Stripped Cylinder head bolts!! I messed up baddd!! HELP!

[makaveli07]

Hey everyone!

I messed up bad, somehow 3 cylinder head bolts on my 787 stripped when i was taking them back off to change the gasket to get my squish within spec! What do i do, these cylinders were bored and new oem pistons fitted i dont want to throw away perfectly good cylinders due to stripped bolts HELP!

Edit: 2 bolts are kind of about to strip, and one is completely stripped

So sad right now.

Any help is appreciated!!

Thank you!!

 

[Rookie_MIB]

Wow, that’s no fun. Two looks like you could chase the threads with the right tap and clean the threads up and replace the bolts. The third is pretty chowdered.

Now because these aren’t under large amounts of torque, threads could be repaired with helicoils or threaded inserts. Both would require some gentle drilling, some tapping, and putting in the coils or inserts (I suggest the inserts, helicoils can be finicky). Then thoroughly clean out the heads and reassemble.

It’s not a hard process, and they’ll use this on automotive blocks and heads so it’s a durable fix. And you might just want to get inserts for all three of those bolt holes to be safe.

 

[makaveli07]

Wow, that’s no fun. Two looks like you could chase the threads with the right tap and clean the threads up and replace the bolts. The third is pretty chowdered.

Now because these aren’t under large amounts of torque, threads could be repaired with helicoils or threaded inserts. Both would require some gentle drilling, some tapping, and putting in the coils or inserts (I suggest the inserts, helicoils can be finicky). Then thoroughly clean out the heads and reassemble.

It’s not a hard process, and they’ll use this on automotive blocks and heads so it’s a durable fix. And you might just want to get inserts for all three of those bolt holes to be safe.

Is the helicoil something i can do at home or do i need to take it to a shop? I noticed a bunch of helicoil kits on amazon i can get in M8 x1.25. The helicoils dont seem to be long enough to cover the whole depth of the original threads, do they just sit at the top? And most importantly is there enough clearance from the piston wall to drill and put helicoil ? (Pictures for reference)

Thank you in advance for all the help!

 

[mikidymac]

Done this a lot.

You want helicoils but you can’t use the standard ones in the kits because they don’t go deep enough for the torque of the head bolts.

What I suggest is to buy the kit so you will have the correct drill, tap and installer then buy extra length helicoils from McMaster Carr. I think I used the 16mm long ones.

 

[etemplet]

Depends on how handy you are at drilling. You have to make sure the drill doesn't walk into the sealing area. Helicoils will be fine just make sure when you set them they are below the surface. You'll have to figure out why the bolts stripped so it doesn't happen again. I think those bolts only take 17 ftlbs of torque..

 

[makaveli07]

Depends on how handy you are at drilling. You have to make sure the drill doesn't walk into the sealing area. Helicoils will be fine just make sure when you set them they are below the surface. You'll have to figure out why the bolts stripped so it doesn't happen again. I think those bolts only take 17 ftlbs of torque..

I know exactly why they stripped now, after blasting the cylinders before i sent them out to get bored, i guess media got lodged in the threads of some of those threads and i didn't do a good enough job of cleaning them unfortunately.

 

[makaveli07]

Done this a lot.

You want helicoils but you can’t use the standard ones in the kits because they don’t go deep enough for the torque of the head bolts.

What I suggest is to buy the kit so you will have the correct drill, tap and installer then buy extra length helicoils from McMaster Carr. I think I used the 16mm long ones.

Would you mind helping me out by linking which ones i should buy ? I know the bolt is M8 x 1.25 but the website you mentioned has tons of different types of helicoils. I measured the threads on the bolt they appear to be around 32.4 mm

Thank you in advance!!

 

[etemplet]

Done this a lot.

You want helicoils but you can’t use the standard ones in the kits because they don’t go deep enough for the torque of the head bolts.

What I suggest is to buy the kit so you will have the correct drill, tap and installer then buy extra length helicoils from McMaster Carr. I think I used the 16mm long ones.

Hmmmm... I didn't know they made extra long helicoils. That's cool. I've been in the machinist trade since I was 18 and the funny thing was, I had never used a heilcoil the whole time I was activly doing machine work, Probably 25 years. Ha ha. We just never used that sort of thing. I don't think I had ever seen one and if I did, I didn't know how it worked. Now that I mess with jet skis.... I have a set for every size. Thanks for posting about the extra length. I'll get some of those.

 

[etemplet]

Would you mind helping me out by linking which ones i should buy ? I know the bolt is M8 x 1.25 but the website you mentioned has tons of different types of helicoils. I measured the threads on the bolt they appear to be around 32.4 mm

Thank you in advance!!

I don't know much about helicoils but you won't need more than 1/2" in length. Just offhand I'd say most are about 1/4" - 5/16" long at least the ones I buy are that long. I've heard from some knowledgeable people that helicoils are stronger than the original thread. I dunno...that might be true for some materials. I know this... they work and have saved me a lot of work. They do require a bit of finesse. Good Luck.

 

[makaveli07]

Okay so i did some research, here is what i found pic attached for Mcmaster Carr sizes ( i think these are the ones) they have sizes all the way up to 24mm . Now the kit i was considering buying with all the tools from amazon is this one.

DAYUAN 131Pc Thread Repair Kit, HSS Drill Helicoil Repair Kit Metric M5 M6 M8 M10 M12 https://a.co/d/b4f6DNK

Which has M8x1.25x10.8mm

1. Should i still get the helicoils that are 16mm from McMaster or go longer?

2. and would the installation tools from this amazon kit work on the 16mm helicoil ?

Thank you!!

 

[makaveli07]

I don't know much about helicoils but you won't need more than 1/2" in length. Just offhand I'd say most are about 1/4" - 5/16" long at least the ones I buy are that long. I've heard from some knowledgeable people that helicoils are stronger than the original thread. I dunno...that might be true for some materials. I know this... they work and have saved me a lot of work. They do require a bit of finesse. Good Luck.

Out of curiosity do you use OEM brand Helicoils or aftermarket ones ?

 

[etemplet]

Out of curiosity do you use OEM brand Helicoils or aftermarket ones ?

I bought Helicoils but I don't know much about them. LOL I still don't know if the different vendor products will interchange so I stick with the Helicoil brand. @mikidymac would be a much better resource than me.

 

[Rookie_MIB]

I would say getting the 16mm should be fine. Again remember that it’s only 17-20 lb ft of torque. Just remember to take your time drilling, and use plenty of lube when you’re cutting the threads for the Gila coil…

 

[etemplet]

It might be a good idea to step drill (go up in increments) to lessen the possibility of the drill walking away from the desired position which is exactly where the hole is at present. Step drilling reduces the forces pushing the drill from one side to the other. Probably one extra size in between the desired size is enough. Helicoils don't require much metal removal so it is just a suggestion. I've seen a lot of simple stuff go south quickly. Automatic transmission fluid is what I use for cutting oil. It works and you may have it in your stash at home. Be precise, pay attention, and don't push hard on the drill. Gently let it cut. Good Luck.

 

[makaveli07]

Done this a lot.

You want helicoils but you can’t use the standard ones in the kits because they don’t go deep enough for the torque of the head bolts.

What I suggest is to buy the kit so you will have the correct drill, tap and installer then buy extra length helicoils from McMaster Carr. I think I used the 16mm long ones.

Quick question regarding the helicoils. There are tons of options (stainless steel, particle free, lubricated, etc..) on Mcmaster; which one is the correct one to use ? I don't know much about the differences with them.

McMaster-Carr

Thanks!

 

[mikidymac]

Yes, you want the 16mm ones, 10mm isn’t enough bolt engagement.

You have to get the correct tap, drill and installer or you can’t install them.

I used McMaster Carr number 91732A788.

 

[POPPS]

For what it’s worth,,,when we have a sheared bolt,,,and since they are stainless steel,,,we send them out to a machine shop that uses lasers etc,,,we get the piece back with perfect threads,,,the original threads,,,it’s expensive,,,but the piece remains original.

 

[etemplet]

For what it’s worth,,,when we have a sheared bolt,,,and since they are stainless steel,,,we send them out to a machine shop that uses lasers etc,,,we get the piece back with perfect threads,,,the original threads,,,it’s expensive,,,but the piece remains original.

Popps What do ya'll do when the bolt is stuck or even break loose? I have a 951 DI and the head bolts are that way.... all of them and the bolt heads are so weak and easy to strip I'll have to sent the engine for full rebuild. I want to do a top end only as the bottom section looks really good.

 

[POPPS]

Hhmm…saw this on a “how to remove sheared bolts” utiuse,,,a common method was to weld a nut to the top of the sheared bolt,,,and remove it using the appropriate socket,,.

 

[makaveli07]

so i got the helicoils, 21/64 drill bit and the complete helicoil kit today, taking it to a shop tomorrow to get the work done. Now with that said:

1. These are 787 cylinders. I noticed the bolt goes in very very close to the cylinder side wall. After the drilling and tapping…. Would that not eat into the cylinder side wall ?

Any knowledge/ help is appreciated!

Side note: These helicoil kits aint cheap, not to mention labour in Canada isn’t either lol. Shop said $100 CAD ($75 USD) to install the helicoils that i bought. But id rather a pro do it with proper equipment.

Thank you!