I have a 70 351 C Mach I, 4v. I've only got a couple of hours on the engine and have had a rear oil leak for awhile. I've changed intakes and gaskets, this time I am NOT going to replace the corks, just silicone. My question is how long do I need to let it dry?
I think I waited less than an hour. I just waited till it got tacky and lowered the intake on, but you have to lay down a nice even bead without spilling any into the lifter valley.
The best way that I have found is to lay down a bead of silicone and also smear a little on the intake, which basically primes it. Then install the intake and only tighten it down evenly to about 5ft lbs (barely tight.)
Let it alone overnight then torque the manifold to specs. Let it cure till later that afternoon and then fire it up.
This method prevents the silicone from being squished out of place and ensures a good seal. Works for me.
Be sure to retorque the manifold after a few heat cycles as they do tend to loosen up.
I did the same. Nice size bead, let it cure for about an hour (skins over). Then a thin layer on the bottom of the intake, set into place immediately and finger tighten all the bolts. Wait 24 hours and then torque down. Retorque after running the engine.
Get the gray silicone that Ford sells or you can buy from Permatex (it's the same stuff).
Get four install "studs" for alignment so you can drop the intake straight on.
Glue the intake gaskets down with contact cement first.
Put the install studs in.
Run a bead across the chinese wall from the notch of the gasket to the notch of the other gasket, roughly half the width of the chinese wall and the same height. You don't have to put a 1/4" pile of silicone on, 1/8" is plenty as it will squish out when you install the manifold. If you put 1/4" on it, that's 4 times as much silicone to squish out. You get my drift.
IMMEDIATELY drop the manifold on (you did clean it first, didn't you?). Don't wait for it to skin - you want it to skin AFTER you have the manifold on and torqued! Install the bolts on the manifold finger tight, remove the install studs, replace with the regular bolts. Torque them in sequence. If you have access to an inch pound torque wrench, even better.
Let it sit overnight. Longer is better, but overnight is good enough. The guys at the Ford garage immediately fill the car with coolant and drive it off in like an hour (seriously). Apparently it doesn't take as long for silicone to set up as everyone thinks, but overnight can't hurt.
FYI, don't try to do a modern O ring gasket like on a LSx series engine or a 4.6 without the inch pound torque wrench. You can radically overtorque a gasket on
a small block ford and it'll still seal. Anything with a plastic intake manifold won't be so forgiving.
All great advice. Something like this you don't want to do twice, wait the 24 hours. There is no substitute for patience and doing the job right. It simply can't be done right if waiting only one hour. You have to get it on there and finger tight and that's when you want to give it the time to set. The next day go to torque them down in the manner Dennis said. Otherwise you're just going to squeeze the wet silicone out. Good luck.
i've always let it skin over for about 10-15 minutes and then go to town reinstalling everything. i've never waited 24 hours to install the intake and never had a leak using this method.
The bead of silicone on the ends of the intake manifold is really just to keep the oil from blowing out. There isn't much if any pressure on that part of the manifold. I waited an hour, only because it was lunch time. Yes, I did retorque the manifold the next day, but at about 21 foot pounds, that really isn't a whole lot of torque. It's just required the second time to make sure the gasket has seated well on the intake ports and the water jacket.
Well, I started it tonight and yes, it is still leaking. I am using the stock intake. This will be the 6th time I have pulled this intake or the aluminum that I had on it. This is a pain!
I noticed you said you only had a few hours on the engine. Did you deck the block or shave the heads? The intake my need shaved a bit if any or both was done. Also are you sure its not leaking out of the oil pressure sending unit. Just thoughts as I doubt any one could screw up silicone that many times. Might be some thing else causing the problem. Oh ya, you do have some crank case venting don't you?
Crank case vent? Just the oil caps on the valve covers.
The motor was completely stock and never been into until I had it rebuilt, as far as I know, no shaving of anything was done. It is the stock intake and I am NOT using the valley pan.
Can you get silicone end gaskets for a Cleveland? I stumbled onto some for my 302 a while back and they were self-retaining and relatively squish-proof. A dab of the blue stuff on each and and all the oil stayed in the engine. The again, I'm using the non-sticky corks right now also with silicone and also with no leaks.
The oil breather caps are the most common crank vents if they are not non vented after market or sealed emission types. If they aren't the pressure can blow out seals. I wanted you to make sure it wasn't comming from your oil pressure sender because it is so close to your leak area that it can fool you. [ Ask me how I know] The little tin cans spring leaks from vibration or a little whack from installing an intake. [ask me how I know] A well degreased block and proper type of rtv shouldn't be giving you that much trouble. Just passing some of my nightmares.
I checked the oil pressure connections, no it's not them, I actually saw the oil coming out of the rear seal and filling the valley where the oil pressure switch is. One of my nightmares was the oil line poping off the gauge inside. I had it sitting on the new carpet and it blew off, I had to grab it with my thumb and tried to keep it from squirting out as I reached over and turned the car off, I was on the passenger side working, what a bummer.
Today, I'm taking my oil pressure cap and the seal out of the valve cover and find a PCV valve and hose. I would think the hose would connect to the vaccum on the rear of my intake like the power brake booster?
Most carbs have a place to hook the pcv to. Some thing about evenly distributing the oil fog to all cylinders instead of one or two back ones. The passenger side would have a hose to your air cleaner with a filter, if you have to worry about emmission inspections. If not just use a breather cap.
I was rereading your original post. If you are using a iron manifold use the tin pan gasket.[What it was designed for]. That will close the gap to your block and give you less hole to fill. If you are using aluminum try the new felpro that has the blue gaskets on the tin pan. I had to order mine from Summit , the local shops all had old stock.