How To: Spare Spark Plug Holder

A friend sent me a photo of a pre WWI Premier with a spare spark plug holder mounted on the seat tube of the frame.  And Dave Mac’s early Rudge had a nice one in an issue of The Classic Motorcycle a while ago too.  I’d always wanted one of these holders, but they don’t pop up on eBay or at swap meets.  So I decided to make one or two.  But the costs to make one or two are the same as making 30, so I sand cast 30 of them.   If you want to buy one or two, send me a note via the Comment link at the end of the article.

 

They are for sale for $15 each for the raw, un-machined part.  That is about 1 pound of brass for you to machine and finish.  Shipping is at cost, I’m not doing this to make money.

 

I don’t want to machine and polish 30 of these things, it would take me forever and I’d get a few dollars per hour for my labor.  Do it yourself, and have some fun!   Make it fit your frame size and your size of spark plug.  Several people pre-ordered parts via the OcchioLungo Facebook page a month or two ago, and the first shipments went out today.  There are a few more available, so send me a note via the Comments link if you are interested.

 

UPDATE AUGUST 1, 2011:  THERE HAS BEEN A GREAT REPONSE TO THESE OVER THE WEEKEND, AND THE FIRST RUN OF 30 PARTS IS ALREADY SOLD OUT.  I’M MAKING A LIST OF BUYERS FOR ANOTHER ORDER, SO IF YOU WANT SOME, SEND A NOTE VIA THE COMMENTS LINK.  I’LL WAIT ABOUT 2 WEEKS TO GET ALL THE ORDERS, THEN HAVE THE FOUNDRY DO ANOTHER RUN OF PARTS.   FYI, IF YOU HAVE A VTWIN OR PARALLEL TWIN, YOU CAN USE TWO SPARK PLUG HOLDERS MOUNTED TO EACH OTHER WITHOUT THE TWO CLAMPS.

Here is that Premier at the Pioneer Run.  Note the cool plug, and the super cool fuel filter.  I think that this plug holder is polished aluminum.

 

This is a different plug holder in plated brass has some neat scallops on the bottom side, and shows a bit of the details of how the part is made and how it attaches to the frame.  This one is mounted on the frame front downtube, the front wheel is on the left side of the photo.

 

Now, to make up my own part…

Step one was to design it in Solidworks CAD software.  It is something that I do as part of my day job, so it didn’t take any time at all.  I wanted the part to have the look of an acorn, so I added some scallops around the top, and a pointed tip at the bottom.  For sand casting, it has 3 degrees of draft all around, and can be pulled from the top surface with simple tooling.

After machining, it will look like this.  There is one big hole to drill to fit the frame (this one will go up to 1.125” or so).  And a hole drilled and tapped for the spark plug (up to 18mm) and two holes for the mounting screws (10-32, or maybe 1BA or 5mm).  Plus a cut down the middle and some deburring.

Then I sent the CAD file to a 3D printer and made up 6 copies in red ABS plastic.  This took several hours to print, then to clean.  Why red?  Just because that material was already in the printer machine.  In this view you can see the sharp points on the bottom tips, plus the scallops.

Then to the local brass foundry, Terminal Brass & Aluminum Foundry in South San Francisco.  Founded in 1920, they know how to do sand casting.  They put the 6 patterns onto a board, added sprues and risers, then pounded sand into 5 copes and drags.  The next time they were pouring yellow brass they made  a few samples for me to inspect.  Soon after, we had 30 good parts on my shop floor.

I spent an hour machining this one in my workshop tonight.  Pretty simple stuff:  drill & tap, saw cut, etc.  It needs some good deburring and polishing, then maybe a coating of nickel plating.

Here it is mounted on my Premier, with a scrap AC plug.  Still no polishing or plating yet!

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