Thermostat Housing Leak

[lettucebereality]

Hello,

New boat buyer, newbie here. Recently purchased a boat with a 2 stroke carbed 200 Yamaha Saltwater Series II on it. Recently noticed a small drip leak coming from one of thermostat housing bolts. Brief Idea below from where the leak is coming from.

(Thermastat housing)

X X
X O (< ---Leak)

The leak is just dripping off of the bolt down onto the engine and the spark plugs. Figured it was a thermostat gasket, I replaced it and when doing so I noticed that that same bolt is shot and the female threads are stripped on the cylinder head of the engine.

Is there a quick and easy fix for this? I'm not that mechanically inclined but my buddy said to try and re-tap the female threads so the bolt can be fully tightened. I don't know how I like the idea of re-tapping threads into a cylinder head.

Any advice would be great, thank you for your time.

[boscoe99]

Helicoil should do it.

[panasonic]

If the threads are gone, then they are gone. Running a tap down there won't really help.

Hard to know what the thread look like from here. Post a picture maybe?

As Bosco said a helicoil will fix it properly.
Drilling,tapping and fitting the helicoil requires some skill.

Can you bring the boat to a machine shop and have someone with experience do it? This can be done by hand if the right person is doing it without taking the engine apart. As long as they got a clear shot at the hole for drilling..ect

[lettucebereality]

I thought the threads went into the cylinder head, apparently, they go into the block, more of a pain than what I thought it was going to be.

Could I just get a longer bolt and see if there are more threads beyond the point of the stripped threads?

[boscoe99]

What is the complete model of the motor? Some models use a thermostat cover that bolts onto a cylinder head cover. Not the head itself or the block.

Installation of a helicoil is usually no big deal. You may be overthinking the effort or cost involved to install one.

[TownsendsFJR1300]

A heli-coil would be the best to use. Just make sure you drill straight and ONLY AS DEEP as the current hole.

Some pic's of a heli-coil mod I do on some small engines. Take note how thin the aluminum is, less than 1/16" where the coil is inserted.

The new threads are installed with RED Loctite, then later chased with a tap. That thin aluminum bowl with the SS threads, is PLENTY to hold the NEW drain screw(same threads as your thermostat:

(My drain bolt IS as tight as your cover). Much stronger than aluminum threads too..

[pstephens46]

I thought the threads went into the cylinder head, apparently, they go into the block, more of a pain than what I thought it was going to be.

Could I just get a longer bolt and see if there are more threads beyond the point of the stripped threads?

You want this to be correct. So that you are confident later to remove and inspect the thermostat and bore without concern. Not a big expensive repair whether you do it or have a shop handle. Be glad you don’’t have a broken stub in that hole!

[lettucebereality]

What is the complete model of the motor? Some models use a thermostat cover that bolts onto a cylinder head cover. Not the head itself or the block.

Installation of a helicoil is usually no big deal. You may be overthinking the effort or cost involved to install one.

There are only threads on half of the bolt, I took the thermostat off I bought a new bolt and I cant hand tighten it all the way down like I can with the other 3. The bolt went past the part of the cylinder head until it started to catch, I'm assuming the threads start where the block begins. Don't want to force it in for a short-term fix, although the stripers will be around in my area within the next 2 weeks. Going to attempt to re-tap the threads with the original size and go from there.

Any Yamaha dealer would be able to tap the next size up or Helicoil?

thanks for the responses.

[rodbolt17]

attempt all you wish. wont work. metal is simply missing now.
it is to simple to buy a 6mmx1.0mm helicoil kit.
measuer the hole depth. wrap the drill bit with black tape for a drill stop. drill,tap,helicoil go boating.
almost 50 years ago I did my first heli-coil repair. if it was difficult I would have a different job.