I have written on this subject over the years and will repeat my experience in parting out 40+ 63/64's over the past 18 years:
It is indeed much, much easier to remove the exhaust manifolds with the heads (or complete engine) removed from the car.  I have never successfully removed an exhaust manifold that has never been removed from an engine while it is still in the car and would never attempt it anyway knowing what I know now.  Assuming you have lifted the engine or removed the head, I do have some good advice.
First soaking the bolt where it goes thru the manifold to is going to do little good in loosening the threads since the threads bolt into the head a considerable distance away from the top where the bolts goes thru the manifold.  I have never tried heat, but understand it can help, but have never had to rely on torching the bolts.
  On removing the head bolts (and assuming you have the original 9/16" bolts) I always use a 6 point 14mm hardened 1/2" drive socket to back them out.  A 14mm socket is slightly smaller than a 9/16" but will fit on the 9/16" bolt. The 6 point 14mm socket vs the 12 point socket will give you a very snug fit. The worst thing you can ever do is slap a 12 point 9/16" socket on these bolts....you might has well go ahead and call the bolt "rounded"! LOL
Also if you have an impact wrench, these seem to back the bolts out with less likelihood of breaking. There is something about the vibrating/hammering action of an impact wrench that backs these bolts out with less likelihood of snapping the bolts off.  On the 27 sets of engines I have stripped, I have never broken a bolt off with an impact wrench, however, when I first started stripping these cars, I did break a couple off with a large wrench or socket.  It has been my experience that a quick, firm turn on a bolt breaks them free easier than a slow, turning action where you build up pressure.  I often free bolts/nuts where I cannot get an impact wrench by taking a LARGE hammer and wacking the wrench and breaking the nut/bolt free. Tthose 5/8" rear drive shaft bolts are a great example of this. 
Again,  the key to getting any bolt/nut off is to have a tight, firm fit before you do more damage than good.  I always use the fact that 14mm is slightly smailler than a 9/16" and that a 11mm is slightly smaller than a 7/16" and almost never use a 9/16 or 7/16 on these old 6 point bolts/nuts.
Jason Edge

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Comment by Kevin Campbell on May 13, 2018 at 1:59pm

My car has 5/8 headed bolts as well Joe. Its doable without lifting the engine up, just a bit time consuming and a general pain un the arse.

I had mine on ramps, I jacked it up and placed the ramps around the other way so I could slide my fat carcass under the car without bashing into the sloping part of the ramps. I have old milk crate with a flat bit of timber bolted to it to stand on for the over the fender stuff while its up on the ramps.

Since I've done mine, I re-checked the bolts again after it was hot and had cooled down again and then again 2 weeks later.

Its about as much fun as having ya nuts crushed in a bench vice, but its only really the time factor and two three hunks of skin you'll rip off ya knuckles that make it difficult.

Comment by Joe DiIaconi on May 13, 2018 at 12:19pm

Going to put her up on my ramps ( when it's not raining here ) 58 lbs of torque.

Comment by Tony and Ginny 429 on May 13, 2018 at 11:56am


Good to here that 

Joe D has a 64 and you a 63 —maybe some difference ?

The  engine blocks  and cars frame  SB the same  In both 


Comment by Russ Austin on May 13, 2018 at 11:43am

I can get all the bolts with a wrench and a long extension and ratchet from under the car. No need to lift the engine up.

Comment by Joe DiIaconi on May 13, 2018 at 11:30am

I noticed an exhaust leak the other day so yesterday morning when I examined it I found the two Center bolts on the driver side exhaust manifold are loose. I was able to get to the front one with a wrench but the one behind it is proving to be quite challenging. The shape of the manifold does not allow the wrench to go on from the top very easily,  and the brake lines to the master cylinder are in the way.

Comment by Tony and Ginny 429 on May 13, 2018 at 11:10am
Joe D

You can put a 2 x4 beow the oil pan and raise the engine on its motor mounts about a 1/2 inch or so if that would help with some bolts
I know you wlll get a real good look at the manifold bolts by removing the tire and inner wheel well
That was how the shop replaced my passenger side exhaust manifold when they did that

Comment by Jason Edge on May 13, 2018 at 9:49am

Joe, correct.  If you want to go original send me an email. I have individual bolts or complete sets. Here are the details on bolts and pricing:
Original Exhaust Manifold Bolts:
12 bolts, 9/16 head, thread is 7/16x14, two left rear bolts are 1 1/2” long & others are 2 1/4” long. I sell the longer 2 1/4” bolts in VG+ condition for $5 each, I sell the two shorter (and harder to find) 1 1/2” bolts for $10 each, or the set of all 12 for $50.

Comment by Joe DiIaconi on May 13, 2018 at 7:33am

So since all of my exhaust manifold bolts are all 5/8" does that mean they are not original ?


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