cylinder studs stripped, drilling and tapping block

Reposting this from Road Warriors where it got no love.

I'm removing the right cylinder on my R1200ST so I can helicoil the lower two cylinder stud sockets -- some genius over-torqued the nuts so badly that one of the bottom two studs got loose enough the nut to fall off in the head. It doesn't seem like too daunting a job, but if anyone's been there and has advice, I'd appreciate hearing it.

Is there anything else worth doing while the cylinder is off? The bike's got 50k on it, and runs fine except for pinging on strong acceleration. Which I was going to start figuring out when I instead discovered that I have some helicoiling ahead of me.

Helicoil not good for high stress areas. Depending on the size you need you can get something like a NormSert(used for car engine fixes) or timeserts(several sizes and designs/shorter/longer) which are designed to be high stress.

This has been discussed repeatedly. The factory even used Heli-coils, as have I a few times for this application. They work just fine!

Just about every threaded hole on a modern jet engine on commercial aircraft has a Heli-Coil insert.

That is either:

A-A perfect testament to the strength of a helicoil

Or

B-Going to really bother me the next time I fly


Sent from my iPhone using Tapatalk

OK, I'll ponder the Heli-coil vs Time-sert issue. Where are Time-serts easily available?

Currently more importantly, how does one remove the cylinder? The head came off easily, but the cylinder has been resisting my mallet. There seems to be some goo between the cylinder and the block that suggests it's on there pretty good. Should there be any goo? Is some RTV supposed to go between the block and the cylinder on reassembly?

Again, constructive input (even on the Heli-coil vs Time-sert question) is deeply appreciated!

Damn, did no one ever clean that thing?

You have some adhesive there, that shouldn't be, meaning someone has been in there before. Keep at it with a mallet, and IIRC there is a flat or two you can safely pry against.

It's not that I'm doubting you..... I am wondering how you know this

Because I worked in the UAL engine shop at SFO for three years. I've removed and installed a lot of Heli-Coils.

Anorak; not doubting but really curious. How do you remove a helicoil insert, and why would you?

Helicoils go back to the 30's & have been used extensively in aircraft piston engines too, both as new construction and as a repair. you have a high tension application, be sure to get coils with enough threads, either that or run two coils. I've never seen a Helicoil fail if installed properly. (almost 40 years as an A&P)

What is your skill set? Drilling and tapping paralell with the original hole
in two axi while in situ can be slightly more than many shadetrees can do well. Any veteran machinist buddy's you can bribe with beer?

Just let that sit in your mind.....

Block of wood + rubber mallet (you could just forgo the wood, but I like double protection.) and tap it. Probably going to take some work being I bet some knob butchered the job previously.

It doesn't look as dirty in real life.

Thanks for all the responses.

Is anything supposed to go between the block and the cylinder on reassembly?

@JVB @Cataract2: a block of wood and a mallet is what I've tried, but I'll keep going.

@concours: my skills are more related to sitting at a keyboard and standing behind a lectern. I don't know any machinists, though, and for better or for worse I'm not too worried about the drilling and tapping.

Airhead stud repair has a guide plate that goes on the remaining studs to give the drill a straight shot. You might want to check if there is a kit for your bike.

R100 kit

make sure you have that one hidden bolt removed too, its sort of in a pocket in the head.


yamabond or similar, THIN bead between cylinder and engine upon reassembly, after a good cleaning of course.

I'm guessing:

A) the A&P's who insert Helicoils on jet aircraft engine have done hundreds and have TONS of experience doing them properly

B) Pratt&Whitney / GE intentionally left enough "meat" in the block for a helicoil to work successfully.

A first timer doing a helicoil on a critical application? I'd hire a machinist (or A&P with tons of experience) to do it rather than learing the hard way what mistakes can be made. Buy the drill guide.... Nothing's as simple as the directions make it sound, machinists ALWAYS know tricks and nopes...

Or find a new (used) block, which is what 99% of all AUTO techs do when faced with head bolts that are stripped in the block.

I would not go with a helicoil, this is from experience. I have an '05 r1200gs that at 600 miles service was found to have a stripped head stud, bmw na' warranty fix was a helicoil in the engine block, I filed a complaint, stating that the fix would not last. 40,000 miles later and it did fail. I found the nut had come off and the washer had dropped into the oil sump. Bmw na refused to do anything worth my while. My dealer stepped up and replaced it with an over sized insert, at no cost to me, not sure what make or type, but he described it as a thick disc of steel threaded on outside and inside.

Having done several of these, and not being a machinist, I can assure you that it is dead simple. Carefully drilling out the hole allows the drill to take off the very tiny amount of metal to clean out the hole before threading the metal for the new helicoil. It is not really precision work! The hole self centers unless you are truly hamfisted!





As for the helicoil holding, they do just fine if threaded right.