Hi Team,
I feel if you study the lower end of the chamber shown with the Install/Remove tooling fitted in the scan you may see that the chamber is threaded as is usual for a screw in chamber--also in the text it says that these chambers are NOT fitted with the usual Hex for the Hex bar type removal tool so suggesting that the chamber is a screw in chamber.

I have done a fresh scan with my later scanner--hope it is clearer-- but the picture is dark in the 8th Edition (1953 Revised) Caterpillar Service Tool Book, Form No :- 30146-01.

EDIT :- link to a previous discussion on these Pre-chambers back in 2013.

www.acmoc.org/bb/showthread.php?18347-D-2-injector-settings

Cheers,
Eddie B.

Thanks Edb for the info. I saw the picture of the pre cup with threads at the bottom and also the “driver” to install non threaded Pre cups. If there was a driver then SOME precups must not be threaded - yes ?

I am not with my parts at the moment ( they are home alone !) but I will check the following :

The outer most ( or upper) threads in my prenup are conventional right handed. I turned my injector counter clockwise to remove it. As I speculated at in an earlier post, could it be that the Inner (or lower) threads are left handed ?
This would facilitate using the outer threads to install the precup and the inner threads to remove it.

Hmmmmm. When I get home I will look at the part numbers you supplied and compare them to the part numbers my tractor “should” have ( injectors, pre cups)

Thank you for contributing the information

Press in type pre, chambers use a saddle type injector and pre, chamber retaining system.
Without the saddle retainer the compression would dislodge the chamber .
At least that is how I see it.

Great point Andrew. Because my injector threads into the Pre Chamber, threads must hold the prechamber in place.

Sorry if others tried to ‘splain this to me and I could not absorb it. I get it now.

Hi Tognot,
as far as I am aware what Andrew says above is correct that a bridge style hold down clamp is used to retain both the Injector and the Pre-Chamber.

I will go out on a limb here and say that due to the small size of the D3400 D2 engine that all early J D2"s would be screw in injectors as also would be the Pre-Chambers that use the double threaded installer/remover tooling--later PC's fitted to the later D3400 engines would use the conventional hex tooling.

One could reasonably assume that the early PC could be replaced by the hex type PC in the early engines fitted with the double thread PC's--they both use the same upper O Ring seal and lower copper sealing washer although the heads have a different P/Number.
PC's for S/No's 5J1 to 1239 use a 2A5745 PC, and 5J1240-up uses a 5B9658 PC in their 3 3/4" Bore engines.
My Special Instruction for using the later hand pump type 5P4150 Cat Nozzle Testing Group show 2 possible Injectors for the 3 3/4" bore engines, namely :- 2A5750 and 5B9237 and both are the type with the big retaining nut as used for screw in chambers.
The difference with the two injectors is the method used to lock the needle lift adjust and the upper cap as can be seen in the scan below from said Spec. Instruction--the actual injector Valve Service Grps. in each injector have a different P/No also.

Parts Book checks show that early designs of larger engines--D4-up-- used the bridge system until Engineers designed the screw in Pre-Chambers and Injectors for them by my Parts Books.

I stand to be corrected by someone who has fitted later PC's into an Early D3400 cyl. head.

I do recall being asked about the double thread tooling when I was in Tech Service Dept and not being able to locate said tooling in the Dealer Tool Crib--I guess they welded something onto the PC to extract it--never heard back for an update.
Cheers,
Eddie B.

I checked and found the lower or innermost threads on the PC are left handed. They are 12TPI.
If the injector threads are 1 3/4” what would the very next smaller step be ? It is also the an imperceptible smaller size.

Thanks for all the input. Here is a better pic of my PC with both thread sizes visible.

Hi TOGNOT,
Thank You for the excellent pic that shows the two threads in question. I also have never seen a two threaded pre-chamber--only the description and Tool Book picture of the tooling needed to Install/Remove them--clears up a lot of unasked and answered questions for many of us.
Thanks,
Eddie B.

So I ordered Some snap ( telescoping)) gauges to Determine accurately the size of The threads in the inner most part of the PC.
My measurements read 1.535”. A 1.5 “ bolt shank should be 1.531” based on charts I have looked at.

I am therefore assuming I need a 1.5” bolt, 12 threads per inch AND left hand thread. This would be my prechamber removal tool. I have looked for way too long online, and sent an email to McMaster Carr , no reply yet.

Before I ruin the pc with a more aggressive removal ,,remember I don’t KNOW it is bad, I’m only removing it because it would be easier than pulling the head to rule out a head gasket leak. If I can’t remove the PC ill pull the head. If the head/ gasket looks good then maybe I’ll have better luck with welder/ heat etc on the PC .

I m all ears if anyone sees something I missed here before I commence to pulling the head

You guys were right head gasket was fine. One of the pc s in the head has been replaced with a hex style. Ill assume the remaining 3 are original.

At least I have some options with the head off. If I can’t get it with what I have in my shop I can transport to a machine shop.

Anyone know of a source for pre chambers ? I have not checked yet but thought I would ask..... illl get em out eventually !!

I have some pre chambers here that have had a large nut welded to them to allow a means to turn them for removal.
Although this may mean sacrificing the chamber. They may be able to be reclaimed by cutting the weld if desperate.
I am not home at present so I can't post a photo