How far back from head to drill to add telltale?

[Panhead Jim]

50ESL73R. Johnson 50HP 1973 model. I've seen the threads here and have ordered the parts to add the telltale to my old Johnny. Will mount in the top of the water jacket after removing lifting eye. Could one of you masters tell me approximately how far back from the head/block interface to drill and tap? Also, even using grease, there's the likelihood of small shavings in the block. Is there a way to flush those out? I'm thinking short-term plumb with a straight threaded pipe and larger hose and blasting with motor muff for a few minutes prior to installing the 90? nipple and correct hose. Any help on either question?
Thank you!
Jim

 

[Panhead Jim]

Re: How far back from head to drill to add telltale?

stroke of brilliance or stupidity, y'all tell me which.
The block on the Johnny is cast iron. Why not use a quality black (cast iron) street ell for the telltale fitting. I can just see myself breaking that plastic OEM fitting off far from the ramp someday when that plastic has become brittle with age...
Jim

 

[bob johnson]

Re: How far back from head to drill to add telltale?

that block was CAST IRON????

you sure about that???


if you look up Durbans XYZ modification, youll find he had a thread about installing a new tell tale on a 3 cylinder 70 hp.....


bob

 

[Panhead Jim]

Re: How far back from head to drill to add telltale?

Bob, not SURE it's cast iron, but it sure looks like it. May be cast STEEL? Maybe somebody will tell us both. If not, I'll let you know when I DRILL it!
Thank you!
Jim

 

[bob johnson]

Re: How far back from head to drill to add telltale?

Bob, not SURE it's cast iron, but it sure looks like it. May be cast STEEL? Maybe somebody will tell us both. If not, I'll let you know when I DRILL it!
Thank you!
Jim

Ill give you my guess :joyous:...Aluminum!!!!!!!!!

did you find Durbans thread??

bob

 

[gm280]

Re: How far back from head to drill to add telltale?

Ill give you my guess :joyous:...Aluminum!!!!!!!!!

did you find Durbans thread??

bob

Let's see, it is a 1973 Johnson 50 HP outboard...okay. I have to go with Bob on this one and say it is cast aluminum as well. I'm not an expert by any stretch, but I don't think Johnson, especially in 1973, ever used cast iron or steel for their head and cylinder units. Weight is an enemy in outboards. As far as drilling into the engine to install a tale tell tube, on my 1976 Johnson 40 HP outboard, there was an unused boss extrusion that was directly over the top cylinder that I drilled out the bottom and taped it with a ?? NPT tap. It worked perfectly without any problems encountered. Maybe you have such a boss extrusion on yours as well... Look it over real good...

 

[Panhead Jim]

Re: How far back from head to drill to add telltale?

Got 'er done. Scary, but non-eventful. Drilled, tapped, installed OEM fitting in block, drilled then dremeled the 11/16 hole in side of housing, installed OEM outlet. All good. Thank you folks for all the help. The block was aluminum, of course.
Jim