinder, verify your plug wires aren't crossed, and set your timing with a light (about 36 deg. @ 3,000RPM).

Are you sure the cam isn't flat? I didn't know mine was bad until I spun the cam around and watched the lifters.

[retodd7711]

Originally Posted by mtdave2

think everyone has missed the point.

I guess your point is - You are very happy that the problem can be resolved inexpensively?
>
>
Or maybe this_ i have argued a few times with people far more knowledgeable than me with motors that i thought the problem was a vacuum leak. i always got a..no no no,, wouldn’t cause that..
And you were right all along?

[hotrod 80]

I guess i missed the point also , but you can take a punch and divot the gasket surface on the underside of the intake. This will give it something to bite the gasket if it keeps giving you problems

[usmcchevy]

I agree with Jim on this one, The gasket you are showing has no effect on vacuum it is there to keep oil in the lifter valley. Also if you look at the #1cyl lifters one of them is slightly open when they should both be completely closed (dots lined up on timing set= #1 at TDC). This means one of two things, 1, the timing set is junk/or the crank gear is one of the adjustable kinds and is not set to 0deg or 2, the cam is junk. Hope this helps.

[Jim_PA]

Double post...

[Jim_PA]

Originally Posted by usmcchevy

I agree with Jim on this one, The gasket you are showing has no effect on vacuum it is there to keep oil in the lifter valley. Also if you look at the #1cyl lifters one of them is slightly open when they should both be completely closed (dots lined up on timing set= #1 at TDC). This means one of two things, 1, the timing set is junk/or the crank gear is one of the adjustable kinds and is not set to 0deg or 2, the cam is junk. Hope this helps.

When the dots are facing each other, it's at #6 TDC.

When the dots are both facing "up" it's at #1 TDC.

But you are right -- the only thing his bad seal will do is leak oil... not a source of a vacuum leak.

[usmcchevy]

Originally Posted by Jim_PA

When the dots are facing each other, it's at #6 TDC.

When the dots are both facing "up" it's at #1 TDC.

But you are right -- the only thing his bad seal will do is leak oil... not a source of a vacuum leak.

sorry about that

[Jim_PA]

Intuition tells us it's the other way around, but we can't all be as smart as the engineers

[haminator]

Originally Posted by Jim_PA

When the dots are facing each other, it's at #6 TDC.

When the dots are both facing "up" it's at #1 TDC.

But you are right -- the only thing his bad seal will do is leak oil... not a source of a vacuum leak.

As far as dots on the cam gear is concerned, it can be installed either way, both #1 and #6 are at TDC. Just be sure #1 is on compression stroke when installing dist. In my experience cam gears that are marked to go in up position do not line up well in the down position. This was probibly off subject. Now to the subject, while the intake is off look at the side gaskets for proper fit, thats where you would find a vacuum leak. Every one keeps saying that a blown end seal would not cause a vac. leak but if the seal was bad enough I don't think the PVC system would work right, hense a vac. leak occurs.

[68gmsee]

A vacuum leak should be more obvious during idle when you have the highest vacuum in the intake. As you increase the opening in the carburetor butterfly valve, you get more air and that decreases the vacuum.