broken injector hold down bolt (fixed)

promisberg

2004, t1n, 3/4t, 140-shc
2004 T1N OM-647 motor.

Here is one solution to a broken injector bolt in the head. Dealer said they would pull the head-no thanks, other local merc mechanics had no special tools for this job and had not fixed this issue.

First, Thanks to all the other posters on injector seal - black death subject all was helpful. Had I followed other suggestion more closely perhaps I wouldn't have broken the bolt during removal! (PB blaster soak, remove with engine hot, tap sharply, if stubborn gently go back and forth). I will say that these bolt break very easily as I definitely was being gentle. My repair started with needing to replace the injector seal, others have fully discussed that so will not explain my nuances here. Other than if the injector is out or fuel line open etc. cover them.

To the point:

#1, order Time-Sert sprinter injector hold down bolt kit. (5ea 17mm deep x 6x1 thread inserts, extended drill, tap and insertion tool)

#2, go to Ace hardware or a hobby shop and buy thin wall brass tubing of 5/16" and 9/32" diameter. The smaller one should be a nice bag fit in the bigger one and the hold down bolt should fit loosely inside.

#3, buy PB blaster and find a straw that fits.

#4, Tools: cordless drill (note this was on #1 cylinder so easy access for me, you may need angle drill), compressed air W gun and super fine tip, I used spray can straw that fit in my air gun, Tallish tap handle, paper towels, powerful small LED light I used my petzl head lamp, possibly need a mirror.

#5, part off 6" sections of the brass tubing and cut 4 slots 1/16" deep on one end. This makes micro brass core drills.

#6, With the hold down fork out of the way, I could see that I had to slightly oversize the hole in the valve cover so I could access the full diameter of the counter bore in the head. You may or may not have to do that. The injector can be in place until tapping. Spray some PB baster in / near the counter bore for the bolt. Chuck up the 9/32 tube drill, I used a rod inside it so the chuck wouldn't crush the tube. Start gently drilling down through the tar/carbon going both directions. I was going around a 1/4" at a time then spraying PB and blowing out into the paper towels then fresh PB in the hole. eventually you will hit the bottom of the counter bore.

#7, now add the 5/16 core drill to the outside of the 9/32 and repeat above until the counter bore is totally cleaned out. You may notice at this time that the 5/16 tube bag fits nicely in the counter bore. Discovery of this procedure was not by design but perhaps divinely inspired or just dumb luck. I was actually preparing for a different procedure / drill guide for using 1/8" left-handed aircraft drill.

#8, part off 4.5" of each size tube and slide them together and insert into the counter bore. This makes a very simple and highly effective drill guide that just happens to fit the Time-Sert drill with a loose bag fit. I was initially a bit worried about the fit but if it worked this saved making another tool and possibly having to do the time-sert anyway.

#9, I started drilling / pecking very gently 1/32" at a time inspecting to confirm I was staying in center. Once I was sure I was on center then I was drilling, removing drill and guide, cleaning all chips from tools and the hole every 1/8" to 1/4" then re-oiling drill tip. I noted that when chips were loading down in the hole the inner brass tube would push up slightly so used that as a guide as to when to clean out. OK you know the drill (pun intended) repeat for this 3.5 or 4 hours! One note is that once I started drilling below the counter bore in the head and into the threaded section the drill grabbed the bolt and tightened it into the head further. Gentle is the key because don't want to drive the bolt into the water jacket. Ultimately the bolt fragment bottomed and I finished drilling it out.

#10, DO THE MATH correctly so you don't drill into the water jacket. When you start getting close you can adjust the chuck on the drill shaft so that it hits the top of the drill guide at measured intervals. I went literally 1mm at a time near the bottom and that paid off as I was able to get all the bolt out and see the factory machining in the bottom of the hole.

Final thoughts were that if I made the 1/8" drill guide on the lathe the the bolt would have spun out and threads were likely still good. However ultimately I prefer the insert anyway because it is more durable. Now I know that the Time Sert procedure doesn't take long so will likely do that when I have to change another seal / injector.
 

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greguseubankus

New member
Thanks for your post! I will likely have to drill out my injector bolt as the bolt head sheared off and the bolt is fairly stuck after trying many other methods of getting it out. Only question is, what is the purpose of cutting the 4 small slots on the bottom of the brass guides? I understand the concept of a core drill and the need to be able to get the guide further down the hole as its slightly larger than what the drill bit is removing but the brass insert isn't rotating with the drill bit is it?
Thanks!
 

shenchman

Member
thanks to all previous posters!
i successfully removed a 2006 T1N OM647 cylinder 1 broken hold down bolt yesterday using a similar method & thought i'd add a few details/modifications others might find helpful:

-i bought 5 new injector bolts here
https://europarts-sd.com/item.asp?cID=386&PID=3922

-torque spec is 62 in-lbs = 7 Nm + 90 degrees to stretch. i used a low-range torque wrench:
https://www.amazon.com/gp/product/B000S7ZRYY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

-the oem bolts require an extended shaft T40 torx driver to clear interference from the exposed top of the injector body. a short T40 3/8" socket barely fit but at an angle which seemed would risk stripping the torx bolt head. i bought this kit:
https://www.amazon.com/gp/product/B006E5P8YI/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

-my bolt broke 58mm down on the 78mm oem bolt length, leaving ~20mm in the head about 58mm down the hole.

-you'll need an extended left hand drill bit & extractor to reach down the hole, to clear the thickness of the hold down fork + to provide ~2" minimum clearance above for the drill chuck to clear interference from the exposed top of the injector body.

-the longest readily available 'jobber length' left hand drill bit i found online was 2-1/8" long which is not nearly long enough. i ordered an extended 12" long left hand 5/32" HSS drill bit from here:
5/32" AC-12L
https://www.icscuttingtools.com/catalog/page_110.pdf
to buy, search https://www.icscuttingtools.com/shop/search.php for 'AC-12L' & add to cart.
i had to buy (5) bits to meet minimum order $, total with shipping was ~$55.

-i had to cut off ~4" of the drill bit shaft to fit my drill + bit below the headwall in line with the bolt hole. luckily it was cylinder #1, cylinders further to the rear likely require the bit to be cut shorter &/or a right angle drill or drill adaptor.

-the inner diameter of the bolt hole is nearest to 17/64" on my drill bit index that i used to measure, so any drill bit centering guide or extractor needs to fit in that size hole.

-instead of the double brass tube drill bit centering guide from previous post, i rummaged around my local Ace hardware store with 5/32" drill bit & drill diameter gauge in hand & found that a 1/4" x 2-1/2" steel 'tension pin' was the perfect inner & outer diameter & length for a guide given the length of broken bolt remaining in my head. make sure that the guide will protrude above the top of the hold down fork when fully inserted down to the top of the broken bolt so you can easily remove the guide from the hole. pictured, same as this:
https://www.amazon.com/Hillman-Group-44318-Tension-10-Pack/dp/B00IZFWF9Q

-reverse drilling went well, i dripped some kroil down the hole first to lubricate the broken bolt & some cutting fluid for good measure, drill on slow speed & in reverse with as much down pressure as i could apply. i drilled about 1cm into the broken bolt. the reverse bit drilled but didn't bite/extract the bolt as it seems others experienced.

-i made an extended extractor using an extended 3/32" allen key. i cut off the short L portion of the allen key & used a grinder wheel to taper & flute the tip of the remaining straight/long portion so it would fit/wedge/grip in the 5/32" pilot hole in the top of the broken piece. see pics.

-the 3/32" allen key didn't fit inside the drill bit centering guide i used, so i just held the extractor as centered as i could & tapped it with a hammer into the pilot hole, observing that i'd managed to tap it ~1cm into the 5/32" pilot hole.

-to turn the extractor i used a 1/4" drive screwdriver + bit holder + 4mm socket hex bit which fit/held the top of the 3/32" allen key perfectly, see pics. it took some torque but the extractor held & turned out the broken bolt easily.

-as others have done, i made a fluted thread cleaner out of an old full length hold down bolt using a dremel tool + grinder wheel, see pics. i made 3 flutes which worked well with 2-3 cleaning repetitions, observing that much grunge/metal bits came out. beware stripping the aluminum female threads in the head towards the top of the hole where the oem bolt threads start to engage the head when you use the cleaner, apply downforce!

-i blew out the hole before & after using the fluted cleaner using an air gun with a small diameter nozzle, this air gun nozzle fits & reaches the bottom of the hole:
https://www.amazon.com/gp/product/B01DCHA3R2/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

-beware stripping the aluminum female threads in the head towards the top of the hole where the oem bolt threads start to engage the head. i managed to strip the top 2-3 rows of threads on 2 of my bolt holes, likely my fault for not applying enough downforce before full thread engagement when installing them. i used the fluted bolt cleaner to retap the threads as best i could, using as much down pressure as i could muster to avoid using the existing threads to drawn the bolt down as much as possible. when installing the new bolts, i also applied as much force as possible on the top of my ratchet to avoid the same. this was dicey but it worked & i was able to fully torque the new bolts to spec (62 in-lbs = 7 Nm) + another 90 degrees.

-if anyone needs help near San Francisco CA USA you're welcome to borrow my kit.

Sacha
 

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Midwestdrifter

Engineer In Residence
A reminder, if you use an old bolt to make a quick-n-dirty tap, run the bolt through a die, or use a thread file to clean of the thread edges. This prevents you from accidentally removing material from the head threads if the cuts fold over any of the thread on the bolt.
 

nebwoodman

2004 T1n cargo bought new 1/2020 has 78K ml.
Very thankful you guys posted your fixes as it gave me some encouragement to fix mine.

Dumb me.... bought a Horrible Freight 1/4 in torque wrench (China garbage) and broke my #4 injector bolt off over tightening.

It was a tough-nerve racking fix being #4 back where mirror and flashlight is needed just to see darn bolt hole bottom.

Found some scrap brass 7.5mm diameter for sleeve then added an inner nylon sleeve (mechanical pencil innards sanded to fit) sized tight enough for 5/32 bit to rotate freely with no sideways play. Essential since I couldn't or didn't pre punch broken bolt head...

Used a jobber 3" (approx) length LH 5/32" drill bit from NAPA and cobbled an extension to clear the engine. Used a right angle drill and Irwin ST-1 straight flute extractor along with appropriate 1/4 drive sockets.

Used the broken bolt along side new bolt to gauge depth so to not drill too far.

What a relief when it came out and with no thread damage. :)
 

newtub

New member
I'll share my experiences with a broken bolt briefly. After pulling injector and cleaning all off the area including the debris out of the threaded hole for the hold down Bolt, I proceeded to torque the bolt 2 the specified foot pounds. Except I got confused between foot pounds and inch pounds and ended up over torquing the bolt and breaking it. Stupid. Because it was in a freshly cleaned out and even lubed up with grease hole , I was able to drill a small hole in the broken off shaft and tap in a mini screwdriver and thread the bolt out that way.
 
I also was victimized by that terrible Harbor Freight 1/4” torque wrench. Ten months later, and I’m struggling with a failed time sert probably about to pay someone to put in a new head.
 

Midwestdrifter

Engineer In Residence
It may seem a bit crazy, but I have epoxied knurled metal inserts in a few situations with good success (not JB weld!). Measure the hole diameter currently, then have a machine shop make a slip fit sleeve/insert internally threaded for the hold down bolt. clean the damaged head hole up (redrill if necessary to the max allowed) then epoxy the insert in place. put a bolt in the insert with a bit of grease on the end to prevent the threads or bolt getting stuck to the epoxy. With a couple inches of good contact, a steel insert should hold fine.
 

Aqua Puttana

Poly - Thread Finder
It may seem a bit crazy, but I have epoxied knurled metal inserts in a few situations with good success (not JB weld!).
...
That's fine. You should offer a couple of alternatives though.

I would suggest that knurling your insert, and running a tap even part way down will provide some tooth for most any *working temperature* appropriate epoxy. A brass insert would be easier to machine and is at least as strong as the original aluminum threads. Dissimilar metals will not be a problem with epoxy included in the mix. Using knurling and partial tapping would probably allow even that nasty old school JB Weld to work.

These epoxy repairs being successful depends heavily on techniques and everything being clean/properly prepped.

:2cents: vic
 
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Midwestdrifter

Engineer In Residence
That's fine. You should offer a couple of alternatives though.
DP420NS/DP460NS should work fine. Shear strength is about 1,250psi at 180F. There are stronger options, but they require heat curing, which would be difficult in this situation.

Looking at the JB weld spec sheet, it has decent hot strength (higher than expected based on its cold strength). So it should work fine with a well prepped hole and long insert.
 
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