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

[karls59tr]

"If it wasn't for bad luck I wouldn't have had no luck at all" When I pulled out the 2nd spark plug wire from the block where it connects to the plug I snapped the wire connection off the wire. Changed the wire out but when I went to install the plug I must have stripped the threads in the block. I thought I could work a new spark plug back and forth with a little tapping oil on the threads but I guess I got ham handed and reefed on it till it jammed. Like an idiot I kept on going. The plug is now most of the way but sticks out about 3/4 " proud of the other plugs! To fix this I guess I'm going to have to pull the head to do it. I was going to run the motor to see if the head gasket was still leaking. My question is would I still get proper spark with the plug most of the way in just to see if I have head gasket leaks then shut it down and pull the head.

 

[NutmegCT]

While waiting for a knowledgeable answer ...

 

[karls59tr]

 

[bobhustead]

Head needs to come off. This repair is helicoil at home or by machine shop repair. No harm in trying to run it as is to leak check it. Stand out of the line of that plug, though. If it's 3/4 proud of the other plugs, though, aint much holding it in. Blown out plugs will damage sheet metal.
Bob

 

[karls59tr]

Head needs to come off. This repair is helicoil at home or by machine shop repair. No harm in trying to run it as is to leak check it. Stand out of the line of that plug, though. If it's 3/4 proud of the other plugs, though, aint much holding it in. Blown out plugs will damage sheet metal.
Bob

I here ya? I've had lots of practice taking the head off so it's routine now. I think there is some kind of tool other than a helicoil available that retaps the threads if they are not too far damaged. I removed the spark plug and looking into the hole it appears that the threads further down are still good so it may be possible to re thread by starting from the other side of the head once I get it off?

 

[RichB4493]

That was going to be my suggestion… to tap it from the inside out if you have good starter threads

 

[karls59tr]

That was going to be my suggestion… to tap it from the inside out if you have good starter threads

Would you happen to know what size tap is required for the TR3 spark plug hole?

 

[mezy]

I hate hilicoils, allways come out with the bolt, they are a bodge, a get you home till you can do the job properly,
I would buy another head befor using a helicoil,
retap it from the inside out, then be very careful putting the plug back in

 

[Hamish Racing]

Does this answer it ?

appear to be 14mm 1.25
Would metric make sense ?

TR2/3/3A - Spark plug threads

Spark plug threads, number 4 plug hole has some drag or minor cross threading on the last couple of threads. I just find it unsettling mostly because I pull the plugs a lot to evaluate things. When I pull number 4 out, there is resistance at first and resistance at the end going in plus I can...

www.britishcarforum.com

 

[PAUL161]

Also put a dab of never-seize on the threads, acts as a lubricant and prevents galling. (On all the plugs). PJ

 

[auprichard]

I think there is a tool which avoids having to pull the head as it prevents shavings from falling into the engine. Let me see if I can get a picture of it.

Also, strange as it sounds, Hamish is right = 14mm 1.25

 

[auprichard]

Powerbuilt 640811, 14 x 1.25 back-tap repair tool

Available on amazon:

Amazon.com : powerbuilt 640811 14mm back-tap thread repair tool

 

[mctriumph]

The yardstick is how much time and $ have you spent on this head(steel seats,port work ect).
If it is little , scrap it for a good one. Then do all of the prep to make it sweet. Again the hot
trick is to have new guides knurled to fit up the old valves, making something of a seal to minimize
oil consumption. Just got one back from the machine shop.Steel seats, guides,planed,valves ground. 500$
mad dog

 

[karls59tr]

Powerbuilt 640811, 14 x 1.25 back-tap repair tool

Available on amazon:

Amazon.com : powerbuilt 640811 14mm back-tap thread repair tool

Thanks. That's exactly what I'm looking for.

 

[karls59tr]

The yardstick is how much time and $ have you spent on this head(steel seats,port work ect).
If it is little , scrap it for a good one. Then do all of the prep to make it sweet. Again the hot
trick is to have new guides knurled to fit up the old valves, making something of a seal to minimize
oil consumption. Just got one back from the machine shop.Steel seats, guides,planed,valves ground. 500$
mad dog

I hear what you are saying but can't find used TR3 cylinder heads in these parts and new ones are $3500!

 

[CJD]

Karl...very important...

You must use a solid insert to fix a stripped plug hole. A normal helicoil is a spring that will let gases wind up the coil. When you look for the insert to repair the hole, it must be a "solid insert", which will properly seal the threads.

At this stage, I would have no problem running the engine for a few minutes with the jammed plug...just to see how the leak is doing. An old mechanic technique was to loosen the spark plugs a bit and run the engine to blow any dirt out of the area before removing the plugs for a tune-up. Just don't stand in front of the plug when running in case it does pop out forcefully.

The head should come off to repair the threads, though. I don't know if there is a cool tool to avoid getting swarf in the head or not...I haven't seen any tool I would trust.

Final note...as a young mechanic I would frequently cross-thread bolts, spark plugs, and anything else possible! After going through the repair procedure, I no longer ever install a bolt that is not going in EASILY with 2 fingers. If it has good threads, then 2 fingers ensures you are not cross threading, and in the case the threads are not good...then using 2 fingers tells you when it's time to chase the threads with a tap or die before proceeding. I no longer cross-thread anything. The repair is to much work!

 

[karls59tr]

Karl...very important...

You must use a solid insert to fix a stripped plug hole. A normal helicoil is a spring that will let gases wind up the coil. When you look for the insert to repair the hole, it must be a "solid insert", which will properly seal the threads.

At this stage, I would have no problem running the engine for a few minutes with the jammed plug...just to see how the leak is doing. An old mechanic technique was to loosen the spark plugs a bit and run the engine to blow any dirt out of the area before removing the plugs for a tune-up. Just don't stand in front of the plug when running in case it does pop out forcefully.

The head should come off to repair the threads, though. I don't know if there is a cool tool to avoid getting swarf in the head or not...I haven't seen any tool I would trust.

Final note...as a young mechanic I would frequently cross-thread bolts, spark plugs, and anything else possible! After going through the repair procedure, I no longer ever install a bolt that is not going in EASILY with 2 fingers. If it has good threads, then 2 fingers ensures you are not cross threading, and in the case the threads are not good...then using 2 fingers tells you when it's time to chase the threads with a tap or die before proceeding. I no longer cross-thread anything. The repair is to much work!

What do you think of the back tap repair tool that Auprichard mentioned in this thread? Looks to me like it would keep the swarf out of the cylinder head. Might be worth a try

 

[Hamish Racing]

Powerbuilt 640811, 14 x 1.25 back-tap repair tool

Available on amazon:

Amazon.com : powerbuilt 640811 14mm back-tap thread repair tool

Got to be worth a go.

this video shows how

 

[CJD]

Well...if I were working on a budget, here is the order I would do everything:

1) Run the motor with the jammed plug up to temp and see if you solved the leak.
2) If you solved the leak, then get the reverse tap and use it. (you probably already got some metal swarf in the cylinder in jamming the plug, but it will blow out quickly on start-up).
3) If the leak is still there, then pull the head and fix the plug properly.

 

[karls59tr]

Well...if I were working on a budget, here is the order I would do everything:

1) Run the motor with the jammed plug up to temp and see if you solved the leak.
2) If you solved the leak, then get the reverse tap and use it. (you probably already got some metal swarf in the cylinder in jamming the plug, but it will blow out quickly on start-up).
3) If the leak is still there, then pull the head and fix the plug properly.

Unfortunately I removed the jammed plug already....should have left it in to test for leaks...as you say I may have got some swarf in the cylinder. So before I use the reverse tap to reline the threads.... I should start the motor briefly with no plug in that cylinder in order to blow any swarf out? Then try the reverse tap. Correct?