adding a tell tell on 70 hp johnson

[Exotic4x4]

Hey everyone I've done a lot of research on the forum about adding a peehole on my 75 70 HP Johnson, I found some people drilled into the top of the head into the water jacket and also another drilled into the block itself by the lifting hook what area is most effective for this mod.? I'm a machinist so drilling and tapping is a daily duty. Just looking for the most error proof area to install this without drilling in a wrong area. Also I read everyone uses a 1/8 tap a .125 npt. Should this be bigger diameter hole? Also I'm lucky I have a bad block to practice on first ;-) . What's Everyone's .002?

 

[boobie]

Re: adding a tell tell on 70 hp johnson

IMHO if you need the pisser go to the top of the block. This way the block fills completly and lets any aereated water out as # 1 cyl runs the hottest. .002 to me means two thousands of an inch. Why?? Stick with the 1/8 " tapped hole.

 

[lmuss53]

Re: adding a tell tell on 70 hp johnson

I've gathered up all the stuff to do this on my 55 in 1/4 npt. Is there a reason to not use 1/4?
I think he meant to type .02 as on 2 cents worth. Some of us machinists get fat fingered once in a while.

 

[Daviet]

Re: adding a tell tell on 70 hp johnson

I have always use an 1/8' npt fitting. You don't want to drain off any more water than necessary.

 

[Exotic4x4]

Re: adding a tell tell on 70 hp johnson

Yes I know top of the cylinder...And I meant .02 lol 20 (.02) thou. Is kinda an unheard number in my trade sorry but yes I read 1/8 so it doesn't have excessive drain to the jacket and also does anyone roughly know the depth of casting to the water jacket? Can I use a standard tapper tap or should I countersink it and use a plug tap (makes full threads from the start) doesn't progressively make full threads if not ill just run the depth Mic down the drilled hole before tapping

 

[lmuss53]

Re: adding a tell tell on 70 hp johnson

I am going to neck it down to 1/4" ID hose right at the 1/4 NPT elbow, so it won't let too much blow by. The hole in the actual telltale nipple coming out of the cover is about 1/8".

 

[Haffiman]

Re: adding a tell tell on 70 hp johnson

You drill about 1/2 inch from the gasket surface on top of the block where the water enters from the exhaust cover. This way you avoid any air-pocket building resulting in overheat alarm. An old service bulletin recommended this position to be used on all engines that had the exit in the middle of the exhaust cover.
The size of nipple and hose is not that important as long as you stay with the original nipple (outlet) in the lower cover. This to keep the proper operation of the pressure release valve in the cooling system.

 

[iwombat]

Re: adding a tell tell on 70 hp johnson

Make sure you use a plastic nipple in the block - that's why the OEM part# is recommended in the FAQ article. Bronze fittings will cause electrolysis.

 

[Exotic4x4]

Re: adding a tell tell on 70 hp johnson

Basically I was thinking of the top middle area in between the lifting hook and the head gasket the area smack dab between them to drill my hole to install. Sound good??? Also I read that a brass fitting is fine to use in the block for an elbow because I'm not in salt water. And I was going to drill and tap my hole to a 1/8 npt and use 5/16 fuel line for the tubing and run it down to the lower cowling I'm actually going to do a.detailed with pictures " how to sticky" because this seems to be a.very VERY.common question on iboats

 

[iwombat]

Re: adding a tell tell on 70 hp johnson

There's already a fully detailed FAQ doc in case you haven't found it yet:

http://forums.iboats.com/showthread.php?t=222677

 

[Exotic4x4]

Re: adding a tell tell on 70 hp johnson

Haven't found that one yet but the 50hp model on the block is the exact setup I'm going to do thanks for the post !

 

[iwombat]

Re: adding a tell tell on 70 hp johnson

I've done a few of these on v-4s but never on the smaller models. Let us know how it goes.