Cross threaded bolt repair - thread file or thread chaser?: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Nov. 10, 2009 2:47 p.m. Xceler8x Dork
Short story is I have two cross-threaded holes into my turbo on the Miata. I had a shop install an exhaust they welded up for me and evidently they couldn't put the bolts in straight..or something. I found this out when the bolts fell out at the track and I was trying to install Stage 8 bolts into the turbo to hold the exhaust flange on.

So..I have the two options I listed above. I've read about
- Thread chasers
- Thread files
Which have you guys used? How have you used? Successful? Any other suggestions? I read about using a helicoil but I have no idea if it would hold in this very hot, very vibration prone area. I also have no idea how to install a helicoil.
Nov. 10, 2009 2:52 p.m. jstein77 HalfDork

IMO, use a helicoil for a permanent repair.
Nov. 10, 2009 2:53 p.m. Dr. Hess PowerDork

If I read this right, you have a hole with stripped threads in the turbo, right? Neither a thread chaser or file will fix that. You need either to Helicoil, Timesert or go next oversize.
Nov. 10, 2009 3:20 p.m. davidjs New Reader

I think the shop needs to look at one of the solutions the good gentlemen have already suggested (or pay to have it done elsewhere)...
Nov. 10, 2009 9:00 p.m. Jensenman MegaDork

If the holes are boogered up enough that the bolts/studs fell out, they need HeliCoiling. Nice HeliCoil tutorial:

http://www.nwlink.com/~kbaker/Automotive/Helicoil_12_04/helicoil_12_04.html

HeliCoils are stainless steel, so there should be no temperature concerns. Alternatively, if you have the room you can use bolts through both pieces with some of those all steel lock nuts. Don't use the nylon types! You might have to drill out the holes to do this but it would probably be easier than HeliCoils.
Nov. 10, 2009 9:05 p.m. SVreX PowerDork

Agree with Jman.

Helicoils are a pain in the butt.
Nov. 10, 2009 9:11 p.m. YaNi Reader

I recommend Timesert over a helicoil. Don't know if you can find it locally but Fastenal and MSC carry them.
Nov. 10, 2009 10:19 p.m. pitbull113 New Reader

YaNi wrote:

I recommend Timesert over a helicoil. Don't know if you can find it locally but Fastenal and MSC carry them.

i never heard of timesert but after googling it it looks pretty cool.
Nov. 11, 2009 6:11 a.m. tuna55 Reader

threadsert over helicoil for ease of installation.
Nov. 11, 2009 6:20 a.m. 44Dwarf HalfDork

Time-serts are great EXCEPT in limited space spots!! they are alot thicker so if the OE bolt is close to a wall or side of a casting you might crack it or make it extreamly thin do to the larger hole needed.

44
Nov. 11, 2009 7:13 a.m. BoxheadTim Reader

davidjs wrote: I think the shop needs to look at one of the solutions the good gentlemen have already suggested (or pay to have it done elsewhere)...

While I generally agree with the sentiment, I think it's a case of "good luck getting the shop to admit they did anything wrong". My freshly painted FC RX7 vert had to go into a shop I thought I had a good relationship with. Heck, I certainly gave them enough money and never questioned a bill.

When I got it back, it had burnt spark marks all over the car. They vehemently denied having anything to do with that ("we don't use angle grinders") even though the car had been to the paint shop, my garage and their shop and nowhere else. And I don't have an angle grinder, but I couldn't prove that it happened at their place.

To add insult to injury, when I collected the car from said shop (that was in administration/bankruptcy at this point), someone had stubbed out a cigarette on the bonnet.

At that point, lacking another RX7 specialist not too far away, I sold the thing for less than the paint job cost me.
Nov. 11, 2009 7:22 a.m. jstein77 HalfDork

Xceler8x wrote: ...I also have no idea how to install a helicoil.

Sorry, I missed that part of the post. Helicoil kits come with everything you need to install them. The steps are:

A) Drill out the hole with the supplied drill size. Be sure to use a shop vac while drilling so the chips don't fall into the engine.

B) Tap the hole with the supplied tap. Again, use a shop vac and lubricate the tap with cutting oil or WD40.

C) Place the helicoil onto the supplied installation tool and thread it into the hole until the top of the coil is about 1/16 inch below flush.

D) Reach into the hole with needle nose pliers, bend the tang over and snap it out. Try not to let it fall into the engine.

Not totally straightforward, but after you've done two or three it's a piece of cake.
Nov. 11, 2009 8:00 a.m. Xceler8x Dork

Thanks for the input guys.

Fart. I'd take it to the shop but if they can't install bolts right when just putting an exhaust in...my faith in them fixing crossthreaded threads is pretty low.

I'm hearing helicoil or timesert. I'll investigate both.

Thanks again guys.