making my own top end oiler...m20 x 1.5 thread for oil pressure sender

[garagepunkfan]

i'm designing my top end oiler for my 83 GS1100ED and want to retain both the oil pressure sender and the oil temperature sensor in the new takeoff block. my question pertains to the tap drill size of the m20 x 1.5 thread used, so i guess this is really directed at the machinist and mechanical engineering communities of the GS Resources board and perhaps Greg B if he feels the information is not proprietary to his product. i have no intention of trying to compete with him, i would just enjoy making my own and a copy for a friend.

the question concerns thread percentage. i measured my existing housing for minor diameter and i got .723" (18.364 mm) which is somewhere between a calculated 80 to 85% thread. a 75% thread would be at .729" (18.539 mm), which i would think would be more common.

the thread form of the plastic sender seems a little odd as well. the major diameter measures .769" (19.533 mm), while Machinery's Handbook calls out a maximum of 19.968 mm and a minimum of 19.732 for a 4g6g fit. it is physically small enough when threaded partially into the original housing to get about .010+ side-to-side movement. i realize that an o-ring seals it but i would have expected more positive thread engagement. perhaps this is to compensate for differing expansion rates of the materials?

any help is appreciated

 

[rapidray]

It is a BRITISH thread.
Ray.

 

[garagepunkfan]

hi Ray, thanks for responding. i'm aware that the TEMP sensor is 1/8-28 BSPT (British Standard Pipe Taper). what i'm referring to is the larger hole in which the plastic PRESSURE sender screws into. thread pitch of this hole and sender is a dead match for 1.5 metric pitch; checked with a thread gage.

 

[GregT]

Quick and dirty way to get tap drill size for metrics is simply to subtract thread pitch from OD. 20 minus 1.5 equals 18.5mm.Close enough for Government work....

I hear what you're saying about the plastic sender piece. I've made a blanking plug for the same place which was a nice 20X1.5 - and a much better fit than OE.
For those who wonder why, the pressure on this motor was done via an electric sender on the oil filter cover.

 

[garagepunkfan]

Quick and dirty way to get tap drill size for metrics is simply to subtract thread pitch from OD. 20 minus 1.5 equals 18.5mm.Close enough for Government work....

I hear what you're saying about the plastic sender piece. I've made a blanking plug for the same place which was a nice 20X1.5 - and a much better fit than OE.
For those who wonder why, the pressure on this motor was done via an electric sender on the oil filter cover.

thanks for the input GregT. that's the basic formula i use as well and pretty close to the 75% thread figure of 18.539 mm. i was just trying to get to the bottom of why the minor diameter of the internal thread was so small at 18.364 mm