can an overtightened lower intake spread/move the heads?

rockin_rick · Oct 30, 2005

I believed that I have overtightened my lower intake (http://forums.stangnet.com/showthread.php?t=590101). Can this result in the heads being shifted/spread apart?

Thanks,
Rick

CManT1914 · Oct 30, 2005

I wouldn't think so. If the heads are torqued down correctly, I think it would take a lot more force than an intake to move them. I think they would warp before they would actually change positions. But I am not positive.

nmcgrawj · Oct 30, 2005

I doubt that the clamping force from the intake bolts is anything close to the clamping force of the head bolts to the block. The bolts in the intake would snap IMO before the head was shifted, unless the head was improperly installed.

final5-0 · Oct 30, 2005

Seems to me that the ends of the manifold would keep the heads from spreading as they would butt up to the block.

Grady

divit250r · Oct 30, 2005

Wouldn't the dowels in the block make it impossible to move the heads at all?

Scott

blk9450 · Oct 30, 2005

ive heard this. people who have or will have headgasket issues often tighten the intake a little less thna spec. like me
turbomustangs.com has info on this

DarkProphet · Oct 31, 2005

blk9450 can you post a link to this topic?

FORCED2DV8 · Oct 31, 2005

There is no way those heads are moving unless they are not tightened down, or your block is cracked in half.

WhiteDevil · Oct 31, 2005

divit250r said:
Wouldn't the dowels in the block make it impossible to move the heads at all?

Scott

Yeah i agree, and plus the fact that the intake only usually is torqued to around 12 ftlbs so over torqued would be around 20ftlbs or so. PLUS the fact that you are running AFR heads which have aluminum threads i would be you would strip the threads out before you moved the heads.

blk9450 · Oct 31, 2005

its not that it MOVES the heads, but it places a static force on them. the tension causes head gaskets to blow easier because there is less force claming head to block becuase of the tension forces from the manifold blots pulling up. i dont have a link and im too lazy to look, but its common knowledge over there

WhiteDevil · Oct 31, 2005

It is amazing to think that somethign Tqed to 15ft/lbs could pull something tqed to 80+ft/lbs off of the block. But im no engine builder so maybe its true

nmcgrawj · Oct 31, 2005

blk9450 said:
its not that it MOVES the heads, but it places a static force on them. the tension causes head gaskets to blow easier because there is less force claming head to block becuase of the tension forces from the manifold blots pulling up. i dont have a link and im too lazy to look, but its common knowledge over there

What you are saying makes sense, but im not sure to the degree of a difference it will make. The angle that the intake bolts bolt into the head are not perpendicular to the head bolts, so then its not the full 12-20-25 or whatever you over torque the intake to pulling up on the heads. Its a fraction of that when u take the angle involved, cos sin whatever, and multiply that by the over torqued magnitude.

After all that, i cant imagine the intake bolts making that big of a difference on the clamping force of the heads. If everything was perpendicular, then maybe, but at the weird way our manifolds bolt onto the heads, i doubt you will be able to make a experiment to prove it.

Post up that link if u do ever find it, im interested in reading about it.

Joes95GT · Oct 31, 2005

blk9450 said:
its not that it MOVES the heads, but it places a static force on them. the tension causes head gaskets to blow easier because there is less force claming head to block becuase of the tension forces from the manifold blots pulling up. i dont have a link and im too lazy to look, but its common knowledge over there

It's a dynamic force - else the head wouldn't be getting yanked that little bit.

And I don't think it'll make a bit of difference if the intake bolts are over tightened slightly.

Joe

blk9450 · Oct 31, 2005

ok: our intake bolts go directly down into the head, which is at a 45 degree angle to the up-down axis of the bolt. so for the 20ft lbs of the torque, its effectively 14.1 ft lbs lifting up on the head (assuming intake is supported by the block) and 14.1 ft lbs pulling towards the intake. i drew a sweet picture but this ****ing ****ty ass forum wont let me upload it. its a ****ing bitmap with a few lines and its too big. ****:SNSign:

blk9450 · Oct 31, 2005

Joes95GT said:
It's a dynamic force - else the head wouldn't be getting yanked that little bit.

And I don't think it'll make a bit of difference if the intake bolts are over tightened slightly.

Joe

well joe maybe you slept through that class. dynamics involves moving objects and statics involves forces with no movement. as i said before, the head doesnt move, its just under a force, that effectively decreases the force holding the head down.

Joes95GT · Oct 31, 2005

blk9450 said:
well joe maybe you slept through that class. dynamics involves moving objects and statics involves forces with no movement. as i said before, the head doesnt move, its just under a force, that effectively decreases the force holding the head down.

I didn't sleep, I actually tried - I failed it twice and dropped it once.

If it's decreasing the force holding the head down, there has to be some kind of movement, correct?

And, doesn't the size of the bolt have anything to do with the magnitude of the force? (Or something) Isn't 80 ft-lbs with a head bolt much different than 80 ft-lbs with a tiny lower manifold bolt. Something about moments or something?! Seriously, I'm not being a smartass - I really only know half of what I'm talking about when it comes to this book-smart crap.

I don't think that 5 extra ft-lbs on a lower manifold bolt would cause any harm whatsoever. Regardless of what physics tells you, it's not really what happens. There's a lot more (important stuff) to a blown HG than a slightly over-tightened manifold bolt.

Joe

rockin_rick · Oct 31, 2005

I was wondering more about the wedge effect that the intake has on the heads. When it's tightened down, it wedges into the heads and (potentially) spreads/slides them apart. What I don't know is how much force it takes to laterally slide the heads while under the clamping force of the head bolts, and how much force is applied from the wedge effect.

Also, I thought that the extra 5 ft-lbs on the upper head bolts was to counteract the "lifting" of the intake...

Thanks,
Rick

blk9450 · Oct 31, 2005

Joes95GT said:
I didn't sleep, I actually tried - I failed it twice and dropped it once.

If it's decreasing the force holding the head down, there has to be some kind of movement, correct?

And, doesn't the size of the bolt have anything to do with the magnitude of the force? (Or something) Isn't 80 ft-lbs with a head bolt much different than 80 ft-lbs with a tiny lower manifold bolt. Something about moments or something?! Seriously, I'm not being a smartass - I really only know half of what I'm talking about when it comes to this book-smart crap.

I don't think that 5 extra ft-lbs on a lower manifold bolt would cause any harm whatsoever. Regardless of what physics tells you, it's not really what happens. There's a lot more (important stuff) to a blown HG than a slightly over-tightened manifold bolt.

Joe

well say there is a 200 lb weight on the floor, and you have a rope on it and youre trying to pick it up, if you get a girl to help you that can lift 50lbs, then you only have to lift 150lbs to get it off the floor. same thing with the head. the bolt is the girl. the more she lifts, easier it is to lift the head (weight)..

doesnt matter how big the bolt is, or the girls arms, 50lbs is 50lbs.

5 extra ft lbs , per bolt times 10 bolts (i think) per side. it adds up

rick, what do you mean lifting of intake? true it will counteract the intake coming up, but this also is the force that pulls the heads at a 45 degree angle up

nmcgrawj · Oct 31, 2005

blk9450 said:
well say there is a 200 lb weight on the floor, and you have a rope on it and youre trying to pick it up, if you get a girl to help you that can lift 50lbs, then you only have to lift 150lbs to get it off the floor. same thing with the head. the bolt is the girl. the more she lifts, easier it is to lift the head (weight)..

doesnt matter how big the bolt is, or the girls arms, 50lbs is 50lbs.

5 extra ft lbs , per bolt times 10 bolts (i think) per side. it adds up

rick, what do you mean lifting of intake? true it will counteract the intake coming up, but this also is the force that pulls the heads at a 45 degree angle up

Looking at your drawing, if you pull straight up on the intake, aren't the heads gonna get wedged against the block?

And for the head to actually lift, dont the bolts have to give? Dont the head bolts "stretch" when the head lifts?So how much force are we talking here to make this happen? And how much force do we actually see?

I understand your concept, but like one other argument i remember(347 vs 331/302 durability) you can not perform a experiment to prove it. Yes, in theory it does show that in some sort of way, it might "reduce" the force needed, but how much is needed to show a difference?

so you have 848 going down, and 25 x 12=210 up. Difference of 638. When does the head lift? When does it become a problem?

blk9450 · Oct 31, 2005

well see those arrows coming OUT of the block, those are the effective forces lifting the block off the head. the red arrow is the bolt force and the green arrows are the effective forces on the plane of the head. yes head bolts strech when the head lifts, although i have no idea what the force is requred to do this. the point is that more force on the intake means less force holding the heads down.

even though i have no idea where you got 12, 25 and 848,
25x12 = 300

can an overtightened lower intake spread/move the heads?

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