This is the procedure I use for rebuilding harmonic balancers (forty years experience).
page HB_19
The procedures are:
'baking' the old rubber 'out'
sand blasting
post heat treatment
If this is a new part to you.
  Mark the front alignment with a ground mark from side to side across the front rubber strip (usually in line with the keyway center line), and on the back side (side toward engine with a double line across.

  This way, you can always find alignment and which way is forward.

   Make some shop notes, a drawing, showing the parts and how they relate to each other, dimensions,
what the rubber gap is found to be, special notes, estimated amount of rubber needed to be mixed, information about the part for future reference. Make, engine size, diesel / gas, cylinder number, weight, and so on. I have found that durable paper and saved in manila folder paper is useful.
 Sand Blasting
  This step is important for good rubber bonding and long service.
  We use # 16 washed sand from the foot hills of the rocky mountains, imported from Idaho, I understand. We order a pallet at a time, but initially just a bag at a time.
  You will need a high pressure air compressor that can support your 12 CFM blast gun. We use a five HP Inger-Sol two stage air compressor and about 150 PSI.
  Before the air comes into the exit hose to go to the sandblaster, it goes through an industrial water trap so that it is dry and keeps our parts being prepared dry and ready to primer as soon as they are done. I blow them off dust free with about 125 PSI air and then immediately apply the chemical primering.
  The important surfaces for rubber bonding get the fresh sand (usually put two cans {2# Folgers ground coffee can) full for each balancer being done.
  The #16 sand breaks down quickly so you do the Hub rubber bonding surface first, the harmonic balancer ring rubber bonding surface second and then all the other surfaces so you have a clean painting surface after rubber bonding.
  The sand will also sand blast the inside surface of the window so I made a holder of clear vinyl temporary window material, on a roll that slides under the window to protect the glass. This gets rolled across at the start of each working day.
  Once sandblasted, I turn the air pressure down to perhaps 115 PSI and bring the hose with the air spray nozzle (I modified so it gives a full blast of air). and hose the parts absolutely clean of all dust, especially the rubber bond surfaces.
  Now it is time to immediately chemically prime the rubber bonding surfaces of the two parts, inner and outer.
  The primer is specifically made for each rubber compound and must be used to get the rubber to bond the parts together.
  The primer we are using (always wearing gloves to protect from any skin contact.) has been tested to produce the strongest rubber bonds for cast iron parts we usually are dealing with.
  From the time of primering, a two hour clock starts. In cold weather, I usually put a desk light with a 100 watt light bulb shine on each harmonic balancer (ring stacked at an angle atop the hub) and exposed to fresh air. In warm, weather, the air temp is fine.
  Use this time as you will to do other tasks or read a book.

'baking' the old rubber 'out'
  This is the 'elephant in the room' that no one wants to notice!
  You notice the large electric kiln on the side and the big three horse powered squirrel cage ventilation built into the wall with a draw vent up near the ceiling . The fan is to provide clean air pulled in from outside for a more healthy work space. This is not an option in this type of business.
  How to remove the existing rubber... It is bonded tightly to at least one surface and is murder to manually try to remove.
  The answer is to bake it at a temperature that will carburize the rubber and turn it into a soft block of carbon that shakes off after the parts slowly cool.
  We have found that smoothly raising the temperature in the electric potter kiln, with electronic temperature, to 1,100 degrees F' and then hold it at that temperature for 1/2 hour and then turn the heating off and let contents slowly cool down.
 All the time, block the front of the lid up about an inch opening; I use a piece of fire brick. I also have a high strength rope on the kiln lid's front handle, and going directly to a pulley system to allow me to raise the lid without getting heat burns. Make the rope lock in the open position so that it could not possible slip, fall, and break the fragile fire brick lid.
   Once the parts have cooled and the carburized rubber is collected on a opened newspaper on the work table, which is then thown away with the carbon. Gives you a second chance to find out what has been going on when you were not paying attention.
  In this work area, be sure that a good draft of clean air is pulling all dust away from you!
  Remember that some of the older paints had lead in the paint and you do NOT want to ever breath any of that.
  The oil sleeve surface now needs to be hand polished with 3M polishing cloth. Then I put on a double row of blue construction tape to protect this surface from the sand blast to follow shortly.
 Now it is time to immediately chemically prime the rubber bonding surfaces of the two parts, inner and outer.
  The primer is specifically make for each rubber compound and must be used to get the rubber to bond the parts together.
  The primer we are using (always wearing gloves to protect from any skin contact.) has been tested to produce the strongest rubber bonds for cast iron parts we usually are dealing with.
 Do not breathe this primer fumes. Be sure that fresh air being pulled toward the center of your work shop ventilation fan flows directly from an open door, across your face and then out the fan path.
  Speaking of the fan system. I made my fan exit into a 14' high metal stack, perhaps 12 to 14" in diameter, open at the top.
  This is an important part of your equipment as the fumes from rubber baking are not necessarily pleasant and you want to vent them up high, away from the immediate surroundings. Remember that the air from the electric kiln is at 1,100 degrees F. and this hot air will rise as the air currents carry it away. Be sure this system will work in your workshop area; your future business depends on it.
  From the time of primering, a two hour clock starts. In cold weather, I usually put a desk light with a 100 watt light bulb shine on each harmonic balancer (ring stacked at an angle atop the hub) and exposed to fresh air. In warm, weather, the air temp is fine.
  Use this time as you will to do other tasks or read a book.
  At the end of the hour you will be mixing the amount of rubber that you need to rebuild today's harmonic balancers, plus perhaps 10% just to be sure you have enough, so you do not have to mix more rubber (a time consuming process).
  The primer we use is the best available, as determined by my own testing of the rubber strips bonded using the various primers for our class RTV mold making silicone rubber.
  The one we use is made by Dow Corning and is called:
DOWSIL 1200 OS Primer CL 309GM
Roughly one pint in metal can with screw on top lid. It has about one year shelf life and costs about $ 100 with shipping. It is source from Europe, where this primer was designed for. {There is another 1200 primer that is distributed in America and more readily available. It didn't quite perform as well as the other version so I did not use it.}
  I order from:
Krayden in Westminster, Colorado USA
(303) 280-2800
 You can expect that it takes up to four months to get it.
Keep it refrigerated and tighten the lid after each use.
Once fluid is poured out it is NEVER put back in; to prevent
contamination. The rubber bond relies entirely on the primer, properly used and applied. I pour the amount I guesstimate and then a 3/8" tinners brush to apply to the bonding surfaces.
  Available in bulk sizes for modest cost.
  This must be applied with a 'flood coat' and never brushed on.
To prevent loose bristles from being left on the surface, I tighten the grip of the sheet metal to bristles by hammering the side of the joint and then flatten on the side.
  Dip the brush in your plastic cup holding the primer and apply by pushing down on the handle thereby releasing a flood of primer to the rubber bonding surface. Hold the metal piece so that the released primer flows in the direction to coat the rubber bonding surface. Shift the position of the metal part in your hand and apply the next brush full in the same manner until the entire surface is coated. I coat the hub section's rubber bonding surface first, then set it to the side where it will remain until removed for fixturing after an hour of air drying.
  You have the shop fan on so that it draws across your work table with fresh air from outside, and out the exhaust vent, without your breathing in or smelling the primer at all.
Next, I do the rubber bonding surface of the harmonic balancer ring as above and lean it on the hub so it rests at an angle and naturally drains. You do not want the primer to pool at any point.
  As it dries, it may leave a very faint white chalky color, which is OK.
  You understand that the rubber bonding surface is never to be touched in any way from sandblasting on in this process.
 This summarizes the primering step in rubber bonding.

 While the rubber has been mixed and is in the vacuum chamber to remove all air bubbles for one hour:
  Your task is to put the two parts in an assembly area ready for the prepared rubber to be applied in such a manner as to flow into the gap between the two parts and completely fill the void without trapping any air bubbles, or running out the bottom for that matter.
  This means that you have to decide which direction to bond the parts together. Best case is that one or both sides are flush with each other on one flat plane. Then decide which is the best (noting on your written shop notes for next time).
  Usually, I use a flat plate of 3/4 USB or plywood that has a clean surface; scrape the surface clean with a new single edged razor blade (a new one every day). Apply a layer of wax paper (Cut Right is the brand I use) to the support, trimming as needed.
  Next is usually the hub section, followed by the harmonic balancer ring.
  Now; there is usually a specific relationship between the center line of the hub key way and the TDC timing mark. If so you want to get this exactly correct. If the parts have not slipped in the rotational direction, AND you correctly marked across the two parts, with accurate witness line(s); you can align these two (while maintaining a consistent rubber gap between the parts.
  By 'consistent', I use within +/- 0.001" gap control.
  With these two things done, your rebonded part will maintain factory timing alignment and be in balance as it left the factory floor.
  I have a whole series of four matched rubber gap spacers, usually brass rod with finely machined sized matching end pins, kept in marked zip lock bags that are hung on the wall. You can do this however you want, but they must be accurate. I just hold the two parts down with finger pressure as I gently remove each pin. Realize that these two parts are going to be sitting on your level work bench with nothing holding them in place. You must not bump them in any way during the rest of the rubber bonding process.
  It should be obvious that only you should be allowed in this area for the amount of time it takes for the rubber to be applied and cures initially. The RTV means room temperature vulcanizing which these class of rubbers will do in, say 70 degree weather.
  If the weather is much colder than this it could take days to initially cure, and if the temperature is say 90 or 100 degrees, the rubber will be curing before you can get it into place, and the bonding process will be ruined. In hot weather, you must start this process early when cool enough. In colder temperatures, you can put a desk light over the part with a 100 watt bulb, near enough to warm it to initial cure.
  For alignment of keyway and TDC I have custom made alignment tools (stored in drawers for each engine maker, and in a labeled zip lock bag with the appropriate information; which side of the balancer should it be inserted in: in from the front, or from the crankshaft side (also on you shop notes, which your religiously keeping...right?) These have to have been made from a non slipped example. If made to go in from the front the hub; be aware that the metal at the end of the crankshaft hub bore has probably been distorted by the mechanics before you when they re-installed the balancer on the crankshaft other times. Since there is often a slight press fit, the mechanic typically uses a metal pipe that fits to the end of the hub, and is driven with a heavy hammer until the balancer seats against the crankshaft flange machined near the end of the crankshaft. The factory has left some extra metal in the hub's bore so that distortion there will not prevent proper re-installation, however your tool will not fit the hub's crankshaft bore unless you dress it up with a round file; or re-bore the front of the hole on the metal lathe; or a rotary carbide file in an air powered grinder head.
  Let's assure you have done all this preparation and everything is ready to receive the rubber that will soon be ready to put into the rubber gap; just two hours after the primer was applied to the rubber bonding surfaces....
rubber bonding
If this is the part we have all been waiting for, however, you notice that although important, it is only a small part of the important stuff... They are all important to this project. Harmonic balancers lead a very stressed life and only two or three rubbers made can do it with success; and then only with the proper rubber primer properly applied, and then the rubber finally cured... etc.
  The forces involved are much greater than you probably imagine.
  I would suggest that slightest deviation to these procedures are only inviting eventual failure. this is the wisdom of forty years of experience and approximately 30,000 balancers, in use in many parts of the world, sometimes for as long as 40 years.
Deviate at your discretion.....
  the rubber I use is made by GE originally and now made by:
Momentive performance materials, Inc.
Waterford, NY
the product is:
VB RTV664 044
MP RTV664 5GA Pail
kit, SAP 38185
I order this from R.S. Hughes company in Portland, Oregon
(503) 289 6715
   This will cost your a bit over $ 800 delivered to your address by UPS.
  I believe that there was once a 'sampler' one gallon size available. Refrigerate the rubber parts for best long term results.
  Having the rubber cool is a great advantage since heat means shortened curing time, which means greater problems for you!
  This is a 44 pound kit ; 40 pounds base rubber (gray color)
4 pounds primer rubber (bright purple color)
  The rubber is mixed 10 to 1 in a plastic container with a flat
bottom weighing out the parts after zeroing out the weight of the mixing container on a modern gram scale (about 5 pound maximum range should be good). Get each part accurately weighed. Then hand mix with a silicone rubber spatula until color is perfectly blended. It will be a light blue color.
 Normally we would want to have a black colored rubber. This can be accomplished by next mixing in 7% of base rubber;
a black synthetic iron oxide powder.;

we use: Bay Ferrox 318m (1094 black oxide)
from: Pacific coast supply (503) 241-8241
This is the black color used in artist oil paints black.
Carefully mix this in until perfectly blended.
  This slightly reduces the density of the finished cured rubber
and was the ratio to change the cured rubber to match the factory balancer I was reverse engineering to match the factory tuned frequency for that model engine.
  Our goal is to duplicate as completely as possible the tuned frequency the factory desired in the original design, so this step is the best I could do (and the result of considerable trouble and testing).
  Now is the time to transfer our hand mixed rubber into a vacuum chamber which is capable of pumping all the air out (perfect vacuum). It requires a very strong chamber to survive.
  I found one on Amazon that was for professionals that had a thick glass lid so you could watch as the vacuum increasing and the air bubbles rise to the surface, and expand the rubber. The mixed rubber can easily expand over the top of your container, causing a big mess. By watch through the glass cover you can shut off the vacuum with a ball valve located there and vent the chamber to pop the air bubbles; then turn the vacuum back on.
  Repeat until no overflow worries, then leave the vacuum on full and wait until the one hour time is up.
  Carry your ready rubber to your work counter where you have one of two 100 ML horse size syringes in upright supports and golf tee blocked bottom holes (enlarged to match rubber gap needed for your balancer); fill toward the top and insert the plunger into the open end with a soda straw on one side to allow air to escape as you push the plunger down to meet the rubber surface.
 Pull straw out. Now when you eject the rubber out, over the rubber gap in a 'C' pattern, leaving an exit area for the air being forced to the side as the rubber falls down the gap toward the bottom. Keep pouring the C pattern so that no air gaps accumulate as gravity fills the gap. Once it reached the bottom is flows sideways filling the air channel. once the rubber is slightly over filled, pop any air bubbles as they rise. Once that stops you are done rubber bonding.
  Once rubber is initially cured, next day probably; use a single edged razor blade or other tool to trim the top surface even.
  Over night, you should cover the parts with a plastic Tupperware type covering to keep moisture from rusting the well sand blasted surfaces.
  The next morning, clean up the part so it is ready for painting and post rubber cure.
  Karen at this point sprays a good black color primer paint and puts the part in a kitchen type over we have in the shop and prop the door open with the thickness of a leather work glove; set the oven at 230 degrees F for an hour.
  After the hour is up, remove the parts and spray on the top coat color (also black in our case). This leaves a satin finish.
  As soon as parts cool down to be handled, this is the time to remove the blue tape that is protecting the oil seal surface.
  You are now ready to package and ship your part. Remember that a thin cast iron surface (such as a fan belt groove) is easily broken during shipping but very difficult to repair.
Pack, really pack, tape, crumbled newspaper tightly packed in and around, cardboard lined, strapping tape wrapping around in both directions outside. this is the time to protect all you careful work!
  This is my thumb nail sketch or outline of how I rebuild a harmonic balancer that has been proven over time.
  I hope this is helpful...
When I was getting started, the industry professional who taught me the right rubber to use, primering, the basic technique, charged me $ 10,000 (in 2 1/2 percent of profits steps).
  this set of information is worth much more than that, so...
  If you are so in inclined and make a business out of this, you might think about sending us a 10 or $20,000 thank you gift someday!
  All the best!