Helicoil

[iwombat]

Chased out the threads on the #1 and #3 cylinder head. On the two inside bolts the threads came out with the tap. Guess that's why I always chase out head bolt threads.

Anyway, anything in particular I need to know about helicoiling for cylinder heads?

 

[F_R]

Re: Helicoil

Bolt hole threads, right? Piece of cake. Needless to say, you need the tool kit. Just tap the hole with the special tap, screw in the coil with the tool provided, and break off the tang. There should be an instruction sheet explaining all this. Spark plug holes are more of a challenge.

 

[iwombat]

Re: Helicoil

Have the kit, and yes spark plug holes are a pain.

I'm wondering if maybe anti-seize or loctite on the head bolt is a good idea to prevent the bolt seizing on the coil. I always put coils in with a drop or two of red so they don't back out later.

 

[kenmyfam]

Re: Helicoil

Have the kit, and yes spark plug holes are a pain.

I'm wondering if maybe anti-seize or loctite on the head bolt is a good idea to prevent the bolt seizing on the coil. I always put coils in with a drop or two of red so they don't back out later.

I have one in one plug on my motor. Each time I change or take out the plug out comes the helicoil with it !!! I now have one spare plug with me with a helicoil already fitted just in case. Loctite is O.K. but does not seem to do much for me.
Did you cross thread the tap when you were chasing the threads ??? or were they just ready to disintegrate ???

 

[iwombat]

Re: Helicoil

I usually have good luck with red loctite on heli-coils.

No cross-threading, they went in clean and came out with a hitch-hiker.

 

[kenmyfam]

Re: Helicoil

I usually have good luck with red loctite on heli-coils.

No cross-threading, they went in clean and came out with a hitch-hiker.

That sucks !!!!

 

[rjezuit]

Re: Helicoil

Make sure you put the tap in square and use plenty of lube. Kerosene works well on aluminum. Rick

 

[iwombat]

Re: Helicoil

Ok, really. I'm not new at this folks. I've been chasing out every hole in blocks for the last couple of decades and this is the very first time I've ever removed threads. Usually it just removes dirt and crud so that the torque values are correct. Just one of those things, I guess.

 

[Ranger 330V]

Re: Helicoil

I have also had good luck using the red loctite on helicoils...and I used pb blaster on my tap...didn't think about kerosine..that would work really well. I also clean the hole out with carb cleaner and let dry before I put the threads and lock tite in.

 

[iwombat]

Re: Helicoil

I just have a big jar of cutting oil I can either dip the tap in, or brush on. I probably bought the stuff 15 years ago. Just says "cutting oil" on it - no idea what's in it.

 

[Ranger 330V]

Re: Helicoil

iwombat...lol...we have ALOT of "mystery" oils and things in the ag shop. That have been there for countless years. What do you think of the pic of my boat this weekend as my avatar?? Thats that 78 140 I worked on last this winter. That was taken on a VERY windy day..you can see white caps in the big pic. I was going 52gps, 5600 rpm, prop shaft is set 3" below pad. 21" renegade bass. Had all my junk in there too...lol. I was proud of that. 30 yr old engine isn't that bad huh?

 

[iwombat]

Re: Helicoil

A little update. . . .

One helicoil went in and held just fine. The second helicoil pulled out the new threads under load. That hole must have had some bad corrosion or something to compromise the metal that far.

Fortunately, I have a friend that welds aluminum for a living. So, I took it over to his place. We drilled the hole out one more size, and welded it all in to about 1/16" shy of flush with the surface. I bolted up the head snug and used a roll-pin inserted into the bolt hole as a drill guide for a pilot. Then, removed the head and drilled out the hole to the proper size for the tap. Tapped some new threads and all looks good. I checked over the mating surface with a straight-edge and all seems fine.

A total PITA, but the head is on and torqued down properly now. Sure pays to know aluminum welders.

 

[olemana]

Re: Helicoil

I have been doing equipment maintenance for the past 55 years. I have had terrible results using helicoils in aluminum or anything else!
A much better solution is a double threaded insert with a strake pin that cuts across all the external threads of the insert. The type commonly sold as spark-plug inserts for aluminum heads are also not very good.
The high quality inserts are commonly used to provide threaded fasterners for aircraft. Those also fail but are much stronger than heli-coils and no more difficult to install.