Helicoil kit to repair idler pulley thread - M6
Discussion
My M6 is in with BMW at the moment having work done on the Vanos, new high pressure oil pump plus some other bits and pieces I believe.
Whilst they were doing this job, they noticed that the idler pulley (I think for the Air-con) was just spinning in the thread. They rang me yesterday basically saying, worst case scenario is that it will need a new block plus crank etc (a nice hefty bill to the warranty company), however they now say they can safely fix it with a helicoil kit?
Now I'm not sure what this is exactly, but should I be happy that this is a safe and good way of fixing it, or should I be thinking this is a bodge fix to save themselves money?
Whilst they were doing this job, they noticed that the idler pulley (I think for the Air-con) was just spinning in the thread. They rang me yesterday basically saying, worst case scenario is that it will need a new block plus crank etc (a nice hefty bill to the warranty company), however they now say they can safely fix it with a helicoil kit?
Now I'm not sure what this is exactly, but should I be happy that this is a safe and good way of fixing it, or should I be thinking this is a bodge fix to save themselves money?
Being an EX- Chief-engineer I can say DO NOT go this route , too much strain on the bolt, new block required at their expense.
A bodge may last a while and could get them through their warrantee, thats their thinking.
PS) IF they insist on doing this "quick fix" get it in writing that they will do the repair again at their expense should it fail in your ownership in or out of warrantee.
A bodge may last a while and could get them through their warrantee, thats their thinking.
PS) IF they insist on doing this "quick fix" get it in writing that they will do the repair again at their expense should it fail in your ownership in or out of warrantee.
Edited by JMBMWM5 on Wednesday 19th February 08:51
Thanks for the advice chaps. I guess the quandary I'm in is whether or not I'd like the BMW technicians to be heli-coiling my block or trust them rebuilding my bottom end 
I want to first find out if this helicoil is an approved BMW fix or not, and as mentioned, get it in writing if it isn't and that warranty will cover any future issues with it.
I want to first find out if this helicoil is an approved BMW fix or not, and as mentioned, get it in writing if it isn't and that warranty will cover any future issues with it.
ChrisMCoupe said:
Thanks for the advice chaps. I guess the quandary I'm in is whether or not I'd like the BMW technicians to be heli-coiling my block or trust them rebuilding my bottom end
I want to first find out if this helicoil is an approved BMW fix or not, and as mentioned, get it in writing if it isn't and that warranty will cover any future issues with it.
This is a must!I want to first find out if this helicoil is an approved BMW fix or not, and as mentioned, get it in writing if it isn't and that warranty will cover any future issues with it.
A Helicoil sounds like a cheap bodge/fix. There is no guarantee with it. It is the 'repairing' of an already weakened part.
Lets not jump to conclusions hear.
From a mechanical engineering point of view you could check the holding tension on a helicoiled thread compared to a thread tapped directly into the block material.
http://www.noblefix.com/PDF/Helicoil/HeliCoil-Cata...
you will need to know bolt diameter, length of bolt and amount of engaged thread.
My initial gut feeling is that a correctly installed helicoiled insert will be stronger than a new aluminium block with a freshly cut thread. The reason for my thinking is that the load bearing area in the aluminium block is greatly increased by the larger diameter threaded insert verses the size of the bolt that was used in the original design. Maybe as much as going up 2 bolt sizes in some instances, ie M10 to M14 once the thread is cut and the insert threaded in.
BMW would be unlikely to do this on a production bases as it would increase costs dramatically, if you put a 10 pound costs against each threaded hole and multiply that against the number of threaded holes the engine would get a lot more expensive.
I also note that the helicoil catalogue makes mention to the effects of temperature on the strength and selection of the helicoil, therefore such a repair in an engine block needs some careful consideration.
If it’s a properly engineered and warrantied solution advised by the BMW engine department then I wouldn’t have a problem with it. If it’s the local mechanic at the dealership trying to avoid replacing the engine I would have a problem with it.
For the record, ive used helicoil on the suspension uprights of the single seater im working on, basically to take the loads from the upper and lower wishbones into the upright and are yet to be tested in action.
best of luck, regards Ryan
From a mechanical engineering point of view you could check the holding tension on a helicoiled thread compared to a thread tapped directly into the block material.
http://www.noblefix.com/PDF/Helicoil/HeliCoil-Cata...
you will need to know bolt diameter, length of bolt and amount of engaged thread.
My initial gut feeling is that a correctly installed helicoiled insert will be stronger than a new aluminium block with a freshly cut thread. The reason for my thinking is that the load bearing area in the aluminium block is greatly increased by the larger diameter threaded insert verses the size of the bolt that was used in the original design. Maybe as much as going up 2 bolt sizes in some instances, ie M10 to M14 once the thread is cut and the insert threaded in.
BMW would be unlikely to do this on a production bases as it would increase costs dramatically, if you put a 10 pound costs against each threaded hole and multiply that against the number of threaded holes the engine would get a lot more expensive.
I also note that the helicoil catalogue makes mention to the effects of temperature on the strength and selection of the helicoil, therefore such a repair in an engine block needs some careful consideration.
If it’s a properly engineered and warrantied solution advised by the BMW engine department then I wouldn’t have a problem with it. If it’s the local mechanic at the dealership trying to avoid replacing the engine I would have a problem with it.
For the record, ive used helicoil on the suspension uprights of the single seater im working on, basically to take the loads from the upper and lower wishbones into the upright and are yet to be tested in action.
best of luck, regards Ryan
ezakimak said:
For the record, ive used helicoil on the suspension uprights of the single seater im working on, basically to take the loads from the upper and lower wishbones into the upright and are yet to be tested in action.
best of luck, regards Ryan
Just my 2P, we have used these on various applications in Aluminium on "not too stressed" areas with good effect.best of luck, regards Ryan
One application that did NOT work was the A/c Pump on a Porsche 928 GTS, the threads had failed and the Helicoil was used , after a very short time the whole thing came loose again luckily not causing too much damage.
The point you make of "going up bolts sizes" makes good sense and should be a good fix if possible and done correctly.
As you rightly mention depth of thread is critical on Aluminium, and trying to re-tap a larger thread with a conventional Tap would be difficult.
Edited by JMBMWM5 on Thursday 20th February 09:43
Make sure that they are actually talking about a helicoil. There are other, better, thread repair inserts, e.g. Keenserts, that would almost certainly give you a permanent repair with at least as much strength as the original.
As mentioned above, I too have used inserts in single seater uprights and run the car with no issues.
As for a genuine helicoil, in aluminium? Not good enough for me.
As mentioned above, I too have used inserts in single seater uprights and run the car with no issues.
As for a genuine helicoil, in aluminium? Not good enough for me.
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