Spark Plug Popped Out, Looks De-threaded.

[davemar 16]

One of my spark plugs shot out while driving home today. Unfortunately it doesn't screw back in, so it looks like the thread in the head is shot. I do have a spare head, but it needs a lot of cleaning up, and I'm not really sure how good the threads are in that.

Has anyone tried using a helicoil to fix this problem? Has anyone tried doing it without removing the head?

Bear in mind this is a 1.9 Mi16 engine, so the spark plugs are deep down.

[Anthony 1,003]

Mattsav helicoiled a spark plug thread in situ for me - he's pretty much on your doorstep as well up in Burgess Hill

[t16ryan 1]

yeah get it helicoiled you can buy them for £4,

[saveloy 8]

Just remember to run the engine without the plug in to release any debris that may have fallen from the threads.

[KRISKARRERA 2 1 Cars]

Ah ha this thread just answered my question about helicoiling.

[Hilgie 16 2 Cars]

Running the engine without the plug in to clear the debris is somewhat dodgy....because the larger metal flakes will just scratch the cylinder walls or junk your valves....

It won't be blown out through the sparkplug hole anyway.

[Richie-Van-GTi 71 2 Cars]

Running the engine without the plug in to clear the debris is somewhat dodgy....because the larger metal flakes will just scratch the cylinder walls or junk your valves....

It won't be blown out through the sparkplug hole anyway.

 

Amen to that, I just ruined a fit 1.9 because something got into the bores and ruined a liner within 7 miles.

[C_W 3 1 Cars]

A spark plug on my Mi16 worked loose, there seemed to be no notice except a sudden loss of power and big misfire. It melted the ht lead in two.

 

The plug went back in but the thread went very tight after a couple of turns so I drove home with it like that. I tightened it up but it felt like it got stuck and I thought the head was gone, but I slowly worked it loose by untightening and retightning. I fitted a new spark plug and it seemed ok, a little tighter than the others but much better. Now after removing it a few times it seems normal.

[saveloy 8]

Any debris certainly will pop out of the spark plug hole.

How else do you propose removing it,without removing the head?

[Alastairh 47]

Well if your hellicoiling the thread its not going to be big metal flakes though is it.

 

Id personally just clean up as much as you can and run it, and any small bits of brit may exit the exhaust/inlet valves, which luckily happened to me when i had a snapped spark plug electrobe and fell in.

 

Alastair

[Rob_the_Sparky 9]

If it were my engine and I'd rebuilt it then I'd take the head off rather than drop a load of swarf into the engine. If it were an old engine and not rebuilts then I think I'd take the risk and get it done in place.

 

Clearly swarf in a cylinder is never going to be a good thing and won't do the bores any good but how much damage? I presume Matt must have some confidence in doing it in place is OK even though my gut reaction is that it is not a good thing to be doing.

 

Rob

[davemar 16]

I picked up a helicoil and tried it on a spare useless head I've got, in the comfort of my living room. Apart from the problem of getting a suitable wrench onto the tap (the 1/2" chuck wrench I bought is too small for some reason?), which made it a bit awkward with using a 3/8" extension bar. The tap has two sizes of thread, the first cm or so is 14mm, and the rest after a shoulder is 15.5mm (ish). It was quite an effort to get it turning onto this larger part of the tap - made even harder in that my head was sitting on a piece of MDF, so kept sliding around! I managed to get the tap most of the way through, but clearly didn't go through enough (again the floor getting in the way, as the tap protrudes from the bottom). It required a lot of force, not only to tap in, but also to come back out again. I would have hoped for less effort to unscrew!

 

Getting the helicoil itself in needed a couple of small pieces of tape to hold it onto the inserter. It screwed in easy enough and the bits of tape stayed attached to the inserter, so that bit worked. I was running out of length on the inserter tool in the hole though. As I hadn't tapped the hole out far enough through, the helicoil didn't go in far enough. The instructions suggest using pliers to remove the tang on the coil, but I haven't coil pliers with noses that long, so had to bash it with the tool to knock it off.

 

The spark plug screwed in freely enough, but as I hadn't tapped out the hole deep enough, the plug didn't go down far enough. I'm glad I tried all this on a spare head!

 

I did notice a lot of swarf being produced, as the tap takes off a lot of metal. So you really wouldn't want all that lying around in there. I might try and do a experimental suck up with the hoover and see how much gets left on the MDF.

 

I'll have to try it again on another hole to really convince myself before trying it for real.

Edited June 16, 2006 by davemar

[Rob_the_Sparky 9]

Normally for a helicoil you would drill the hole to the proper size (larger than required for a non-helicoiled thread) then tap it and fit the helicoil. Not sure how well it will work without drilling, hence the concern about swarf. TBH though my main contact with helicoils is at work where they are fitted from new where we need a stronger, more durable thread. It may work OK without drilling for a stripped thread...

 

Rob

 

P.S. The idea of the tang in the cylinder, not nice...that thought hadn't occurred!

[davemar 16]

Supposedly the design of the two-stage tap is so that drilling isn't required. I had another go tonight on another hole, and tapped all the way through this time. It did feel a little easier, and came out very easily this time, so much more promising. The problem I now came against was how far to screw the helicoil in when doing it blind. OK, I was doing this on a seperated head, so could check, but you don't get any physical feedback to when to stop. The only way to make sure you don't overrun is to count the number of turns - in this case 13.

 

I haven't got round to hoovering up the swarf yet, so I'll try that next...

[davemar 16]

Another way I've thought about for getting swarf out is by sticking some blu-tak to the end of a stick and pick it up that way. Has anyone else tried this?