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Old 08-19-2014, 01:39 AM   #1 (permalink)
Cyborg ECU
California98Civic's Avatar
Join Date: Mar 2011
Location: Coastal Southern California
Posts: 6,297

Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 66.42 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
90 day: 3671.43 mpg (US)
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Stripped valve cover thread repair DIY (1998 Honda Civic)

Chasing down fluid leaks so I could install a full bellypan (undertray), I stripped-out a valve cover bolt by applying too much torque. I found little step-by-step guidance online for how to use the helicoil, and I have never used one before.

Still, I wanted as close to a perfect OEM repair as I could manage. I think I got it.

The cover is now back on, no leaking, and car running fine. The tricky part is the fact that the head was still on the engine, so drilling out the hole meant aluminum shavings could scatter into the oil.

Tools and supplies:

1 helicoil kit thread repair kit from O'Reillys (M6x1)
1 drill with 1/4 drill bit
1 pin punch thin enough to punch out "tang"
1 ratchet with 8mm socket
Painter's tape (or any tape, really)
paper towels or clean cloth


Drill bit, taped to match the bolt's depth:

Helicoil tap, taped to match bolt depth:

Drilling done (forgot to take pictures), here's the tap ready to go in:

Tapping the hole. You see the paper towel tucked in all around the repair area to catch the shavings. I still had to chase down all the bits that escaped:

For both drilling and tapping, I used this copper pipe to judge the perfect angle. I had to go very slowly, and it was a little nerve-wracking when I had to start over once. The pipe is standing snugly on one of the 12mm rocker arm bolt heads:

Here is another shot, showing how nicely aligned the tap came out:

The Honda valve cover bolts are unusual because of the "bulge" that rests on the rocker arm and the fact that the threads are tapered. So if the helicoil insert is to work, you'll have to sink it deeper than generally recommended or the bolt threads will pass it by and then not fit properly:

Knock-out the "tang" ... all along the process I used the tweezers and the valve cover bolt itself, dampened with a little oil, to get the shavings out of the hole. It was slow work, but you cannot blow the shavings out of the hole because they will go everywhere and get into the oil. I let the tang sit in the bottom of the hole, along with some shavings. There was more than enough room:

A perfect OEM fit:


Took just over an hour.

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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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