***Added detail that was not captured on Video***: I lightly lubricated the Neoprene seal surfaces with Silicone based grease. When I checked one of the standard Chemical Compatibility charts, https://www.coleparmer.com/ChemicalR..., I saw that Grease has a "Poor" rating which means that it is absolutely NOT compatible with Neoprene. I played it safe and used Silicone to lube the seal areas.

Final assembly actually goes pretty quickly if all of the work leading up to assembly is done correctly. The only clearancing step left for final assembly is rotor timing. Rotor timing as shown in the Detroit Diesel manual can be confusing with the “C” and “CC” clearance designations, and the two sets of diagrams, depending on which model engine and blower is being checked. I cut right to the chase and only showed the step where I checked for interference between the rotors as if they were being driven while they were in operation.

Machining off the back of the blower gears is typically described as a “race blower only” clearancing step, but I disagree with that. My passenger side gear shim that was on the blower when it was being run on a diesel, was in relatively rough shape, so this tells me that these shims have a tough life even in normal operation. It takes very little work to do it the right way, and select machine the gear shoulders to get the final clearance that I wanted, so there was little reason not to do it. In the end, the rotor timing exercise is pretty straightforward: If you want to decrease the clearance between the rotors, machine material off the drivers side gear. Machining .003 off the rear shoulder of the gear will tighten clearance between the two rotors by .001 of an inch.

There will be at least one more video remaining in this series, with the next one being the video of how (and why) I designed and machined the carb adapter plate out of a piece of Magnesium plate. I have an idea for a really cool sight glass to put into the triangle opening in the front cover, but haven’t decided for sure if I will do it. Stay tuned to see where I go with that.
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Disclaimer: This video series is not intended to be an exhaustive “How to do it” tutorial on how to rebuild a 671 blower for Gasoline use. Rather, it is meant to be a “How I did it” journal of one of many projects that I undertake in my home workshop, using hobbyist equipment and methods. If you attempt to duplicate any of these methods, you do so at your own risk. Therefore, I will not be held liable for any incidental or consequential damages as a result of trying to duplicate these methods.

Sources for clearances and tear down/assembly details referenced the Detroit Diesel assembly manual, with additional details referenced from the SA Design book “A Doityourself guide to: Street Supercharging” by Pat Ganahl, ISBN 0931472172. If you are not an experienced mechanic/machinist, do not attempt to replicate this work. Take your Blower to a professional Blower builder.