Where some time with a 4.5" razorblade, a flap wheel. and a couple of files can take you

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CopperNick

Master Mechanic
Feb 20, 2018
406
63
Canada
So back when I posted about my header issues, which, by the way, are still issues. several of the respondents mentioned what they had done by way of modifying the motor mounts they had to gain needed clearance. Since I am waiting for parts, again!!, and had dedicated the afternoon to some mig driven rehab work, it occurred to me to see what I could do by way of creating a pair of suitably modified upper engine mounting clams, just in case my speed shop couldn't persuade the distributor to credit me for their mis-applied part number tubes. The pictures that accompany this post show what I came up with

DSCN2367.JPG



This first pic is of the upper mount that I ended up using after my first choice didn't want to drop cleanly onto the frame shell and urethane inner biscuit. This is one of a pair of clams that I used when I did the mockup of the clutch linkage and found that I had to reshape the ears through which went the cross bolt because originally they wouldn't drop into place either. With the 400 acting as my dummy block, an with the services of the engine crane, I could raise and lower the assembly to trial fit the upper clams and see what I had to add or remove to get a clam that would work.
DSCN2368.JPG


For contrast, here is a picture of one of the first pair of upper mounts that I originally attempted to use. Unlike the first version, this one has two reliefs or pockets in it that were put there by the factory as part of the stamping process. Apart from this difference everything else remains about the same, including the distance between the inner surface of both mounts and their respective outer edges, about 1.75". The matching clam to this one was the part that became my victim (Insert blood curdling screams and moans
DSCN2369.JPG


And this was the result of my whittling efforts. The width of the material removed from the upper edge/face/surface worked out to about n inch, leaving me with about 5/8ths - 3/4 of an inch of shoulder.

DSCN2371.JPG


And, finally, a comparison shot of the stock, unmodified upper mount sitting beside the one that has already been played with. This is not the actual final shape will end up being used, this is more of an "in progress" shot. After I took this, I revisited the concaved curve that I had created between the modified upper edge and the mounting ear and dished it in more deeply, removing some additional material from the upper edge of the bolt ear in the process. That is where the shape lies now, but it may still not be the final configuration as I am thinking of shaving an 1/8th or 3/16 of an inch more out of the curve to make it even rounder and deeper. At this point I have no firm idea as to exactly how much the amount of material might be that I need to remove in order to gain the clearance and room that I need. I also have no real plan to go ahead and use these variants unless the cannot score the set of headers that I have identified as a proper fit, If I end up stuck with the Flowmasters then it becomes a case of unbedding the motor and swapping the resident clams for the ones that I have modified and hoping that I got my sums right. All of the pictures presented as alternatives show mounts that have been radically trimmed back, including the store bought variant. Not thinking that radical, just looking for a result that both works and that, at first glance, will appear normal and baffle the looky-lous.

Nick
, here!!)
 
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565bbchevy

Geezer
Aug 8, 2011
7,730
113
Michigan
In Chevy applications where I have done this many times the interference has only been on the driver;s side rear upper corner on a downward angle so I do mock ups to see how much I need to take out of the corner and only cut what is necessary for it to clear and when installed it is relatively hard to see,
After all of your work you could still end up still having a clearance issue without having a mock up to know where the clearance is actually needed.
Many times depending on the header that cut will be very deep in the corner so I prefer to leave the rest of the mounts integrity intact. IMO
 
Oct 14, 2008
6,280
113
Melville,Saskatchewan
Pfffft, and people say Oldsmobiles are hard.
That's why I used 403 Trans Am mounts to replace the knocking swirl port sbc turd in my 94 Z71 with an Olds 350. There is ways around it, even used the sbc frame mounts. JK, headers can be a b*tch with any motor make.
 
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CopperNick

Master Mechanic
Thread starter
Feb 20, 2018
406
63
Canada
Clipping only the rear upper corner was an option that I considered when I first encountered this nuisance. A few of the pictures posted to a previous thread showed clams that had really been heavily relieved. One respondent even posted an aftermarket version which looked like a sheet of 3/16ths or 1/4 inch flat plate had been introduced to a humungous press for the purpose of giving it ears and holes. Just the absolute minimum of material needed to do the job. Had a pair fitted to his Malibu. I do agree that the "How much" of how much to remove can be speculative. As far as what I created, the upper shoulder is not going to get any shorter or closer to the block than it is now. I am going to increase the radius of the concave curve that flows upwards from the mounting ear to the upper shoulder; not by much, maybe an 1/8 or so. At this point it is more of an aesthetic exercise than increasing my clearances. Should my header problems continue, it is likely that I will retrieve the Flowmasters from the speed shop and then I will have to swap in this pair of clams. If I make them pretty much identical then which one goes on what side becomes moot. Either part will fit either side. if someone goes to all the trouble of peeking then what they get to see is symmetry that looks like it belongs with the modifications that were made tending to look like factory items and disappear for that reason. Mission accomplished.
 

CopperNick

Master Mechanic
Thread starter
Feb 20, 2018
406
63
Canada
No pictures for them but the final version of the modified clams ended up with the top shoulder being 5/8" high and extending evenly from the front side panel to the rear one. The relief in the side panels is 5/8" at its deepest point which is just below where the side panel curves up into the shoulder, and extends in a smooth curve as far as the beginning of the ears where the mounting cross bolts go through, by which point it faded away to nothing. The relief is deep enough and extends far enough down each side panel that the top face of the upper shell of the frame mount is just starting to be exposed. Picture is worth a 1000 words so will post a couple when I take them.

Nick
 
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