125hp headbolt thread stripped

[spool]

Hey guys,

So the previous owner of my 125hp has stripped 3 threads from the block (All on Cylinder 1), they've attempted (poorly) to helicoil it, tried running a new helicoil into the end of the thread where it was the best however any attempt to torque it pulls out the helicoils. they're 1.5D helicoils.

I am trying to torque the bolts to 18.75ft/lb as per the service manual.

I've been looking into other solutions such as thread replacements such as full torque but i can't find anywhere that will sell them.

Does anyone else have any ideas? I Could oversize the bolts and drill/cut a new thread but im worried about how this might affect the head as id have to oversize the hole for the bolt too.

 

[jerryjerry05]

Re: 125hp headbolt thread stripped

Drilling a bigger hole shouldn't be a problem.Unless they enlarged the holes too much.
I'd do that before I'd use a HELLIcoil.
Pics?

 

[Frank Acampora]

Re: 125hp headbolt thread stripped



Don't bother drilling and tapping for Heli-Coils or equivalent. The stripped holes are just the right size to be re-tapped to 3/8 - 16. You will need to ream out the head itself to clear the 3/8 bolts though. I just did this on an old Chrysler 105 And bought some grade 8 headbolts and washers from Fastenal

 

[spool]

Re: 125hp headbolt thread stripped

View attachment 190829View attachment 190830View attachment 190828

Don't bother drilling and tapping for Heli-Coils or equivalent. The stripped holes are just the right size to be re-tapped to 3/8 - 16. You will need to ream out the head itself to clear the 3/8 bolts though. I just did this on an old Chrysler 105 And bought some grade 8 headbolts and washers from Fastenal

Frank, as per my original post, someone has previously drilled out the holes and cut a 3/8 thread which doesn't seem to hold heli coils as is, it MAY hold a bolt which i guess i can try first but i fear i may need to go bigger as someones tried to repair it and failed. I've got a drill press and will have no problems oversizeing the headholes but how large can i go?

 

[gm280]

Re: 125hp headbolt thread stripped

Frank, as per my original post, someone has previously drilled out the holes and cut a 3/8 thread which doesn't seem to hold heli coils as is, it MAY hold a bolt which i guess i can try first but i fear i may need to go bigger as someones tried to repair it and failed. I've got a drill press and will have no problems oversizeing the headholes but how large can i go?

Manny many years ago I use to work in DEPOT repair section and we used an item that was the whole insert and not just a Heli-Coil (which I also used with good results too). This insert was threaded into a larger hole drilled and tapped to accept the insert. So when all was said and done, that insert was the new threaded section for your original head bolts. I can't remember what they were called, but they worked great and held as good as or better than the original threads. Those threaded inserts looked like a long bolt with threads inside the bolt that was of the same thread size as the original threads you’re trying to repair...



Make sure you use some type of glue or adhesive when installing one of these threaded inserts so it stays in place when you remove the head bolt again... :joyous:

 

[spool]

Re: 125hp headbolt thread stripped

Manny many years ago I use to work in DEPOT repair section and we used an item that was the whole insert and not just a Heli-Coil (which I also used with good results too). This insert was threaded into a larger hole drilled and tapped to accept the insert. So when all was said and done, that insert was the new threaded section for your original head bolts. I can't remember what they were called, but they worked great and held as good as or better than the original threads. Those threaded inserts looked like a long bolt with threads inside the bolt that was of the same thread size as the original threads you’re trying to repair...

View attachment 190979

Make sure you use some type of glue or adhesive when installing one of these threaded inserts so it stays in place when you remove the head bolt again... :joyous:

That's exactly what im looking for, i've seen a few instructional videos but cant find where to buy them.

I'd really perfer to stick with the 5/16 headbolts. I might call round some speciality bolt shops and see what i can find.

 

[spool]

Re: 125hp headbolt thread stripped

Ok, found some..

Recoil 73051 Thread Keysert Insert UNC 5 16 18 | eBay

It's a solid insert and uses locking pins to hold it in place.

External Diameter is 7/16 which is good because i can bore it out a little more and cut brand new threads. the finished job should be just as strong as standard.

 

[gm280]

Re: 125hp headbolt thread stripped

Ok, found some..

Recoil 73051 Thread Keysert Insert UNC 5 16 18 | eBay

It's a solid insert and uses locking pins to hold it in place.

External Diameter is 7/16 which is good because i can bore it out a little more and cut brand new threads. the finished job should be just as strong as standard.

Yes believe me, when properly installed they are much better then just threaded aluminum. In fact that is exactly what most aluminum black boxes on DOD aircraft use for their threaded inserts. Hope it all works out for you perfect... Just google threaded inserts for even more options and places to purchase. They are not hard to find and really not that expensive either...

 

[Frank Acampora]

Re: 125hp headbolt thread stripped

There is not a lot of meat on the fuel pump side of the block as you can see from my photos. Some day I intend to experiment with using longer 5/16 bolts and putting nuts behind the bosses.

 

[spool]

Re: 125hp headbolt thread stripped

yeah, i've already measured it all frank, it *should* be ok with a 7/16 hole.

I thought about installing nuts behind the bolts however 2 of them are blind holes and have no access behind.

From the looks of it you tap a 7/16 hole then bang in the pins which lock it in place permiently.

 

[spool]

Re: 125hp headbolt thread stripped

FYI - I fixed the threads by using thread inserts, they worked excellently.

Once fixing the headbolts i discovered the piston rings are shagged and the whole thing needs a rebuild

Here is the finished product, these have 4 locking pins and do not need to be glued in, they will never turn them self out and are actually stronger than the original thread

 

[tcraft1]

Re: 125hp headbolt thread stripped

The insert you found is called a Key-insert in the states, most people call them keenserts (brand), you can get them at any supply house like, fastenal,mcmaster-carr or car-lane. Helicoil also makes an insert called a twinsert that is used when the STI tapped hole gets dummyed up. It uses the same thread only bigger ?. I have used many of both and they work well when installed correctly.