Broken fuel injection cylinder head temperature sensor bolt

[christyxy]

Hey there, first time post from UK. First time bug owner since a few months ago. Have been

I seem to have 'bricked' my FI bug by trying to change the cylinder head temperature sensor (CHT). The bug was running rich and I read if the sensor is corroded with poor ground/high resistance it can think the engine is cold all the time and run extra rich.

As the sensor was pretty corroded and really stiff, I used a deep well socket and was trying to undo it when SNAP! Think I'm screwed...

It looks like the bolt section of the sensor is stuck in there, probably the thread is corroded or something. In the final picture below you can see I got a reverse thread screw extraction kit on it that I'm thinking of trying with some penetrator spray... any tips or advice on how to proceed? I'm scared to try it just yet before seeking advice in case I make things worse!

I will try the reverse thread extractor in the final picture if I have to, but has anyone found a way to use a replacement sensor elsewhere in the engine? Maybe a sensor that will give similar resistance readings and trick the fuel injection brain to thinking its the CHT when it isn't??


Help!!

Cheers,

Christy

(This is her:
https://www.thesamba.com/vw/gallery/pix/2333439.jpg
https://www.thesamba.com/vw/gallery/pix/2333438.jpg )

[diamondblue1969]

Maybe drill it a little thinner , you don't want to break off the extractor tool
in there. There are thread repair kits if the exhisting threads are damaged.

[busdaddy]

Welcome!

Sorry to hear about your misadventure.

If the threads are so stuck that the head broke off the reverse thread extractor won't do anything but make a mess.
You'll have to drill it out, if you are careful you can drill bigger and bigger to just barely the inside of the threads and pick the remnants out like a coiled spring. Worst case scenario you go oversize and install a thread repair device like a Helicoil or Timesert, the threads are M10X1.0.
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[KKiley]

I was getting ready to post Busdaddy alert, haha.
That is the solution, you can fix it.
Kevin
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[Eric&Barb]

You could use a center punch or dull chisel to grab the edge of the stuck part and get it to turn, then and only then use the Easy Out. Tapping vibration should break up the corrosion and allow the part to move, it does help to use a good quality penetrating oil also. If you do not loosen up the broken bit first a EO is too easy to break off in there. Being that the EO is a hardened material it will be impossible to just drill that broken bit out. Personally spent MANY hours fixing that when someone broke off one or more EOs in flight and flight line equipment.


Link


Due to being made of brass, do not suggest trying to drill the remains out, unless you are good at regrinding the drill bit/s to work with brass. Otherwise you will end up breaking off drill bits....

Do use a little anti-seize on the new sender threads.
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[christyxy]

Many thanks for the advice so far. Think I will start with the chisel method, then try the easy out tool, then try the reverse thread drill bits in that order and hopefully one of them will get it sorted... The new part seems hard to come by in the UK too, I'm waiting for the supplier to confirm they've got one to send!

What a nightmare, hopefully can get it fixed before winter properly sets in as I gotta get it over to the garage by then!

[airschooled]

Once you’ve exhausted all your options this season, you can use a short jumper wire to bridge the white TS2 wire to any clean metal ground. The car will start, though it might run roughly until warmed up. I keep a wire permanently hooked up and waiting on my FI cars… helps with the quality of some sensors.

Robbie
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[KTPhil]

Something to look for is if the other side head has the threaded hole, too. Most replacement heads are universal and so the other one may be "virgin."

A longer wire, maybe some clever routing to avoid cutting tins, and you may be able to just abandon that broken off piece.

I assume Bugs are like Type 3s in this respect, and this may be the easy method.

[Eric&Barb]

[Eric&Barb]

Also it can help a lot to loosen that by first trying to turning tighter, then looser and repeat. Tightening just ever so slightly often crushes the corrosion. Either way once you get the broken part moving both ways even just a tiny noticeable bit you have won 90% of the battle. If it gets hard to turn as you are turning it out, stop and reverse course while applying some oil. Better to take the time to work it back and forth here and there than to get it to seize up. Which will gall the threads up, in essence micro welding the threads together.
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[MuzzcoVW]

When you get it sorted, use some NoOx on the threads. NoOx is something we use in the electrical trade and is made to stop corrosion while being conductive...unlike dielectric grease. I use it on mine and also put a dab in all my spade connectors when reassembling my car. Electrics work great now!

[VW_Jimbo]

[christyxy]

Hi all thanks for your messages and suggestions.

Chisel method did not work, nor did the thread extractor as it just kept churning the metal without extracting, so have had to resort to drilling out what is left of the temp sensor bolt... Have been using a left hand/reverse thread drill bit up to 8mm so far (pics below), was kinda hoping the anti clockwise drilling would rip the bolt loose but alas! It seems completely merged with the surrounding metal...

I'm going to have to go to 9mm with normal right hand/clockwise drill bits next (pics attached are from 8mm LH drill bit). Also I had to remove the air intake distributor pipes with the fuel injectors to get a straight shot at drilling it out... Nightmare so far!

Really hope after using the 9mm bit that I'm able to extract/pick out the thread like busdaddy suggested, but I think it will probably have to be repaired/rethreaded somehow

Comments or tips welcome. I will look at those suggestions for No0x grease, but am also looking at buying this to do the thread to M10x1 as was suggested? https://www.amazon.co.uk/gp/aw/d/B01CHRFLE8/

Cheers again!

Christy

https://www.thesamba.com/vw/gallery/pix/2334954.jpg

https://www.thesamba.com/vw/gallery/pix/2334953.jpg

https://www.thesamba.com/vw/gallery/pix/2334952.jpg

[VW_Jimbo]

Use some heat to break the corrosion bond, then try twisting it out. Without heat you are trying to twist out solid aluminum! Just a little heat can help ALOT!
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Jimbo

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[christyxy]

Ok I've made some progress: After drilling wider and wider, I managed to pull part of the broken bolt away from the top of the thread (see picture 1, just above the drilled out sensor well you can see part of it)

I'm a bit worried that I can't drill any deeper to get the rest of the bolt out though, as there seems to be a small hole that's appeared... Does this mean I've drilled too far and into the cylinder head itself!? or is there a small well beneath the sensor bolt?

So far the new sensor will only screw in 1/3 to 1/2 of the way (see pic 2 below), so the good news is that the top of the thread is in tact, but not sure how to proceed with uncovering the rest of the thread yet given the small hole,

I also bought a thread tapping device (pic 3) but have since realised it's basically useless because of the shallow thread depth so it wont even bite.

What to do next!

[busdaddy]

Hmmm, a bottoming tap would be better there.
Measure the length of the thread on the new part and compare to hole depth, looks from here like you've hit the bottom of the old sensor.

To gauge how deep you can go remove a rocker cover and measure from the top of the boss to the inner top of the rocker box, the existing hole isn't that deep, but it'll give you a rough idea how thick the area is.
Another indication is whether the stuff coming out is magnetic, old sensor is, head material isn't.
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[christyxy]

Thanks for input, though I'm now a bit confused as to if my sensor is in the right place from your comment. Also I found this post elsewhere on the forum where there was a similar problem but the sensor looks to be in a different place to mine? https://www.thesamba.com/vw/forum/viewtopic.php?p=9653860&highlight=#9653860

So is my sensor in the right place? Is there another place I can put it near the valve/rocker compartment?

Pics below showing where mine is/was before i broke it trying to unscrew it!

[busdaddy]

That looks correct, when all the tin is out f the way it looks like the one below (upper in pic), the sensor is over the rear edge of the rocker box, not the combustion chamber.

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[christyxy]

Ah ok that picture is re-assuring! Thanks very much - So if i keep drilling through the bottom of the old sensor, the filings/pieces that fall into the hole aren't gonna cause any damage as it's just an empty well/hole underneath?

In this previous post it looks like the sensor is in a different place, like on the side of the rocker box underneath... or is it just the way the picture is orientated? https://www.thesamba.com/vw/gallery/pix/2185929.jpg

https://www.thesamba.com/vw/forum/viewtopic.php?p=9653860&highlight=#9653860

Thanks again for the advice, I'm feeling more confident about getting this sorted with each post.

[busdaddy]

That's an odd location for L-jet on a bug, maybe it's a type 3 with D-jet?

Yes, there should be ~1/4 of hole beyond the end of the sensor, worst case you get into the rocker box, but that's more than an inch deep.
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