Jabsco toilet pump self-tappers

[Oily Rag]

I changed the pump on the Jabsco toilet several years ago. Recently, I tried to repeat the process, but as I removed the four self-tapping screws, they brought with them some spirals of the hard plastic they had been screwed into. The new pump could not be fitted to the now-enlarged holes.

I’ve looked at the self tappers Jabsco use and they have a two start spiral thread, one high and one low. I normally fit screws by rotating anti-clockwise until I feel the thread drop in, then tighten up. But with double start threads of this type, there are two possible start positions: one for the high and one for the low thread of the screw. I think using the thread a second time, after factory assembly, gives a risk of cutting a second deeper thread rather than reusing the existing one. Then, when the screw is removed, it brings out a spiral of swarf.

Any thoughts - or experience?

 

[NormanS]

I had the exact same problem some years ago. I drilled and tapped the base, probably IIRC to fit 8mm studs made from screwed rod. Obviously had to increase the hole size in the pump base as well. No problem since.

 

[Oily Rag]

Thanks Norman. I suppose my query is really about whether high/low self tappers - or even any self tappers - are suitable for a joint that is to be made and remade several times over the lifetime of the toilet.

I prefer your solution using studs.

 

[Malish]

they are built to a (cheap) price..

 

[Plum]

Thanks Norman. I suppose my query is really about whether high/low self tappers - or even any self tappers - are suitable for a joint that is to be made and remade several times over the lifetime of the toilet.

I prefer your solution using studs.

I have refitted the ones at the base of my pump 3 times and the ones at the top 4 times, so far, without a problem. The heads is 26 years old so those self tappers are, to me, a suitable design choice.