Do I need to tap for shift cable?

[system-f]

Bob/Bond-o/other merc guys I need to know if I have to tap my housing for the newer style shift cable. My assembly is a 71 merc 165 and here is the cable end I unscrewed out.

Here is the cable before removing it.

Here is the cable end. I cut the rest of the cable housing off to get this out. It came out from the fore side of the drive housing and pulled to the front.

and here is the threaded hole in the housing itself

 

[Don S]

Re: Do I need to tap for shift cable?

Yes you do. Merc (and others I think) sell a straight thread tap. There are places that say you can use the regular tap, but you usually end up a little off, then you have binding in the shift cable.

 

[rodbolt]

Re: Do I need to tap for shift cable?

DO NOT attempt to use a standard pipe tap.
odds are HIGH you will crack the housing.
you need a 1\4 STRAIGHT pipe tap.
a standard pipe thread is tapered.
take the straight pipe tap,start it from the fwd side of the housing and thread it aft.
the new cable threads in from the aft.
do not attempt to start the tap from aft.

 

[erikgreen]

Re: Do I need to tap for shift cable?

FYI the tap type is NPSF, I got one from mcmaster-carr.

Erik

 

[Bondo]

Re: Do I need to tap for shift cable?

There are places that say you can use the regular tap, but you usually end up a little off, then you have binding in the shift cable.

Ayuh,... As deep as ya gotta go,... I find that foolhardy...

 

[system-f]

Re: Do I need to tap for shift cable?

Thanks for the help guys.

 

[Fishermark]

Re: Do I need to tap for shift cable?

To be specific, you need a 1/4X18NPS tap (National Pipe Straight). You will probably not find it at your local hardware store as it seems to be rarely used for any other purpose. I ended up ordering one online.

 

[erikgreen]

Re: Do I need to tap for shift cable?

To be specific, you need a 1/4X18NPS tap (National Pipe Straight). You will probably not find it at your local hardware store as it seems to be rarely used for any other purpose. I ended up ordering one online.

It's NPSF, not NPS. There's a difference.

I'm not sure where I got NPSF from, maybe from the mercruiser manual that shows the replacement process?

Erik

 

[Fishermark]

Re: Do I need to tap for shift cable?

It's NPSF, not NPS. There's a difference.

I'm not sure where I got NPSF from, maybe from the mercruiser manual that shows the replacement process?

Erik

I would be curious where you got that info as well. Not suggesting it is wrong... just never heard of the need. From what I gather the only difference between NPSF and NPS is the "F."

And the "F" stands for fuel.

Both are designed for low pressure sealing - but the "F" type of tap is used primarily to tap holes designed for fuel and oil lines.

 

[erikgreen]

Re: Do I need to tap for shift cable?

The F is for fuel as you say... my understanding is that it's meant to be a threaded seal that's fluid tight without any sealing gasket, tape, or dope, IE just the metal.

I am 90% sure I got the info from a Mercruiser manual or service bulletin that detailed how to re-tap and replace the lower shift cable... but that was 8 months or so ago, and I don't remember exactly where. Sorry.

Erik

 

[Don S]

Re: Do I need to tap for shift cable?

Did you guys somehow forget to look at the picture I posted as the first reply to this thread. It includes ALL of the information you're discussing, exactly what tap (and part number) direction to tap from, and what to seal the threads with.

Yes you do. Merc (and others I think) sell a straight thread tap. There are places that say you can use the regular tap, but you usually end up a little off, then you have binding in the shift cable.

 

[Fishermark]

Re: Do I need to tap for shift cable?

Did you guys somehow forget to look at the picture I posted as the first reply to this thread.

That's too funny! Did you edit that and put it in later?

 

[rodbolt]

Re: Do I need to tap for shift cable?

Nope
DonS posted it right the first time.
I was reiterating because I have seen cracked castings cause the guy bought a standard 1/4 pipe tap from ace for 6 bucks instead of the STRAIGHT pipe tap for about 20 and tried to force it through.
it will go but odds are high it wont work.
the original hole was drilled with a straight drill and a standard pipe tap is tapered smaller at the front and way larger towards the rear.
ya simply run out of room and something is gonna give.
by the time you run the tap from fwd to aft and created enough thread on the aft side you have seriously screwed the fwd side,usually ya cracked the casting.

 

[Dryon]

Re: Do I need to tap for shift cable?

There is a book called ?Machinery?s Handbook? that details the four classes of pipe threads. The NPSF thread is a dry-seal straight pipe thread that is general used with soft or ductile material. It is used for internal threads only and normally doesn?t require using any type of sealing compound for a pressure-tight joint. This is accomplished by some modification of the thread form and requires greater accuracy in the manufacturing/use of the taps. This is the reason for their higher cost compared to tapered taps. Though not required, the use of some type of lubricant or sealant will help minimize galling. The ?NPS? stands for ?National Pipe Straight?, but there are different types of straight threads and therefore the fourth letter designates the thread type for different applications.

The Merc manuals have a great deal of information and you can't go wrong following Don?s advice with these manuals in hand. If you're unsure of what you're doing, then take your boat to a certified merc mechanic.

 

[WizeOne]

Re: Do I need to tap for shift cable?

I am having trouble interpreting the first picture in the right column of Don's illustration. What exactly are we looking at here? It does not look like the 'bell housing'?

Why does it show installation of the cable thru the shift cable bellows? Doesn't the bellows have to be removed to re-tap. Also, is there enough room to drive the tap with a standard tap tool? An is there an alternative to the 'special tool' to tighten the new cable nut?

 

[Don S]

Re: Do I need to tap for shift cable?

The shift cable bellows doesn't hook to the bellhousing at all, it hooks to the gimbal housing.
That first picture (RH) shows a cutaway view of the bellhousing/gimbal ring/gimbal housing.

Also, is there enough room to drive the tap with a standard tap tool? An is there an alternative to the 'special tool' to tighten the new cable nut?

Never, ever use a regular tap, rodbolts reply explains why.

That SPECIAL socket can be made by welding a shallow socket on top of a deep socket. OR, if you are using an OEM cable, unscrew the white plastic guide from the cable, use a regular socket to tighten, then reinstall the guide.
DO NOT try that with the cheap aftermarket cables, you will destroy the cable.

 

[WizeOne]

Re: Do I need to tap for shift cable?

....Never, ever use a regular tap, rodbolts reply explains why.......

Don, I wasn't refering to the tap itself, but the device needed to turn the tap. I understand about the non-tapered tap.

Many a time there is not enough room to swing either one of the tap wrenches around 360 degrees. I have always threatened to have 'tap' sockets made, in the various square tap shank sizes, so you could drive taps with a conventional ratchet using the appropriate length extensions.

 

[Don S]

Re: Do I need to tap for shift cable?

There are special tap sockets, mine came from SnapOn (Spendy). There are also sockets out there for square headed bolts, I have a 1/2 and a 3/4 that I got from NAPA years ago, and Sears used to have them, they are 8 Point sockets.

 

[mkast]

Re: Do I need to tap for shift cable?

Many a time there is not enough room to swing either one of the tap wrenches around 360 degrees. I have always threatened to have 'tap' sockets made, in the various square tap shank sizes, so you could drive taps with a conventional ratchet using the appropriate length extensions.

If you look around, you'll find a tee handle for taps that has a 1/2 inch drive on the head of the tee handle. Remove the tee, a 1/2 inch extension pops into the handle.

 

[Don S]

Re: Do I need to tap for shift cable?

Those adjustatble tap handles are too big around where they attach to the tap, and will not fit between the tap and the side of the bellhousing.