Heli Coiling a head

[da83moon]

1979 Evinrude 55HP.

Was cranking down the head when all of sudden nothing happened and it got loose on me. Of course my heart dropped and I was like craptwhat have I done. I unscrew the bolt and out comes the threads. I was like crapt. From reading everything it appears the elicoil is the best option to fix the situation. Is there any tricks or anything I should know before using it? Also is there any tools that would make it easier?

 

[elhombre]

Re: Heli Coiling a head

I helicoiled 3 headbolt holes on my v6 this spring, so far so good. If you don't take it to a shop, figure out the correct size helicoil to use (not too big), drill straight, use a "bottomig tap", and if corrosion is an issue chase the remaining holes with the correct size tap to clean em up prior to torqueing.

 

[iwombat]

Re: Heli Coiling a head

Doesn't hurt to put some red loctite on the outside of the helicoil before insertion either.

 

[Randybeall]

Re: Heli Coiling a head

There is a product called Timesert. It is a thread repair like Helicoil but Timesert is a solid tube. We use them in Porsche all the time with great success.

 

[samo_ott]

Re: Heli Coiling a head

If it's a head bolt and not the plug, usually there's enough metal around the bolt hole that you can just drill one size bigger and re-tap. Of course you will need the next size bolt up and to also make the hole bigger thru the head.

 

[Tim Frank]

Re: Heli Coiling a head

And if you have access to metric fasteners, there is usually a metric size that falls between the original inch thread and the next larger inch size.
e.g. if the head bolts are 5/16-18, you could try an M8 tap and bolt. If that doesn't work, you still have 3/8-16 to fall back on.

 

[Bear 45/70]

Re: Heli Coiling a head

Using a torque wrench to tighten steel bolts in aluminum engines prevents this sort of thing.

 

[Benny1963]

Re: Heli Coiling a head

get the proper helicoil kit ,drill it tap it and use insert to bring it back to original size have about 8 helicoiled bolts on the one i just rebuilt two in the head bolts as they said use some locktite ,and retorque to sequence

 

[jtexas]

Re: Heli Coiling a head

Grease on the drill bit and the tap to keep shavings out of your work. Work the tap in & out, 2 or 3 turns in, back out, then back in, it'll work fine.

Get the name brand, even if you have to go out of your way -- I used some store brand from autozone once, the inserts were just a hair off the right size. Made for a real hassle.

 

[James R]

Re: Heli Coiling a head

All of the information you have received is generally good.
The problem with drilling is that the drill tends to wander and you can get into a missalignment. Going to the next size in metric, providing you have enough meat, is probably the best option. You will not necessarily have to drill. However be carefull not to break the tap. Turn the tap untill it binds then back off a 1/4 turn. Make a turn and a half in steps then remove the tap and clean it. Re lub the tap and hole and go again. Take it gently and you will be successful. Clean the remaining bolts and threads and use antisieze during assembly. If already assembled you can remove the other bolts one at a time and clean and reassemble with antiseize. This will allow correct torquing and minimize the bolt or thread damage.

 

[Bear 45/70]

Re: Heli Coiling a head

All of the information you have received is generally good.
The problem with drilling is that the drill tends to wander and you can get into a missalignment. Going to the next size in metric, providing you have enough meat, is probably the best option. You will not necessarily have to drill. However be carefull not to break the tap. Turn the tap untill it binds then back off a 1/4 turn. Make a turn and a half in steps then remove the tap and clean it. Re lub the tap and hole and go again. Take it gently and you will be successful. Clean the remaining bolts and threads and use antisieze during assembly. If already assembled you can remove the other bolts one at a time and clean and reassemble with antiseize. This will allow correct torquing and minimize the bolt or thread damage.

Actually with the bolt hole already there, the drill will tend to stay centered in the hole. It's why center punching and pilot holes work so well. Having an odd sized bolt in the bunch is not a good idea either.

 

[TN-25]

Re: Heli Coiling a head

Caution! Be aware that when using anti-seize or lube on the headbolts, your torque values will be higher than indicated on the torque wrench because of the reduced friction of the bolt going in. If you torque it all the way to the final spec'd value with anti-seize you are esentially over-torquing, potentially pulling out more threads or snapping bolts. If it doesn't come to that, you will be at the very least over-stretching the bolt and won't realize it.

There must be a general chart out there somewhere showing the adjusted torque values after using anti-seize or lube.

 

[James R]

Re: Heli Coiling a head

Sorry. Should have said to torque to the lower end of the spec to avoid issues.