Exhaust manifold/header fit

[alanr]

I would welcome some thoughts on the best way of solving an issue with the fitting of my +2 exhaust manifold/header. See pics.
The PO fitted a new SJS stainless manifold, however number 3 downpipe is resting hard on the main chassis which causes vibration and obviously needs sorting. I dont think the manifold will come off without removing head or engine.
So...What would you do?
1.Just get stuck in and remove engine and modify number 3 pipe? i.e cut and TIG weld to fit, however may be difficult to make nice job even when off due to other pipe close behind.
2.Remove head and do same?
3.Disconnect engine mounts and try and move engine over enough to file and 'notch' chassis? (which I am very reluctant to do).
4.Be extremely brave and try and get a an Oxy flame in the area to bend/put dent in the No 3 pipe?
5.Remove engine or head and go off and buy alternative manifold that fits properly?

Thanks,

Alan.

[innesw]

I have removed and refitted larger bore "fast road" manifold/header from my +2 several times, it is a total P.I.T.A. but completely possible, the same side engine mount needs to come off ( so the engine needs supported...)

and the second answer (my preference) is notch the chassis (only needs to be very small notch unless your engine runs very rough!)

Each to their own but changing/bending/denting the no3. pipe just sounds like a unbalanced restriction (minor i know).

I am aware balanced length manifolds of a larger bore (like mine) take up more room but a little surprised the SJS manifold touches the chassis, just to check the engine mounts are on correctly with the spacers??

Innes

[billwill]

I doubt if you can remove the head or engine without taking the manifold off the head at an early stage.

On the other hand you possibly cant get the manifold pipes out of the engine compartment without removing the head, no matter how you wiggle it around.

The usual approach to your problem is to cutaway a portion of the sub-frame (chassis) where the manifold touches it, or make a few slots there and bend over a portion of the sub-frame to create a semi-circular notch. Best approach is then possibly to weld a stengthening plate around the notch.

There should be some photos of the mod on this site.

[Gray]

Many chassis from early on in the car's life (or probably from new) had a small 'adjustment' to the chassis to clear the exhaust manifold. I think a small tweak with a hammer, or bending with a mole wrench, is far better than cutting a section out. Cutting and welding strengthening probably needs to be done with the body off.

A Spyder chassis has more clearance so hopefully my manifold will fit without any issues.

[alanr]

I have removed and refitted larger bore "fast road" manifold/header from my +2 several times, it is a total P.I.T.A. but completely possible, the same side engine mount needs to come off ( so the engine needs supported...)

and the second answer (my preference) is notch the chassis (only needs to be very small notch unless your engine runs very rough!)

Each to their own but changing/bending/denting the no3. pipe just sounds like a unbalanced restriction (minor i know).

I am aware balanced length manifolds of a larger bore (like mine) take up more room but a little surprised the SJS manifold touches the chassis, just to check the engine mounts are on correctly with the spacers??

Innes

Hi Innes,

With the engine mount removed will the manifold wiggle out of the bottom of the car? Or are you saying with engine lifted a bit off its mounts it will it come out of the top without removing the head?
Engine mounts are new with spacers correctly fitted.

[69S4]

Hi Innes,

With the engine mount removed will the manifold wiggle out of the bottom of the car? Or are you saying with engine lifted a bit off its mounts it will it come out of the top without removing the head?
Engine mounts are new with spacers correctly fitted.

It is possible - although something approaching infinite patience is required - to get the manifolds out with the rest of the engine intact. Or at least I've managed it with every set I've had so far. But it's a lot easier if you remove the engine mount and raise the engine a few inches. For the sake of your blood pressure take the mount off

I had the same hits the side of the chassis problem when I bought the previous manifolds and went down the grind a clearance notch route. The intent always was to weld in a support patch underneath next time the engine was taken out but 15yrs later I've not had to so the notch has stayed unsupported and is still fine. You only need to remove a small amount of metal and although I'm not an engineer I don't think it causes any problems.

[crannyr]

Definitely bend the sheet metal chassis as needed to provide clearance around the pipe. Do it cold, no heat, for a number of reasons; heat softens and weakens the metal, fire ignites oil, gas and fiberglass, cold bending actually should make the area stiffer at the point of the bend. Finally the header pipes will not be as efficient if they are redesigned by either cutting or denting for clearance. I like others have been able to bent with reasonable ease using hand tools(mole grips, vice prips, monkey wrench) once you get access.

Rick

[StressCraxx]

I had the identical issue when I installed my headers and replaced my motor mounts at the same time. Instead of cutting or bending on the chassis I removed both rubber motor mounts, put them in a bench vise and slotted the mount holes about 1/4" in the horizontal direction. I did not touch the motor mount brackets on the chassis because these are a known weak area. With the slotted holes in the mounts, I reinstalled the bolts loose, then pushed the engine towards the intake side to obtain the required clearance. I think you can do the same to your +2 easily.

Regards,
Dan

[steve lyle]

I just put headers on my DHC Sprint, so if that's any guide to your +2, there's no need to pull the engine.

First, mark the chassis flange where the pipe abuts it, so you have some idea of where and how much material to remove.

Put a floor jack under the engine, with a block of wood between, and take the load off the motor mounts.

Remove the mounts.

Push the engine to the right side of the bay. Remove the headers.

In my case, I took a mini die grinder with a carbide cutter in it and took about 1/4" off that chassis flange opposite the third pipe to create clearance for the header. A file or grinder could also do the job.

No need for any strengthening plate, imo. Material removal is minimal, and there isn't a meaningful transverse load on the chassis at that point anyway. Loads are vertical, and that horizontal flange doesn't provide any vertical strength anyway, it just serves to help prevent buckling of the vertical member.

Assembly is the reverse.

[RichardHawkins]

Alan,

I cut a notch in my chassis to provide clearance. I also took Rohans advice of replacing the studs with bolts (Rohan actually advised socket headed cap screws, which I have not found necessary). Using bolts gives you a bit more wiggle room, but does make installing the gasket more tricky. I did this whilst I was overhauling the engine. As the head is aluminium, the thread in the head is easy to damage. I fitted helicoil inserts for added toughness.

Richard Hawkins

[rgh0]

......

No need for any strengthening plate, imo. Material removal is minimal, and there isn't a meaningful transverse load on the chassis at that point anyway. Loads are vertical, and that horizontal flange doesn't provide any vertical strength anyway, it just serves to help prevent buckling of the vertical member.

Assembly is the reverse.

While I agree with the conclusion the stress analysis of the chassis at this point is incorrect. The chassis is under bending loads with the weight of the engine down at the mount and the front suspension further forward pushing up. The flanges on the chassis resist that bending like the I beams you see used in structural steel. While cutting out a small section of the flange or bending the lip over for clearance does not affect the chassis functioning you do want to do the minimum to get clearance with the headers

cheers
Rohan

[steve lyle]

Just like on an I-beam, it's the vertical component of the beam that resists bending due to vertical loads. The horizontal components contribute very little strength in that direction. Their purpose is to prevent the vertical web from buckling horizontally.

Take a wooden board, maybe 1"x4", say 4' long. Lay it flat between two supports at the ends. Put a significant weight, say 40 lbs, on it in the middle, and watch it bend. Now take the same board, put it on edge, and the weight in the middle. Very little if any bending.

I certainly agree that you want to remove the minimum of material. There's no point to do otherwise.

[alanr]

Well, thanks folks for all the input, very much appreciated. You have all really helped my thought process.

I have now decided to disconnect the engine mounts with the engine suspended and then I should be able to ascertain how much it will take to give me approximately a 1/4inch of clearance from the chassis at the No3 pipe. If I can then get away with elongating horizontally the engine mounts as suggested that will be good. The worst that can happen is that I ruin a couple of engine mounts in the process which are cheap enough anyway to replace.
If that doesn't do it then I still think I want to modify the pipe as apposed to trimming the chassis. If the body was off the car and I could strengthen a 'notched' area that would be different but it isn't, so at this stage I just don't fancy that option.

Thanks all...update to follow!

Alan

[rgh0]

Just like on an I-beam, it's the vertical component of the beam that resists bending due to vertical loads. The horizontal components contribute very little strength in that direction. Their purpose is to prevent the vertical web from buckling horizontally.

Take a wooden board, maybe 1"x4", say 4' long. Lay it flat between two supports at the ends. Put a significant weight, say 40 lbs, on it in the middle, and watch it bend. Now take the same board, put it on edge, and the weight in the middle. Very little if any bending.

I certainly agree that you want to remove the minimum of material. There's no point to do otherwise.

Your example is valid.... However I am sorry but your wrong as to the purpose of the flanges.

The vertical web works mainly in shear, the top and bottom flanges are there primarily to contribute to the strength in bending.

The concept is all around having the maximum amount of material the maximum distance from the centre of bending, hence the flanges. Certainly a board on edge is stiffer in bending than a flat board but put flanges on the board on edge top and bottom and its much stiffer still.

Your correct that the flanges also help prevent the centre web buckling just as the centre web prevents the flanges buckling but that is not the primary purposes of the flanges or the centre web

If you have an mechanical or civil engineering engineering degree you should understand.... if you don't then I don't think I can explain it as the concepts are difficult and have to be built up in a way that's beyond what possible here.

cheers
Rohan

[rgh0]

Just like on an I-beam, it's the vertical component of the beam that resists bending due to vertical loads. The horizontal components contribute very little strength in that direction. Their purpose is to prevent the vertical web from buckling horizontally.

Take a wooden board, maybe 1"x4", say 4' long. Lay it flat between two supports at the ends. Put a significant weight, say 40 lbs, on it in the middle, and watch it bend. Now take the same board, put it on edge, and the weight in the middle. Very little if any bending.

I certainly agree that you want to remove the minimum of material. There's no point to do otherwise.

Your example is valid.... However I am sorry but your wrong as to the purpose of the flanges.

The vertical web works mainly in shear, the top and bottom flanges are there primarily to contribute to the strength in bending.

The concept is all around having the maximum amount of material the maximum distance from the centre of bending, hence the flanges. Certainly a board on edge is stiffer in bending than a flat board but put flanges on the board on edge top and bottom and its much stiffer still.

Your correct that the flanges also help prevent the centre web buckling just as the centre web prevents the flanges buckling but that is not the primary purposes of the flanges or the centre web

If you have an mechanical or civil engineering engineering degree you should understand.... if you don't then I don't think I can explain it as the concepts are difficult and have to be built up in a way that's beyond what possible here.

cheers
Rohan