The Magna, being an early 80's design, has a relatively weak frame.  This was due to many reasons.  A list of possibles are as follows:

1.    Honda figured that cruiser riders desired more flexible frames.
2.    The aluminum frame technology wasn't where it should be.
3.    A 'stiff' aluminum frame did not match the 'cruiser' style.

etc., etc.  Either way, IMO the Magnas frame has plenty of room for improving the stiffness. This can be felt as wallowing in the corners, or any number of flex-induced handling difficulties.  Add to this a very powerful engine, and the difficulty worsens.  This isn't to say that the stock Magna does not handle good.  Compared to most cruisers, and especially the over-rated cruisers of today, it is hard to find better. This is a shame, considering that the Magna technology is more than 15 years old.
What can be done?  Follow as I make the first attempts to strengthen the frame for street use.

Objective:
To stiffen the frame to reduce frame flex, and to allow for more rigid attachment of luggage and other accessories.  I want to keep the engine 'rubber-mounted' to keep the smooth ride.  Maybe at a later time I will hard mount the engine.

Step 1: Research
Very few people have experience or the desire to strengthen the frame of a 15 year old motorcycle.  The few people who have strengthened the frame have done it more for drag racing at the track.  David Dodge has provided some insight to the frame locations that might be optimal for strengthening.

Step 2: Exploring the Magna's Frame
The Magna's frame is a dual - downtube design.  The two-piece frame area where the coolant is routed is a weak point.  The fact that there are no 'cross frame tubes' at the top further back than the carb area is another concern.  The only 'cross members' rearward of this point are thin, stamped metal crossovers that are U-shaped, and add little to rigidity.  The rear of the Magna has no direct crossovers.  It has a 'sissy bar' across the top.  I don't think this was meant as structural.  In addition, the swingarm pivot is far away from any 'cross-reinforcing.'  According to David Dodge, in the corners, the frame will stretch enough in this area to 'unload' the swingarm bushings, thus adding to a rubbery feel in the corners at high speed.

Above shows some views of the magna frame.   Look at the top view, to the left, starting from the steering head back.   Point 'A' is the last tubular cross support of the frame moving towards the rear wheel.  Points B, C and D are cross supports, but they are thin metal.   Obviously they provide little support.  In fact, points B and D are U-shaped, which provides even less support.  Point D also provides support for the passenger part of the seat, while point B provides semi-support for the front of the seat.
Moving from the steering head now to the swingarm, the frame takes a 60 degree or so bend, down to point F, where another tubular crossmember can be observed.  This is the main support for the swingarm.  In the detail to the right, you can see that the frame support tube is far above the swingarm pivots.  There is a thin metal plate (shield) located there, I assume to protect the various components from engine heat.
The only other cross-support is the bolted on water coolant-carrying frame piece, point G, which can be seen at the front of the frame.  The steering head is supported pretty well, but the 'insides' again are thin pieces of non-supportive metal.  All in all, pretty good for an early '80's motorcycle.  better than most cruisers today.   But not as good as it can be!

Step 3: Identification of Areas Of Improvement
1.    First off, there seems to be little room between points A & C for any type of cross-support.  Any tube or structure would interfere with the seat, engine, or any number of additional stock Items.  Looking between points C & D, you will notice the shock mounts.  It would be nice if the shock mounts were connected by some sort of tube.
2.    Point E is the rearmost part of the frame, and the frame tapers off to a non-tubular spot in which the siderails are bolted to.  When hard luggage is mounted, the flex is visually apparent.  The whole rear of the bike shakes independently of the rest of the frame.  This is not a very desirable condition.   This undesirable situation is Magna-fied in corners, when there are multiple stresses, which tend to shake the luggage in random directions.  Not a good feeling!   It would be nice to have a cross-frame tubular support here also.
3.    At any point where the frame takes a sharp turn, it would be wise to think about putting a gusset.  This occurs at the head, and at the point at rear where the frame 'drops' down to meet the swingarm, between points A &  F.

Step 4:  Do It!
Point E:
This was the easiest to do, since no frame welding was necessary.  After measuring the 150-80ZR 16 wheel, and its travel, it was concluded that if a straight bar was put across, it wouldn't hit.  I have 13.5" Progressive Suspension shocks, so it was easy to remove the spring and bottom the shock.  This is not so easy on the stock shock, since you need a spring compressor to get the shock apart.  The photos to the right show the piece that was made.  The  left photo shows the piece sitting in the frame.  It doesn't quite reach, this was done on purpose.  Spacers will be placed on either side to make up the distance.  The right photo shows the bar alone.   The inset photo to the right shows the end of the bar.  An 8mm nut was welded to the end of the (hollow) bar.

There is obviously one thing missing.  How can we bolt to the bar??  Well, it's obvious.  But let me tell you, I thought long and hard about the next step.  Do I really want to drill into the grabrail?  Well, not really.  But I know I can get some 8mm stainless steel allen head bolts that will polish up just like chrome!  And oh how easy it will now be to solid mount the luggage.  So I did it.  The first pass is below.  The grabrail has plenty of meat in that area, and it is perfect for countersinking.  The hole you see is smaller than needed.  This was the 'pilot' hole.  I used the existing hole as a guide, so I used a drill bit that would just fit in without marring the threads.   The next step would be, without taking the rail off the drill press,  to change the bit to a bigger bit and it will be self-aligned.

Between Point D & E:
This was a very hard decision.  I knew that the frame should be braced in this area, due to the shocks being mounted there.  However, there is little room to put a cross brace.  A 'flat' piece of steel would be marginal, and, IMO, not worth it.  After all, the frame has plenty of those flat-stamped-useless steel braces. A chrome-moly tube was the only way.  But how to make it fit?   Again, the wheel is a problem.  Will the wheel hit the tube?  And what about the plastic fender?  Could a tube be fit in-between the fender and the seat?   The answer is NO!  There is no way to put a decent sized cross tube in without cutting or interfering.  So I resigned myself to having to cut something.
If you look at an un-modified plastic fender, you will see that it has a 'corner' right at the point that the shocks intersect.  This 'corner' is logically the furthest point from the wheel, since the wheel is round and corner is 'square.'  Thus, a position is found!  Step 1 was to get a piece of chrome-moly tubing, and test fit it.  This was to make absolutely sure it would not hit the wheel.  Measurements were taken, but only time will tell!
The tube was welded in place (Top left) and the fender was cut (top right).  When the fender is inserted (bottom left) it fits perfect.  Of course I have to now figure out a way to waterproof this.  I made the tube as high as possible, using the bottom of the seat as an upper limit.  As the figure on the lower right shows, there is very little clearance between the seat and the bar.  The photo is with the Corbin seat, but measurements were done with both the Corbin and the stock.  The stock seat had more clearance, so keep this in mind if you have a stocker and want to upgrade one day to a Corbin.
Note in the bottom left drawing that the wiring harness is just hanging there.   There is barely enough room to fit it under the brace.  This is a tradeoff that must be suffered with.  The harness will NOT fit between the seat and the tube, obviously.  When it is inserted under, the fender will probably have to be secured with tie-straps, as well as the stock bolt.

Point F: Behind The engine.
Looking at the diagram   to the right, you will see point 'F' repeated for convenience.   This  area contains a flat, indented shield made out of very thin pliable metal, and is held on by two phillips screws.  I think it is meant as a heat shield, since the rear exhaust pipes There is a crossmember on top.  The piece welded (4130 steel) was to replace the  flimsy metal with an actual support structure.  The only concern here is the piece possibly hitting the back of the engine.  To assure this doesn't happen, the 'nubs' that originally mounted the plate must be ground or cut off, and the 4130 steel placed as far back as possible.  Also it must be placed high enough to clear the swingarm.  This is an important detail, 'eyeing' it is not enough.  The swingarm must be swung its full travel to assure clearance. 

Gussets
There are some obvious spots on the Magna Frame that seem ideal for gussets.  The photos below show the gussets I had welded to the frame.

A gusset was put on the spot where the frame starts to turn down.  This should increase the rigidity of the whole tail section.  Care must be taken to make sure the gusset clears the fuel sending unit on the left, and the coolant tank on the right.

Left and right side gussets at the tube junction just under the gas tank.  Do you think they clear the gas tank??

This gusset connects the steering head to the lower part of the frame.  I was going to put one above, also, but   that's where the Pichler fairing is connected.

Results:
Wow.  What a difference.  Previously, the Magna would wallow in high speed corners.  No more!  Solid as a rock!  I can sort of feel how it 'wants' to wallow, but it doesn't.  On a trip to the SME in NC, I had a chance to see how the bike would handle fully loaded two-up.  High speed stability both on the straight and in the corners was tremendously improved.  At supra-highway speeds, where pre-mod it would feel shaky and not planted, it now felt firm.  In the corners, it used to give a little 'front wheel wobble' with a full load.  this was almost non-existent.
When I mounted the luggage and 'shook' it, the bike would not shake, where pre-mod the whole back of the bike would shake independently of the main frame.
In conclusion, the frame mods were a fantastic success.  The handling and of the bike is greatly improved, and the stability of the bike with a full load is vastly better than without the mods.  I would recommend this to anyone wanting to improve their Magna's overall stability and rideability.

Frequently Asked Questions
If I send you my frame, can you modify it for me?
Sorry, but no!  The 'frame strengthening,' since it has only been done on one bike, is still experimental. As you read, I was in awe that it worked out so great the first time, with no rework. I was willing to take the risk on my bike, but not on someone else's. What if I shipped it back, and the engine did not fit because of the additional trusses? What about the seat/tire clearance? Not a risk I'd be willing to take on someone else's machine. For example, there are a lot of SabMaggers who I've known for years who want to do the oil mod. They can do it over my house, I will help them or do it every step of the way, but I refuse to drill the hole in the main gallery. Even though I've done it successfully on 3 of my bikes, I do not want to take the risk of trashing someone else's engine.

How much did it cost?
The whole thing cost me about $250.  This was an exceptional price, considering the amount of time that the welder put into this.  You would be at an advantage, since there is no more R&D to be done, just the welding.

Where did you have it done?
I had the welding done by George Reynolds, of Reynolds Lab, in Derry, New Hampshire. He can be reached at (603) 432-7327.


Other Frame Related Topics
Frame Breakage / Cylinder Head Cracking On `83 Magnas
Keith M. has an `83 V65 Magna which has experienced frame breakage... four times! According to Keith, there is a Honda service bulletin which indicated weld trouble within a specific range of serial numbers of `83 Magnas. Keith's serial number is "#....001647". All cracks he experienced occurred within an inch of a factory weld, and Keith theorizes that the metal has become weakened by too much heat from the improper welds. Further info?