Plus gas for glow plug removal prep, which one?

[Big Rig]

Planning on changing the glow plugs in my 1.7cdti Astra. Was going to start soaking them for a few days before to try and help them come out.

There’s 2 different ones on Amazon, which one is best? Or is there anything better than these available?


Plusgas English Abrasives 803-10 Tin 500ml https://www.amazon.co.uk/dp/B0001P02RU/ref=cm_sw_r...

English Abrasives 809-10 Plusgas Tin 250ml https://www.amazon.co.uk/dp/B0001P02S4/ref=cm_sw_r...

[rigga]

50/50 mix of nail varnish remover and ATF

[Dave.]

Both look to be "Formula A", I think it's just the way it's dispensed is what the number refers to.

[imagineifyeswill]

Agree with Rigga, acetone and atf 50/50, if you havent got acetone cheap thinners works just as well.

[Captain Answer]

Either of those but can be tricky getting it into some bits... 500ml will then ensure there's plenty to leave to the grandkids

The aerosol version is quite decent too

[Penelope Stopit]

How does anything run down the threads?

[donkmeister]

I use the plusgas in a tin, and for awkward areas I use a syringe with a blunt needle (I buy them in packs on ebay). Dip the needle into the can, fill up the syringe and then you can squirt it into really tight gaps.

[donkmeister]

Penelope Stopit said:

How does anything run down the threads?

When you cut threads they don't mate perfectly, there is always some room between the male and female thread; this is called thread tolerance, it's designed in, and defined in the standards for the various thread types. Without this built-in looseness you'd find a lot of combinations of nuts and studs very difficult to tighten or loosen. I believe thread tolerance is even present with interference threads but couldn't swear it.

Plusgas and similar concoctions all have very low viscosity so can get into these very small gaps, and they are drawn into those gaps through capillary action.

[Wiry PAYE]

Not familiar with this particular engine but if the plugs are easy to access then get the engine to max temperature( not just a little trip round the block but a good long run)before trying to remove them this can make all the difference between make or break.

[imagineifyeswill]

They are very prone to corroding to the extent they just shear in these particular engines.

[markcoznottz]

Penelope Stopit said:

How does anything run down the threads?

It doesn’t it’s bro science. As someone else pointed out, they corrode into the head, two dissimilar metals causes galvanic corrosion. Plus most are quite fine threads, and you really don’t want to be shearing glow plugs it’s a nightmare. The only reliable way is to cherry red them and squirt with cold water, this shocks them out the same as exhaust studs. The best thing is an induction heater, failing that a torch, but be careful not to damage anything in close proximity.

[Penelope Stopit]

markcoznottz said:

Penelope Stopit said:

How does anything run down the threads?

It doesn’t it’s bro science. As someone else pointed out, they corrode into the head, two dissimilar metals causes galvanic corrosion. Plus most are quite fine threads, and you really don’t want to be shearing glow plugs it’s a nightmare. The only reliable way is to cherry red them and squirt with cold water, this shocks them out the same as exhaust studs. The best thing is an induction heater, failing that a torch, but be careful not to damage anything in close proximity.

Thank you bro

[donkmeister]

Penelope Stopit said:

markcoznottz said:

Penelope Stopit said:

How does anything run down the threads?

It doesn’t it’s bro science. As someone else pointed out, they corrode into the head, two dissimilar metals causes galvanic corrosion. Plus most are quite fine threads, and you really don’t want to be shearing glow plugs it’s a nightmare. The only reliable way is to cherry red them and squirt with cold water, this shocks them out the same as exhaust studs. The best thing is an induction heater, failing that a torch, but be careful not to damage anything in close proximity.

Thank you bro

Really not bro science; it's observable, it's repeatable.

The heating/quenching approach mentioned does essentially the same thing - reduces the friction in the thread interface by increasing the thread clearance. But, heating the crap out of stuff isn't always safe, especially with a naked flame.

[InitialDave]

Donk is correct, the difference in tolerance bands between an internal and external thread mean that an assembled thread does not become a single lump of metal, and the creeping nature of penetrating oils is so they get down in there to help with lubrication.

If you're particularly bored, BS3643 is a typical standard for metric threads and you can compare the tolerance limits for different thread classes in there.

[markcoznottz]

donkmeister said:

Penelope Stopit said:

markcoznottz said:

Penelope Stopit said:

How does anything run down the threads?

It doesn’t it’s bro science. As someone else pointed out, they corrode into the head, two dissimilar metals causes galvanic corrosion. Plus most are quite fine threads, and you really don’t want to be shearing glow plugs it’s a nightmare. The only reliable way is to cherry red them and squirt with cold water, this shocks them out the same as exhaust studs. The best thing is an induction heater, failing that a torch, but be careful not to damage anything in close proximity.

Thank you bro

Really not bro science; it's observable, it's repeatable.

The heating/quenching approach mentioned does essentially the same thing - reduces the friction in the thread interface by increasing the thread clearance. But, heating the crap out of stuff isn't always safe, especially with a naked flame.

Thanks mr logic. The difference being my method works, you really really don’t want to snap a plug of in one of these engines, taking the head off is a nightmare, as is getting the broken stump out. Heat is a mechanics best friend. Rothenberger type torches with mapp gas can generate enough heat, hardly anyone uses oxyacetylene any more.

[Penelope Stopit]

donkmeister said:

Penelope Stopit said:

markcoznottz said:

Penelope Stopit said:

How does anything run down the threads?

It doesn’t it’s bro science. As someone else pointed out, they corrode into the head, two dissimilar metals causes galvanic corrosion. Plus most are quite fine threads, and you really don’t want to be shearing glow plugs it’s a nightmare. The only reliable way is to cherry red them and squirt with cold water, this shocks them out the same as exhaust studs. The best thing is an induction heater, failing that a torch, but be careful not to damage anything in close proximity.

Thank you bro

Really not bro science; it's observable, it's repeatable.

The heating/quenching approach mentioned does essentially the same thing - reduces the friction in the thread interface by increasing the thread clearance. But, heating the crap out of stuff isn't always safe, especially with a naked flame.

Ok I've got it, was under the impression that the glow plug to cylinder head faces created a seal

[InitialDave]

A glow plug is threaded in like a spark plug, but does generally have a washer on it to seal.

Injectors are more commonly a plain fit into the head with a sealing washer, held down with a separate clamp or flange.