Friday, July 12, 2013

JB Weld is magic

A great many people scoff at the use of JB Weld as a permanent repair. The stuff is amazing, but it's (perhaps not unfairly) associated with half-assed repairs that cause more problems than they solve.  Well, I'm here to say that if you apply it properly, and there is minimal stress on the part, this stuff is amazing.

Years past, I came across a CX500 motor, where the owner had somehow busted the water jacket (blown head gasket and massive overheat). It was broken right around the steel cylinder, a big V-shaped chunk was missing. He repaired it with JB Weld, of all things. He said he carefully cleaned and dried the aluminum, applied the JB weld, and sanded it down to the same level as the head. Then installed the head gasket and drove it for 10,000 miles. Eventually he decided he wanted a new motor, and he drove it to my dad's place. We swapped his motor for a low-mile motor in good shape... but we just had to remove the right head to see his repair. It was still holding strong, and it took quite a bit of effort to chip out so that we could see the extent of the damage.

Now, a busted water jacket repaired with JB Weld is impressive. The sealing surface of the head gasket right around the cylinder experiences wild temperature variation, as the engine heats up to operating temps. There's constant pressure from the head gasket, and the JB Weld was exposed to moving coolant. But that's still not magic.

Repairing an entire missing chunk of a motor. THAT is magic. I picked up a 1993 CB750 Nighthawk that had been wrecked, for $500. The owner locked up the front wheel, had a lowside slide, and then slammed into the back of a car. The bike went under the car, and the electronic ignition cover on the left side of the bike was sheared off by the undercarriage -- taking a big chunk of engine case with it.

See the missing chunk of metal? 

Not only that, but all of the bosses for the bolts that hold the cover on were busted off as well. This side of the motor contains the pickups and the timing gear, and it runs in an oil bath. No pressure, but the crankshaft has no seal on the end, so oil that comes out of the crankshaft bearing makes its way to the oil pan by draining through this area. So the bike can't be operated with a big hole in the case here.

The very first thing I did was load the bike in my truck, and bring it to my welder. This is the guy I use for any welding project that I'm not capable of. The guy is deaf as a doornail -- I have to scream at the top of my lungs, or write down my instructions, because 40 years working in a machine shop without ear protection has rendered him almost entirely deaf. I've seen him fix aluminum wheels that were curb-checked and cracked all the way through. I've seen him cut, shape, and weld extreme rake into a chopper. I've even seen him weld super-thin sheet metal without distorting it.  But, he wouldn't touch this. Said it was beyond repair, that the porous nature of cast aluminum combiuned with 20 years of oil contamination would prevent a quality weld, and that I should look for a replacement motor.

So I was looking on eBay for a used motor, but thought I'd give a shadetree fix a try. I went to the auto parts store and bought several tubes of epoxy putty. These are the size of a roll of quarters, and consisted of aluminum powder suspended in a two-part epoxy putty. Squish the putty together to activate it, and then apply and wait for it to harden. Since I had such a big area to cover, I found a piece of quarter-inch think aluminum, bent it with a BFH (Big Fucking Hammer) so that it had a curving radius, and then cut it with an angle grinder to fit the hole as best I could. I cleaned and roughed everything up, and then applied the putty to the case and to the aluminum piece. I also built new bosses with the remaining putty. After it dried, the repair looked like this:

I made the bosses oversized, so there is enough 
material there to support  a bolt.  I still need to 
drill and tap the last hole
Same angle as above, case is repaired.
I sanded the JB Weld down so it was level, and you can see some of the aluminum piece that makes the gasket sealing surface. It wasn't completely level, so there is some putty on top of it in places to level everything. I bought a new cover and used it to locate the last hole. I drilled and tapped it, then applied a THIN layer of silicone to a gasket, and bolted the cover on. I didn't dare tighten the cover too much, but I didn't have to. There's no pressure in here, and just a little more than finger tight is all it took to keep the cover on. There was a very, very infrequent oil drip, which I later went back and fixed by doubling up two gaskets with silicone sandwhiched between them. (The trick is, apply a thin bead of silicone both sides of both gaskets, snug everything up finger tight, and then let the silicone dry overnight. THEN tighten a quarter turn or so)

This worked for more than 15,000 miles without any problems. I even went touring hundreds of miles from home, and I wasn't worried a bit. I never did find a good used engine for a good price, and I eventually sold the bike for next to nothing, because of the damage. It still looked pretty nice from a few feet back though.

Nice new cover bolted right on
From a few feet back, she actually looked pretty nice. 
Not bad for $500
So JB Weld may have a bad rap, but it turned a $500 parts bike with a clean title into a runner. I spent less than $70 on the repair, and most of that was the new cover and the timing trigger. And this is why JB Weld is magic. Given the right situation (no shear stress) it can do amazing things.

I had no reservations taking it touring in the
Blue Ridge Mountains
A marvel of modern science

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