so here is the story, i have a 2003 mc with 126k miles on. great car, love it death, tons of fun. but today while taking a nice drive home from work, i hear a loud POP and the car starts to sputter and has no power whatsoever. the first thing that came to my mind was "crap, something happened to my exhaust". upon getting it home and popping the hood, i notice that the #1 cylinder spark plug was not in the engine. it was sitting on top of the engine still in the wire boot. i pulled out my flashlight and looked down into the head and the threads for the plug were completely gone. i know that the worst case scenario would be having to replace the entire cylinder head, and the only other option is re-threading it, if there is enough space and material left. has anyone else experienced this? or am i just one lucky SOB?

 

It actually is more common than you think and it has been discussed in a bunch of threads. There is the KD BackTap, TimeSert, and new head. All have been discussed with in Spark Plug Popped Out , or Spark Plug Blown Out and probably a few more threads.

I have personally used a BackTap with success. But it depends on a lot of variables. I also re-torque my plugs every 5,000 miles, 20 ft/lbs stone cold. Some say it’s the brand of plugs. I don’t buy that myself but...

Are you doing this yourself or are you bringing it somewhere?

///Rich

 

I'm possibly dealing with a similar issue. I have similar loss of power though I didn't have my plug come out. When I checked the plugs, number two was very loose. Replaced the plugs, no issues tightening but no improvement in how the car runs, essentially cylinder two is not functional.

Shop I took to, after leak down test and other observations, stated that plug two wiggles a lot even after being tightened. Seems strange to me, but they claim that air is pushing past the plug, through the loose threads. If this is the case, then I'm thinking about repairing the threads with one of the previously used methods described on this forum. However, if this is not actually the issue, then I just scrapped my head in terms of using it for a core (I'm assuming).

Anyway... any thoughts on this?

 

There are 2 or 3 different products sold to put threads back in a head while in place....all have some risks, but if done right, can save big $$ compared to removing the head, and sending it to a machineshop.....
A few threads around have a ton of info, but since you are potentially destroying a motor with metal shards dropping down into a cylindar, you want an experanced hand that knows tricks...also the threds that are inserted must be at the proper depth....
So check with a few different shops...the first, best, but most $$$ option is remove the head, mechine it, the reinstall wilth a new headgasket....so it is offered first. Next are the different insert products.....by name i think they go by ...threadsert, timesert, etc..they work for some, but can have risks....
One cavat...if you fix the threads,to find out the head must be pulled cause you have a burt valve...thuss the lack of power...most of the head removal/headgasket charges would have been incured.....so ask carefully how sure they are of the issue.

 

PS
A "core" is not scrap...it is a repairable head...it it is not repairble, you WILL get a bill...

 

Repairing sparkplug threads in the car has been done for decades, I used to do them on VW beetles all the time, back in the 60's.....although in those days it was usually because someone cross threaded one putting it back in.

A couple of tricks to keep from getting metal shards where you don't want them - make sure both the intake and exhaust valves are completely closed, and stuff a bit of panty hose down in the cylinder before you start to tap the threads. Then, load the tap with grease which will also grab most of the thread shards, then just follow the kit's mfr's requirements and go after it. Don't forget to pull the panty hose out when you're done!

If you have access to an air hose, give it a good blowing out and put the plug back in, torqued properly.

I don't understand those who feel they have to torque their plugs every 5K, I've never had a plug come loose in anything I've owned - ever. Put em in right, tighten properly, end of issue.

 

So, I tried to replicate movement in the plug, can't get it to move side to side at all. The plug was torqued to spec and visually I don't see anything wrong with the threads, though really I can't see much.

Does the "air past the plugs causing loss of compression" theory make any sense? Any thoughts on testing I can do?

I'm willing to repair the threads, but I need to try to figure out if this is an issue.

 

You Should be able to tell with the motor running..heck, even just cranking it... in a a few cranks...the sound of air coming out should be obvious....I would be careful in getting too close to the spark plug-boot...there is a chance it COULD get blown off...with the plug, creating a projectile!

remember a SparkPlug has a crush washer to keep it sealed and tight...if the treads are there to TQ it down, it should be fine...but if lots of threads are missing...

Various spark-plug inserts have been used for decades, but I think the questions regarding using them on higher compression motors are justified....lets face it, older motors ran at much lower combustion pressures...inserts are a Quick, cheap fix, but for how long?
They might be the right choice for many, getting a few more miles at the lowest cost, perhaps lasted the "natural" life of the motor for many.....but for some who will track the car or run it at 110% with mods...it might not be the "best" choice IMO.

 

Right on, those thought crossed my mind and I was actually out tying to get more information. Here's what I came up with:

-With #2 plug removed, and car running there's an expected amount of air pushing up from the spark plug hole.

- With plug installed, no air pushing from spark plug hole. I could not feel any with my hand and holding a paper towel above the hole (both with the plug wire attached and removed) there is no air pushing up from the plug hole.

 

This happened to me about two months ago. We did the tap and the put a band aid on it but I lost pressure shortly their after... After my mechanic and I not knowing what the problem is with keeping the head on, we decided to pull it. I ordered a new head (used but very low miles on it) and we found that the problem was a chip out of one of the exhaust valves, the air was getting pushed out that hole so there was no way for combustion to occur. A new valve would have fixed it, but since I had the new head and the old one had a tap keeping a plug in place I had the new one machined for better valve seats and installed. Runs better then before problems even started happening! I know there is a cylinder head on here for a gen 1 type S going at a decent price FYI

 

I re-torque them every 5000 when I change the oil. It’s a routine I established since Artoo was new. My plugs are IK-20 DENSOs and I think the difference is that the plugs have to be torqued into cold heads. Mine have never been loose but I have been hearing about ejected plugs now for almost 10 years and the five minutes it takes to check seems like good insurance to me.

///Rich

 

I lost spark #2 about 15 months ago. The dealer quoted about $4000 to replace the head, I found the thread insert on sale at Napa for about $27. I followed the instructions, the suggestions in this website, and handy clips from youtube. I noticed spark #2 didn't work for the first few seconds, I turned off the engine, turned on again and spark #2 came back to life. I thought the ECU had cut the power to that spark, then, for some reason, I assumed it detected a working spark. This is my theory, I asked here if somebody knew about it, but didn't receive any reply. I would disconnect the battery for few seconds, I don't know if it'll work, but worth the try. This is my opinion, I'm not a professional mechanic, so if somebody want to drop a nasty reply, please don't.

 

The vast majority of loose spark plugs are due to improper tightening when they are installed, typically too loose.

During plug torquing, the crush washer causes torque to build over a fairly large angle and many mechanics - deathly afraid of over-tightening and stripping the plug - don't continue torquing until the crush washer is full crushed. And if the crush washer still has spring left in it, this spring will be compressed away by the the vibration and heating/cooling cycles the engine goes through. When this happens, the plug becomes loose.

Unless you have a very good feel for this sort of thing, use a torque wrench.

- Mark

 

Dead right, Mark.

And a helicoil, properly installed, will be stronger than the original threads in the aluminum, so don't worry about the higher compression of modern engines. But do get the correct length helicoil - if the pugs have 3/4" of thread length and you use a short helicoil, a part of the strength is lost since the threads no longer have contact, and the plug can overheat too.

 

This is bumming me out the I told the mechanic to keep the previous head that had a helicoil because I wouldn't ever need it! I could have had that thing ported and installed later.