my big mouth intake manifold for my 86' made by edelbrock keeps leaking oil and i have already had it put on twice. it keeps leaking from the back, just along where the manifold sits on the block. the silicone should be enough but its not working. is there some kinda pressure valve or somthing that could be messed up blowin out the sealant? i checked the valve that sits in the valve cover and it rattles which im pretty sure means its good...help somebody!

 

First, there are a few steps you have to take to insure the intake won't leak.

Clean off all the old gasket material and, using new gaskets just sit the intake on the block/heads. Check the gap between the intake and the block at the front and rear; 5/16" or smaller is about right. If it's greater than 3/8", it may prove hard to seal tightly.

Only use sensor-safe silicone sealant!

Silicone sealant won't stick to anything that has grease or oil on it. So you need clean both the block "china walls" and the underside of the intake manifold of any oil/grease, etc.,

You then need to use a metal punch and dimple those four areas - I have a long doc file that gives more detail on this. Basically, the dimples give the silicone sealant something to bite into.

You then need to apply a thin coat of silicone sealant on both sides of the intake gasket. THIN so that it won't get squeezed into the intake port opening and interfere with airflow.

The intake has to be set down straight with NO back or forth movement to align it. Straight down.

You should follow the bolt torquing sequence in the manual. Do not use the old way of starting in the middle and working alternately to the ends. GM calls for a specific bolt torquing sequence.

Use at least five steps to tighten the bolts. Then let the intake sit for several hours, after which retorque the bolts. As the intake sits, the gaskets will take a set and the torque will loosen.

Continue going over the bolts until they all hold at the setting you're using: I torque mine to 35 ft/lbs.

If you want the doc file email me jakejr266@sbcglobal.net and I'll send it. I believe I posted it in the Tech Tips Section on this Forum, so you could check there too.

Hope this helps.

Jake

 

thank you very much for the info im gonna have to talk to my mechanic and give this a shot.

 

Okay, you're welcome.

BTW, dimpling the underside of the intake and the china walls is an old "racer's trick, been around since Hector was a pup. So I can't take credit for it.

In fact, on BB Chevy's we use to dimple the block between the center two cylinders for added bite for the head gasket. Also, some guys dimple the areas around the intake ports so that the intake gaskets seal better.

I've never had to resort to dimpling the intake ports, but dimpling the BB deck was common practice when I use to build BB engines.

Keep me posted on how you make out.

Jake

 

I'd also recommend that you use Permatex "The Right Stuff" when you do the install. I've used it on two different intakes on my car and niether has ever leaked a drop.