Cost to install a spark plug insert?

[bobinyelm]

A friend with a 740i managed to take the threads out with a spark plug, and the dealer says BMW does not authorize a field repair, and the only fix is a $9000 head replacement.

No local shops will warranty the job, and they want almost $400 to do it at that, which my buddy says is outrageous (I say it's cheaper than $9000, though!). The cost for an insert/heli-coil is under $10, so what is a reasonable fee he should have to pay to have one installed, and do they usually hold up?

Thanks

[Timm]

I know loads of members who have done this job themselves - there are Helicoil kits available everywhere specifically to fix stripped sparkplug threads:

https://www.ebay.co.uk/sch/i.html?_f...l+kit&_sacat=0

The sparkplug wells are pretty deep on the V8's - but although a bit fiddly it is quite easy to do even on cylinders 4 and 8. One important point is to make sure you catch the tang that snaps off the Helicoil and all the swarf - a good plan is to use loads of grease to catch it all......

[motion]

Consider checking into Timesert's it's a solid bushing not a spring, more pricy but produces a better job.
http://www.timesert.com/

[Martinator]

Lisle has a tool for this. Used it on an e39 528i about 2 years ago. Still holding.

[Grantnz]

Believe it or not, I have seen this helicoil job done successfully (on a Jaguar) without removing the head. The cost to remove the head etc. would have made the repair uneconomical for that particular car. The very experienced old mechanic carefully placed a grease covered rag down the plug hole to catch the swarf from the tapping process, and removed it with what looked like surgical tweezers. No guarantee of success, but a gamble worth taking if the other option was to junk the engine/car.

[bobinyelm]

Well, here's the REST of the story for anyone curious about doing the job at some point on the future.

My friend asked me to do the job for him, so I ordered a HeliCoil SOLID insert kit from Amazon and a bottle of Hi Temp thread locker. Unfortunately, Amazon or the USPS lost the order and Amazon refused to send a replacement (I now need to see if they will return my money).

I then bought a similar Australian-made kit ("Save-A-Thread) from Advance Auto Parts, but could not locally source the Hi Temp stuff, so I decided to use the blue stuff with Permatex activator for better strength.

I found the tap is made for 3/4" socket, which unfortunately will not fit into the BMW plug well, so I had to decider whether to try to grind the hex down to 11/16" (my thin wall 11/16" socket would JUST fit into the well), or alternately weld a 3/8" drive socket to the top of the tap to turn the tap. I decided to sacrifice a 9mm socket I'd never used in the 30 years I owned it, so cut it down by 50% and tapered it to provide a gap for MIG welding, and welded it centered on the top of the tap. This gave me the option of using a 3/8" locking extension on the tap, or a 3/4" deep socket (for other vehicles) to drive the tap.

I wrapped the space between the tap head and threads with solid lead solder to prevent it going completely into the cylinder where unscrewing it w/o damage would be doubtful (the tap bottomed on the larger diameter solder wrap after the fist threads entered the combustion chamber).

I used grease on the tap's flutes, naturally. and got LOTS of cuttings. I used a liberal amount of spray brake cleaner multiple times to remove any remaining grease, and spun the engine to expel any cuttings and brake cleaner, then blew out the cylinder with air.

I LOADED the threads of a new spark plug with anti-seize and threaded on the insert onto it a few times to distribute it on all the threads full length. I also applied some at the top to seal the gap between the insert and the plug washer so later thread locker couldn't get in there and fuse the insert to the plug later.

I liberally coated the threads w/ Locktite and ran the plug w/ insert in/out a couple of times to distribute the Locktite, then ran it in with about 10 pounds of torque (this bottomed the plug washer on both the top of the head casting and the insert). I didn't want to crush the plug washer and maybe need to exert enough torque to accidentally back the insert out later, figuring the Locktite and swaging (later) of the insert would hold it in place, and left them overnight to cure.

Today, I backed the plug out (came out easily and clean), then used the swaging punch supplied with the kit to hopefully lock the insert at the top (the top few threads are segmented to allow the top to be expanded into the alloy head to lock it in better). Then I did a (cold) compression check on that cylinder (which I couldn't do before due to the bad threads) and threaded the new plug back in and torqued it to about 30ft-lbs.

Unfortunately, the cold cranking compression check showed woefully BAD pressures on ALL cylinders cold (the highest was 155 pounds, and a few were in the 30-45psi range). I have done a LOT of compression tests in my 50 years or wrenching, and my experience is that while cold pressures are lower than hot pressures, they DO overall reflect the relative seal of the rings and valves. Amazingly, this engine ran flawlessly before, so I suspect that at warm idle or above the seal was FAR better than at cranking speed. The engine "looks" tired, and some of the plug wells had some oil in them, and when I checked the cooling system level, I had to add 3 quarts of fluid to fill it to the high mark (I used the high mark cold figuring there's enough air trapped in the system that the level will come down when the air is later expelled).

I don't know how much longer this engine will be viable, but for now at least, it will live a bit longer. The car's body is flawless (not a nick, dent, or scratch on it) and the transmission shifts perfectly, and the interior is an "8," but doubt given the book value it's worth even a used engine transplant. The owner was offered only $800 on a trade-in, and street value of a well-running example is probably under $3000 or so.

Fingers crossed...