Harley-Davidson VL Engine Case Final Prep | Thread Cleaning & Glyptal | Riding Vintage

Harley-Davidson VL Engine Case Final Prep

By Panhead Jim | Published June 16, 2026

This final round of Harley-Davidson VL engine case prep came after the earlier VL engine case cleaning and disassembly work was finished. At this point, the goal was simple: chase every threaded hole, scrub out the debris, seal the inside of the cases with Glyptal, and get the cases ready to send to the machine shop. For the rest of the build sequence, see the VL Tech archive.

The VL engine cases ready for final prep after the repair work was completed.

Now that all my repairs were completed, there were just a few more things to do before the cases could be sent to the machine shop for rebuilding. I started with chasing the threads on all the tapped holes. This is easy to do, provided that you have all the different size taps available. Then it's just a matter of carefully running the tap down each hole.

Cleaning the Tapped Holes

After the tapped holes were chased, wire brushes in a hand drill cleaned out chips and old buildup.

Once all the threads had been chased, all the holes were cleaned with wire brushes attached to a hand drill. This removed any chips made by the tap and cleared out any remaining gunk that had built up over the years.

Washing the Case Halves

The case halves went into a warm soapy bath for more cleaning with bristle brushes.

Then it was off to a nice warm soapy bath and more cleaning with bristle brushes.

Drying the Cases Before Glyptal

Compressed air finished the cleaning process before the inside of the cases was sealed with Glyptal.

Finally the cases were blown dry with compressed air to complete the cleaning process. Now it was time to coat the inside of the cases with Glyptal.

Sealing the Inside of the Cases

Glyptal is an enamel based sealer used inside of engine cases to, you guessed it, seal the porous case walls to help prevent oil from leaking through. It also has the added benefit of smoothing out the castings which keeps the oil moving around inside the case more efficiently. Of course you don't want to get it everywhere, so I taped up all holes and outside surfaces first.

All holes and outside surfaces were taped off before the Glyptal was brushed into the case interior.

The Glyptal smells a bit like your old lady's nail polish, so you'll want to make sure you're painting in a well ventilated area. I applied it to the cases with a 1" paint brush and carefully worked it into all the nooks and crannies. Once I had a good even coat, each case half was baked for two hours at 275 degrees Fahrenheit, per the manufacturer's instructions. The result was a nice smooth coat of burgundy enamel.

Final Wash Before the Machine Shop

After two hours at 275 degrees Fahrenheit, the Glyptal left a smooth burgundy enamel coating inside the case.

Lastly, both case halves went back into the warm soapy bath for another scrub before being dried with compressed air. Then they were bolted back on the engine stand and sent off to the machine shop.