OM648 injector hold down bolt - PeachParts Mercedes-Benz Forum

MB140300SD · #1 03-11-2023, 07:05 PM

I am replacing the number 1 injector as it is returning too much fuel. The hold down nut has a nut on top of the hold down piece using it as a spacer. This is also the case on #5 and 6. Apparently the bolt does not go all the way into the bore. I have cleaned out the hole, used a small screwdriver to try and dig out any crud in the bottom of the hole and it seems like it is hitting metal to me (not crud). Still the bolt will not go in all the way. I am wondering if there is a piece of broke off bolt from a previous repair down in hole, which is why it feels like the screw driver is hitting metal at the bottom. If its not actually metal and a whole bunch of crud, what is the best way to clean it out? Small drill bit ran slowly down the bottom? If its a piece of broken bolt, what about that? I do not really like the idea of using a nut as a spacer on top of it.

ah-kay · #2 03-12-2023, 06:43 AM

Measure the hold down bolt.

Bolt Dimensions M6 x 79mm

You are supposed to replace it when removed. It is very unlikely the bolt is broken inside. Also clean out the thread real good. You should be able to thread down the bolt all the way down by hand.

MB140300SD · #3 03-12-2023, 10:19 AM

New bolt measures right about the same as the old one per visual comparison. This guy apparently had a piece of the bolt break off in the hole:

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

TimFreeh · #4 03-13-2023, 12:11 PM

Quote:

Originally Posted by MB140300SD

New bolt measures right about the same as the old one per visual comparison. This guy apparently had a piece of the bolt break off in the hole:

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

Sure seems like he had the bolt break off down at the bottom of the threaded section. I'm kind of surprised to see that since the bolts that hold down the clamps are stretch-to-yield bolts. The section of the bolt right at the top right below the driven part of the M6 bolt seems to be narrower that the bottom threaded section if I recall correctly. If the bolt was going to break it seems like it should break at the top narrower section?

I've changed a bunch of these seals and never had a problem, the torque spec is 7Nm+90 degrees 2X as I recall? There was a you-tube video of some guy changing his seals and he apparently thought it was 70nm as the initial spec because he kept twisting away with a 3/8 torque wrench until the bolt just snapped off - it broke on the narrow shank and he was able to remove the bolt by hand since the threaded section below was intact. The bold didn't separate in the threaded section.

It's not a good sign that someone was in there and apparently used a nut on top of the injector hold-down clamp as a spacer. That would sort of indicate to me that whoever was doing the repair didn't have the knowledge or desire to lookup the correct procedures and therefor didn't replace, or worse yet, just used some random M6 bolt in an application that's engineered for a stretch to yield bolt.

If I were in your shoes I'd remove the valve cover and inspect all the injector hold down bores. They should be all the same depth, any that are different will need to be investigated further.

The guy in your referenced You-tube video used a Timesert repair insert - that's a high quality permanent repair. The free-hand drilling is more than a little scary - hopefully you don't have any broken bolts remnants in the bores.

MB140300SD · #5 03-13-2023, 08:57 PM

I went ahead and installed the new injector using the nut spacer deal. When I have more time I will probably pull all the injectors, valve cover, and sort it all out properly,

engatwork · #6 03-13-2023, 09:24 PM

Anytime you pull an injector that has been leaking inspect the "seating" surface of the injector closely. Ive had one in that was leaking and after cleaning the injector I noticed that there was a crack in the seating surface.