Rebirth of an American Classic: Case Repairs

 

Before the engine could be rebuilt, the cases needed some additional work to repair a damaged portion of the front baffle.  It appears that an unknown piece of debris was wedged between the backside of the baffle and the flywheel which eventually knocked a hole right through the baffle.

 

 

 

Since HD engine cases are made from aluminum, the best method for repairing the hole was to use a TIG welder to fill in the missing material.  The hole was located at the thinnest portion of the baffle, so a piece of copper plate was used to cover the hole and provide support for the weld.

 

The entire case half was then placed in a parts oven set to 400 degrees Fahrenheit for 45 minutes.  This helped to bake out the old motor oil which had impregnated the case over the years and ensured that the entire case was at equal temperature for welding.  The heating also revealed that there were a number of cracks radiating out from the hole which also needed to be fixed.  By the time the hole, the cracks and the casting imperfections had been repaired, I was left with a good deal of weld to grind away.

 

 

The backside of the baffle was easy to reach and was ground back into shape with the help of a curved template and a flap wheel mounted to a hand drill.  The top of the baffle was much harder to grind with standard tools, so it was necessary to make a custom router bit using an aluminum sleeve epoxied to a ½” four fluted end mill.

 

 

Working slowly, I removed about 1/32” of excess weld with each pass of the router.  Liberal amounts of Teflon lubricant was used throughout the process.  After every pass the chips were removed and new lubricant was added to make sure no damage was caused by the aluminum sleeve riding against the case.

 

 

After some final shaping, the repair was complete and I moved onto chasing the threads for all the tapped holes.

 

 

Next, both case halves received a thorough cleaning.  All the holes were cleaned out with wire brushes attached to a hand drill to remove any aluminum chips and other debris.  From there the cases were soaked in warm soapy water and scrubbed with bristle brushes.  Then each case was carefully blown dry with compressed air, paying careful attention to blow out all holes and orifices.

 

 

Once the cases were clean and dry, the last step was to apply a coat of Glyptal to the inside of both cases.  Glyptal is an enamel based sealer, so once it dries, it is tough to remove.  To insure that the sealer only coated the intended surfaces, each case half was carefully taped and covered.  Once the Glyptal was applied, it was cured in an over for two hours at 275 degrees Fahrenheit.  The result was a hard slick coat of Glyptal and a set of cases ready for assembly.