GP crossthread near miss
This isn't completely related to the GP thread damage thread (sorry about the pun!), but I feel it's somewhat relevant.
As a relative newbie, I followed Wingnut's excellent GP diagnosis and replacement guide with trepidation.
I learnt alot and wanted to log my newbie experiences into Wingnut's GP 101. Will hopefully do that more fully when I get a better chance, but I felt a brief summary might be useful.
The Veteran's may find the write up below obvious and adding little extra knowledge, but I hope that it may prevent someone else having a possible GP crossthreading mishap.
In my situation, I had to replace all 4 GPs. (I had been driving for several years with 4 completely dead GPs and didn't realise it! What is suprising is that the Dealer didn't even point this out).
0) Ideally remove engine cover and gently wash the engine parts around the GPs with engine degreaser
a couple of days before removing GPs. As sthussey, DBW, HermTDI and others have pointed out, the grease/grit and other contaminants not only make GP replacement alot more difficult, they can also harm the engine and GP threads/hole.
1) Allow engine to warm up to mid temperature guage. Remove GP wiring harness then spray WD40 around seat of GP and allow to penetrate. I then let the engine cool down for around 20 mins.
2) GENTLY loosen all GPs. (I used a 10mm deep socket attached to a 6 inch extension on a 3/8 rachet: for my 1Z engine).
Only remove and replace ONE GP at a time. That way if you have a problem reinserting/crossthreading a glowplug you won't panic at the thought of this happening to the remaining GPs, since you can simply retighten the GPs you haven't yet removed.
3) If you are replacing all GPs, work in a systematic way so that it is clear which GPs have been replaced. i.e. left to right. On a 1Z engine I found left to right to be a particularly good order, since the leftmost GP is easily accessible and less fiddly.
Further, starting with this easier GP will give you a good
feel for how easily a plug should come out and the tightening torque, which becomes important when dealing with the more awkward middle GPs.
4) When a GP is removed, carefully but thoroughly clean the GP hole with a clean lint free cloth. This is important, otherwise the new GP's threads may be contaminated with dirt/grit preventing the new GP from screwing in. Capping the hole with a cloth, I also cleaned around the hole to allow proper GP seating and prevent possible dirt ingress.
5) As Wingnut describes, apply
a small amount of Copper based antisieze/copper paste to the thread of the new GP. Inspect the thread to ensure that there is no dirt/grit on the thread.
6)
Patiently try and carefully screw the GP back into it's hole by hand, for 3 turns (this is more difficult for the inner two GPs).
If the plug doesn't turn in, remove it and try again. It may be necessary to remove any grit/dirt that has just been collected in the GP thread, and to clean and reapply copper antisieze.
7) Again using a 10mm Deep Socket on a 6 inch extension, try and tighten the GP back into the hole.
In my case, this seemed to work without any issues for the easily accessible GP (leftmost). However, the inner GPs (2nd from left, 3rd from left) always seemed to
crossthread when tightened.
This is where I panicked, since I had read about cross threading resulting in serious cylinder head removal issues.
After some thought I realised that the less accessible GPs, made an awkward angle with the socket, and that this was probably causing the crossthreading. Wingnut suggested using a wobble socket, so I used a
Universal Joint to couple the 10mm Deep Socket to the extension bar. i.e.
10mm deep socket=>Universal Joint=>6 inch extension bar=>rachet.
The lack of accesibility made the rachet sit at the wrong angle to the glowplug, but when employing a Universal Joint, the UJ allowed the Deep socket to sit squarely on the GP reducing the possibility of crossthreading.
The first few turns were quite loose, but then the GP became more difficult to tighten and so I thought the glow plug had been installed, but checking the height of the GP above the engine it was clear the GP had many more turns before it was seated.
I continued tightening the GP despite the resistance, all the time thinking about the possibility that I may have been cross threading it. Fortunately, the GP wasn't cross threading, it was just that after the first few turns more torque was required to tighten the plug.
8) I tightened the GP, until it was sitting at the surface of the engine. For the all important final tightening I tried using a Torque Wrench to achieve the 15Nm Tightening Torque, but this felt as if it was overtightening and hence leading to possible damage.
Instead I opted for hand tight, plus 20 to 30 degrees of additional tightness.
Personally I feel that
a) being gentle and patient
b) only removing one GP at a time
c) using the Universal Joint on the 10mm Deep Socket
d) ensuring that the hole threads and GPs are dirt/grit free
helped to reduce the possibility of crossthreading the GPs.
10mm DS | UJ | 6in extension | rachet
Apologies to UNIX users for the pipe analogy.