Hi all,

Unfortunately my first post on the forum couldn't be one on a more positive note but I happened to pull a head bolt thread on my L98 build yesterday and am looking for advice on what options there are and experience from others on what can be done. I hope this thread can serve others in their search for solutions to this problem and advise them about all the options in one place.

For context; bought a freshened up L98 for an engine conversion (Australian variant of the 6L with LS3 heads), was a week away from putting the motor into the car, pulled the tape the last owner placed over the exhaust ports and found metal shavings on the underside of some exhaust ports. I decided to be on the safe side and pull the heads to check the bores as I had already turned the motor over by hand when installing the rocker arms. Luckily, no scoring or damage to the cylinder walls so purchased new head gaskets and bolts and got to work putting the motor back together. First head with new gasket went on, torqued the new bolts to correct specs, no issues. Second head with new gasket went on, torqued to the first stage and second with no problems. Tightening #9 M11 bolt on the third stage and the bolt went spongy - at this point I knew it was pulling the thread so I stopped. Pulled out the head bolt and parts of the aluminum thread were on it. Undo the rest of the already torqued head bolts and remove the head, inspect the thread and yep - thread is damaged - there goes a brand new set of head bolts, a new gasket, and of course, the thread.

It appears the options for repairing these threads are (surprisingly) limited or cost prohibitive especially considering the support the LS platform has as once of the most built platforms in current times. A quick google search later and various older threads on this forum and others suggested things such as helicoils, time-serts, studs, etc. So here I am, wondering in 2020 after thousands of LS builds have been complete, and the likelihood that many others have damaged head bolt threads in these blocks, what options have we got to sort this out? As I see it:

• Helicoil - A lot of debate on this working/not working. Many say they won't be strong enough and aren't ideal for head bolts yet others say stainless steel helicoils will be stronger than the original thread and work better when correctly installed. This is irrespective of the fact the LS uses an odd M11 x 2.0 thread and I haven't found a helicoil kit in this size to complete this job - someone please link me if I've missed something?
• Time-sert - These are apparently stronger and better suited for head bolt repair, are made specifically in M11 x 2.0 size to suit LS head bolt repairs, and come in a comprehensive kit that includes everything you need to complete repairs on ten threads (all M11 bolts for one head). Pricing is astronomically high by the time I land this in Australia (Over $1K AUD).
• 7/16" helicoil and head bolt to suit - 7/16" is the closest imperial size that could be used for a helicoil. Bolt hole will be drilled and tapped to suit the helicoil and a 7/16" head bolt will be used. Issue I see here is mixing the conventional style head bolt with the LS TTY style bolts. Even if torqued to the correct LS head bolt specifications - will this provide the correct clamping force and distribution?
• Studs for the one thread or full stud conversion - Drilling and tapping the damaged thread for a stud and converting that one thread. As above, clamping force and distribution from mixing TTY and one stud might be a concern, potential issues about having to machine the holes in the head if going too large with the stud. Alternatively, a full stud conversion which adds time to strip back to a bare block and the obvious large cost of the studs and machine work.
• Machine a custom stainless steel sleve - Machine a stainless steel sleeve that is threaded M14 on the OD (ideal size for existing hole) and M11 x 2.0 on the ID. Tap the hole the full way in the block to M14 and insert the stainless sleeve with loctite. OEM head bolt can then be utilised with nearly no chance of stripping the new thread in the block.

These are just some options I've come up with after a day of research. As above, if anyone has any ideas/comments/concerns to add to the discussion please do so and hopefully we can provide a solid place for others to reference off. I'll be keen to see what has already been done and if the repair is holding up as I'm looking to do this repair fairly quickly and have the motor in the car and running within a month or two.

 

Had this happen once to me. I was using a stud kit and pulled the threads out of one hole. Had a machinist make a stud tapped the hole and never had an issue after it.

 

Interesting to know... Did you go oversized with that one stud, use a helicoil/other thread repair style, or something else?

 

He made the stud. (My friend worked for a professional race team at the time) Just used a larger thread and tapped the block. Worked well.

 

If it were me, I'd get an oversize bolt that I can cut, center bore it and then tap it for the head bolt size...drill and tap the block to fit the insert and loctite it in. Pretty much the same as your last option....Not sure i'd use stainless tho. Sometimes stainless causes more problems. Maybe use a grade 8 bolt instead.