Not Good - Stripped Plug

[Harry]

I have essentially completed the 230SL rebuild and while installing the new plugs this afternoon to do my first start, number three stripped when it was being torqued.  It didn't come near torque before it went.  Very disappointed.  All other plugs torqued right up.

So - I'm familiar with keenserts and I suspect that is the only viable path but I wanted to run it by the pros before I did anything.  Hopefully, some other poor soul has run into this as well and can offer a reasonable solution, e.g. can this be repaired with the head installed?  What is the correct path forward?

Thanks,
Harry

[Shvegel]

I have rethreaded plug holes in situ when I was a line mechanic at a Saab dealership.  I would make sure the piston is at TDC on the compression stroke so both valves are closed.  Coat the tap with grease so most of the metal chips will stick to it and the blow the hole with compressed air to remove as many chips as you can before reinstalling the plug.

[Harry]

Thanks Shevegel.  I spoke with someone else who shared the same advice.  Need to get a 14mm two stage tap.

[Jack Jones]

I have used Timeserts many times and the repair if done correctly is permanent. I have never used keenserts so I cannot comment on them but I am sure others can offer their opinion on both products.

[specracer]

+ one on a timesert. I just used one for the 1st time, on an exhaust stud that was stripped out of an aluminum head of a different car. I liked the system.

https://www.timesert.com/

[cfm65@me.com]

I have had an insert fitted on my E Type engine in situ.  No problem since.
Regards
Chris
Cape Town

[ja17]

I've used this tool before with good results. You will need to use the same brand inserts if you use it. Be sure to use 3/4" length.

https://www.autotoolworld.com/KD-Tools-2123-14mm-Spark-Plug-Insert-ReamerTap_p_146436.html?msclkid=441b5b400971167dff6a05e99233e276&utm_source=bing&utm_medium=cpc&utm_campaign=Google%20Shopping&utm_term=4585238368591926&utm_content=All%20Products

Also you might need to turn the engine so the piston is down a little so you do not run into it with the tool. As Pat mentioned, use grease on the tool to collect the shavings. You can also Tape a small tube on the end of your shop vac and vacuum out the cylinder when you are done. The soft aluminum shavings are not likely to cause any problems in most cases anyway. Also as Pat mentioned, cranking the engine with the plugs out afterward will expel any remaining debris in the cylinder.

[stickandrudderman]

Time certs are brilliant.

[MikeSimon]

In addition to all the tips when doing a thread save on a head installed, take a piece of thick wool or soft string and smother it in grease. Insert it into the plug hole in a way that you will be able to pull it out with tweezers. Tap your threads and pull the string out. All of the debris should come out.

[WRe]

Hi,
what about rethreading the plug thread not top-down but bottom-up with this tool.
I would assume that in most cases the lower thread is in better condition so the tool can be threaded more easily and the shavings come out better.
...WRe

[badali]

I used the tool WRE shows and it worked well on my 4.5 sedan.

[hansr433]

Hi,
what about rethreading the plug thread not top-down but bottom-up with this tool.
I would assume that in most cases the lower thread is in better condition so the tool can be threaded more easily and the shavings come out better.
...WRe

Hi, what do you mean by bottom-up?  Remove the head?  Also, perhaps it might help to speak with an old-school machine shop about tricks of the trade in fixing plug threads in situ?

[MikeSimon]

If the head is off the motor, I see no reason why we have to even discuss this issue.

[badali]

The tool shown by WRE slips through the hole.  You expand the tool and it re taps the hole starting from the inside threads as you screw it out of the hole.

[hansr433]

Brad, thank you for the explanation.  I had to blow up the photo of the tool in order to see what you mean.  Very clever.

[WRe]

Hi,
no, you work from outside, you don't need to remove the head. The tool has two parts which can be screwed together, a conus expands the die. It's thinner than the plug hole and it can be inserted, screwed together and you can rethread from inside out.
...WRe

[66andBlue]

The tool WRe shows is known here as a "back tap" and available on eBay, Amazon:
https://www.amazon.com/Powerbuilt-640811-Back-Tap-Thread-Repair/dp/B0014FGVVW?th=1
Here is a video explaining how it works:
https://www.youtube.com/watch?v=3UK8kEAnHVk
You need the 14mm tap!

[WRe]

Danke Alfred! :-)
...Wolfgang

[MikeSimon]

Gosh. You learn something new every day. And here I thought I had all the tools I personally need. And for the very few I do not, I go to one of my friends! ( I do have some!)