injector over-torque - PeachParts Mercedes-Benz Forum

carneades · #1 11-10-2019, 08:52 PM

I recently replaced my injectors on an 83 240D. This was my first time doing it. I purchased re-built injectors with Monark nozzles from a reputable (I think) source, and followed instructions published by a different reputable source. The instructions, however, contained a typo: "Install the injectors and torque to 70-80Nm foot pounds." For reasons that are now beyond me, I simply assumed that it meant to say "70-80 foot pounds" rather than "70-80 Nm". I have since realized my mistake.

Is it urgent that I remove them and re-torque to 59 foot pounds? Or, if they are going to get damaged by this, is the damage already done? I'm unclear about the mechanics of how over-torquing can damage the nozzles, so I'm not sure how much I should panic, or whether re-torquing them would be pointless now.

Jarod · #2 11-10-2019, 09:11 PM

Re-torquing would be useless in my opinion, the crush washers/heat shields are one use from my experiences. I had quite the nightmare of carbon buildup and quite possibly nozzle damage from reusing them recently.

carneades · #3 11-10-2019, 09:23 PM

I have extra heat shields; that wouldn't be a problem. I'm just short on spare time. I also have no garage or indoor workspace, and it's getting cold where I live, which makes the hard-line wrench dance a lot less fun. I'm just wondering how much I should prioritize this over other tasks to get it done before winter sets in properly, or whether it would be futile now that I've already over-torqued. I'll likely be learning how to re-build injectors sometime next summer, and could get new nozzles (if these are damaged) and go at it all again then.

Diseasel300 · #4 11-10-2019, 09:37 PM

If you don't have a lot of runtime on the injectors, re-torquing should be done ASAP. The destruction to them is cumulative in the form of accelerated wear and possible pintle seizure. If this is something you just did, correct it now and you shouldn't suffer any ill effects.

carneades · #5 11-10-2019, 10:00 PM

I installed them last weekend, and have put about 200 miles on them. I couldn't possibly get to this before next weekend, and another 200 miles. But if it is cumulative damage -- that is what I wasn't sure about --then obviously it should be done ASAP. Thanks!

ah-kay · #6 11-10-2019, 10:22 PM

You over torqued the body of the injectors or installation into the car. I wouldn't worry too much about it if it is installation. injectors body probably is ok too.

carneades · #7 11-10-2019, 10:45 PM

Installation into the pre-chamber. Conventional wisdom is that over-torquing damages the nozzle, but I've never seen an explanation for why, which is what led to this post. Do you have a reason for thinking it wouldn't lead to damage? Curious about the thinking behind alternative views.

ah-kay · #8 11-10-2019, 11:07 PM

Can't see why over torqued into the prechamber can damage the nozzles. Doesn't make sense. You may have issues removing it down the road, the prechamber may stick to the injectors when you unscrew it. It happened to me before. The injectors body can be over torqued with no ill effect. Not my opinion. See post #5 in the link.

http://www.peachparts.com/shopforum/diesel-discussion/122334-tech-specs-injectors-torque-bar-pressures.html

Diseasel300 · #9 11-10-2019, 11:32 PM

Over-torquing the injector halves won't hurt anything. Too much torque and you'll crack the injector body. Over-torquing into the prechamber can cause problems over time. The injector nozzle itself crushes and deforms the heat shield to form a seal. Not only does the heat shield seal combustion gas from escaping, but allows a very slight spring action to allow the injector nozzle to expand and contract with heat cycling. If jammed down in the bottom of the prechamber, that expansion can't take place, the result is rapid wear to the pintle or potential seizure. It's happened and is well documented elsewhere on the internet if you care to look into it. I doubt driving 200 miles will do any measurable damage, but if you have the spare washers and an hour of free time, pop them out and do the job properly, if for nothing else just the peace of mind.

Diesel911 · #10 11-10-2019, 11:41 PM

Installing new heat shields and re-torqueing them would no do any additional damage if there is any.
Also get a magnifying glass and look for a hair line crack on the Injector sides of the treaded part.

However, when the injectors are out look at the threads on the Injector and the threads inside of the Pre-chamber retaining rings. Take a good look because the rings seem to be rather softer then the Injector.

ah-kay · #11 11-10-2019, 11:42 PM

The heat shield is > 2mm thick. Can't see how one can FLATTEN the heat shield by over torquing it. I would not worry about it. However, if it makes one feels better then by all means retorque it.

Diseasel300 · #12 11-11-2019, 09:18 AM

Quote:

Originally Posted by ah-kay

The heat shield is > 2mm thick. Can't see how one can FLATTEN the heat shield by over torquing it. I would not worry about it. However, if it makes one feels better then by all means retorque it.

Nobody said anything about flattening the heat shield. Over-torquing will remove the residual spring left in the lip seal. It's the same reason you can't re-use a heat shield.

Why are we even arguing about this? It takes <30 mins to pull all 5, drop in new shields, and torque properly. Do it once, do it right.

ah-kay · #13 11-11-2019, 11:01 AM

Nobody is arguing. I am just saying don't worry if one over torqued into the prechamber. The injectors probably were tightened by 1/8 to 1/4 turn. No big deal. The sky is not falling.

carneades · #14 11-11-2019, 11:32 AM

Quote:

Over-torquing the injector halves won't hurt anything. Too much torque and you'll crack the injector body. Over-torquing into the prechamber can cause problems over time. The injector nozzle itself crushes and deforms the heat shield to form a seal. Not only does the heat shield seal combustion gas from escaping, but allows a very slight spring action to allow the injector nozzle to expand and contract with heat cycling. If jammed down in the bottom of the prechamber, that expansion can't take place, the result is rapid wear to the pintle or potential seizure. It's happened and is well documented elsewhere on the internet if you care to look into it. I doubt driving 200 miles will do any measurable damage, but if you have the spare washers and an hour of free time, pop them out and do the job properly, if for nothing else just the peace of mind.

Diseasel gave the kind of explanation I was looking for, and it seems plausible, given that it derives from the logic behind crush washers generally speaking. But even if fears of over-torquing are inflated, I'll re-install them so I can sleep at night. There's no sense worrying about a pintle seize when an hour's labor will make things right. As I said before, the main reason I raised the question was because I didn't know if I had already damaged the injectors by over-torquing, or if reverting them would prevent damage. And that question has now been answered to my satisfaction. Thanks for all the help, everyone!

Diesel911 · #15 11-11-2019, 02:42 PM

My thought was to check the threads on the Injector and the Pre-chamber Retaining Ring which the Injector threads into. And of course to see if it cracked the Injector Nozzle Nut.

If you look at that attached picture where someone used and alternative measure to remover the pre-chamber rings (a Chisel?) you can see that the pre-chamber rigs are soft.
Since the rings are soft that is where one would expected damage threads if the Injector was over torqued. So that is a good place to look for evidence of the threads being distorted/pulled.