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Striped threads on Oxygen sensors

peter roberts

Well-known member
Joined
24 Aug 2015
Messages
47
Just tried to fit new sensors to my 3.4 C4. On removal the threads stripped on both sensors and cats.
I am sure i am not the first person to do this so is there any solution out there to rectify the problem.
I have looked at used replacements on ebay but all are fitted with sensors. if i buy and try to fit my new sensors i may strip the threads again so back to square 1. I could try to get vendors to take out the sensors and guarantee the thread is OK but i am sure most would refuse.
Next option is to weld up and recut thread but would need a special tap to do this.
Does anyone out there supply new sockets that i can weld on after cutting off the old ones.
Are there any other options?
 
easiest option would be to grind off the old boss and weld on new, just google 'lambda boss'

If you have a custom exhaust centre locally then they will probably stock them or the good old ebay if all else fails.
 
Stripped oxygen sensor thread

Thanks guys i guessed it would be a regular problem. Will source solution on Monday and advise.
 
How badly damaged are the threads? I had a custom manifold on a TVR and the lambda bosses (which were redundant on my car) were blanked off with a spark plug! The point being, can you use a new spark plug of the correct size to "chase" the threads and get enough back for the lambda to purchase? Maybe run the plug up and down the threads with a little copper grease then install the lambda with some silicon sealant to take up any thread wear. Worth a try?
 
the threads are gone completely and as i am selling the car would not want to do a repair that may not last
Googled Lamda Boss as advised and found replacement bosses at £2.50 each. Cats are off so tomorrow i will cut off the existing bosses, grind back and get them welded in when they arrive.
Thanks for all your help, great forum, great members. But you would expect that as we drive such great cars.
 
I stripped one of mine recently and I thought I had taken all the threads from the cat but I bought one of the thread chasers.
It did seem it was beyond saving but what had happened was the threads on both the cat and sensor had just spun off and although it took a little time to chase the thread with plenty of WD40 and reversing each quarter turn I did repair it successfully.
 
Same here, earlier this year I replaced my lamda sensors and found one of them to be totally jammed in and cross threaded. I had to cut down the old lamda and beat a socket onto it to then be able to turn it out with a ping bar. The thread looked knackered, but I bought a proper two-stage tap kit and chased it out, and the result was perfectly fine and accepted my new lamda easily.

However, in the OP's case, as he has no thread remaining at all, a new boss welded on really is the best solution.
 
Any chance of a helicoil?

MC
 
As suggested bought some taper and plug taps and run them through.
it appears the thread in the cats had not dtripped but the threads on the sensors had stripped off and were in the threads of the cat. Tpas cleaned them out and sensors are fitted and pulled up tight with no sign of coming loose.
Thanks for all the advice. I only hope that this is why it is running rich and not faulty injectors.
 

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