270 CDi injector shot out

jibcl500

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270 diesel, 5th injector has blown itself upward dragging the bolt and clamp with it, threads for the stretch bolt are gone so a new bolt wont night, anyone suggest the right bolt to replace it, I know I have to retap the hole but I will still need a bolt.
jib
 
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andy@pcd-ltd

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It all depends on what size its retapped and helicoiled to the place i use to do my head repairs supply the correct size bolt togo in it as well.

Who are you going to get to repair it because if they can supply you with the spec of the size of the thread a company called orbital fasteners do the perfect size bolt to go in it and it has a 7mm allen key bolt head on it which works perfect for that sort of job before. If you want the original bolt to go back in i cna supply you the part number for that

What has caused it to come out in the first place
 
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jibcl500

jibcl500

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Im fixing it as its a customers car, the injector blow out last night and took the bolt and clamp with it.
The threads for the bolt are gone nowt left to bite to, Mercedes helicoil the hole and use the same but new bolt, Ive heard it can be tapped out to a larger size and then a bigger bolt fitted, I need to know the bolt size and does anyone or have they done this, I assume Sam unit possibly has in the past.

jib
 
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andy@pcd-ltd

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I tend to go for the bigger bolt option as its a lot stronger.

But i dont carry out the repair myself as its easier and quicker to let my local engine machine shop do it for me and the usually only charge about £60 to do it for me
 
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jibcl500

jibcl500

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So whats the spec on the bolt you use?
jib
 

Alex Crow

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it will be an m7x1.00. i would go for a double helicoil or timesert and the original bolt as it is supposed to be a stretch bolt, think on.
 

5pares

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In the past Ive drilled the hole to 7.5mm and tapped an 8mm thread ,using 203 anti roll bar bolts to clamp it with.
 

kebo57

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Hi the origional bolt is a 6.0mm dia X 1.0mm pitch
I would re tap to standard 10mm x 1.5mm pitch then make a solid insert from stainless steel 10mm thread o/d & 6mm thread i/d bore lock tight it in then your back to a 6mm standard bolt

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Number_Cruncher

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>>I tend to go for the bigger bolt option as its a lot stronger.

How do you torque it down? - a bigger bolt - a bolt with different material properties will apply a different load to the injector compared to the MB bolt.

I think the note of caution sounded by AP above is very wise.

I would drill and tap for a helicoil which would then accept the standard bolt.

I'm beginning to suspect that a possible root cause for all of these failures is that the cylinder head material is not sufficiently strong, and the female threads are prone to pulling out.

As a helicoil increases the area of parent material being sheared (both by virtue of working at a larger diameter, and by virtue of better load sharing between threads], it reduces the shear stress in the threads, and hence produces a stronger joint.

As I've written before in aerospace applications, it is standard practice to heli-coil aluminium parts from new, and it's automotive cost cutting that sees female aluminium threads being used.
 

exeng

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i will supply you an insert that enables the use off standard parts so you can use correct torque settings you can also install in the original position and it has a much higher pull out strengh and you still have the stretch in the bolt.
 
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jibcl500

jibcl500

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All sorted, thanks all, I tapped the hole bigger and used a bigger bolt. It took some time to tap all the way down but it worked in the end, due to the increased size of the bolt I had to guess how tight to take the bolt and to be honest I put the thing in pretty tight, it wont be coming out in a hurry thats for sure.

I assume steel inserts should have been standard engineering practice but mercedes bean counters could see the savings by not fitting them hence the problem of the female threads pulling out.

The force of the injector breaking free has damaged the engine cover quite badly. Theres a lot of force when one of these goes pop.

Thanks again all and in future I will do the same repair as I think it is far stronger now than when it left the factory.
jib
 


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