Stripped out my thread repair...

[nola mike]

Stripped out my Mani/reservoir thread. Tried using some thread repair epoxy, which was a spectacular failure. Inserted a helicoil...and think that I probably put in the wrong sized thread. The old bolt is definitely too big. It was the same size when I compared it to the tap, but of course I didn't take into account the insert :facepalm:
My stupidity aside, I'm trying to figure out the best way to proceed. I feel like removing the coil and rethreading will be a huge PITA (not sure how difficult it is to remove the thread). I had the bright idea to just replace the bolt with a smaller one that will fit (3/8-16). Any reason not to take this route? I'm guessing the old one is 7/16, and I only need 30 ft-lbs into aluminum...

 

[ziggy]

Re: Stripped out my thread repair...

sorry, i don't know what a mani/reservoir thread is on your 170. that aside.
check out the torque values of bolts. see what grade bolt ya need to comply with 30 ft-lbs. try it and see if it works. don't got much to loose if it don't.
if not. i assume ya broke off the drive of the helicoil. assumein so, i would guess heli coils are spring steel. if ya can get one corner bent up some how. maybe create your own drive and drive the coil out.
last resort, maybe a reverse drill bit to the proper size heli coil size or one size down and see if ya can slow speed snag the heli coil and drive it out. worse, drill out the spring steel and hope ya don't go over size for the proper heli coil.
what ever ya do with the drill bits gonna hose ya drilling hard metal mounted is soft metal. ya go off center and the soft metal will suck yer drill bit that direction to the point of no return. ya drill and your gonna have to go straight the first time.

that's my experience with stuff like that.. maybe other ideas out there too.

 

[fat fanny]

Re: Stripped out my thread repair...

This happens all the time at work and the machinists are expected to fix it! Either use a easy out or a chissel and cut the coil in half or result to using a sharp puch and pry up the end of the coil and grab it with needle nose plyers and pull it out. If you do get it out use a threaded plug they are more reliable and a sounder repair. good luck and post back.

 

[RCAnderson]

Re: Stripped out my thread repair...

So you put a heli-coil into the stripped thread without drilling and tapping using the correct tap ? You may be able to use a very small screwdriver or chiselto pry the outside end of the helicoil out and make a bend in it, then grab that bend with needle nosed pliers and thread the insert out. This is my preferred method. If that doesn't work, since you are going to have to drill anyway, just drill it out. Go slowly, as the helicoil insert is stainless steel, and will work harden if you look at it wrong. You will probably break some drills and smash your knuckles when the drill grabs. Have fun.

 

[nola mike]

Re: Stripped out my thread repair...

Yeah, that's exactly what I did, and how I was originally going to remedy it. I'm concerned that I'll FUBAR it trying to drill it out, as has been suggested. I guess I could just worst case use an oversize bolt (and then have to drill out the riser hole as well)....
I think I'm going to just use the smaller bolt and see what happens first. I'll keep you updated.

 

[fat fanny]

Re: Stripped out my thread repair...

If the old thread was 7/16 the threaded INSERT (best replacement option) tap is 5/8-11 use a 17/32 drill and then tap it out auto stores sell the threaded inserts at any length up to an inch in 1/8 incriments do it right so you have no issues later with a less than desirable repair now! Good luck

 

[1977 SILVERLINE]

Re: Stripped out my thread repair...

Do not try to remove the heli coil. They are hard to remove and you have the possibility of making things worse. Yes you can use a 3/8" bolt as long as it is a grade 5 or 8. They can be tourqued to 35 lbs+ no problem.

 

[nola mike]

Re: Stripped out my thread repair...

So I got a 3/8" SS bolt rated for something like 250 ft lb. Checked both surfaces, which were flat. Mani surface had a very small amount of pitting, so I held my nose and put a thin layer of gasket sealant on. Even though the old one hadn't been fully compressed, put on a new mercruiser gasket and torqued everything down. The repair held no problem. Went on a 15-20 mi ride between 3-3500 rpm for the most part, with a bit of time at 4k. Everything ran fine, no coolant loss.

The more I thought about it, the less sense it made to try to remove the insert. Worst case, the insert would have pulled free of the aluminum, in which case I would have accomplished the goal of removing the insert, and I could drill it out to the proper size at that point.

 

[Bondo]

Re: Stripped out my thread repair...

So I got a 3/8" SS bolt rated for something like 250 ft lb. Checked both surfaces, which were flat. Mani surface had a very small amount of pitting, so I held my nose and put a thin layer of gasket sealant on. Even though the old one hadn't been fully compressed, put on a new mercruiser gasket and torqued everything down. The repair held no problem. Went on a 15-20 mi ride between 3-3500 rpm for the most part, with a bit of time at 4k. Everything ran fine, no coolant loss.

The more I thought about it, the less sense it made to try to remove the insert. Worst case, the insert would have pulled free of the aluminum, in which case I would have accomplished the goal of removing the insert, and I could drill it out to the proper size at that point.

Ayuh,... I believe a 3/8" bolt is Plenty for the task, though I probably would go with steel...

The Chevy based motors use 3/8" riser, 'n manifold bolts...

 

[nola mike]

Re: Stripped out my thread repair...

Yeah, it was stainless