Exhaust manifold bolt holes stripped

[Redland1]

I replaced gaskets and bolts on the exhaust manifold a couple of months ago and when I was torquing I the bolts three kept turning. I ended up putting in helicoils. Recently I started to hear a loud exhaust leak and isolated the cylinder from where it was coming from and retorqued the bolts but the lower one just turned endlessly which has a helicoil. I’m thinking of drilling it out to the next size up and using timesert’s on all bolt holes so I don’t have to deal with this again. Will be ordering a new manifold,and gaskets. Will drilling it out to the next si.•ze up and putting in timeserts work ?
Also is there a drill guide or something to get a perfectly straight hole ?

[Rawze]

I have had a TON of experience with heli-coils in my past ...

Personally, I have never seen a proper heli-coil break when done right... not even come close to breaking even when over-torqued, unless it was severe. - Something else is wrong?.

Did you use a torque wrench to set them ??.

What torque were you torquing the bolts to?.. and was your torque wrench accurate?.

How deep are the threads that are tearing off?.

What is the width of the bolts (shank diameter in mm) ?.

Are you using OEM bolts, and OEM stand-offs?.

Is it an OEM manifold?, and is that manifold on any TSB list for an upgrade or modification?. One similar to this:? https://rawze.com/forums/showthread.php?...2#pid66592

How deep are they threading into the head (in mm)?

what size heli-coil did you use?, and how deep were its threads (in mm)?.

Possibly bad de-mandate tuning that overheats the exhaust / manifold, or perhaps over-boost the engine like mad?.

Something does not sound quite right there.
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as far as a drill guide, you can get one at amazon, home depot, etc ....
https://amzn.to/4yIq735

[Nostalgic]

Echoing most of what Rawze said, and adding that Timesert kits come with the drill bit, chamfer bit, tap and inserts to do it correctly. I will add that I have no experience putting in helicoils personally, I've always used Timeserts, but I have tore down stuff and found helicoils. Sometimes they're good, and others....it depends on the installer.

[Redland1]

If I had to guess it was definitely a bad install due to the way I installed them and you’re going to blow a gasket with what I did lol. The stripped original threads happened when I did the retorque after a week of the install and all the bolts did was turn so I didn’t want to take everything apart and just tapped right through the manifold (critical mistake). The manifold is an oem 870 manifold and the bolts gaskets and spacers were {non-oem}. Helicoil size is M10x1.5. As far as drill depth I wouldn’t be able to tell you right now because u don’t have it apart yet but will in a week from now.

My plan is to use a Big Sert 5015 kit that will keep the M10x1.5 size.

[Rawze]

non-oe bolts, gaskets, spacers ... and then wondering why things stripped out under high heat loads?.


For all anyone knows, those spacers or bolts may not even have been the same metallurgy designed for the same amount of proper heat expansion. Threads might not have been the same depth,.. etc.etc. -> Just saying.