Spark Plug Threaded In Mi16 Head

[C_W 3 1 Cars]

I decided to insure/tax/mot etc my 205 over the summer and went to prepare it for an MOT this weekend but I've got a big problem in that one of the spark plug threads has gone and cross-threaded. It happened originally a few years ago but I managed to get the plug out and it screwed in and out ok but now the thread has given up completely; it will turn by hand and not tighten up at all. The aluminium thread has just come away (was stuck to the spark plug when I removed it).

 

Is it possible to fix this without removing the head?

[jonnie205 1]

only real way is helicoil or time sert but with all that swarf it will be head off unfortunately, if you knew thread was dodgy why not leave that plug alone?

[C_W 3 1 Cars]

The plugs were already out whilst it wasn't in use (just with centre spark plug cover over) because I turned the engine over every now and then - it was when I put them back in that it failed. Was strange as it was with hardly any force that I could feel that it gave up.

 

What would happen to the swarf if the engine was ran, you reckon it would just get blown out of the exhaust valves?

[saveloy 8]

Definately helicoil time. Although I think you may be able to get away with doing it with the head in situ.

You need to be extremely careful, ofcourse. A load of wet tissue in the chamber may catch most of the swarf. A screwdriver afterwards will get most of the excess, and starting the engine without that plug will blow the rest out.

[Coonper 0]

Yes, agreed, a helicoil will do the trick. It worked on my old motorbike head and its its still going strong 5 years later, with plug changes every couple of months.

 

You might struggle to do it with the head in situ though. I wouldnt fancy the swarf that is gonna drop into the bores...

[jonnie205 1]

will be very hard to drill down a plug hole apparture that deep

[davemar 16]

I recently had the same problem, The spark plug shot out while I was driving and wouldn't stay in. It sounded like a WWII Spitfire while I nursed it home.I managed to Helicoil it in situ. To remove the swarf from the chamber, I used a length of copper brake pipe and stuck some blu-tac to the end of it, and that picked up the swarf from the top of the piston. Several months later the headgasket needed changing (unrelated to that!), and there was no sign of any swarf in that cylinder when I inspected, so the method works. Fortunately being a tilted engine, it all drops into the corner (if you can have a corner in a circle!!), so you're not hunting around for it.And take the rocker cover off to make it a bit easier.

[KRISKARRERA 2 1 Cars]

Is this just because these alloy heads are getting a bit long in the tooth now and have had many a spark plug change or is it just the plugs have been over-tightened?

[davemar 16]

Probably a bit of both. I think some Rooney-type-gorilla had a go at my plugs once and either overtightened them or cross-threaded one. Most of us haven't owned our engines since brand new, so we don't really know how well the plugs have been inserted in the past.

 

The ref was a scouser tonight, Liverpool were so lucky. Sorry, totally OT, but I had to get it off my chest!

[Anthony 1,003]

Helicoil with the head in-situ will work just fine if you're careful - Mattsav at QEP did one for me, and it's still fine years later.

[C_W 3 1 Cars]

Thanks for all the info. I've managed to find a local person who reckones he can do the helicoiling in situ so will hope that fixes it ok!

[richsmells 2]

Out of interest does anyone have a set method of tightening/removing spark plugs?

 

I use a proper spark plug socket with the larger wrench in my socket set and just tighten until it's tight but not stupidly tight. (Excellent method i know, but you get a feel for these things)

Edited April 9, 2008 by richsmells

[Tom Fenton 1,542]

With conical seat plugs it is something like screw down until it touches then +1/16 of a turn

 

With plugs with a crush washer is is something like screw down until it touches then +1/2 a turn to compress the washer.

 

This info is usually printed on the box when you buy new plugs.

 

Having bust a plug off in a head before now (motorbike type plug, 10x1 thread) I always tighten them down with caution.

 

On my old 405 MI16 I found that the straight piece of breather hose from the oil filler cap was the perfect size to slip over the porcelain on the spark plug, I then used to use this to get them started in the head, so that if they did start to cross thread, the pipe would slip around the plug and hence you couldn't damage the thread. This worked a treat and I used to do it everytime. (mainly as I didn't have the right sized proper spark plug socket at the time)

Edited April 9, 2008 by Tom Fenton

[C_W 3 1 Cars]

Has been fixed now with a helicoil (mobile serviceman came out and did it for £50 - I saw some kits to do it yourself for £60 so it was worth getting someone with experience to do it and it wasn't worth the risk of ruining it myself)

 

On my old 405 MI16 I found that the straight piece of breather hose from the oil filler cap was the perfect size to slip over the porcelain on the spark plug, I then used to use this to get them started in the head, so that if they did start to cross thread, the pipe would slip around the plug and hence you couldn't damage the thread. This worked a treat and I used to do it everytime. (mainly as I didn't have the right sized proper spark plug socket at the time)

 

I use an old HT lead with the lead part cut off.

[skeggyrik 3]

So it lives (again) to be thrashed another day.

 

If that was a CAT engine how many of it's 9 lives has it now used? Groan

Edited April 9, 2008 by skeggyrik

[C_W 3 1 Cars]

Hehe, I'm hoping there isn't much/any swarf left in the engien but will be taking it for a run before the MOT, can't run it yet till Sat though.

[base-1 17]

Mobile for £50 sounds good! Glad it's sorted.

 

I do spark plugs up with a torque wrench

[jackherer 543]

Can't argue with £50.

 

I noticed Petert mentioned in another thread that he has a block that he describes as being softened by an engine fire, it made me wonder if the fire you had could have softened the metal and therefore contributed to this problem...? http://forum.205gtidrivers.com/index.php?s...c=89040&hl=

[C_W 3 1 Cars]

Can't argue with £50.

 

I noticed Petert mentioned in another thread that he has a block that he describes as being softened by an engine fire, it made me wonder if the fire you had could have softened the metal and therefore contributed to this problem...? http://forum.205gtidrivers.com/index.php?s...c=89040&hl=

 

I don't think so as it's piston 2 and they're pretty far away from the source of the heat anyway being so deep in the head (the HT leads were superficially melted under the cover but nothing major).

 

I think the original cause was I didn't tighten up a set of new plugs enough (I always fear getting one stuck in the head!), and one rattled itself loose and must have unwound itself whilst driving and eventually blew out and the thread was never the same.

[M@tt 77]

out of interest did you watch him helicoil it?

 

how did he make sure he drilled the hole exactly perendicular to the head and get it straight? did he have some sort of stand and massively long drill bit?. As i understand it you redrill the hole slightly larger, tap a new thread into it for the helicoil and screw the helicoil into it, correct?

Edited April 10, 2008 by M@tt

[C_W 3 1 Cars]

out of interest did you watch him helicoil it?

 

how did he make sure he drilled the hole exactly perendicular to the head and get it straight? did he have some sort of stand and massively long drill bit?. As i understand it you redrill the hole slightly larger, tap a new thread into it for the helicoil and screw the helicoil into it, correct?

 

I didn't watch over him as he did it, but he showed me the taps he uses (there was no drilling); it's a two-stage tap which has two diameter taps on (the larger following the smaller tap); the first tap is the same size as the original spark plug I think; this means the tap follows the original thread (or what's left of it) and then the larger tap follows to create the thread for the helicoil. Although we ran the engine without the plug in to try and remove any debris left over he reckosn the gel he uses on the tap usually brings most of it out.

[KRISKARRERA 2 1 Cars]

Soz, got dig this up to add something...

 

For years I've been tightening up spark plugs just by hand with this t-shaped tool, because I've been worried about stripping the thread in the alloy head.

Well now my dads bought a decent torque wrench and I used that today and set it to just 15lbs (5 less that it should be) and discovered that it tightened them up ALOT tighter than my old crappy method. My old plugs were so loose that the sealing rings weren't even compressed!

So I test drove the car and it feels faster now obviously because there's better compression.