anyone have experience fixing stripped spark plug threads?

[silver911rdb]

I just finished putting together my rebuild with my freshly rebuilt heads. Apparently the threads weren't in the best of shape. When installing the spark plugs on cyl #3 the thread pulled. I was using the torque wrench and setting to 28nm. At around 22nm I felt it start to go. Anyways, anyone have any experience fixing this? I really don't want to pull everything apart to fix this. If I repair this with the engine together, how do I keep the chips from going into the engine? Any tips would be appreciated on how to do it and brand to use. I see heli-coil and time-sert have systems available. Anyone prefer one over the other?

thanks

[fred cook]

When I worked in an Alfa shop back in the late 70's, this is how we would repair a stripped spark plug thread:

1) Turn engine so the piston in the affected cylinder was at the bottom of the stroke.
2) Cut a piece of shop rag into one long strip narrow enough to feed into the spark plug hole.
3) Soak the rag in oil to catch chips and feed it into the cylinder.
4) Rotate the piston to hold the rag in place against the cylinder head.
5) Drill and tap the hole for the plug insert and blow off with compressed air.
6) Lower the piston slightly
7) Reach into the plug hole with long needle nose pliers and pull the oily rag and metal chips out.
8) Install the thread insert and plug.

We did quite a few engine repairs this way without having any problems crop up later. The oil on the rag does a good job of catching all the metal chips. The only thing I might do differently now would be to use a piece of cloth that was less likely to leave lint than a typical red shop rag. Good luck!

[faverymi]

Not in 911s yet.

Back on the honda days I did it a few times with the kit repairs from your local auto parts store. Aluminum heads, not hard and a very predictable fix.

Hope it helps.

[JFairman]

Seems like the directions in post #2 would work if you lower the back of the motor down around 5-8 inches on to a jackstand and remove the left side engine tin if needed for better access and work from under the car on that side.

I've seen inexpensive extra long hemostats at harbor freight tools that are much thinner than their long needle nose pliers that would probably reach into the spark plug hole.

12" Locking Clamp

[Rob R]

I have used Timeserts on VW heads a few times. It worked great.
++ TIME-SERT SPARKPLUG Standard Repair ++

[silver911rdb]

I actually have the engine on the stand with both induction and exhaust off. I'm guessing I would be able to blow enough air through it from both valves and spark plug holes (twin plug) to get rid of the chips. Never did it so only a guess

[HawgRyder]

It helps if you coat the heli-coil tap with heavy grease before using it...that catches a lot of chips too.
Bob

[porterdog]

I've used a shop vac with a metal tube (~6mm OD) and some duct-tape adaptors to suck debris out of a cylinder.

$0.02...

[silver911rdb]

I bought the time-sert system. Super slick system. I was able to repair the thread with ease. I was very careful not to get chips everywhere. I also made sure both valves were closed so chips didn't land on the valve seat. Every few threads I cut I removed the tap to clean off the chips. I didn't use grease on the tap. I figured if the grease fell inside the cylinder loaded with chips, it would be harder to remove. Once I finished I used a small dia rubber hose and blew from the inside of the cylinder. Chips flew out the spark plug opening. I was able to move the tube to make sure I blew every part of the cylinder. As a final check I used a bore scope through the spark plug hole. I also opened both intake and exhaust valves to check with the bore scope. I didn't see anything so I should be good.

For any one looking to do this same repair in the future. You'll definitely need the extended reach kit. The standard kit is too short

Thanks for the help

[faverymi]

Originally Posted by silver911rdb

I bought the time-sert system. Super slick system. I was able to repair the thread with ease. I was very careful not to get chips everywhere. I also made sure both valves were closed so chips didn't land on the valve seat. Every few threads I cut I removed the tap to clean off the chips. I didn't use grease on the tap. I figured if the grease fell inside the cylinder loaded with chips, it would be harder to remove. Once I finished I used a small dia rubber hose and blew from the inside of the cylinder. Chips flew out the spark plug opening. I was able to move the tube to make sure I blew every part of the cylinder. As a final check I used a bore scope through the spark plug hole. I also opened both intake and exhaust valves to check with the bore scope. I didn't see anything so I should be good.

For any one looking to do this same repair in the future. You'll definitely need the extended reach kit. The standard kit is too short

Thanks for the help

Rich

What brand/supplier/store did you end up using?

Thanks.

[silver911rdb]

I ended up going with Bel-Metric in Mass. They're a stocking distributor. A bit of a haul for me in Connecticut but I drove out to pick it up. I need my engine running for an event this weekend so every day counts. Great guys with lots of stock. Pretty close to you if you're in the Boston area.

[SteamWolf]

Solid inserts. I have used helicoils but they can be problematic. Anything that protrudes into the cylinder can cause pre-ignition from the wire acting like a glow plug.
Good (cheap) ebook on it here:
Thread Repair | Yellamundi Self Publishing