Modifying chassis rail on a W111 Coupe to fit a 5.0 M117 - Mercedes-Benz Forum

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post #1 of 12 (permalink) Old 04-06-2010, 01:08 AM Thread Starter
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Modifying chassis rail on a W111 Coupe to fit a 5.0 M117

Hi all,

As some of you already know I am fitting a 5.0 M117 out of an r107 450 SLC 5.0 into a W111 Coupe. I would like to retain the tri-Y exhaust manifold system but unfortunately the rear right manifold does not clear the right chassis rail. The solution is to modify the shape of the chassis rail so that it can clear the manifold. Below are two pictures of a modification that has been done by a professional body shop on a car I have in Europe fitted with a 5.6 engine and the same manifolds. The rail was cut, and new metal brought to the shape was welded in:

As you can see, I need to gain less than one inch towards the right and something like half an inch downwards on a length of four inches. I would like to do the job myself but I do not have the necessary material to cut out the chassis rail and I don’t know how to weld. I was thinking of buying a heat gun, heat the hedge of the rail and hammer the hedge down at an angle of 45° until I get the required shape.

Would that be a sound technique? Any recommendation?

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post #2 of 12 (permalink) Old 04-06-2010, 07:46 AM
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A heatgun will not get close to the temp needed to melt metal. Since you don't weld, I would suggest you call up a local welding shop and tell them what you want done. A lot of shops have mobile rigs set up for welding so they could come out and weld what you need which would be less hassle than towing your car there. Later.

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post #3 of 12 (permalink) Old 04-06-2010, 08:35 AM
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please keep us posted on what happens with this project i have 2 5.0 motors one from an 84 and the other from a 86 both euros.. one will go in my sec the other id like to eventually put in my w111

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post #4 of 12 (permalink) Old 04-06-2010, 10:01 AM
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Frame rail mods

If you were to cut out clearance and fit the new piece in yourself, then have the weld done by a pro. it may work well.

Have the "new part" built with slightly thicker material. full weld all.
I have done this with other cars (1941 Willys) to clear the exhaust.

Brian O
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post #5 of 12 (permalink) Old 04-06-2010, 10:27 AM Thread Starter
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I was recommended on another forum not to do it as this would weaken the chassis rail with serious consequences in case of head-on collision (engine coming through the firewall).

An option would be to use the 560 SL lug manifold that would clear the chassis rail but abandoning the tri-Y system would cost me 15 hp... Not really what I want.

Any idea on how modifying that rail while retaining safety? Would the recommended thicker plate palliate for altering the shape?
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post #6 of 12 (permalink) Old 04-07-2010, 05:43 AM
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Hey if you're in a head-on collision in a "classic" car you're toast anyway. Another way to look at it is; how many classic cars do you see in a head-on collision? Most folks will drive a classic car with a greater amount of caution than they would a modern "throwaway" car. That's why the bone yards are full of modern cars and not classic cars.

I say make the modifications to the chassis, just have the welding done by some one who is competent.

If it's not broke it dosen't have enough features.
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post #7 of 12 (permalink) Old 04-07-2010, 08:25 AM
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You may be able to modify some headers from another make vehicle to fit by cutting off the flanges and welding on universal round port flanges that match the heads. I toyed with this idea a bit but most available headers have 1 5/8 or 1 3/4 tubes which are too big for a 3.5L engine. From examining pictures of different makes it looked like most would work on the right side but on the left side the steering box was in the way so there might be some trial and error. Anyway something to consider.

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post #8 of 12 (permalink) Old 04-08-2010, 06:33 AM
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Love it!


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post #9 of 12 (permalink) Old 04-08-2010, 01:53 PM
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Hi, GGR, the central bushing is not arrived (eastern) but when it is in germany it will fly to you.

I've seen what you've done, well i would prefer the SL- Style tubes. You've done so mutch work chosing a 5.0 engine and not the later one, to make it look nealy original so 15 hp less will not be a problem. If not use a tubulare type Mustang manifold and adapt it to the M117. I remember the 6.3 pagoda (black), w126 wheels and cage.
I know that Reiner used ones a time a idraulic press to modifie the chassis but I will recommend this in any case.
The other question is if that the first 5.0 needs this type , because the heads are near to the old M117 4.5 heads with smaler inlet and outlet channels, so a 560 SL pipe will do the job well.
Amg mades for the the M117 other pipes, perhabs they clear the chassis, becaus the fierst go up, then down.

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post #10 of 12 (permalink) Old 04-09-2010, 12:59 AM
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if the "u" shape in the rail is what you mean by the chassis shop cutting/welding to make the manifold fit-- that is something i wouldn't worry one bit about. hell, i'd try to "clearance" the frame rail with a hammer first. you can dent in the area and make it clean to give the appearance that it was cut, inverted and welded/sanded smooth.

this is a common issue when bigger engines or huge turbos get crammed into tight engine bays. you wont be the first or the last person to do it.
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