The mechanical lift pump on my 4-108 failed about a year ago - a two bolt model. I bought a rebuild
kit for it. The manual showed a shaft that passes through the pump body and the rocker pivots on that shaft. However in my pump model the shaft does not pass through the pump body, it is supported by steel
U-shaped pieces at each end (same shaft though apparently). Anyway, the U-shaped pieces had deformed and damaged the aluminum
pump body (guess that is why they changed it).
The replacement U-shaped pieces solved
the problem (they came in the rebuild
kit) but since the casting was slightly damaged these pieces eventually deformed again. Now I know the diaphragm
is new in the pump since I replaced it a year ago. So I put in a NAPA electric fuel pump ($40) and it pumps fuel right through the mechanical pump as others have posted. It works just fine and I carry a spare electric pump. But I can still operate the manual pump if necessary - it just does not pump enough to keep the injector pump
supplied with the bit of slop at that pivot shaft. Eventually I will replace the mechanical pump. If you have a fuel pump with a recessed pivot shaft design I would recommend replacing it.
I mounted the electric pump away from the engine just before the primary filters - even if the engine is not running, I can run the fuel pump and fuel circulates through the filters and returns to the tank. If I have concern about contamination of fuel, this is a useful feature.