Butchered injector threads - PeachParts Mercedes-Benz Forum

octanematt · #1 11-09-2022, 01:04 AM

Best way to fix this? It came out pretty easy using my Torx socket as I didn't realize someone had changed it out. So it wasn't that tight. And there was some sizeable metallic debris in the hole after I got the bolt out. Doesn't seem like it was doing much and the injector seems pretty stuck. In fact it look like it might be held in with JB weld...

My thought was to get the injector out and then properly fix the hole so I can use the proper sized (metric) bolt rather than the 1/4" one that was kind of in there.

How big can I drill the hole to effect the repair??

octanematt · #2 11-09-2022, 02:42 AM

The 'new' bolt is 5/16", not 1/4" (and not 8 mm).

There was a small roundish chunk of metal in the hole when I removed the bolt. I assume it was in there already but tough to imagine there was enough room for it and the bolt. I removed it with a magnet. Remnants of a broken bolt perhaps?

I'd like to get the injector (#2) out to further investigate but it's pretty stuck. I had #5 out and it was able to pull it out by hand. This one will be more difficult.

JHZR2 · #3 11-09-2022, 08:19 AM

I don’t know what we are looking at. One picture of an oily surface, one that looks like a prechamber hole, one that looks like two screws.

What exactly is busted?

I had issues with a stuck injector heat shield in my 602 this summer. Wouldn’t come up and ended up ruining the prechamber. Had to remove the old prechamber, get everything super clean, and then reinstall. Took two tries…

octanematt · #4 11-09-2022, 10:38 AM

First picture is the area just next to the injector. The second is the injector hold down bolt hole threads--it looks like there's a 5/6" helicoil in there.

The 'oily mess' is hard as a rock. Almost like someone had epoxied in the injector because the replacement bolt only engaged a couple of threads.

Murkybenz · #5 11-09-2022, 03:11 PM

Good practice to use the correct size bolt (factory) as it expands at the same rate the cylinder head does , aftermarket bolt like the one you have got out expands at different rate and eventually strips the threads and escapes doing damage to the threads.
Engine is an om642 ?

resto108 · #6 11-09-2022, 05:47 PM

Middle pic looks like the tail hasn't been broken off the helicoil

ah-kay · #7 11-09-2022, 09:18 PM

Don't butcher up the hole.

If you don't know what size is the bolt then leave it to the professional. You don't want to replace the head, $$$$. It should be 6mm metric. After the clean up or repair, you should be able to thread the new bolt all the way down by hand. If you can't, check again and again. Good luck.

Diesel911 · #8 11-10-2022, 12:35 AM

Quote:

Originally Posted by Murkybenz

Good practice to use the correct size bolt (factory) as it expands at the same rate the cylinder head does , aftermarket bolt like the one you have got out expands at different rate and eventually strips the threads and escapes doing damage to the threads.
Engine is an om642 ?

He/she should give that info.

If it is an OM 642 and the bolt is what holds down the injector clamp, I thought I read or saw an ad for a re-threading kit somewhere.

Diesel911 · #9 11-10-2022, 12:51 AM

If the helicoid has been damaged it can be replaced of the parent metal is still sound.

The problem is going to be if a US, SAE helicoid was used compared to a metric one. In that case it may be already oversized to the point that the correct sized metric insert will not work.

Not on a Mercedes. When I had that problem of the hole to big to be reused and there were no commercial inserts, I took an oversized bolt and drilled and taped for that and I cut the threaded part of the bolt off and put it into my lathe and drilled and tapped it for the correct sized bolt.
I got the correct sized bolt and 2 nuts. I threaded that into the homemade insert and used the 2 double nuts as a stop. You are going to use that to thread the insert in. I degreased that insert outer threads and the threaded hole with brake cleaner and let it well evaporate.
I coated the insert outer threads with the slow curing JB Weld, slow curing because it can take heat that the fast curing one cannot take, and I screwed in the insert.

I let that cure and loosened the double lock nuts and unscrewed the bolt and it was good to go.

I realize that most people don't have a lathe. But having in insert made is cheaper compared to removing a cylinder head.

The hard part is drilling the hole in the cylinder head straight.

In the last picture is the longer bolt the stock one that was supposed to be there?

Diesel911 · #10 11-10-2022, 01:02 AM

I don't know if this is the correct kit: Laser 6958 Injector Clamping Bolt Thread Repair Kit - for Mercedes-Benz
The kit comes with 5 inserts.
I don't know if the hole is too big to be drilled and rethread for the new inserts.

Don't know how much drilling can be done till you hit the coolant.

Diesel911 · #11 11-10-2022, 01:09 AM

Injectors hold down thread repair.

https://www.youtube.com/watch?v=wn0nEmz2YtE

Note this is the other type of more minimal drill and tap kit.

octanematt · #12 11-10-2022, 05:33 PM

2008 OM642 in Mercedes R320.

I imagine the engine had black death at one point on #2. Someone tried to remove the injector hold down bolt and it broke off. Rather than removing the broken bit, they helicoiled the top portion of the hole for a 5/16" bolt (about 8 mm). The engagement wasn't great, so they used JB weld to help seal/hold the injector. Or at least that's my theory.

I've had no luck with a small slide hammer so I have a bigger one. And I'll put some heat to it. Once the injector is out, I will work on hole repair. The bolt wasn't that tight so I think the JB weld is largely holding it in place and will need heat to release.

I now have a short 5/16" bolt with a pilot hole. I'll screw the bolt into the helicoil, and then use the bolt to guide left-handed drill bit to drill into the broken M6 and start the extraction process.

Once it's all said and done, I have a feeling I'll end up with a Timesert.

I assume the M6 hole in the head is threaded right from the surface? How deep is it approximately?

If I replace the threads with steel, then 10mm of engagement should be sufficient. If the threads start at the same spot, then the distance from the first thread to the clamp will be the same, so the clamp load/spring should be the same as OEM. Mercedes added an extra 90 degrees of torque to the bolts so it wasn't very well engineered from the start anyway.

Diesel911 · #13 11-11-2022, 09:29 PM

Quote:

Originally Posted by octanematt

2008 OM642 in Mercedes R320.

I imagine the engine had black death at one point on #2. Someone tried to remove the injector hold down bolt and it broke off. Rather than removing the broken bit, they helicoiled the top portion of the hole for a 5/16" bolt (about 8 mm). The engagement wasn't great, so they used JB weld to help seal/hold the injector. Or at least that's my theory.

I've had no luck with a small slide hammer so I have a bigger one. And I'll put some heat to it. Once the injector is out, I will work on hole repair. The bolt wasn't that tight so I think the JB weld is largely holding it in place and will need heat to release.

I now have a short 5/16" bolt with a pilot hole. I'll screw the bolt into the helicoil, and then use the bolt to guide left-handed drill bit to drill into the broken M6 and start the extraction process.

Once it's all said and done, I have a feeling I'll end up with a Timesert.

I assume the M6 hole in the head is threaded right from the surface? How deep is it approximately?

If I replace the threads with steel, then 10mm of engagement should be sufficient. If the threads start at the same spot, then the distance from the first thread to the clamp will be the same, so the clamp load/spring should be the same as OEM. Mercedes added an extra 90 degrees of torque to the bolts so it wasn't very well engineered from the start anyway.

Scary but unscrew one of the other injectors hold down bolts to see how much goes inside of the head.

Unfortunately experience wise I am stuck bac in 1984 when my 300D was made.

Find some Youtube vids on helicoil removal and there is some on removing the stuck injectors.

I would be using PB Blaster (which they sell locally at Home Depot) or Kroil to try to soak that into around the injectors.