How to repair stripped hole in rear subframe?

[SWFL_NSX]

I'm in the process of reinstalling the transmission after swapping in short gears. Last night I tried to torque the bolt that attaches the upper A arm to the rear subframe and the threads pulled out! The rear subframe is aluminum, the bolt is M10x1.25 and the torque value is 43 ft lbs.

What is the best way to make this repair?

1. Helicoil
2. Timesert
3. Keensert
4. Replace the entire left rear subframe

 

[drew]

I prefer helicoil style, but I'm sure any of those work just as well.

Helicoil was the approved fix on the Space Shuttle. Some parts required a helicoil as spec. My Ferrari buddies have a whole shelf of helicoils for such things

A repair in this instance is better than new.

 

[Honcho]

Option 4! J/K

For engine block work, timeserts seem to be the preferred choice of most machinists. However, helicoils work well too. LarryB used them on many NSX repairs. Stripping the aluminum subframe bolts is more common than most people think and there are plenty of helicoil repairs out there running just fine.

 

[BrakeExpert]

I'd vote for timeserts. I've seen the quality of metal they use, and its a formed sleeve, while some use a "spring", a timesert is actually machined similar to and meant for the use of bolts. I've used them myself for oil pan nuts, exhaust studs in the engine head, and timing belt boss holes (for the adjuster on a timing belt tensioner.) the strength of metal is peace of mind, and they are effectively "forced" in there on install so the odds of it coming out like a cheaper helicoil in the future is pretty much zero. Always remember not to overtorque bolts into aluminum.

 

[SWFL_NSX]

Thanks for the input-I'm going to go with Helicoil but am having trouble figuring out what length the insert should be.

Helicoil has a chart that explains what length of insert to use, but it depends on knowing the sheer strength of the parent material and the tensile strength of the bolt. It looks like the sheer strength of cast aluminum is about 180MPa, but I'm having trouble finding the tensile strength of the bolt based on the marking on the head.

Here is a pic, does anybody know what this symbol (10? 01?) indicates on a metric bolt head that is from a early 90's Honda product?

Helicoil insert length guide. the 1, 1.5, 2, etc stand for 1.5*thread diameter of the fastener, or 10mm in this case. I suspect I'll end up at either 1.5 or 2, so either 15mm or 20mm

 

[Honcho]

The "10" is a Japan-spec JIS marking for high tensile steel, roughly equivalent to a U.S. Grade 8 bolt. So, you're looking at about 1,040 MPa.

 

[centerpunch]

I can't imagine any downside to using the longest helicoil that will fit.

 

[SWFL_NSX]

The "10" is a Japan-spec JIS marking for high tensile steel, roughly equivalent to a U.S. Grade 8 bolt. So, you're looking at about 1,040 MPa.

Ah! Thanks Honcho, that's great information. Just ordered the appropriate kit and am looking forward to trying out my new JDM gears.