mtwoolford

After looking at every tube on the rack, and actually reading the intended usage, RTV sealants either claim to be resistant to oil or petroleum based products ONLY or are specifically NOT recommended for use with gasoline.....HOWEVER....I have found ONE specifically recommended FOR USE WITH GASOLINE, and while I don't have the tube in my hand I am fairly certain it's Permatex Moto Seal Ultimate Gasket Maker GREY

blackozvet

I know one thing for sure, if you use RTV silicone to seal a pillow to a piece of wood it will leak !

If you think RTV will seal up the gap between the manifold and the head surface, well it depends on how big that gap is.

I'm just trying to help you and save you some grief, you need to measure that gap as per the drawing I posted, the difference between the top and bottom on each side will tell you how much of a problem you have, and how much (if the gap is too great) will need to be machined off the manifold to make it seal effectively.
You just push the feeler gauges in from the front of the manifold, and if there is some crush is doesnt matter, you are comparing the difference between the top and the bottom. Then you compare the left side from the right side. If your block (or heads) have been machined there usually is a difference.

While you have everything undone is the time to measure it up properly.

rithsleeper

I did my best to measure and it seems like it is the same. The part I was talking about is in between the runners and the head not the front. I think this might even be from varience in the gasket. There is no gap in the front to fit a feeler gauge unless I pry and shove it in. I think I'm good from the looks of it.

Now the gap from the block to the manifold is huge due to the thicker gasket . Guess I'll just pile up the rtv a little more than usual. I think I'm going to try this gasket again dry. Not sure how I'll know if it is leaking or not but I might could put my camera in and see something. Or look at the spark plugs and if they are really black.

Thanks for all the help. Ill see if this works. I've lost a lot of motivation on this engine. It better be as awesome as it should be.

blackozvet

I will try and give you some motivation to get it fixed right,

dont worry about the gap along the middle of the manifold, and dont try and fix it by pouring silicone in, it will end up squeezing into the ports.

If you have a reman block you can bet it was cut on the decks, it only needs to be a few thou out of being perfectly straight up when it was cut on the machine to cause you a problem. The engine builder wont be able to pick it until the inlet is measured up.

use a hard gasket, like the felpro, I dont know what gasket you have in there now but the mr gasket's are soft and not ideal for measuring. you can clean up your old ones if they are still in one piece, the felpros can be re-used, the mr gaskets usually tear up.

with a felpro in place, put the manifold on and use 3 bolts each side, finger tight or just nipped up. now measure up from the front at the 2 points on the diagram. Just go half the feeler gauge in. make sure that measurement is tight. looking at the pictures you posted when it came apart, there WILL be a difference top to bottom.

write those measurements down (copy that diagram) then take the manifold to a good machine shop, when they machine the gasket face they do it in small increments and they keep going until the surface is completely flat. So they will correct the angle and get rid of the high and low spots along the gasket surface at the same time.

your manifold should then drop in perfectly, and the holes should line up, and the only place you will need silicone is around the water ports and the china walls.
If you have lost a lot of material you can then use a thicker (1266) gasket.

rithsleeper

Well sorry it took a while to get some time to work on the thing. I think I have tracked the problem with some help from you all. I really went in and measured the angles the best I could. The protractor was less than perfect but the angle seemed to check out. maybe 1* off or so. Then I too my feeler gauges. Without a gasket I could detect .008" difference from top to bottom (imo more than safe, and the gasket should seal it...)

So I got to thinking and I took a straight edge and putt it length wise across the runners and would you guess what happened, there was a gap in the middle.... so I took it to the local machine shop and talked with them a while. They put it up on the mill machine and put a bubble gauge and found the entire manifold was warped!!! Apparently when whoever did the modification to clear a corvette hood, they did not have it bolted to a head while welding. it was really bad.

They took off .030"!!!! to get the thing flat. So now I'm back to measuring angles and I'll test it tomorrow morning but I'm sure that was the problem. I have another extra thick gasket .120 which should be enough. Hopefully this resolution can help someone in the future.

I'm just hoping when I go back and try to re-port match, I don't warp the thing again! I doubt it will make even close to the heat welding the manifold did.

Thanks again all, I will keep updating as I progress.

blackozvet

good work, now that its been machined you can be confident it will seal up properly,
when you drop it in that valley for a test fit it will make a certain sound and you will know the difference from how it was before

WW7

I've been following your progress on this thread since the beginning and the guys have given you some excellent advice...The one thing I will add is , if you still have that large gap between your china wall and the intake manifold after the intake has been milled, try using "The Right Stuff" sealant instead of rtv sealant..The Right Stuff sealant is much more resistant to being pushed out from between the opening and it forms a much better seal to the metal then rtv...You also don't need to wait for it to "set up" like you do with rtv and parts can be installed immediately..For a large gap you can also dimple the china wall and the manifold with a punch to give the sealant something to hold on to so it can't slip out...Since I first tried using The Right Stuff years ago I haven't used rtv since, it's that good..I'm glad to hear you figured out your problem with the leak..... ...WW

cardo0

FYI i found that most of the gasket mfrs sell extra thick intake gaskets - 0.120" available. And the machine shop probably will need to trim down the manifold ends to match the runner flanges. Due to geometry the ends are clearanced a different amount than the runner flanges.

Good luck and thx for posting.