How F am i? Cross threaded injector threads in prechamber
 

Hello, everything was going fine until today when taking an injector off and trying to put it back in it wont go in. I discovered the upper threads were completely gone and cross threaded. Will i need a new head?
The image is here: https://files.fm/f/g3k629z24r

Ouch! I suspect if you can locate him there is a guy out there who can fix it.

What engine is it please?

I think you could just replace the prechamber and the injector, no?

It is an OM602 engine.

How hard is it to remove the prechamber?

I have several 602 heads.
I THINK they all have prechambers that can be replaced when damaged.
I have the pc removal tool as well...

Be sure to remove the glow plug first...

First the big warning that I myself forgot. The glow plug has to be removed before the prechamber comes out.

If your prechamber retaining ring has 2 big slots for the removal installation tool the injector threads are in the retaining ring and a new ring is the fix with its new threads. And there is no absolute need to remove the prechamber from the cylinder head.

If your prechamber is splined as in the below ad the Injector threads directly into the top of the prechamber. Remember, if you remove the prechamber the glow plug is the first thing to come out.

https://www.taiwanautotools.com/Product/Detail.aspx?id=1331

From your picture you have the splined retainer and that means it is the top of the prechamber that is stripped. The puller uses the threads on the prechamber to screw the tool into to pull the prechamber out.

The question is going to be after the glow plug is removed and the retaining ring is removed if there is enough threads left to allow the forced needed on the tool to pull the prechamber.

Post number 1 has a picture of the prechamber tool and the thread sizes.
http://www.peachparts.com/shopforum/diesel-discussion/263938-question-about-precombustion-chamber-pulling-tool.html

One way to go would be at blast with an air gun to get any chips out. Put a small rage in the bottom and degrease the stripped area with brake cleaner and do the same with the proper end of the puller tool. (After the glow plug and the retainer ring are removed.) Coat the inside threads of the prechamber with slow curing JB Weld and the threads on the puller. Screw the puller in and just tighten it a bit. Give it the full cure time like till the same time next day. If it is cold out, you need to find some way to heat it to at least close to room temperature in order to cure the epoxy.

Laser Tools is an English Company that has tools made for them in China. From the ones I have used would say they tools are good quality. They are sold on US eBay.

Thread in the slide hammer, after removing the glow plug, and hammer out. Not a big deal if the threads are ok. Thing is, even the slide hammer can damage the threads. The angled injector setup isn’t great for removal. The threads are weak.

I’d chase the threads on the prechamber. And be prepared to have to cut new ones and use some kind of adapter to hammer it out.

One would think that there is a Mercedes special tool out there for the stripped thread issue. But maybe not.

It is hard to pick what to do when you are not there.

In theory if the threads were nonexistent if your adapter has long enough threaded area someone could get a skinny arc welding rod and weld it to the lip of the prechamber.

The other option is to rethread the inside of the chamber and make a puller adapter to thread into that.

Another option is removing the cylinder head and driving the chamber out.

Any cross thread or thread damage would require change of the prechamber anyway.

I have the OE MB slide hammer. Its threads are somewhat weak themselves.

When I had an un-removable head shield, and it ruined my prechamber, I didn’t have a great ability to get the hammer threaded on. I forget why but the prechamber threads weren’t great. It all worked out. If not, rethreading the prechamber would have worked. Then the new bolt thread would just need to be adapted to the slide hammer.

https://i.imgur.com/K3Rs3HEl.jpeg

https://i.imgur.com/HTlRGpll.jpeg

Might be time for a full blown automotive machine shop
 

I remember growing up; my father was a master auto mechanic. However, once in a while he required a full service automotive machine shop for a particular repair. In those days some of the NAPA auto parts stores also had a full service auto machine shop. They had expensive specialized auto machine shop equipment on the ready and they could perform just about any service you might need.

I don't know if NAPA still has these machine shops because I haven't seen them for awhile, however it might be worth inquiring about. Also, you will probably need a flat bed to tow your car to the machine shop and be prepared to leave it for a week. One thing about it, you could screw this one up to the point of no return which means you would have a very expensive boat anchor on your hands. At least a competent (check out their trust pilot and yelp.com reviews FIRST) machine shop could get you back up and running.

I have a metal cutting lathe assuming it is still working I can drill down the center of something like a bolt and get a tap stated into it straight if not doing the whole tapping job on the lathe. Few have that.

The next best option is putting the bolt in a drill press vice and using the drill press. That does not guarantee the hole goes down the center, but the hole will be parallel to the sides of the bolt even if it is off center.

If I had to drill into a bolt head with a handheld drill motor to tread it for a slide hammer for sure I would not get it straight down the middle. How much that would effect it in use I don't know.

Next is that most people don't have a 5/8x18 tap and proper sized drill hanging around their workshop. That is the size the autosome free large slide hammers used to be threaded for.

If someone cannot do any of those it is pulling the head off or towing the car to someone who can do the job.

I don't know if it possible to get something down in there to hook onto the ball pin. Not read of anyone exploring that idea.

A machine shop is a great resource, but this is being overthought. Those prechambers are robust. Not much of anything can fall from the bottom due to the design. Retread the prechamber, make or weld a tool to attach the new thread size to a slide hammer, and remove the prechamber IAW the FSM. No boat anchors here. It’s pretty simple.

The hardest part of one does not weld, would be making a tool that fits. I would look at the right new thread size and see if a piece of rod or a big bolt could be turned down and then threaded to a slide hammer. Or else weld two together.

Yes, if someone feels confident in their abilities I say go for it. Since the price of a remanufactured cylinder head isn't cheap, it might be worth finding a competent auto machine shop.

My father was a trained diesel engine mechanic. Anyone who witnessed his mechanical magic knew that there wasn't too much he couldn't fix or repair when it came to cars, trucks, SUVs or heavy diesel powered equipment, i.e. Caterpillar tractors, etc. And yet, there were a few times along the way he towed his machinery over to the NAPA machine shop. In those days, NAPA machine shops always delivered.

I’d chase the threads on the prechamber. And be prepared to have to cut new ones and use some kind of adapter to hammer it out. krnl.fun
hdstreamz apk

another idea; you could heat up the head/prechamber using a map gas torch before trying to remove it. After removal, it might be possible to literally weld the slide hammer tool to the prechamber. I'm not a welder however I have seen some welders work magic on various projects. If all else fails you could remove the cylinder head then work to remove the prechamber from the underside. Even then, laying down some MAP gas torching to the underside of the cylinder head might help.

Here is my idea in motion:

1. Cut heat shield material using a template to fit properly around the pre combustion chamber. The heat shield is to protect the cylinder head when using a welding torch.

https://www.amazon.com/Fireproof-Resistant-Retardant-Material-Plumbers/dp/B096LS732Y/ref=sr_1_10?adgrpid=1341404756023098&hvadid=83838036847828&hvbmt=be&hvdev=c&hvlocphy=97282&hvnetw=o& hvqmt=e&hvtargid=kwd-83838154234422%3Aloc-190&hydadcr=8431_13498573&keywords=welding%2Bblanket&qid=1706399613&sr=8-10&th=1

2. Take a one inch round steel rod (you will need to take a digital caliper and measure the interior diameter of the pre-combustion chamber so you can purchase the correct size steel rod) and weld to the end of your slide hammer.

https://www.amazon.com/Steel-Round-Diameter-Length-Rolled/dp/B0CJ1D9NSM/ref=sr_1_5?adgrpid=1346903217163823&hvadid=84181737580652&hvbmt=be&hvdev=c&hvlocphy=97282&hvnetw=o&h vqmt=e&hvtargid=kwd-84182401640438%3Aloc-190&hydadcr=26077_13566981&keywords=1+round+bar+steel&qid=1706398846&sr=8-5

3. Take the one inch round steel rod and insert into pre combustion chamber. Weld the one inch steel rod to the pre combustion chamber. Allow to cool overnight.

4. You can get a syringe from your local animal supply complete with needles so you could inject Kroil Oil directly around the pre combustion chamber. allow it to sit overnight and then put some more Kroil Oil in it the next morning.

5. next day use your MAP gas torch to heat up the cylinder head around the pre combustion chamber.

6. Use your slide hammer to remove the precombustion chamber.

7. Install a new pre combustion chamber.

this idea will involve some fitting and thinking. Also, it may end up costing you a slide hammer by the time you weld the one inch steel rod to the slide hammer.

I think the issue is there is no easy way for a typically equipped and adperson someone mechanically skilled to do it at home.

A regular automotive machine shop is not going to have the large taps or a means of making an adapter to attach the slide hammer.

In order to weld something to the prechamber someone needs to be a skilled welder to get down in there and not damage the head and only weld what needs to be welded. Once it is welded it is already hot.

I regular machine shop can re-thread and make an adapter to attach the slide hammer but that is expensive.

Make sure the glow plug is removed and the prechamber retaining collar before you start.

suggestions. Make sure your auto club is such that you can get 2 fee tows.

You go to autozone or someplace where you can get the free rental slide hammer, the large one. You need like a 5 pound weight.

You take the long saft part of the slide hammer to the hardware store and find a Rod Coupling which is essentially a long nut that will fit the slide hammer. See the attached pic. The far left one is a rod coupling.

You take the rod coupling and if you need to grind or fil off a small portion of the hex corners on one to fit inside of the prechamber. Attached is a mockup of that in the middle picture.

You need to discuss what you want done with a welder. You tow the car to a welder. The welder welds the Rod Coupling to the prechamber where I put the red lines but of course all the way around it.

After the weld cools enough to solidify while the prechamber is still hot thread the slide hammer into the Rod Coupling and use it to pull out the prechamber.

When you pull it out it will look something like the last picture.

Note that the per-chamber pictured is from a 617.952 and it may be slightly larger. I am not very good at welding and I think there is enough room for even me to get inside there and weld it

That’s a great work up but I don’t think you even need that. The threads could be redone with a helicoil or time sert, if it fails after the pullout so be it. It could also be threaded into the narrow lower shaft, below where the heat shield sits. Just tap it. Maybe even 5/8” rod would fit there.

Lots of options before needing to get a machine shop into this.

And if we are talking about hiring welding services, I’d just find the right thread that we could cut into the prechamber and then make a piece that fits a slide hammer offsite. Tap the prechamber and move forward.

I think your option is a few failures distanced from the first step OP should take :)

If it all fails, then agree with the approach. Is there something that OP would then want to request or mandate as best practice since they would be welding on the head? Is a cheap wire flux welder ok for this (both parts seemingly being “heavy”, or is MiG or TIG needed?

apparently, rod coupling also comes in a round format versus the standard hex design:


https://www.amazon.com/s?k=rod+coupling&ref=nb_sb_noss


a round rod coupling design might be easier to weld to the prechamber.

Callie appears to be some sort of spam bot.

Did you get the prechamber out?

Welding something like the coupling nut shown to the inside of the prechamber should shrink it as it cools. Old trick we used to use for pulling bearings that wouldn't even press out, weld around the inside and then as the weld cools they just fall out.

I would probably try a Helicoil first if available in the right size.

Never use a cheap wire flux welder anywhere inside an engine compartment or near threads of any sort. Too much spatter. MIG as the minimum requirement, IMO. I would try this with my MIG if I had exhausted other options.

Whenever removing chambers/injectors/glows I always idle the engine until everything is hot, if it can be run. Much better chance of success.

The threads on his prechamber are what center the injector so it will seal on the heat shield. I don't see any way to create a precision hole and precision tap the prechamber and also that thins the walls of the prechamber.

The shrinking part after the welding may not help as there is a like 1/16 area under the prechamber lip that is take up by an aluminum spacer. After that there is about 1 inch of prechamber body below that that has some press fit to it and the tip of the prechamber is a somewhat loose fit in the bore in the head and that fills with carbon and around the tip gets coats with some carbon and other combustion deposits.

So, it is really the deposits and the body press fit that hold it in.

Anyway, the method you speak of is likely the cheapest way to go. You have the cost of the rod coupling and the cost of the welder. The slide hammer is a free if you return it.

If you have auto club towing the car to the welder would be free if they are local.

If you made a deal with a auto repair that has a good welder on site they may tow the car for free.

Again, make sure the glow plug is removed before pulling the prechamber and you need a special socket to remove the prechamber retaining ring and to torque it when the new prechamber is installed. Those sockets don't cost much.