MGB Exhaust Re-Do (Part 2)

Picking up where I left off, we have the MGB front end on jack-stands and the old exhaust sitting in a heap in the driveway. Today's post will be about getting the new exhaust installed. Recall, it is a ceramic-coated stainless steel Bell system. I left the packing plastic bags on the pipes as I handled them to protect the finish, removing the plastic as I installed them.

Setting The Scene

exhaust hammer example
from streettechmag.com

With break time over, we set to trying to install the new exhaust. The Bell system has 5 pieces: the header, a straight-ish pipe, the center resonator, another straight-ish pipe with a support bracket attached and then the tail muffler. They go on in that order. The hardest part, like with any car, is getting the header to fit around all of the various other things in the engine bay. I watch car shows on Velocity and some of those installs require hammering on the pipes to get them to fit. That would really suck. Spend all that money for a "bolt on" set of pipes and then have to dent the snot out of them to fit an otherwise stock engine and compartment. Doesn't seem right, but does explain the custom fabrications they do on some of those Velocity shows. Even then, it's usually because they're slamming a huge non-stock engine into a classic-ish car. For a built-for-stock engine, hammering dents into the pipes shouldn't be necessary. Anyway...

From Below?
For the MGB, this saga starts with getting the front end way up in the air. We had a good 18" of clearance and still couldn't feed the header up from below. Some internet posts I've read indicate this is super easy, but I suspect anyone who installed that way had a lift or a pit. We have neither so we switched to going in from above. That meant removing the bonnet.

From Above

attached for fitting the rest
of the pipes

The bonnet is held to the hinges with 2 bolts per side, but remove the hood prop first. Once the prop is off, one person holds the hood still from the front while another person (K2 in this case) loosens all the bolts, and removes one from each side. At this point, it would be wise to put a shop towel or something soft under each rear corner of the hood. Then, remove a final bolt from one hinge. Balance the hood on your shoulder and let it slide down onto the towel. Repeat with the other side and then each person grabs a side of the hood and walk it off the front. For fun, we set it (on pads) on top of the 280ZX hood. The MGB hood looks like a toy hood compared to the Zed hood. The MGB hood is at least 6 inches smaller all the way around.

center-mount bracket

With the hood removed, you next loosen the driver side engine mount. The two nuts which hold the engine to the mount are the easiest to get to, and present the least necessary to separate the engine from the frame rail. With nuts safely stowed, place a wood block on a floor jack and slide it under the driver-side of the oil pan / engine block. Carefully lift the engine from below (setting the block of wood so the oil pan and other parts are not damaged) an inch or so. Once you feel considerable resistance to the lift, stop lifting. Now, have your helper fit a pry bar between the engine mount and the engine and then apply pressure to shift the engine slightly towards the passenger side. The engine will more roll anti-clockwise than slide left-to-right, but this creates enough space. Hold the header vertically, with the head-tips pointing across the top of the engine. Slide the header as far down into the largest space you can go before rotating the header so the head-tips point up and away from the firewall. On this particular header, there are pinch-welds along the sides of the collector. These pinch welds wanted to hang up on pretty much everything on the way down. With some gentle and some not-to-gentle persuasion, the header pushed past the space between the block, the steering column and the frame allowing us to wiggle it into the right spot near the head. At this point, the pry-bar leverage can be released and the floor jack released, letting engine rest back on the mount. We had to wrestle it a little bit, but it settled. Our header ended up with a couple minor scuffs, but no scratches.

To get everything else to align, K2 bolted the header onto the head. K2 was done for the day at this point, and the rest of the install was not going to be as straightforward, so I cut him loose.

Body Brackets

header from below

While K2 attached the header to the head for fitment / alignment, my focus was on the 2 mounting brackets. The center mount reuses the original body mount holes with a new steel and rubber mount that simply threaded in with new bolts (in the kit). The rear mount also reuses the original body mount holes. If yours are still in great condition, you could reuse them. With the body brackets on, I could start lining up the pipes, and get a feel for what went where.

The fourth pipe (second straight-ish) had a bracket that was a simple flat bar wrapped around the underside of the pipe with a round hole at each end. The center-mount kit provided a bolt, 4 large flat washers, 2 plastic sleeves, a bit of metal flashing with holes and some small nuts and bolts. There were no instructions, but you could tell that the bolt went through the holes in the flat bar. A flat washer went between the flat bar and anything else that touched it. Between the ends of the flat bar, on the bolt, went the plastic sleeves and the nut went on the end. Neat. With some careful bending of the flat bar with my channel-lock pliers, I was able to get the operation together. The bit of metal flashing was to wrap around the plastic sleeves and then bolt to the center-mount bracket I had just attached to the car.

second straight-ish pipe mounted

To get the fourth pipe and centermount to align and fit, all of the pipes between that mount and the header need to be in place. Start with getting the pipes in the rough spot you expect them to be. A straight-ish pipe (one that has a gentle bend or two) has those bends for a reason. Align them with the path of the original pipes. Once set in the right location, fit a pipe clamp between the pipes and then slide them together, wiggling the fit so they stay together and are in the right alignment. With careful use of a rubber mallet, I was then able to drive the various pipes together. Remember to set a pipe clamp at each junction before you start pounding things together or you won't have a way of clamping things together.

Rear Muffler

The final hurdle was figuring out the rear muffler mount. The old mount was a real hack job where a prior owner had taken a u-bolt that roughly fit the original body mount and threaded a nut on each end. So bad, but I really shouldn't judge. The original mount was almost German in it's over engineered solution. To the bracket is attached 2 rubber mounts pointing away from the exhaust pipe. To these rubber mounts, a hexagon bracket (with one leg removed) is attached, with the missing leg on the bottom. The missing leg has a pair of holes, one at each end, for attaching a pair of semi-circular clamps. These clamps hold the pipe in place. Unfortunately, they are sized such that if you put them on without any spacers (not included) they will either pinch the exhaust pipe because you tightened them too much or the lower clamp will fall off because you didn't tighten them enough... because you didn't want to pinch the pipe. To remedy, I found a pair of oversized nuts that would slip on, acting as spacers, so I could tighten everything down without pinching the pipe.

Header to Head

see the gap?

Once I had it all assembled front to back, I moved from back to front, tightening the mounts and pipe clamps. Once snug, I shifted to the very front to consider the mating of the manifolds to the head. The MGB came with a few types of exhaust, with 2 particular versions for the models before emissions standards became so tight (in 77) that the exhaust manifold needed to be redesigned. These 2 types have a different thickness of the material through which you send bolts to attach it to the head. The older one (#12H709) is thicker than the newer one (#12H3911). This is important because the intake and exhaust share studs and corresponding nuts. If the thickness of one manifold is not a match for the other, there is not a uniform amount of torque on the various manifolds, creating leaks. This applies to pretty much any combination of intake and exhaust, unless you stay completely original stock. Since the prior owner had replaced the dual carbs on my MGB with a side-draft Mikoni carb, and hacked together a home-grown exhaust, I was going to have to deal with this regardless.

When the header was attached for fitting the other pipes, I didn't look very closely. It didn't matter. With a closer look, you can see the washers were not sitting flush. Adding insult, only two of the thickness differences for the 4 shared studs were the same. To remedy, I grabbed some fender washers of varying thickness, and cut them in half (across the hole) to use as spacers. To hold the spacer in place during install, I used a very thin smear of the copper gasket maker I used on the header gasket. This plan worked great. In about 30 minutes I had spacers in place, and the header torqued down with washers sitting flush.

gap gone

Testing
All of this, nearly 2 full days of effort, lead up to the test fire. Of course, I had to re-assemble the air cleaner, and the hood is still off, but after verifying everything was back together, it was ready. I had been trickle-charging the battery, too, so I was pretty confident it was going to start right up. Fortunately, it did. It sounds great. It has a nice deep tone without being too loud. The biggest difference, I think, is that all of the growl sound comes from the rear of the car now. It must have had leaks before. With all of the rust, that's not a surprise. I wound the engine up to 3000RPM to get a sense of how it will sound on a power pull and it sounds pretty awesome. With the top down, the garage doors open and the rev counter around 3k, I still hit 90+ dB. So, it is no quieter... in the garage with the doors open. On the road, it is quieter in the seat, but I don't have dB numbers to prove it. Just my ears.

That's it for today. I had started reading about how to do automotive interiors (trimming) in preparation for doing the seats and cards on the MGB. I have parts on-order to complete the trunk and woofer box as well. Once those are complete "major operations" will have completed and I will be shifting focus onto the Zed... and then back to Hapy. Thanks, as always, for following along-