I will admit to breaking a hold down bolt. I popped the injector up and out. Then unscrewed the broken bolt with my fingers. It ain't the end of the world...but where are you going to get the replacement bolt you now need? I had a couple of engines to scavenge off of, but the average guy does not.

 

Loctite 243

 

I was trying to look up what Grade and size the bolts are but none of the descriptions given for Ford Part F4TZ9R523A say. Even the people selling the injector hold down bolts have no specs other than the length.
From what I can gather it is an M5 bolt since it has an 8mm head. The torque ratings will depend on the Grade.
Anyone know for sure?

 

I'd guess 12.9

 

Guessing won't do any good here. A fairly simple test with a vice and some scrap iron/steel drilled and tapped with another chunk of scrap to bolt to it and a nice torque tool should tell you the torque it broke at. Maybe someone can do a dry test and a lubricated test. Loctite counts as a lubricant!

 

I wonder if it would sacrifice a head. If one of those bolts was cranked down to the point of total failure a number of things could happen. 1) Bolt break above head, removal would not be difficult. 2) Bolt threads strip off, not a major problem. 3) Head threads strip out, that one could be a problem.

 

Have you used a torque wrench to find out how much torque it takes to loosen an old injector hold-down bolt? I have... with a Delco Digital Torque Adapter. I don't think I've ever seen factory torque over 100 in-pounds.



140 is pushing the limits of the bolt, but the saving grace it the hold-down plate - more on that later.

Heat cycles are the cause of the difference in original torque and end torque - that is precisely why hot-torquing has been so effective for those who have tried it. You might find skeptics in those who haven't tried it - but not in the list of those who have.

The thread locker is not ineffective at head temperature (rarely above 100 degrees C), but it can dip as low as 75% of original strength at max temp of typical operation while towing.

The vast majority of us don't have the calibrated arm that registers the difference between 100 in pounds, 120 in pounds, and two pieces.

The torque on the rocker arms is 20 ft pounds, but that is a different configuration. I don't recall the size of the bolt - but it may be worth looking up.

The injector hold-down is more likely to break while tightening than it will down the road - again... the configuration has a lot of "impact" on this. I'll explain later.

I have used a wide array of torque wrenches - mostly out of curiosity. I can say that they not only nail the torque value, but some of them "drift" in value - particularly those of the Horrible Fright variety. I've been checking the accuracy of their settings with my Delco torque adapter while it was locked in a vice.



Absolutely. T-shirt earned - it's in the drawer. Air gun clears the oil nicely.

Yeah... air gun, unless you're thread lockin'

Last link in my signature - the typing smiley. Click that one. Powerstroke folder - and grab the engine assembly PDF. The torque spec is 10 ft-pounds, but I would use the 240-250 in-pound wench recommended earlier in the thread.


I looked specifically at the cure time without activator - because it takes time to warm the engine before the final torque.

The injector hold-down bolt is not the same thing as most of the other bolts - it has a tapered head. Believe me when I tell you I've tried everything to get those things to stay put.



Here is the final piece in the puzzle that is so easy to overlook - like the jigsaw puzzle piece that's the same color as the table top: The Injector hold-down bolt is not holding the injector down directly - it's holding down two ends of a see-saw. The bolt is about 1 to 1.5" from the contact point that actually touches the rim of the injector - effectively making the hold down bracket a "spring" that holds 2800 PSI at bay. If the spring comes up even a tiny bit, it's gunna slap back down with a resounding thud. The sewing machine sound of the engine comes from not letting that spring up in the first place.

 

Sorry, i didn't mean to add to the confusion, official torque spec for the injector hold down bolts is definately 120inch pounds. My post on the 35 foot pounds was meant to show the highest spec i could find for the hold down bolts holes in the heads to show when theads might begin stripping out, not a torque for the injectors.

I went to the same torque as Byron, and my bolts felt like they were less than another 10in pounds from stripping or snapping. And i did not go that high lightly, or quickly. I spent months reading thru thousands of threads, anything Google could produce on the subject, days researching torque wrench brands to eventually use, and cross checking bolt torque tables.

 

Went for a short drive this morning and the truck does sound much quieter than before.

 

finally found the lil bugger

The hold-down bolts are M6-1 grade 10.9, which in the table is specced for 133 in-lbs dry but only 99 in-lb when lubricated.

Thread

 

Thanks. I searched in vain trying to find those specs.

According to the Engineering Toolbox the maximum torque rating for the M6 grade 10.9 bolt is 17 Nm, 12.5 ft/lbs or 150 in/lbs
https://www.engineeringtoolbox.com/m...ue-d_2054.html

That might explain why people are getting away with 140 in/lbs of torque. Of course these stats would only apply to "new" bolts and not those that had been repeatedly heated and cooled for 20 years as well as re-torqued multiple times.

 

I believe part of the problem is that you have to tighten the bottom bolt to spec first (like Jason I too rarely use a torque wrench on stuff that calls out for such low torque rating) if you tighten the bottom bolt first to spec then the top bolt (oil spout side) to spec then there will be no need for a hot torque. I too had a problem with a hot torque was necessary, not no more, I have done a couple of sets since then with no problems.

 

There are few places that I'll use a torque wrench. Inside the engine, cylinder heads and the nut on the HPOP pretty much sums it up. I have not touched my injectors yet.

 

I worked on a truck today for a customer. While doing glow plugs, I checked the injector hold down bolts. The passenger side bolts were much looser than the driver's side. I did not get an exact torque value, but they were more than 80 and less than 100. I do not believe they have ever been touched. Totally stock '00 F350 dually. 168k miles.

 

That's about what I find in every untouched engine I've come across - and a number of times that I didn't hot-torque my aftermarket injectors.