Removing D4 Pre combustion chambers

With the head off, you can clean the tiny bit of the chamber that sticks into the combustion chamber and spray some kind of penetrating oil on them and let them soak for a while. I know some have used air wrenches on them, and that might not be a bad idea, since the shock might break it on loose better than a long pipe. I wouldn't keep unscrewing it if it doesn't break free and come easy, instead respray the threads and go back in a bit before trying to come out again. That's most likely when you will be removing threads. If it comes easy, and the threads are damaged, that's probably one someone else did sometime before and installed it back into a damaged hole.

Clean em good and anitseize them before you reinstall.

Cheers for the advice guys, Much appreciated,

I thought about a small amount of heat But was worried I might crack the head,

what about also using a 10lb hammer and a drift to shock it before attempting to unscrew it ? or would that possibly fracture the pre com?

Regards Simon

Simon - Heating the head in the area around the the precom thread is O.K., to assist with removal. A lot depends on whether the previous installer used anti-seize .. and you can pretty well guarantee they didn't. In which case, there will be corrosion between the head and precom threads.

Heat is the best thing to break down rust. However, let the head cool before trying to unscrew the precom, to allow some expansion, as the heating will effectively shrink the threaded hole in the head. Once it's cooled some, soak the thread area in penetrant, and leave it overnight if possible.

The two biggest worries are .. A .. threads 'picking up' (galling) and tearing the thread out of the head .. and B .. the end breaking off the precom .. leaving you with the job of drilling and removing the remnants of the precom. Either one is not a pretty scenario, and you can best avoid either scenario, by using some modest heat (just barely dull red) around the thread area, to degrade the corrosion bond.

The precoms come out best with a big rattle gun .. however, if you don't have one, a length of cheater pipe on a 3/4" or 1" drive bar is the next best idea. Make sure the head is well secured when you try this. Most precoms will soon start talking when this kind of persuasion is applied.

DON'T hit the precom with a 10lb persuader and drift .. you're liable to fracture the precom where the threaded section meets the body. Some heat down the centre of the precom when you are waving the gas-axe around, will also assist with rust bond breakdown, but once again, let it cool to a modest temperature before applying any removal pressure.

I have used a little heat,that worked on two chambers.I drilled out the chamber threaded end and then cleaned up the thread.The threads were great.
Always use antiseize compound when refitting them.
Martyn
Out of interest are they available from Caterpillar and what at what cost?

Thanks Oz and Marty, a great help

I will use the gas axe and WD40 over the next couple of days as I have a weeks wait on parts
I have a rattle gun or I can use a cheater bar on the 3/4 set,

I just hope the rattle gun won't snap the chamber as that is my worst nightmare😮
I will keep the hammer out of my hands😄

Marty yes the pre combustion Chamber are still available for the D4 6U
They are $50 Aussie each and the part number is
2S1273 ( 1 piece chambers without glow plug holes)
Pre com Removing tool is 5F8353 and is about $20 Aus

you will also need the bottom steel gasket and the upper o-ring, I don't have the part # for them yet , but when I do I will post it here for you

Simon