Broken injector bolt, what torque on Time-Sert w/steel bolt?

[Mike Rancourt]

I have a broken injector bolt (#3). Many people use/recommend Time-Serts (for example: here, here, here).
However, if you go to the manufacturer's website, you find that the kit everyone uses and ID Parts sells is now labeled "Obsolete," and they recommend instead using a kit called "Big Serts." The main difference is that the "Big Sert" uses a (potentially shorter) M8 hardened steel bolt instead of the stock M6 stretch bolt. This is probably great because that hardened M8 is going to be a lot more reliable.
However, nowhere in the instructions does it say anything about the proper torque for the bolt. With the old kit, it was simple: 62 in-lbs + 90 degrees (or 180 degrees). As is well discussed in Vic's legendary black death/injector thread, the 90 or 180 degree turn is stretching the bolt.

My Question: I have to assume with the hardened steel (non-stretch) bolt in the Big Sert, the proper thing to do is torque to 62 in-lbs and do no more turning. Does that sound right?

FYI:
1. Instructions for the older kit others have used can be found here
2. Here's the text on "obsolescence" from the Time-Sert website: "KIT p/n 1610E2 OBSOLETE We now offer 5812D below." The description for part number 5812D says, "Dodge sprinter / Mercedes injector hold down clamp bolt BIG-SERT OVERSIZED If you have a broken bolt at the bottom of the hole the 5812D will also take care of that problem. We now put an oversized BIG-SERT at the top of the head but you must use a larger M8x1.25 grade 8 bolt you can purchase separately at your local hardware store."
3. Here's a nice video on how to install Time-serts shared by another member.

4. This one is just for your amusement: I didn't break off the injector bolt the way you're thinking; not because it was "stuck" or because it was reassembled improperly. I had loosened the bolt in attempt to "pop" the injector (while driving 15 miles to Europarts SD to get my stretch bolts and copper seals, BTW), and when I wanted to tighten it again, I unwrapped my brand new cheap-o 1/4" drive in-lbs torque wrench, set it to 62 in-lbs, and promptly snapped the bolt. It turns out the wrench has an on-off switch. I never knew torque wrenches had that. I guess I just got lucky every other time I used a torque wrench that the person before me left it "on." Haha. This mistake has cost me a couple hundred dollars and many hours of work, and I'm not even done. But at least you can laugh at me for it. Ooops.

 

[220629]

I've never seen an On-Off either.

You didn't ask this.

I'd be concerned that after proper torque the OEM TTY bolt continues to act a "spring" to accommodate heat/cool cycles during operation. A bolt from "local hardware" will not have that design. Not to mention that a bolt from the local hardware may not meet any real specifications.

vic

 

[Mike Rancourt]

I'd be concerned that after proper torque the OEM TTY bolt continues to act a "spring" to accommodate heat/cool cycles during operation. A bolt from "local hardware" will not have that design. Not to mention that a bolt from the local hardware may not meet any real specifications.

Good points. I wonder if there is an M8 stretch bolt option. The older "obsolete" design seems simpler.
Mike

 

[Midwestdrifter]

Changing bolt size inevitably changes the clamping force. I would use the torque value in the manual. DO NOT perform the stretching angle steps.

 

[Mike Rancourt]

I sent an inquiry to Time Sert and got a reply:
Sent: Wednesday, July 31, 2019 6:30 AM
To: contact01@timesert.com
Subject: Subject

Name: Mike Rancourt
Email: xxxxxxxxcc
Phone: xxxxxxxxx
Message: I purchased Big Sert 5218D to fix a broken injector hold down bolt on my Sprinter van. In the Sprinter community online, people speak highly of the "obsolete" 1610E2, which uses the OEM stretch bolt. However, the Big Sert option using hardened steel seems to overlook the purpose of the stretch bolt in the stock design and in 1610E2 Time Sert. As one member of a Sprinter forum wrote, "I'd be concerned that after proper torque the OEM TTY bolt continues to act a "spring" to accommodate heat/cool cycles during operation. A bolt from 'local hardware' will not have that design. Not to mention that a bolt from the local hardware may not meet any real specifications." So, I just don't know what I should do. I don't suppose you tested this before discontinuing the old part.
———————————
Hello,
No we did not do any testing on the BIG-SERT p/n 5218D we only offer the tooling and it has worked for customers that had broken bolts they could not remove.
If you want to buy the original 1610E2 we can sell it to you but there is no warranty on the tooling as people were breaking the tap and driver probably by bottoming out the tooling without correct measurements as you do not want to bottom the tools out. We sold the tooling for many years without any issue but as time went by we heard complaints so we discontinued it. So use at your own risk if you decide to purchase.

P/n 1610E2 price $118.24 Please mention quote 1028 so you can buy it.
——————————

 

[Mike Rancourt]

Well, I have to do this today, so I’m just going to use the steel bolt at 62 in-lbs and consider getting an M8 stretch bolt in the future if it seems to be a problem.
What symptoms would you expect to show up that would indicate the bolt is a problem? How will I know if it it’s a problem?
Mike

 

[Midwestdrifter]

The only issue you will have, is the injector combustion seal will leak. So make a note to check every oil change for leakage around the injector.

 

[Nautamaran]

In my opinion 62 inch pounds is unlikely to crush the copper seal sufficiently to create a tight seal. The 90 turn takes significantly more torque to accomplish...

If you have a spare seal, I’d suggest experimenting with assembling/disassembling the injector at progressively higher torques until you can see the seal has been crushed, then swap in a fresh seal and torque to that number.

For reference, the last crush washer I removed has a crushed thickness of 0.059”

Good luck,

-dave

 

[Midwestdrifter]

Okay, some back of the envelope math.

The MB bolt has a diameter of 5.26mm (0.207"). Its yield strength is between 640-940MPa. That works out to a clamping force of 13900-20400N or 3124- 4586lb-f.

We need the same clamping force from a 8mm bolt. Assuming dry threads (0.2COF), you would need to apply 32.5N-M of torque to get 20740 N of clamping force. Thats about 288 in-lbs, or 24 ft-lbs.

M8-8.8 bolts have a proof load around 4766lbf. So They should be fine at 24 ft-lbs. But they may stretch a bit depending on thread condition. I would go to 20ft-lbs first. Then sneak up on 24. If the torque stops rising, you are either stretching the bolt, or the insert has pulled.

Use at your own risk.

 

[Nautamaran]

Okay, some back of the envelope math.

The MB bolt has a diameter of 5.26mm (0.207"). Its yield strength is between 640-940MPa. That works out to a clamping force of 13900-20400N or 3124- 4586lb-f.

We need the same clamping force from a 8mm bolt. Assuming dry threads (0.2COF), you would need to apply 32.5N-M of torque to get 20740 N of clamping force. Thats about 288 in-lbs, or 24 ft-lbs.

M8-8.8 bolts have a proof load around 4766lbf. So They should be fine at 24 ft-lbs. But they may stretch a bit depending on thread condition. I would go to 20ft-lbs first. Then sneak up on 24. If the torque stops rising, you are either stretching the bolt, or the insert has pulled.

Use at your own risk.

My envelope agrees.

Still, since 32Nm is on the higher end of torque for 8.8 bolts (many tables recommend torquing to 30Nm), I would consider stopping to 20 ft-lbs (~16kN clamping force) and checking the seal thickness achieved.

Measuring a few new seals, their thickness is 0.059" across the radius (ie: one side), but since the seals are slightly conical they measure 0.062" thick across their full diameter.
My old #4 seal pictured above has been crushed flat but not compressed, measuring 0.059" across both the radius and diameter. My old #2 seal (replaced in 2017) has a flat thickness of 0.056"

So an alternative approach might be to put a dial indicator on the top of the injector, preload the M8 bolt to 62 inch pounds, zero the indicator, then turn the bolt until you either achieve 0.003" of compression, or hit 20 to 24 foot pounds on your torque wrench.

(It's perhaps worth stressing that the #4 seal pictured above had been leaking.
The head's seating surface was quite polished from a previous repair (as can be seen from the shiny ring on the copper seal). I used a bit of medium grit emery cloth stuck to a wood dowel to make concentric circular scratches in the bore before reassembly, with the idea that the copper would get a better interface with the scratches as it deformed. I used a similar technique when I replaced my #2 seal. New seal in #4 @ 184,000 miles, Sept 2018; #2 @ 155,000 miles, Feb 2017; Van now has 193,000 miles and is leak free for the moment...)

-dave

 

[220629]

Thanks for checking with the manufacturer.

...
———————————
Hello,
No we did not do any testing on the BIG-SERT p/n 5218D we only offer the tooling and it has worked for customers that had broken bolts they could not remove.
If you want to buy the original 1610E2 we can sell it to you but there is no warranty on the tooling as people were breaking the tap and driver probably by bottoming out the tooling without correct measurements as you do not want to bottom the tools out. We sold the tooling for many years without any issue but as time went by we heard complaints so we discontinued it. So use at your own risk if you decide to purchase.

P/n 1610E2 price $118.24 Please mention quote 1028 so you can buy it.
——————————

I'm not getting a warm and fuzzy feeling about that. Doesn't that = No data?

They had some complaints. They offer a new solution of a larger sized "local hardware" fastener, but didn't bother to take the time to test it??? How many new style units have been sold? How many hundred thousand miles have their customers put on the product to report back so they do have at least some type of data?

I really do believe that Bosch DID do some testing when they designed the hold down fastener type and torque spec for their fuel injectors. Is Bosch so stupid that it never occurred to them to move up one size on the fastener and walk down to their local hardware for a bigger bolt?

It all seems odd to me. But I'm just some guy on the internet.

Once the repair that requires a different fastener size/type is installed the owner has set their course and they are committed.

*****

Your newly installed untested bigger bolt didn't work as advertised?
A possible rescue.

Guys these are wimpy remedies and once the 6mm x 1mm thread pocket is damaged its a crap shoot trying to find a helicoil and/or or timesert of the length dimension to successfully hold down the bolt and get sufficient bite to extend the bolt into tension/torque yield .

Without the torque to yield condition the injector will work loose and start leaking the combustion gases all over again.
A big time waster.

I used to use an original bolt many moons ago filed with a side flat to clean out the carbon and crud from the threads but I now have taken to using an aircraft standard 8" long thread tap to thoroughly clean and recover the existing threads where possible.

The other big issue is a sheered bolt. It is very diffident to drill out the existing stub in situ without damaging the parent threaded bore!
Get too rambunctious and you run the very real risk of puncturing the cooling jacket.

Now a few years ago I devised a method that which I cobbled up in the shop.
The injector hold down bolt hole is a stepped hole wider at the top until the threaded step is encountered.
Using a 3/8ths drill I punched the hole out including the broken stub portion.
Now conveniently 3/8th is the standard thread tap size for 7/16 UNC which is 7/16 x 14 thread pitch. Once cleaned out it is easy to thread cut the entire hole to this final thread diameter blowing the swarf (chips) out with a shop line.

Now this is where your fab skills come in handy if you have some!
Take a 8.8 grade 7/16 UNC bolt and centre bore it to accept a 6x1 mm thread. I used a lathe but you could do this I suppose in a vice with some tenacity! OMG!
Cut the length to be at least one inch long.
Once threaded you can then part off the head and the threaded stub to make a grub screw.
Now put two lock nuts on the grub screw to hold it in the vice then cut a screwdriver slot in the top.
Try a good used old injector bolt into the thread, ensure it runs up and down freely. Grind down a 6mm nut to act as a lock nut then use the injector bolt to act as a driver placement tool.
Then use a screwdriver the place the grub screw firmly into the bottom of the threaded hole you have made.
This will allow you to refit the injector and bolt to the prescribed torque.

Now these days I use the Indians in Chennai; Gupta and Gupta Bros to make small batches of these in S/S with an allen placement female socket on the end.
Good machinists are Indians, and great to do business with!
"Not desperately cheeply but cheeply than many for small batch production quotas"
Must try to say this while wagging my head from side to side!
A suggestion to this dilemma!
कमबख्त आसान
Dennis

...
The parent hole is exactly the same size as a 7/16th UNC cutting size, so bore a thread all the way down into the hole.--yes 7/16th UNC
Now get a machinist to part off some 7/16ths threaded bar (thread stock) one inch (25mm) long and bore /thread the centre 6x1 mm. Now you have a perfect insert that will hold the bolt once you have cut a screwdriver slot in the end for placement. Blow the whole clean with shop air pre-lube and install by hand .
I have had some made up in SS and having a hex end for ease of install. Made in India 'cos i couldn't fin anyone in the US to tackle this machining exercise.
This methodology works the best and its my remedy for this repair exercise which can present some challenges and often results in lots of green clams exchanging hands to fix.
Dennis

I like the 7/16" UNC idea. My experience with fasteners in aluminum masts and other aluminum parts has me believe that a coarser thread in aluminum is better than a finer one. Eg. - 10-24 holds better than 10-32 even though there are less threads per inch.

Why not just use a 7/16 UNC ss steel bolt or mild steel all thread to drill and tap to 6x1 mm? Chuck the stock in a lathe and drill/tap. Then cut your screwdriver slot. I don't see where being more concentric than that is critical.

http://www.grainger.com/product/GRAINGER-APPROVED-18-8-Stainless-Steel-Threaded-WP168688/_/N-8k5Z1z0o3o3?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/29DH90_AS01?$smthumb$

Back to the Freightliner job.
...

vic

Carry on.

vic

 

[Mike Rancourt]

Thanks, everyone. I got the time-sert installed just before all the demands of my day caught up with me. I did not actually get to install the injector (still need to check the seal seat and clean it out). I hope to get to it tomorrow.
Here are a few notes for anyone doing this in the future:
1. The drill bit that comes with this kit is actually not long enough for a Sprinter (at least an OM612) unless you have a drill with a really narrow chuck to fit into the valley.
2. This mod DOES require enlarging the hole on the clamp. And that is not easy. My brand new cobalt bit had no effect on it.
I do intend to try that hardened steel bolt, but here's the thing: I didn't get a grade 8. I got a 10.9, so that envelope math seems great, but I am guessing it applies only to grade 8 (although I think I am going to try to get a different bolt before installing, anyway, and it might end up being grade 8.
A note on Vic's concerns regarding Time Sert not doing any testing: If you look at their language, they seem to see themselves as selling tools, not clamping solutions. I don't think they know anything about Sprinters or really claim to. And I believe the Big Sert was an existing product that they think Sprinters folks could use; whereas the older kit was too problematic to keep producing. I talked to a local(ish) Time Sert distributor today, and he didn't have any insight into stretch bolts or torque, either. Nice enough interactions with these people, but they just don't have answers to these things. They're not Bosch.
Mike

 

[Nautamaran]

Well, I have to do this today, so I’m just going to use the steel bolt at 62 in-lbs and consider getting an M8 stretch bolt in the future if it seems to be a problem.
What symptoms would you expect to show up that would indicate the bolt is a problem? How will I know if it it’s a problem?
Mike

I'm not getting a warm and fuzzy feeling about that.
...
vic

The use of a stiffer M8 is certainly not my favourite idea ever, but as Mike had indicated his intent to get this done today, I offered my best guidance. Torquing to 62 inch pounds was a guaranteed seal failure.

I certainly prefer Dennis’s solution over this M8 Big-cert offering. We can only guess at the reliability of Mike’s repair, but sometimes you dance with the one you brought...

I was of the understanding the Big-cert was simply a thicker walled product with an M6 internal thread. It’s disappointing to find out otherwise. With the Time-sert option off the table I’ll need to be extra cautious with my hold-downs in future... happily I’ve got machinist friends with lathes who would make the 7/16” insert for me if it ever comes to that (though drilling and tapping stainless can be a b**ch as the surface tends to work-harden, so you need to get under it with a course cut or risk breaking your tooling. This makes taps especially vulnerable as they usually make shallow cuts that end up recutting the hardened layer...)

Good luck Mike.

-dave

 

[Nautamaran]

Mike: I would do your best to find an 8.8 bolt. Going up to a 10.9 further increases the bolt’s stiffness, taking you further from the original M6 design.
The 20-24 foot pounds of torque is a guess based on thread pitch and bolt diameter, not the M8’s yield strength, so if you must use the 10.9 you can torque it to this estimate to achieve the presumed clamping force. If you have a dial indicator to measure clamping movement then all the better.

Based on the geometry and materials, I believe the M6 bolt acts as a spring clamp, contracting slightly during heating cycles as the aluminum head expands further upward than does the injector body, so the holding pawl moves upwards further than the shoulder on the injector. Without this stretch, your M8 bolt may loose clamping force at elevated temperatures. Or... the ball that the pawl rests on may move furthest upward, levering against the bolt and increasing the strain on the bolt, which is now stiffer and may pull out its threads?
So watch your repair closely during the first few warmup cycles.

Best wishes,

-dave

 

[Mike Rancourt]

I've never seen an On-Off either.

You didn't ask this.

I'd be concerned that after proper torque the OEM TTY bolt continues to act a "spring" to accommodate heat/cool cycles during operation. A bolt from "local hardware" will not have that design. Not to mention that a bolt from the local hardware may not meet any real specifications.

vic

Mike: I would do your best to find an 8.8 bolt. Going up to a 10.9 further increases the bolt’s stiffness, taking you further from the original M6 design.
The 20-24 foot pounds of torque is a guess based on thread pitch and bolt diameter, not the M8’s yield strength, so if you must use the 10.9 you can torque it to this estimate to achieve the presumed clamping force. If you have a dial indicator to measure clamping movement then all the better.

Based on the geometry and materials, I believe the M6 bolt acts as a spring clamp, contracting slightly during heating cycles as the aluminum head expands further upward than does the injector body, so the holding pawl moves upwards further than the shoulder on the injector. Without this stretch, your M8 bolt may loose clamping force at elevated temperatures. Or... the ball that the pawl rests on may move furthest upward, increasing the strain on the bolt?
So watch your repair closely during the first few warmup cycles.

Best wishes,

-dave

Dave
Thanks, again, for all your thoughts. So, maybe we ended up chasing a rabbit down the wrong hole here.
Is there any reason NOT to get an M8 stretch bolt? If that's what I should do, then, heck, I guess I should just do it. I have no idea how to find the right bolt--an internet search for "m8x1.25 stretch bolt" seems to yield literally nothing. This is one reason I haven't asked about it in the thread, but maybe I should ask. Anyone know where/how to find such a thing? BTW, I have to admit that I did not drill out the entire screw, so I actually need a bolt less than 60mm. I know, I'm sure this was the wrong thing to do. Life is hard.
Mike

 

[Nautamaran]

Based on MWD’s envelope, an 8.8 bolt will be close to yield at 24 foot pounds torque.
We haven’t got a true picture of the original M6 design basis, just conjecture, so in your place I would probably proceed with the M8 and monitor it for leakage. The big-sert has significantly more thread area engaging into the head, so is likely to hold the bolt down, but I mingle too closely with engineers to be able to freely say it’s guaranteed to work. Bolted assemblies are much more complex than they first seem, especially those with dissimilar metals and broad temperature ranges, but I don’t know that you are risking much beyond the seal leaking and having to revisit the repair somewhere down the road.

-dave

 

[220629]

... Bolted assemblies are much more complex than they first seem, especially those with dissimilar metals and broad temperature ranges, but I don’t know that you are risking much beyond the seal leaking and having to revisit the repair somewhere down the road.

-dave

FWIW.

My earlier post and concerns aside, I agree that it very well may work. Any risk is probably minimal. Mostly I was just a bit taken aback by a reply from a repair manufacturer that "No we did not do any testing on the BIG-SERT". Sprinter owners often need their truck to remain reliable.

Dennis' Fix. Stainless Steel ss vs mild steel.

I don't quite understand the need for a ss insert. The repair uses the OEM stretch bolt. The original threads are tapped into aluminum. The aluminum threads do sometimes fail, but for the most part they work as intended. The similar number of mild steel threads should be stronger than the aluminum.

SS doesn't corrode and is tougher, but are those properties needed? The OEM fastener is steel. I see no reason that the insert can't be mild steel. I envision using a bolt or a piece of all thread as the base stock.

Point me in the right direction if I'm wrong.

vic

 

[Midwestdrifter]

I personally would not use SS inserts in Aluminum. To much galvanic potential difference. I see no advantage to using SS over regular steel.

I see no reason that a M8 bolt in the non-deformed regime but properly torqued won't provide good service. The likely reason MB uses a stretch bolt, is that the clamping force is very consistent, regardless of thread lubrication, torque wrench calibration, etc.

Of course we are just guessing at the proper torque. The good news is that the M8 inserts threads are not likely to pull out of the head if your overshoot. I have seen a couple of repairs where a M8 bolt was used directly into the head, and it worked. So it can be done. In fact you could probably torque the M8 8.8 to yield, and still get good results. But I would avoid that on the off chance the threads fail.

 

[NORTON]

In the 05 service manual there are torque preferences for bolts according to bolt class, diam,thread,head type and use in cast iron or aluminium
http://www.diysprinter.co.uk/reference/05 service manual.pdf#page3

 

[Tflash09]

Hello all,

Are the time-serts in the Sprinters sunk deeper as the threads start deeper for the fuel injector bolt? Or do they remain flush with the top of the head? All time-serts are counter bored to to widen for the lip of the time sert?

thx