Helicoil or Machine oversize for 1985 15hp Johnson Head Bolt with a catch...

[Calcasieu]

Hi All,

Long story short my 15hp Jonson wasn't cooling properly so I pulled the head off to replace the thermostat (this motor is a pain in the ass to work on in that regard). I noticed a helicoil repair on the center-right head bolt (bought the motor used three years ago). No big deal, I thought...I couldn't get it to torque correctly and after putting it all back together the head was leaking water so I shut the motor off immediately. After pulling it back apart I noticed the old helicoil repair had backed out which was the cause for my leak.

After removing the old helicoil and inspecting the block there were virtually no treads in the block holding the helicoil in place and it looks to be impossible to put a new helicoil in. Whoever installed it looks like they may have drilled too deep as well as too large.

It looks like my only options now are oversized threads to be machined but if you look closely in the pictures you will notice a gouge in the top of the threads in the block. And I don't even know if it would be possible to machine a larger hole since the clearance on the edge of the existing hole are thin enough already...

The motor is in EXCELLENT shape other than this. It had 115psi compression on both cylinders before and ran great.

Just curious if anyone has any other ideas. Before I consider a new block or likely just buy a new outboard.

Thanks in advance.

 

[racerone]

Look into using a product called ----lumiweld---- Or similar product.------I certainly would not resort to a new motor for a simple repair.----And simple is my opinion , others will argue.

 

[F_R]

Two suggestions:

1. How thick is the bottom of the hole? Thick enough to drill it on though and tap it to the original thread size?

2. Ream the oversize hole as large as you dare, then fabricate an aluminum plug to fit the reamed hole. Use high strength Loctite to fix the plug in the hole (use Loctite Primer). Now drill & tap the plug to original thread size.

 

[Calcasieu]

These are great suggestions! I like the idea of an aluminum plug. For option 1 the hole is too deep to drill through and tap.

I know a guy with a machine shop who can probably help me with that.

 

[Spartans]

X2 on either the aluma rod or the plug. Don’t attempt to make any larger. I’d try the aluma rod first and backfill the hole and retap at normal size. If u don’t like the jb stuff You could always tig a shorter collar plug in there and then tap that too if the rod doesn’t work out

 

[Calcasieu]

I took it to a machine shop. They installed a fastenal thread repair. It's a lot beefier than a helicoil and has tabs that you drive into place to keep it from moving. They did it on the spot and chased the threads on my head bolt as well for $50 out the door. I will be putting it all back together tonight.

I know you normally install these gaskets dry but with the amount of water that was leaking would it be okay to put Evinrude gasket sealing compound on it for good measure? I have the gasket and the sealer in a picture below.

 

[Scott Danforth]

look at a thread-sert or time-sert vs a helicoil. they have a larger thread.

 

[Calcasieu]

Hey Scott,

Spot on. That is pretty much exactly what the shop installed. The only question I have now is a dry head gasket or to use evinrude gasket sealer with the brush for good measure to ensure no leaks.

 

[Calcasieu]

I went ahead and put a very thin coat of omc gasket sealer on the head gasket. If anything it made it extremely easy to install by holding it in place while I got the head just right. The Fastenal thread repair feels solid as a rock and I felt no slippage while torquing the previously problematic bolt. I will try and start it tomorrow evening and report back if it still leaks or not.