Stripped Cylinder Head Threads - Repair all or only damaged?
Discussion
So my 2013 Mercedes A45 has had a HG failure and on tearing it down I've found that 2 of the cylinder bolts on cylinder 3 have stripped the threads out of the block 
The threads are ~75mm below the surface of the block so helicoiling is not an option as they don't do a kit that can reach that far down but fortunately timesert do a deep thread repair kit in the right size. Now my quandary is whether I should repair just the 2 threads that have failed or all of them as a precaution as its not a job I wish to repeat.
I've got a mobile thread repairer whose got the correct kit coming to do it and basically the price will be the same as its a days work for him with travel so I can have just the 2 or all 10 done for the same price.
I'd welcome others experience/ thoughts. Obviously its an expensive engine so I don't want to unnecessarily damage/weaken the already highly tuned/stressed engine.
What would you do?
The threads are ~75mm below the surface of the block so helicoiling is not an option as they don't do a kit that can reach that far down but fortunately timesert do a deep thread repair kit in the right size. Now my quandary is whether I should repair just the 2 threads that have failed or all of them as a precaution as its not a job I wish to repeat.
I've got a mobile thread repairer whose got the correct kit coming to do it and basically the price will be the same as its a days work for him with travel so I can have just the 2 or all 10 done for the same price.
I'd welcome others experience/ thoughts. Obviously its an expensive engine so I don't want to unnecessarily damage/weaken the already highly tuned/stressed engine.
What would you do?
Had a similar situation with an M52B28, aluminium block. One thread pulled out when putting head back on.
It made sense to me that the repair was stronger than the original thread and also that the others that had torqued down ok that time were seemingly as likely to fail when being torqued down for what would then be the 3rd time after the repair so if one other was to fail you then go through the same process of every other one having to be torqued again etc etc........
I decided to do them all. Unfortunately about a week later the engine died from a completely unrelated fatal failure in the bottom end. But in my head they would have lasted the life of the engine and made me much less nervous about avoiding taking head of in future. Also really not much extra effort/cost to get them done compared to the effort of having to take the head off and do them later.
It made sense to me that the repair was stronger than the original thread and also that the others that had torqued down ok that time were seemingly as likely to fail when being torqued down for what would then be the 3rd time after the repair so if one other was to fail you then go through the same process of every other one having to be torqued again etc etc........
I decided to do them all. Unfortunately about a week later the engine died from a completely unrelated fatal failure in the bottom end. But in my head they would have lasted the life of the engine and made me much less nervous about avoiding taking head of in future. Also really not much extra effort/cost to get them done compared to the effort of having to take the head off and do them later.
As long as repairs are done properly, then yes they will be stronger than the base metal thread.
Timesert do require a bigger drill hole than a helicoil, so hopefully there is enough meat in the block to allow it.
Dont really see why depth would affect a helicoil, it's just a drill bit and tap and 75mm isnt particularly deep in that respect. And whoever is doing it will need to ensure everything is done nice and straight !
Timesert do require a bigger drill hole than a helicoil, so hopefully there is enough meat in the block to allow it.
Dont really see why depth would affect a helicoil, it's just a drill bit and tap and 75mm isnt particularly deep in that respect. And whoever is doing it will need to ensure everything is done nice and straight !
Yes even if you have to make tools (welding extensions onto taps etc) helicoils are still possible and although timeserts might have their advantages, deep helicoils in this situation might be better as require far less material removal. Guessing they are bolts that hold the head on?
MattA45 said:
The threads are ~75mm below the surface of the block so helicoiling is not an option as they don't do a kit that can reach that far down
That's easily solved. Long series drill bits can be bought in any size, taps can be driven down deep holes with tap extensions and the helicoil inserter is just a rod with a slot in the end. Any old bit of thin bar and a hacksaw can make one of those.Mignon said:
MattA45 said:
The threads are ~75mm below the surface of the block so helicoiling is not an option as they don't do a kit that can reach that far down
That's easily solved. Long series drill bits can be bought in any size, taps can be driven down deep holes with tap extensions and the helicoil inserter is just a rod with a slot in the end. Any old bit of thin bar and a hacksaw can make one of those.227bhp said:
They look suspiciously like helicoils already in the first pic....
Hard to tell.....even the block has some appearances of iron which would make thread pulling very odd.If alloy block, the surface machining looks pretty rough, and the threads pulled do look very clean cut much like a helicoil insert.
GreenV8S said:
227bhp said:
They look suspiciously like helicoils already in the first pic....
They look exactly like helicoils. Is it possible to 're-helicoil' a thread? Timeserts or similar larger inserts might be your only option.If a helicoil has wound cleanly out then yes a new one will go back in, it's when they come out fighting and all mangled up that you're in for a long day.
Maybe the OP will come back one day....
Come on, those are not helicoils, it’s just the thread pulled out of the block and unscrewed with the stud, probably stripped on assembly at the factory(by machine) and the reason for HG failure!
Helicoil inserts are some kind of stainless spring steel so will not break up like the bits in the pic. And iron blocks tend to crumble. Yes I have stripped a few threads in my time but it happens on old poop, it’s about having the correct tools to repair it correctly.
Helicoil inserts are some kind of stainless spring steel so will not break up like the bits in the pic. And iron blocks tend to crumble. Yes I have stripped a few threads in my time but it happens on old poop, it’s about having the correct tools to repair it correctly.
227bhp said:
They're either factory fitted or someone has been in there before. I'm not familiar with that engine and am wondering why they are 3" away from the surface. If they are it's unlikely a Timesert will do it.
If a helicoil has wound cleanly out then yes a new one will go back in, it's when they come out fighting and all mangled up that you're in for a long day.
Maybe the OP will come back one day....
A well designed block will have the threads on the lower platform. Having the threads for fasteners right at the block deck is the worst place for clamp and distortion....but it's the cheapest.If a helicoil has wound cleanly out then yes a new one will go back in, it's when they come out fighting and all mangled up that you're in for a long day.
Maybe the OP will come back one day....
Although a well designed block wouldnt have threads pulling out of it lol which seems all too common with some German crap.
99hjhm said:
Come on, those are not helicoils, it’s just the thread pulled out of the block and unscrewed with the stud, probably stripped on assembly at the factory(by machine) and the reason for HG failure!
It would be obvious to anyone with their hands on whether that was broken casting or spring steel, but from the picture it's hard to tell. GreenV8S said:
It would be obvious to anyone with their hands on whether that was broken casting or spring steel, but from the picture it's hard to tell.
You can clearly see that the outside of the thread is flat with a granular surface, exactly what you'd see when the original thread has been pulled out. A helicoil would not fail like that, particularly not in an alloy block.Sorry for the delay in replying , there was an issue with the forum, they temporarily banned new members from posting for a couple of days as there was some spamming issues apparently.
Anyway in the pics it is the remnants of the threads I've unpicked off the head bolt, they definitely haven't been helicoiled before and its the original block thread that has failed.
Here's a link to the particular timesert kit that needs to be used. It includes an sort of jig and bushing that ensures everything is straight and true when replacing them. It seems they developed it specifically for Toyota RAV4's as they seem prone to it and happen to have the same thread size.
https://www.youtube.com/watch?v=51nOHO5p_qg
I think I'm leaning towards having all 10 done, as others have said and from further research it would seem that the timesert will definitely be stronger than the original threads anyway. These would be the "standard" timesert insert not the "big-sert" which would require quite a substantially larger hole to be drilled.
I do appear to be one of the first people to have such a failure on this engine although mine is one of the earliest cars and probably higher mileage (80k)
Hopefully the guy's coming this week so i'll update with progress
Anyway in the pics it is the remnants of the threads I've unpicked off the head bolt, they definitely haven't been helicoiled before and its the original block thread that has failed.
Here's a link to the particular timesert kit that needs to be used. It includes an sort of jig and bushing that ensures everything is straight and true when replacing them. It seems they developed it specifically for Toyota RAV4's as they seem prone to it and happen to have the same thread size.
https://www.youtube.com/watch?v=51nOHO5p_qg
I think I'm leaning towards having all 10 done, as others have said and from further research it would seem that the timesert will definitely be stronger than the original threads anyway. These would be the "standard" timesert insert not the "big-sert" which would require quite a substantially larger hole to be drilled.
I do appear to be one of the first people to have such a failure on this engine although mine is one of the earliest cars and probably higher mileage (80k)
Hopefully the guy's coming this week so i'll update with progress
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