Just lucked out and picked up a 'running' 87 and I've completely dissassmbled (except deep engine and trans components). Hoping to rescue / restore her without needed a wallet rescue myself.
After dissassembly I found the following; Oil looked clean and free of major gunk, No loose parts running around or serious metal shavings.  Found a rock jammed in between the drive belt and casing that probably would have sliced the belt in half in the next 50 miles, had to shatter that with a screw driver / hammer to remove. Front brake rotor minor grooves, I'll see how it feels after I'm done. But when I got to the cam shaft I noticed wear on the second journal from the gear and similar wear on the head and upper casing. I've gathered from other posts hear that this model does not utilize the slip in bearings you would find on a car engine. So my question is this..
Before anyone screams hear me out, 3 out of 4 journals look great, so my wallet tells me to smooth out the grooves as well as I can and keep an eye out for excessive shavings in the oil.
But my head and the fact that I'm falling in love with this bike tell me to take it to a machine shop and see what they can do with it. I just don't want to go in there uneducated and get ripped off. Can't stand the thought of giving him 3 times what I paid for the bike for unnecessary work.

A couple of people have "claimed success" in recovering a journal using JB Weld Epoxy.  They said they put it on the cleaned still rough aluminum head and cover journals and lightly greased the slightly cleaned up cam journals so that the epoxy could not stick to the cam.  They bolted it up "dry" for 48 hours for a good cure with no packing sealant on the cover faces then took it apart and cleaned up the excess ooze.  The JB "cleaned up the roughness and filled in all the scratches".  

Adding the required liquid packing sealant to the head and cover faces adds appropriate additional oil film clearance to the zero clearance bearing this would make.  The JB can be lightly sanded with fine wet paper to increase clearance BTW if the "as cast" clearance isn't enough to permit free rotation of the cam shaft.

We hear this stuff and understand the theory behind it (that the oil pressure float film protects the soft epoxy just like it does soft babbit bearing materials in a car engine) but we struggle to really believe it as a long term fix.  At start up the epoxy would be in contact with the journal and some wear would occur at each start before the oil pressure gets there.  (I would switch to 20-50w oil for better start up protection)

Still, JB is a lot tougher than other epoxy stuffs and my wallet would wish that the trick would work for all the folks with bad head bearings.  Heads are expensive, even used.   Good used  heads are rare.  Somebody should take pics of the JB Weld process and give a long term report on it -- if it really works it should be in the Tech Section.

I bought a HiTemp epoxy online. I used it to fill a gouge on a block to keep the head gasket happy. No idea yet if it will be a grand thing. But, point is, you can get hitemp, harder than JB weld epoxy online. Pricey, but hey..Next time Im onut in the shop Ill get the name.

Somebody has to do it and prove it out with some time on the engine followed up by a teardown.

That's the rub, folks do it -- say they did it -- and then disappear sometime later before any follow up is done.   Nobody then knows if it really worked or not.

I have tried to get a volunteer "scrap head" to play with, but so far nobody will give up their dead head for an experimental play toy.

So we try it the other way -- fix your head and take some pics while you do it.

Let's do a little homework first and be a little cautious -- I would be.  Can't always trust what people "say", especially when they don't back it up with pictures and an after-action report.

http://www.jbweld.net/faq.php    
is the JBWeld frequently asked questions.  

Me, I'd read them all.  And having read them I'd use J-B Weld instead of J-B Quik since it is harder and twice as strong and I'd use acetone or lacquer thinner to clean the journals before application.  

And I'd stop by the auto parts store and buy some plasti-gage to clearance check the journals (all of them) after building up the bad journal and sanding it down to get to the correct oil clearance figure.

=============

Q: How much heat can J-B Weld withstand?

A: J-B Weld (Part # 8265-S, 8265, and 8280) can withstand a constant temperature of 500 degrees F. The maximum temperature threshold is approximately 600 degrees F for a short term (10 minutes).

Q: Will J-B Weld work on an automotive exhaust?

A: Because of the extreme temperatures of exhaust systems, we do not recommend J-B Weld for use on exhaust manifolds and catalytic converters. Nor do we recommend the product for repairs within the combustion chamber.

Q: How can I remove J-B Weld after it is fully cured?

A: When fully cured, J-B Weld can only be removed by grinding or filing it off, or by directly heating the product above the 600 degree maximum temperature threshold.

Q: Is J-B Weld available in large sizes (quarts or gallons)?

A: No. The largest available size for the original J-B Weld is our Industro Weld product (part # 8280). Industro Weld consists of 5 ounces of resin and 5 ounces of hardener for a total of 10 oz. of usable product.

Q: Is J-B Weld toxic?

A: No. J-B Weld is non-toxic. However, we do not recommend consuming the product.

Q: What can I use as a surface cleaner before using J-B Weld?

A: We recommend using acetone or lacquer thinner. In the absence of these two, soap and water can be used. Just be sure that the surface is completely dry before applying J-B Weld. DO NOT use alcohol, or any other �cleaner� that will leave a petroleum residue.

Q: Is J-B Weld resistant to water and/or gasoline?

A: When fully cured, J-B Weld is completely resistant to water, gasoline, and about every other petroleum product or automotive chemical. For wet-surface or submerged water or gasoline repairs, see our J-B Stik or Waterweld product information.

Q: Will J-B Weld hold up to extremely cold temperatures?

A: J-B Weld has proven to maintain its characteristics to temperatures as low as -67 degrees F.

Q: Will J-B Weld conduct electricity?

A: No. J-B Weld is not considered to be a conductor. It is an insulator.

Q: What is the tensile strength of J-B Weld and J-B Kwik?

A: J-B Weld has a tensile strength of 3,960 psi. J-B Kwik has a tensile strength of 2,424 psi. For more physical properties information, please see the "PRODUCTS" section of this website.  (note: Babbitt alloy tin has tensile strength of 10,000 psi so this epoxy stuff is weaker than normal bearing materials.  Cast aluminum is good for 30,000 psi)

Q: What is the difference between J-B Weld and J-B Kwik?

A: The simple answer is that J-B Kwik is about half as strong as J-B Weld in both strength and heat resistance. The other differences are somewhat obvious by the name. J-B Kwik sets in 4 minutes and cures in 4-6 hours, whereas J-B Weld sets in 4-6 hours and cures in 15-24 hours.

Q: Is there anything that J-B Weld WON'T bond to?

A: J-B Weld will not adhere to, or bond well to:

   * Any flexible rubber surface
   * Leather
   * Vinyl
   * Canvass
   * Polypropylene plastic
   * Polyethylene plastic

Q: What color is J-B Weld when it cures? Is it clear?

A: J-B Weld cures to a very dark gray (steel-like) color. We're still working on a clear version that's just as strong as the original.

Q: Do you make a J-B Weld specific for aluminum or stainless steel?

A: J-B Weld works great on ANY metal surface (lead is an exception). Use as directed on package and J-B Weld will get the job done.

Q: Can I thin J-B Weld to make it pour easier?

A: Yes. Add up to 1 tsp. of acetone or lacquer thinner per 2 oz. (1 full package) of mixed product.

Q: Is J-B Weld microwave safe?

A: Yes.

How tough.... simple test....

Mix a blob of JB Weld and let it cure per instructions.

Then.... get a piece of Aluminum, and a nail.  

Push nail into Aluminum to make a mark.
Push nail into blob of JB Weld to make a mark,  using same amount of pressure.

Compare the marks.   Smaller mark is stronger material.

Epoxy is not as strong as lead or babbit.   But is metal filled epoxy (JB-Weld) strong enough to support a spinning cam shaft?  PSI is pounds per square inch and you have most of a square inch sitting there in the bearing saddle block half.   It can support a like ton and a half of pure static pressure before deforming the epoxy.

More to the point, will the oil film stand as much pressure as the epoxy can before allowing the spinning shaft to hit the epoxy material?  I think not -- therefore your epoxy repair is going to catch some periodic wear from contacting the spinning shaft.

Heck, but so did the durn aluminum -- that's why it got all gouged up in the first place.

Is it going to hurt something to try it?   No, not really -- head is junk otherwise.    Is it bullet proof?   No, not really.

Could it be used to patch a bike back together that is otherwise junk?  Maybe, for some period of time anyway.  

That's the point -- we don't know how long it lasts.   Maybe well enough for the folks to sell the scoot and leave the list,  maybe well enough for them to forget about it for a while.   WE DON'T SIMPLY KNOW ....

What the oil clearance supposed to be?
I'd get some teflon tape and wrap the shaft with it.
You could even lay down directly over the jb-welded area and over the journals too.