TR2/3/3A Stripped threads in spark plug hole

[mgedit]

That is a cool tool, but I wonder how it will work on a TR3 head. Seems like most I saw on Amazon in Canada are designed for aluminum heads. Cheers, Mike

 

[mctriumph]

Karl NO do not start a motor on 3 cylinders and one plug out!! Pull all 4 and spin it to clear out
any swarf
MD

 

[karls59tr]

That is a cool tool, but I wonder how it will work on a TR3 head. Seems like most I saw on Amazon in Canada are designed for aluminum heads. Cheers, Mike

That's a good question. Woud the tool cutter effectively cut threads in the cast iron?

 

[sp53]

I have tapped cast iron before; it is a slow process probably a 1/4 turn at a time with a lot of presser and a little backing up of the tap to clear it. I tapped a slightly stripped out plug with new tap and with the tap covered with grease to catch the little pieces The plug holes are metric even back then. How stripped are the threads can you take a picture?
steve

 

[karls59tr]

Steve Have you used this tool.....Amazon.com Powerbuilt 640811 14mm back tap thread repair tool. It looks like it might work provided the threads are not too badly damaged. I did try twisting the spark plug in quite forcefully thinking I could get the plug to catch! I guess if the threads near the bottom of the plug are still good I may get lucky and by using your method I may be able to slowly rethread from the inside. Might be worth a shot before pulling the head to repair? I may be able to borrow a boroscope to take a picture. Karl

 

[bobhustead]

you do not want to thread from the outside. it will relocate (DESTROY) the good threads you have in the bottom of the hole. starting from the comb chamber will lay down the repair threads to meet the good threads were they used to meet before you destroyed the outer threads.
bob

 

[karls59tr]

you do not want to thread from the outside. it will relocate (DESTROY) the good threads you have in the bottom of the hole. starting from the comb chamber will lay down the repair threads to meet the good threads were they used to meet before you destroyed the outer threads.
bob

The "Powerbuilt 640811 14 X 1.25 back tap repair tool" threads from the inside. In the advertisements for this tool they show the tool being used on aluminum cylinder heads. What I'm wondering is will the tool be able to cut threads in cast iron effectively?

 

[mctriumph]

Cast iron is not as hard as one might suppose. I think it will work ,as the threads you need
to fix are just the last few coming out/
MD

 

[sp53]

What Bob said is the correct way to look at this problem. I fixed a very slightly damaged hole many years ago with the grease on the tap. I learned it from a mechanist when I was in a panic. Trying to tap it from the outside is a gamble and would be less of a gamble if you did the tapping from the inside out. The head is not that difficult to remove when you are already in the process of fixing it

Cylinder heads are not cheap and I would hate to see you damage the hole more.

I seem to remember you have some casting cracks that you were uncertain about. What John suggested about having the old spark plug in there and doing a startup and looking for cracks sounded good to me.

steve