81 xj550 maxim - broken cylinder head exhaust stud

Can the exhaust stud bolt on the head be removed and replaced?

 

Yes, be real careful, heat and the right tool will extract the stud.
Get a new one from chacal, or fin a m6x1.0mm by however long stud to replace

 

You can replace with a bolt, however the bolt can only be torqued to 6 ft/lb 72in/lb NOT the 8 ft/lb 92 in lb the stud nut combo will allow, therefore needing constant re torque or possible ex gasket leakage

 

Ok good. There should be enough threads left to put 2 nuts on and be able to turn it out with.

 

Ya, or just grab it with vice grips or mini pipe wrench, penatrating fluid and heat, but not too mych are your friends. Add a touch of patience and yr golden

 

Remember, if you eff it up you have to pull the head to have it properly helicoiled (thread repair) even an hour plus is less time and cost than doing a head gasket...

 

Give it a good soak with penetrating oil before you try to remove it. A week or so should suffice.
Trying to just back it out will likely result in more damage. BTDT.

 

Heat the stud with a torch, just the stud, until it smokes and then soak it down it with penetrating oil as it cools (PB Blaster works for me). Try to tighten it just a small bit to get the threads to release before you try to back it out. Backing it out alone can cause the threads to remain seized and you end up ripping them out of the head.

 

If you need to repair the threads, use a Time-Sert insert not a heli-coil. Those suck in aluminum from experience. They're OK for low-torque steel applications. I've had several fail and rip out of aluminum in situations like these. A Time-Sert may cost a little more but it's a permanent repair that will never give you problems. My $.02 anyway from installing them in 6061 suspension components and never having a failure even after repeated re-torquing to 120ftlb.

 

Aircraft and aircraft engines are aluminum (mostly). Timeserts are not FAA approved. Helicoils are.
But there are many inserts on the market that will work for an exhaust stud hole repair on a ground vehicle.

 

Nothing is accepted by the FAA unless enough money is put into promoting it to be a standard practice.

 

Cite your source.
Helicoil has been FAA approved since the 1930's based entirely on engineering specifications (documentation is publicly available online for free).
There are several other brands of threaded inserts that are also FAA approved. If money changing hands was the process for certification, then Helicoil would be the only FAA approved threaded insert.
There is nothing wrong with a Timesert, but asserting that Helicoils don't work in aluminum under heavy loads, or when encountering broad heat ranges, is incorrect.
All threaded inserts (when properly installed) are stronger than threading a fastener directly into aluminum.

 

I think as with a lot of things, correct preparation and execution of the repair will determine its effectiveness. I usually opt for the timesert mostly because I have more experience using them over helicoils. I have seen helicoils fail but also cannot speak to whether they were properly installed or not. To each their own though

 

Since I've been a licensed A&P mechanic for 32 years used helicoil in aluminum engine cases with no issues ,pulled studs are common . Care and patience and using a quality helicoil kit are keys . Kmoe is absolutely spot on about our friend the FAA they are always there to "help you" ..LOL

 

Thanks for the info. A little torch heat and double nuts I was able to easily unscrew it. Get the new stud in a couple days then I can finish putting the bike together and then I will be flying on it.

 

I know. It just irks me that those things have never worked for me and yet they are "FAA approved" for head repairs. Sorry, but I'll never use another helicoil. Especially after doing the pull-out testing on my sway bar adapters and exceeding 6000lbs on 2 m10 x 20mm time-serts in 6061 aluminum.