Kg7 stripped spark plug hole.

[Henry Withers]

I have a Mercury KG7 with a major stripped spark plug hole.  I tried to fix it with an insert but it didn’t take and is leaking under compression.

Is it possible to have a machine shop weld it up and tap it?  If not, does anyone have a block I could purchase?

I’m really bummed out about this as I think they are getting rare as hen’s teeth and I have it together at the moment.

Anyhow, any suggestions/ direction would be greatly appreciated.

The block is standard bore.

Thanks

Henry Withers

 

[boscovius]

Ok,  So you used a helicoil type insert?  And it failed?   Or just leaks?

Did you use any kind of high temp goop as a thread sealant?

Seems like there should be a way to salvage this situation.

[joecb]

We need to know what kind of insert you used?  Helicoil ? or one of the threaded bushing types?

Joe B

[Mumbles]

These steel spark plug inserts are what you want to use, not the regular wire inserts used for thread repair.

[joecb]

I’m making an observation here, hoping to get clarification. I have always used the wire Helicoil inserts for stripped spark plug holes with good success. If I recall correctly the OMC service bulletins also recommend the wire inserts. Now I see on the  ( bushing type) “Save-A- Thread” package that the spark plug pictured is the type with a tapered seat ( no gasket). I can see where the wire Helicoil insert would not work for this type spark plug because you lose the tapered sealing surface in the cylinder head. Thus you would have to use the sleave type insert with this kind of plug.  Conversely, I question whether the sleave type insert, once installed with it’s tapered seat will work properly with the gasket type spark plug that we use on our outboards.   Because the coil type inserts only require a minimal enlargement of the original hole, there remains ample flat sealing surface for the spark plug gasket to seat and seal. I have never had a seal leak after using the coil type coils.

Just thinking … looking for your experience and observations.

Joe B

 

 

[Mumbles]

The Sav-A-Thread inserts can be used with both tapered and gasket style seats. They lock into the head, don’t leak, and have better heat transfer characteristics than the regular wire inserts which can wind out of the head, leak, and require a change in the spark plugs heat range. All in all, they are a better mouse trap!

[billw]

I see serrations on the inserts you show but please explain how those “lock.” We used to use solid inserts with gasketed plugs for awhile. Almost every time, when you removed the plug, the insert came out with it. It was maddening so we went to wire inserts.

Long live American manufacturing!

[crosbyman]

the installation requires the insert  to be punched to lock it in place. ..if I remember ok   I installed one years ago on a cyl head  on a 7.5  AD   it   worked great

Joining AOMCI has priviledges 🙂

[Mumbles]

To install these inserts, new threads are cut in the head with the provided tap, red hi temp silicone is applied to the threads on the insert before screwing it in, then the serrated part of the insert is expanded by using the large punch which is included in the kit. The punch has a taper on it which does the expanding.  I find one or two good blows with a two pound hammer does the job. After the insert has been set, clean up any excess silicone and allow it to set up before installing the spark plugs or running the motor and you are done.

For the record, I’ve never had one of these inserts back out when removing the plug but I have had the wire inserts come out with the plug. That can be a pain as now the wire insert is tight on the plug and can be a bear to remove.

• This reply was modified 2 years, 11 months ago by Mumbles.

[billw]

That’s very interesting! Thanks for that! I will have to try them again sometime.

Long live American manufacturing!

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