1990 alpha 1 mercruiser shift cable thread/tap size

[gr8_lakes]

I did do a search and the results are confusing to me. I post very little and read very much. But, this has me questioning my findings (not the wisdom of those providing answers).
Trying to remove the shift cable from my 1990 alpha 1 bell housing and the search revealed a special tap - 1/4X18 NPSF.

1/4 x 18 NPSF HSS Tap (Straight Dryseal) | Engineering-Supplies.com

I have drilled out to 27/64ths and am now just getting to the threads. I'm not familiar with tap sizes but would this tap fit a hole that is already that large?

 

[Eric 3.7LX Alpha 1]

Re: 1990 alpha 1 mercruiser shift cable thread/tap size

1990 bellhousing will be an Alpha One... you will not have to tap the housing. It should already thread in from the aft end of the bellhousing.

Cut the end of the cable off, and use a 9/16" deep socket to remove the brass nut that is part of the cable.

Did you have issues removing the cable and now trying to fix the bellhousing??

 

[gr8_lakes]

Re: 1990 alpha 1 mercruiser shift cable thread/tap size

yes, I fought a good battle so far. The cable was cut. The 9/16ths stripped the nut. Tried a long chisel on an angle, no go. Tried left hand drill bits. Nope. Got to where the old cable is drilled out to where I can see threads. I'm hoping I can run a tap through to clean up the threads.

 

[Eric 3.7LX Alpha 1]

Re: 1990 alpha 1 mercruiser shift cable thread/tap size

I don't know how far you are with drilling and tapping it. What I usually do when I can't get a threads out in a case like this (I am a plumber) is to drill a hole in the center , then use a skinny blade like a hacksaw blade or coping saw blade if necessary. Make a slice from the center hole outward until you get close to the threads. That will weaken the brass and you can then tap the nut inward towards the slice then unscrew what remains.

if it's cut off flush, then I make the same slice from the hole outwards, and use a small screwdrive or cold chisel and tap the damaged portion inward towards the slice. It works for me 90% of the time without any damage to the threads.

 

[NHGuy]

Re: 1990 alpha 1 mercruiser shift cable thread/tap size

Eric, that's a great tip. Mainly the tapping toward the center to move the stuck part away from the threads of the part you are trying to avoid damaging. Love it!

 

[Bt Doctur]

Re: 1990 alpha 1 mercruiser shift cable thread/tap size

Machinist Pipe Thread Tap - Drill Size Chart ANSI - Engineers Edge
Fractions to Decimals

 

[gr8_lakes]

Re: 1990 alpha 1 mercruiser shift cable thread/tap size

Thanks for the replies! When I drilled it I was slightly off center. This is why I stopped at 27/64ths as I could see the threads on one side. I tired picking the threads out. I tried a chisel to knock the thicker side nut head into the center. Nothing is moving this. Closely inspecting the threads with an otoscope I can see some type of filler or material that looks like JB weld. I'm guessing I'm not the first one to fight with this bell housing.
Is there a repair process like a time-sert/helicoil to fit this? I'll try the tap first but looking at my options.

 

[Eric 3.7LX Alpha 1]

Re: 1990 alpha 1 mercruiser shift cable thread/tap size

You have to make the slice first with a saw blade then the remaining thread will be super weak and it will unscrew. You have to make the slice all the way and even as possible, that is the key. I have removed many 100 year old heating radiator valves from cast iron radiators that wouldn't budge otherwise. It takes some patience as it's not the easiest to cut the slot by hand but when you do the rest will remove with ease.

 

[achris]

Re: 1990 alpha 1 mercruiser shift cable thread/tap size

BTW, that is the right tap...

1/4 x 18 NPSF HSS Tap (Straight Dryseal) | Engineering-Supplies.com

Chris.......

 

[gr8_lakes]

Re: 1990 alpha 1 mercruiser shift cable thread/tap size

Thanks to all that replied to my thread and to those that are providing info to all! I have a happy ending to my story. I used an extra long carbide bit to grind down the old cable nut until I could see the threads. I then used the tap listed above to chase the threads. Worked like a charm to push out chunks of the old cable nut.
Again, thanks for the help.