Flywheel bolt threads stripped

[Cory S]

LOL. Smart phone they say.... I'm leaving it cause helicopter coils are way cooler than heli coils all day long.

Damn right they are! Ordering some tonight.

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[ORRadtech]

I just want to know how this can even happen……

Yeah, I wondered too and did a quick Google search. Apparently it happens quite a bit across several different brands and models.
It seems the most recommended fix, short of replacing the crank, is the heli coil one. The second most suggested fix is drilling and tapping for the next larger size bolt.
Personally I don't think I'd much trust either.

 

[NGOT8R]

If he drills the one hole for a larger bolt, would that pose a balancing issue? If so, it would seem that all holes would need to be drilled and replaced with the same size bolts. I would even go as far as to say that the machinist who does the work, would probably want to use a drill jig to get all holes and threads straight. Don’t forget the flywheel holes will also need to be enlarged (using a jig as well).

 

[WD Pro]

Done properly, a helicopter coil would be the best resolution - it should as as strong as / as good as the OE thread

WD

 

[Cobra Jet]

The bigger question would be:
Can such a repair be done by a DIYer laying on their back, under jack stands, and at an angle (properly)?

OP hasn't been back on since his posting - but with limited info and only assuming this was an at home, in the garage/driveway "oopsy" with the car NOT on a standard lift, Quick Jack, or Max Jack... and it's sitting on stands, I don't see the feasibility in being able to do it totally 100% correct without the possibility of further damaging the affected threaded hole in the crank.

---

Yes, if one enlarged the affected threaded hole and had to use a larger bolt (leaving all others "stock" size) the balance of the rotating assembly would be off kilter for sure - and be worse as MPH/RPM increased.

---

Just a word of caution to those doing any such engine/clutch job for the first time:
- Always hand thread bolts to make sure the bolt is going in straight and clean.... If there is the smallest amount of binding, back it out and CLEAN the threads on both the bolt AND the threaded hole.

 

[Rapid Red]

The bigger question would be:
Can such a repair be done by a DIYer laying on their back, under jack stands, and at an angle (properly)?

OP hasn't been back on since his posting - but with limited info and only assuming this was an at home, in the garage/driveway "oopsy" with the car NOT on a standard lift, Quick Jack, or Max Jack... and it's sitting on stands, I don't see the feasibility in being able to do it totally 100% correct without the possibility of further damaging the affected threaded hole in the crank.

---

Yes, if one enlarged the affected threaded hole and had to use a larger bolt (leaving all others "stock" size) the balance of the rotating assembly would be off kilter for sure - and be worse as MPH/RPM increased.

---

Just a word of caution to those doing any such engine/clutch job for the first time:
- Always hand thread bolts to make sure the bolt is going in straight and clean.... If there is the smallest amount of binding, back it out and CLEAN the threads on both the bolt AND the threaded hole.

Yes it can, rotate the hole in need of repair to 6 0-clock. Use Tap Magic for lubrication when cutting threads. Tapping, cut some threads & back off 1/2 turn and proceed until completed.

I don't know how much space there is back side of crank to block, that could affect the depth that a starter tap can cut full threads. In that case, a bottoming tap can finish the job.

One more, run the tap in and out at lease 2x to get the threads for the insert clean, you do not want the Helicoil to bind going in it will break.

OP might want to take some scap to get the hang of what to expect.

Helicoil is stainless, balance, seriously doubt that will have any effect. Threads are light and the OME bolt weighs the same.

Very effective thread repair, for instance, drilled and installed Helicoils in the aluminum cases of a Harley owned, making the threads less subject to galling.

 

[NGOT8R]

I used this thread chaser kit on my crank before installing new bolts for the flywheel. Just as Cobra Jet said, I could very easily screw the new bolts in by hand afterward.

I‘ve used this method for years on just about every threaded hole or bolt that I use in a project, especially if loctite was used on the bolt. It cleans out all of the residual loctite and makes sure the threads are ready to receive the hardware without issue.

 

[GregO]

@Peyton10p
Give this some thought.
https://www.timesert.com/

 

[RoGCobraRV]

Learned the hard way as a teen back in the day on my 85 GT that you can't use just any old similiar looking bolts on the flywheel. One depress of the clutch sheared em all off.

 

[HKusp]

I also learned the hard way on my Whipple install a few months ago. I was not listening to the "feel" in the wrench and just wanted to get the bolt down snug. I broke off one of the hold down bolts in the aluminum head on the passenger side. Absolutely should have backed it out and run a thread chaser in, but I didn't listen to my gut. I then used an extracter to remove the broken bolt and ended up tearing up the threads. I ended up having to use a thread repair similar to helicoil but its called Powercoil, and I believe they are out of Australia. It worked like a charm, and according to those in the know, it is stronger than the stock threads in an aluminum head. If you take your time and do it correctly, it's not hard at all.

 

[Rapid Red]

Learned the hard way as a teen back in the day on my 85 GT that you can't use just any old similiar looking bolts on the flywheel. One depress of the clutch sheared em all off.

The same goes for the flex plate.

 

[Q Tip]

I spent about a year and a half pulling broken bolts out of military aircraft. Behind the Flir on an AH1 Cobra was the worst for me. What a clearance nightmare.
You want to do everything you can to start your drill on center. Typically the bolt breaks unevenly....use a carbide burr (small one) to flatten the broken bolt and get a good divot on center. Use magnification and good lighting. Go slow....a carbide burr will tear up the hole if you aren't very careful. Then use a machinists center drill to finish prepping for your regular drill. The center drill won't flex and pull your hole off center.

They make lefthanded drill bits...try one first. Often times after drilling a short way, the bolt will back right out.
Otherwise, know how far you can safely drill and drill on thru the bolt....you can feel it when your drill exits the bolt before it hits the parent metal of the hole. Stop there!

Make sure you get on center. If you start crooked, you can save it with the carbide burr by "pulling" the starting divot back on center.

Use your easy out to remove the drilled thru bolt. Use a new one. If it rounds over, use another new one or sharpen the edges on a grinder. You can also make your own by grinding edges on a tool steel lathe bit blank. Keep it cool by dunking in water to keep the temper. Get that bolt out....rejoice! Have a beer.

Chase your threads. Start with a taper or starter tap and progress thru plug and bottom taps. Keep it clean and lubed! Try some green "anchor lube".

You should be fine now to go back with an original size bolt. Put some blue loctite on it when you reinstall.

If you have to use a heli coil or other insert, consider a "Keensert". They are general what we use on aircraft. Hella strong....look em up.

If you need to drill the next size up...do it. You should be ok on a rotating assembly of that mass turning less than 8500 rpm.

If not....drill em all up.

Go slow and get on center, know how deep you are drilling. Mark your drill.

 

[Zooks527]

I spent about a year and a half pulling broken bolts out of military aircraft. Behind the Flir on an AH1 Cobra was the worst for me. What a clearance nightmare.
You want to do everything you can to start your drill on center. Typically the bolt breaks unevenly....use a carbide burr (small one) to flatten the broken bolt and get a good divot on center. Use magnification and good lighting. Go slow....a carbide burr will tear up the hole if you aren't very careful. Then use a machinists center drill to finish prepping for your regular drill. The center drill won't flex and pull your hole off center.

They make lefthanded drill bits...try one first. Often times after drilling a short way, the bolt will back right out.
Otherwise, know how far you can safely drill and drill on thru the bolt....you can feel it when your drill exits the bolt before it hits the parent metal of the hole. Stop there!

Make sure you get on center. If you start crooked, you can save it with the carbide burr by "pulling" the starting divot back on center.

Use your easy out to remove the drilled thru bolt. Use a new one. If it rounds over, use another new one or sharpen the edges on a grinder. You can also make your own by grinding edges on a tool steel lathe bit blank. Keep it cool by dunking in water to keep the temper. Get that bolt out....rejoice! Have a beer.

Chase your threads. Start with a taper or starter tap and progress thru plug and bottom taps. Keep it clean and lubed! Try some green "anchor lube".

You should be fine now to go back with an original size bolt. Put some blue loctite on it when you reinstall.

If you have to use a heli coil or other insert, consider a "Keensert". They are general what we use on aircraft. Hella strong....look em up.

If you need to drill the next size up...do it. You should be ok on a rotating assembly of that mass turning less than 8500 rpm.

If not....drill em all up.

Go slow and get on center, know how deep you are drilling. Mark your drill.

Hey, if you're only going to post 10 times a year, make them good ones!

 

[Q Tip]

Thought of a couple more things. When using a carbide burr, a regular drill probably won't have the rpm necessary. Use a small right angle die grinder. Good ones, while worth the money, are hideously expensive. Luckily, Ingersoll-Rand offers an inexpensive one that will get you by. I got mine at Advance Auto I believe.

While it probably won't help the OP, a GOOD Tig man can work wonders on many broken bolts by welding on a nut if the break is exposed, or even a T handle on some that break off below flush! Notice I said GOOD Tig man. It's amazing how well this works. Something about the intense heat expanding/contracting.

On exposed breaks, its often possible to grind flats on the exposed shaft with a cutoff wheel, and grab those with an adjustable wrench. Doesnt work that often but sometimes it's all that is needed.

Taps can be had in ground oversized .003 or "GH3" size. Know what you have.

If that tap squeaks....it's close to breaking teeth or completely in half.

Taps are very brittle. You will break them. They can often be broken up with a punch and picked out of the hole. Be careful not to destroy your hole.

Carbide drills will whip right through the toughest bolt. They break very easily....they won't take shock or side loading.

Sometimes, despite your best efforts...you will lose.

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