Updating an old thread. Thanks to Parker Jameson (I don't remember the screen name he uses here) I was inspired recently to look into rebuilding some of the primers used on the large McCulloch saws with the MAC/Walbro carburetors.
As others have also observed, the primers tend to leak after a while and often stop pumping as well making the saws hard to start. I had tried a number of times to pull them apart, even tried threading the hole in the end of the plunger to use a small slide hammer but I was never able to get one apart. Someone told me Parker had come up with a solution so I contacted him and he freely shared everything he had learned.
To get the primer apart, the key is to drill a hole in the back end directly in the center, and press it apart. He used a 3/16" drill but I went slightly smaller so I could tap it for a 10-32 set screw to seal it back up when the work was complete.
Parker recommended using a 1/2" drive socket to hold the primer which work perfectly with the 1/2" square aluminum body of the primer. Be sure to drill the hole dead center so you can press squarely on the plunger to get it apart.
Parker's press set up using a vise.
I made some special tools for this project starting with this to work in my small arbor press. I made a few modifications to the press a while back including drilling a 3/8" diameter hole in the center of the ram to serve as a tool holder. I used a short section of a #25 drill bit for the punch portion and made the body long enough that I could grip it with a pair of pliers to give it a twist as needed when I pull it out of the ram.
Once the primer as been pressed apart you can see the simple arrangement inside. Since this was not intended to be a serviceable parts there are no official names or part numbers for the components so I have applied some for the sake of clarity. There is only one o-ring used in the location shown, and the cup or v seal has completely disintegrated into tar.
When I disassembled several primers for rebuilding I noticed two different plungers (one steel, one aluminum) that utilize two different cups or v seals.
Digging through my assortment of McCulloch parts I found two different cups / v seals that were apparently the same as the ones used in the primers. Both of these are used in the manual oilers on different front tank saws. 24104 matches up with the cup on the aluminum plunger and 67116 matches with the cup on the steel plunger.
After removing all of the old deteriorated cups and o-rings it is time to reassemble. As I mentioned, I tapped the back of the primer body to accept a 10-32 set screw, Parker has the ability to weld aluminum so he simply welded the body closed.
The cup, 1 o-ring, and gland installed on the aluminum plunger.
It is important to get the gland pressed in to the correct depth in order to achieve a good seal with the o-ring (after all, the main reason to go to all this effort is to stop the leaking...). Too deep and the o-ring between the gland and the retaining ring will roll back a forth, not deep enough and the o-ring will be compressed and will prevent the plunger from operating freely. To achieve this, I made special arbor tool to seat the gland in the correct position.
To be continued...
Mark