Solders18

i was wondering if this amount of gap is normal between the block and manifold. it seems like alot to me to be filled with rtv also it seems like the back of the manifold isn't lining up with the back of the block correctly. the front of the manifold is flush with the block and all the holes are lined up. let me know what you guys think. thank you in advance

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mlynch001

Perfectly Normal. In Fact, this looks identical to my 85 305 El Camino TPI Project. Red or Black RTV is how GM fills the gap. Before the days of RTV, it was those horrible rubber or cork strips that you could not keep in place.

When using RTV you need to make sure the intake and block are clean and free of oil. Use a bead about 1/4" Diameter on the block and get everything in place and ready to set the intake straight down onto the gaskets and RTV. Once in place, bolt it all together and move on. Allow plenty of time for the RTV to cure before you start the engine. You can trim off the excess RTV with a razor knife if you did not do such a neat job or used a little too much RTV. Some people wipe the excess off before the RTV cures. Some people do not do anything with the excess. Whatever floats your boat, I suppose.

88fastgta

iTrader: (9)

that does not look normal to me... its suppose to sit nearly flush onto the block... something is either hitting it or something is not straight. when i did my FIRST intake swap the manifold had a gap just like that....

i did all the normal stuff rtv on the front and back of black and around the water passages. and i always put a good amount of bead whenever i put on manifolds.... the entire intake was on and everything was hooked up... i began filling up coolant through the radiator and coolant was coming out where the manifold meets the block... i was pissed off... i had coolant in the engine block.. so i had to drain it.. the coolant came out first then the oil... i flushed the engine three times with cheap oil to make sure i got all the coolant out.... come to find out the the manifold was hitting the ridge of iron l98 heads... i had the grind the manifold down so it can sit flush on the block..... problem solved after that and not a spot of leak anywhere....

Solders18

So probably just rtv it up good let it set a bit then set it on and bolt it down a little and let it set some more, then torque it down and it should be good? I am using ultra grey rtv. The guy at the shop told me it holds up better to being blown out in that location of the manifold. I also checked how it was sitting on the heads and it is flush with all the gaskets and sitting where it should.

BlackenedBird

iTrader: (5)

Either return the manifold & get one that fits, or get it machined to fit. Don't just pile up RTV in the hopes that the gap will seal.

92RSTPI

You're going to end up with RTV in your oil and everywhere else. Take it off and see why it is hanging up. No reason to do it wrong so you can redo it again.

Solders18

The thing is, it just came off that engine and didn't have any gap. Could it be the intake gasket is just too thick?

Apeiron

Solders18

So when i got home from work i took the intake gaskets off and set the manifold back on there to check the gap. its more what i would like to see. should i find a thin gasket?

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mlynch001

When you remove the intake side gaskets and set the intake down in the hole, you will find that the manifold will almost touch the block as in your second picture. You will also notice that the bolt holes do not line up any longer.

I assure you, I have been building these things for 40 years, what you are seeing is 100% correct. The technical reason that there IS a gap at the front and back of the intake it to allow for differences in thickness of head gaskets, intake gaskets and milling the heads SLIGHTLY. This also to allows for expansion, contraction for the engine and to compensate for compression of the intake side gaskets.

All SBC engines have about a 1/16-3/16 gap at the front and rear of the manifold between the block and manifold. It varies from engine to engine If you use a thicker intake or head gasket, the gap will increase, slightly. If you use a thinner intake or head gasket the gap will decrease slightly. The reason you do not want these areas to touch is because contact will cause the intake side gaskets NOT to seal. The gap at front and rear is essential and is a "designed in" gap, NOT a "mistake" or something "wrong" with your parts.

Over the years, GM used several methods to seal this area.

From 1955 to the early 60s, they used cork strips similar to valve cover gasket material. These were a constant source of problems!

From the early 60's GM switched and used molded neoprene with tabs on the sides to maintain alignment. This coincided with the advent of the PCV system., the old cork gaskets would "suck in" due to the negative crankcase pressure created by the PCV system.

Sometime in the late 60's or early 70' s GM changed the design of the neoprene gasket and the block to include holes in the block and corresponding "pegs" on the bottom of the gasket to keep the gasket in place.

Some time after that, GM discovered RTV and the gaskets were omitted altogether. RTV is the best solution, it conforms exactly to the particular gap that exists on your engine combination.

Your combination of head and intake gaskets will affect this gap. If you chose very thick head gaskets and very thick intake gaskets then these gaps will be considerably wider, up to 3/16 ". If you chose very thin head gaskets AND very thin intake side gaskets then the gap can be as small as 1/16".

If you want a little less gap, find some thinner intake gaskets gaskets. GM gaskets tend to be thinner than Fel-Pro and others so the gap does get larger if you use Fel-pro Print-O Seal type gaskets. The gap will decrease when you torque the intake down and the gaskets compress.

RTV is the correct and the factory recommended solution to filling the gap. I have used Red, Black and Grey over the years. GM originally used the RED RTV almost exclusively. You do not want HUGE gobs of RTV, Just enough to fill the gap completely and have a little squeeze out.

Solders18

Thank you for all the advice. I used the same fel-pro gaskets I had and rtv'd it up good with a nice 1/4 inch bead on the front and back and it turned out really nice. The manifold also sucked down a bit and closed the gap some and the rtv did as it should. Thanks again for all the in put. Love third gen!