The Stovebolt Site Forums The Shop Area Engine Shop The Nuts and Bolts of it

Hi:

Could you tell me the size, and hardness of the intake and exhaust manifold bolts for a 49, 216 engine? Further, who might have a set and do the bolts have washers or not. Thanks in advance for the help

God bless,


Dave

Hy Panelit, Are you asking about the hardware to mount the intake/exhaust to the engine, or the hardware to bolt the intake and exhaust manifold together? In either case I would not recommend anything stronger than grade 5, hope that helps.

3B,why would not use any thing harder than a grade 5?just curious,,,

Grade 8 is harder/brittle sometimes that's a disadvantage.

The bolts that hold the manifolds to the head have specially shaped pieces to secure it, not washers.

All the bolts are 3/8 coarse thread that retain the manifolds to the head. There are 2 different lengths that I dont know offhand. The Ace hardware near me has all the sizes in grade 8 which I always use. They are also available at farm stores. Its a good idea to put a grade 8 SAE flat washer under the head of the bolts also.

Hy johnhull, grade 8 bolts are very strong, but they are also brittle, when the manifold expands from heat it could actually break (pop the heads off) grade 8 bolts. I learned this lesson very early in my career, grade 8 bolts are not the best for shock loads or heated components, the "factory" bolts for the manifolds that I have seen have no head markings on them, which means they are not that strong, but can accept many heat/cool cycles, hope that helps.

the reason i asked is,my first 20 years as an adult, worked on military aircraft,the next 21 years iworked on. bradly fighting vech.the next 18 until now i have alsway used grade 8.the major differance is shear load.just my 2cents,not tring stir up anys----.besides it has been rainning al day and can,t go out and play

3b,

Slight difference of opinion, but a grade 8 bolt is not going to fail before a grade 5 bolt, -unless it is not torqued properly-. That's the whole point of a grade 8 bolt. It has a greater tensile strength, and a greater shear capacity than an equivalent grade 5 bolt. Before you could stress that grade 8 bolt to the point where brittleness could come into play, the grade 5 bolt would have already yielded and failed.

One reason not to use a grade 8 bolt however is where you cannot torque it properly without damaging the assembly. Looking at a torque chart, a grade 8 bolt requires about 50% more torque to be "tight" A bolt is tight when it starts to stretch but is still elastic. It acts like a spring. If you don't torque a bolt enough, it can experience fatigue failure because it is being loaded and unloaded as working forces are applied to it.

Anyway, I would be leery about using a grade 8 bolt on a manifold because the manifold might crack if you actually tightened the bolt as it should be, not because the bolt would fail from being brittle.

But it should also be said that if you use a grade 8 bolt on a manifold and don't tighten it properly, at some point it may experience fatigue failure.

In general the grade 8 bolt may fail by breaking catastrophically rather than by stretching beyond the elastic limit, as in a lower grade bolt, but this failure will happen at a much greater load.

Kurt

My Friends:

Thank you, but we are getting a bit far a field of the issuse, my purpose here is to find out exactly what size the bolts are supposed to be in the manifold of a 49, 216 engine. The bolts in mine where stretched and thus I cannot get a good measurment as to their length. I have discerned from this discussion that they are 3/8 and should probably be a grade 5, but what is their lenght, and number of threads per inch for both the exhaust and intake maifolds. In addition to mine being stretched some where changed and are wrong. Again thank you for your help, it has been great. I called NAPA to get a set today and even they don't know what size they are so any help you can provide is much appreciated.

God bless,

Dave

Hy Guys, I'm not an engineer, I'm a mechanic, and most of my learning comes from "experience" (experience is what older guys call their mistakes), early in my career and friend asked if I could help him with an exhaust leak on a Chev small block V8. I took his exhaust system off the engine (ram Horn manifolds), and I took them into work the next day, to the machine shop to check them for face flatness, they were in perfect shape. The company where I worked had just started stocking "Lamaloy" bolts so I bought the correct length bolts to install the manifolds, that night after supper I installed the manifolds and torqued them to spec. everything cold, I phoned my friend and told him his car was ready, he came over and picked it up. The next night after supper my friend called to say the car was noisier than ever, I asked him to bring it over if he could, he did, and when we checked it, ther were no heads left on the bolts, the manifolds were hanging on their now grade 8 studs. I did learn in other circumstances where grade 8 bolts were not appropriate, but this was my first experience, and I have never forgotten it. I redid the exhaust manifold job the next weekend using grade five hardware, and he had no more noise or problems while he owned the vehicle, at least three years.

I think wrenchbender stated they were 3/8 inch coarse. You should be able to determine the length by setting the manifold up on the head, and use a wire in place of the bolt. Mark where the bolt head should be on the wire pull the wire out and measure.

Kurt

I think 3B got some defective bolts. I have been useing grade 8 on every manifoldv I pull for 40 years. I have put hundreds of 292 manifolds on with them. 292 ex. manifolds are probably the hotest running out there when used on the one ton & larger trucks. They glow red hot after a hard run. I also have used the grade 8 on many small block manifolds & others also. I have never had a broken bolt on any of these. I throw grade 5 bolts in the scrap metal pile when they come with a new part. If a part is constantly stretchred or flexed as it is used it will eventually fail. If a part is strong enough not to give it will last infinitly.

Yeah, I think there had to be something funny going on with those bolts 3B used. They should have been far stronger than the manifold. Another point is that the bolt will also expand (lengthen) as it is heated, and even though the coefficients of expansion would be somewhat different between the manifold and the bolt, I can't see that an expanding manifold would be able to pop the head off a grade 8 bolt.

Hey, but then I don't know everything either.

Kurt

You will want 3/8" x #16 bolts
You need (2) 2 7/8" x 3/8" #16 bolts
you need (4) 1 3/8" x 3/8" #16 bolts
manifold bolts
manifold bolts pic

The two larger bolts are installed on the very end of each side of the manifold with the keeper that is next to the large bolt.
The smaller bolts go in-between with the keeper shown.


Tim

Tim:

Thank you, I greatly appreciate the information.

God bless,


Dave

Before I rebuilt my '48 235 I only had 4 long keepers, 2 big washers, and two nuts with lock washers holding my manifolds to the engine. Today I was able to find two short keepers at my local yard.
Were these used on all models? I feel that I have seen many trucks with only the long keepers and then washers.
I measure the bolts I have and compared them with lengths called out in a previous post 2 7/8 & 1 3/8, I have 1 7/16. What is the correct size?
What should be placed behind the nuts securing the manifolds to the head? I previously had a lock nut and lock washer, should there be a washer as well?