Wednesday, April 30, 2014

Steam Engine Restoration Part 7 - Refinishing the Crankshaft, Crosshead, Connecting Rod, and Piston

Before beginning the fine mechanical repair work, I finished sandblasting, cleaning, and repainting the major mechanical components that I had decided to reuse. The crank bearings will need to be rebabbitted, the crankpin has to be reground, and various missing or damaged parts must be remanufactured from scratch.

The crankshaft as removed from the engine. The shafts cleaned up nicely, but the crank pin is toast.

Taped off for sandblasting

The sandblasted crosshead

Assembled to check for fitment

Ready for paint

Taped off for paint

The extremely corroded crank pin. This will have to be professionally reground

A lovely shade of red

Disassembling the piston

Side view

Hand-cleaned with Scotchbrite


Flywheel ready for paint

Cleaned and ready for paint

Hung for painting

Fully Sandblasted and Repainted.

The next step is the fine mechanical work.

Friday, April 18, 2014

DIY Engine Repair Part 1 - Salvaging Engine Components with 2-Part Epoxy

As a followup to my previous post, I decided to dive a little deeper and give a full overview of the process behind repairing engine components with epoxy.

Either your best friend or worst nightmare, depending on the mechanical aptitude of the previous owner.

2-part epoxies, such as MarineTex and J-B Weld, are commonly used to repair damaged engine cases when a weld repair is not economical or practical. I will use the subject of my last post, smoothing a rough gasket surface, as the example. The first step is to fully (FULLY!) clean the surface that will be epoxied. Any oils or paint left behind will cause a bonding failure, and sooner or later the entire repair will fall off and you will be back to square one.

Fully cleaned with acetone and a stiff brush.
This step is especially important when using the epoxy to repair a crack that oil is seeping though. In addition to cleaning the surface, you must try to clean the oil out of the crack itself, so that any oily residue in the crack does not prevent an internal patch of epoxy from fully setting. I usually do this with a can of carb cleaner, an aiming straw to inject solvent into the crack, and a comprehensive list of creative swear words for when the spray ricochets back and hits me square in the eye.

Mixing the Epoxy
 Epoxy dries better when everything is warm, so either keep a heater near the parts you are working on, or move everything indoors. Once everything is up to temperature, mix the epoxy on a clean dry surface with a wooden paddle. I prefer to use MarineTex epoxy.

In this case, I used the epoxy to build up a rough surface so that I could smooth it down. For the first step, I spread a thick layer onto the metal, on the area to be sanded.

Next, I used a razor to scrape off the excess, only leaving behind a small amount in the cracks. This is just the first application to fill in the worst cracks, so it doesn't have to be perfect. You should use multiple small applications of epoxy to build up the surface, because one thick layer may not set correctly or harden thoroughly.

I allowed the epoxy to dry for 24 hours next to a heat source, and then mixed a second batch.

The second layer of epoxy was applied and smoothed with the razor, but not scraped flat like before. I once again allowed it to dry for 24 hours, and then  used a sanding block and 600 grit sandpaper to smooth the surface down.

In progress

Finished! All the missing metal has been replaced with epoxy and sanded smooth.

Saturday, April 12, 2014

BSA Bantam - Rebuilding the Top End

The Bantam that I rebuilt developed two air leaks during the shakedown runs, so it was necessary to strip the top end and repair the problems. The leak on the exhaust side was caused by an incorrectly installed exhaust gasket (easily repaired). The leak on the intake side was caused by two factors: The rubber carburetor manifold had become dry-rotted, and the mating surface on the cylinder head was heavily pitted from the rust that I had sandblasted off. Replacing the manifold was easy, but smoothing out the mating surface required a bit more work.

Condition when purchased

When I purchased the bike, the cylinder was heavily rusted, and required sandblasting and machine work to repair. It was rebored, and the head surface was skimmed. However, I never had the carburetor mount cleaned up, and thought I would just seal it with silicone when the time came.

Pitted surface

To seal, the rubber manifold has a machined groove on its underside, and a rubber o-ring is glued into it. However, this system only really works on a perfectly flat surface, so I added HondaBond sealant to try to solve the problem. Eventually, this was sucked out by the engine vacuum, so it was necessary to find a more permanent solution. 

I disassembled the top end of the engine, cleaned off all the oil and sealant from the mating surface, and applied a coating of MarineTex 2-part epoxy to build up the surface. I scraped it flat, allowed it to dry, and then repeated that step two more times. Once the epoxy had fully set, and sanded the surface flat with 600 grit wrapped around a block. This filled in all the pits, and gave me a perfectly flat surface to seal out the air. I then installed the new manifold, and went to the next step.

Sanding the surface flat

Ready for reassembly

Piston and rings

Because of the air leak, the piston had suffered some minor scuffing on the skirt (soft seizure). Before I could reinstall it, I had to smooth the skirt to prevent further damage.

This can be fixed by lapping the piston. Using 1000 grit sandpaper soaked in motor oil, I gently sanded down the damaged section, and also smoothed out all the rough edges on the rest of the piston to cut down on friction.

Light scuffing

Smoothing the entire piston with 1000 grit, with focus on the seizure marks.

Fully smoothed and ready for reuse

Rings reinstalled

Back together 

Wednesday, April 9, 2014

Machine Tool Spotlight - Modifying the Hardinge Lathe

Since I finished recommissioning my old Hardinge production lathe, it has given me many hours of reliable service. It was extremely well-designed and robustly built, and operates much more reliably than its 70+ years of age, and previous hard life on a factory production line, would lead you to believe. However, I have occasionally run into a problem when performing a specific machine operation, and I wanted to solve it before damaging either the machine or the parts being machined.

The tailstock of a lathe has a tapered bore, which matches the taper of the tools that are placed into it. This tapered mating surface has a large area of contact, and the the surface friction between the tool and shaft keeps them locked together. The friction is increased when the tool is driven into the machined material, because the force presses the tapered contact surface tighter.

Normally, this system works very well. However, since there is no positive means of locking the two, when a large drill bit is used, or a soft material is drilled into, the drill bit can "catch" on the material and pull forward out of the tailstock.

I decided to add an internal pin to the tailstock to prevent my drill bits from spinning. In addition to the taper, most tools also have a notched end which can rest against a pin and provide a positive lock. 

Tapered drill bit with a notched end


Marking the length of the tooling inside the tailstock tube.

The black line shows the length of standard tapered tools without a keyed end. The scribed line shows the eventual location of the lock screw.

Starting the machining process with a center drill

Tapping threads in the hole

Turning down the diameter of the screw head

Resized screw head

Checking the clearance

Installed with Loctite