99 135 Optimax - stripped #1 spark plug

[JerEazy]

Doing a spark plug change on my 99 135 OptiMaxx and when I took out the number one spark plug it was very hard to get out and just as I feared when reinstalling a plug the threads were shot.

so i’m going to attempt to run a tap in and clean up the threads. But I’m not very confident and I’m looking towards just replacing the head with they take off from eBay.

so 2 questions:

Does anybody know the tap size that I would need to try and get those threads squared away?

And any special concerns I should worry about when removing the head? I find a head and a head gasket fairly easy but I keep reading things about O-rings for the injectors. But can’t really find any information.

Don’t have a physical manual I am using what is online

This is my first Mercury engine. So there’s a bit of a learning curve

 

[JerEazy]

Probably should be more clear. When I look at the diagrams in the manual for removing the head it doesn’t mention anything about injector O-rings. But I’m assuming if the injectors are in the head and I’m putting a new hat on there I need to get new O-rings. If that’s the case, part numbers would be appreciated if anybody has them

 

[Chris1956]

Optimax heads are much more complicated than ordinary 2 cycle OB heads, due the the high pressure fuel injection. Replacing them would be expensive.

Why not fix the stripped spark plug thread? You can buy a solid steel insert, tap and drill kit for your spark plug threads.

Some will say that you don't really need to even remove the head to insert the solid insert, but you risk getting metal chips into the engine when tapping the head. I would therefore recommend you remove the head and then fix the issue.


BTW - some will suggest helicoil inserts. However, those are not solid inserts. I have only used the solid inserts, and they worked well.

 

[JerEazy]

I found them on eBay for about $100 for the head and head gasket. I wasn’t sure what else was needed to finish the job. I did end up using a tap and sleeve and it seems to be doing just fine for now. I guess it was more of a curiosity, and just in case for the future

 

[Texasmark]

I was a teen and young, stupid, inexperienced, and ambitious. I was working on dad's 1955 Scott Atwater 10 hp....that didn't have anything wrong with it ,and removed and reinstalled the spark plugs, just to look at them......wanted to just tinker with it. Not knowing anything about torque values, and cast aluminum, and all that technical stuff, I stripped one out on the way back in. I guarantee you that I never did that again.....never to this day.