Stripped head bolt, failed helicoil again in 346 Flathead

[gary griffin]

This is a repeat of last year.  I was hoping to drive the restored 1942-6719 to Las Vegas but head bolt stripped at an old repair. I put in new helicoil and the engine ran fine but when I re-torqued it the new coil gave way.  I gave up and flew to Las Vegas for the Grand National which was a great trip and my first GN.  Been a busy year, flew to Chicago and rented a car and drove to Muskegan Mi to see the Silversides submarine museum. My uncle served on the Silversides in WW- II so it was an important trip and we followed up with a week in Kalamazoo for the Cadillac Club "Fall Festival" at the Gilmore museum which I highly recommend. We flew home after spending a week in Chicago so I could have new knees installed..  Long story but the reason the 42 is still sitting.

Now that my knees are getting better it is time to try to figure out the problem with the 42.  The front middle head bolt in the left bank below the water outlet to the radiator.  I purchased a "Big Sert" kit to drill and insert but have some reservations.  The Big Sert has a special drill bit to counter sink the sert so there is less thread engagement. I am very concerned about the status of the bolt hole. I can make a jig and drill the hole correctly but not sure how much metal is left and if I strip it again what can I do?? I am seriously considering torquing to a lower rating than the usual 55 or 60 ft lbs??  The front center tier bolt is only serving one piston and the bolts above and below it are less than 7 inches apart.   

Looking for some advice here??  If this fails the next step is a big one.   

[Bobby B]

Gary,
Hi. Got your PM, but since you posted, I'll just post back. Happy New Year! Glad to hear that you're back on the '42 again. Before you get crazy and panic, there are some options for you. If the hole is not holding, oblong, etc., I have seen some methods that have had good results. You could tap out the next size up, but in fine thread. Cut the head off a fine thread bolt that will allow you full depth in the hole. Slot the top so you can use a screwdriver to turn it in, just a hair below deck height, and use some Loctite. Once it sets up, you'll need to make a jig to drill straight through at the correct angle and spacing between the other bolts. You could use the head as a jig, but I think there's a lot of slop for using a bit/tap afterwards. Probably make something that bolts down with 3 holes in it, so you can use the outside holes to bolt it to the block and you have a center hole to do your thing in the perfect position. I've seen this done before with good results. Here's another Company that's worth checking out. They have some excellent products available that are able to withstand the torque that you need. They are a step above the normal Heli-coil/ Time-sert. Give them a call and explain your situation. I'm sure they'll be able to help. Keep in touch and let me know which route you decide to take. Good Luck!
                                                                                                                                                Bobby
http://castingrepair.locknstitch.com/category/full-torque-products

[Jay Friedman]

Bobby,

If I understand correctly, the danger is that a drill bit will not necessarily drill in a straight hole, which can be corrected by making a jig of some kind.  (The 3 hole type sounds good.) 

I was wondering if a further way to ensure a straight hole would be to drill the hole to a size .010 or .020 smaller than required and then use a reamer to enlarge it to the diameter needed for a tap.  Along with the jig you suggest, it may be that a reamer would provide a straighter hole.

Jay

[harry s]

Gary, Good to hear you got the knees fixed, not so good to hear about the engine problem. Bobby, That fix looks to be the solution and certainly good information to have. Here is video showing the process:
https://www.youtube.com/watch?v=9XfTORBtcSE
Harry

[savemy67]

Hello Gary,

Have you been able to determine why the coil gave way?  From your post I gather that the coil insert in the block did not hold.  Do you think this was due to a poor quality insert?  Or is there something about the casting at that hole that is suspect?  It was repaired previously, so maybe something about the hole is not quite right.

If a close examination of the hole (suggest using a strong light, magnifying glass, Prussian Blue) shows flaws in the casting, you may want to consider how effective an upgraded insert may be.  Hopefully there is enough good "meat" at the hole for the upgraded insert to work, but consider calling the manufacturer as Bobby suggested.

Harry, thanks for the video link.  I have seen similar before along with the lock-n-stitch process.  Do you ever wonder if these fixes get used in other than perfect-world, laboratory conditions?   You could eat of those castings.

Respectfully submitted,
Christopher Winter

[Bobby B]

Bobby,
I was wondering if a further way to ensure a straight hole would be to drill the hole to a size .010 or .020 smaller than required and then use a reamer to enlarge it to the diameter needed for a tap.  Along with the jig you suggest, it may be that a reamer would provide a straighter hole.
Jay

Jay,
  The higher (height wise) you make the jig, the straighter the guide will be for drilling your hole. With something like this, I would think it through, take my time, and spend whatever it took to avoid taking the engine out of the car, or having the hole Mig welded up and starting from scratch. I have  a Heli-Coil or two in my Block that I did, and knock wood, no problems. Like Chris pointed out, I would look at why it failed before I Jumped the Gun. You also have to worry about a hairline crack going towards the cylinder. Maybe there was just not enough metal there to grab.
                                                                                                                                                                         Bobby

[Steve Passmore]

I agree about checking out thoroughly why the helicoil didn't hold.    I had an engine years ago that needed 18 helicoils ( yes 18!) It still runs as far as I know but there are two main reasons for failure, the first being the underside of the casting corroded away. One engine I have seen had barely 3/16" of cast left holding the coil, the rest was just dangling in the water jacket. The thinness of the casting at this point is a problem with these motors.
Having to undo heavily corroded head bolts until they break will gouge out the corroded casting underneath also.

Second reason is someone just getting stuck in with a drill and tap not getting a perpendicular hole and thread and then having to re-cut it, hence leaving little thread for the bolt to grip.

[fishnjim]

Since it's already had a heli-coil insert, it's already larger than the original hole. 
You'd have to assess, how much metal is left, before you make it bigger.   So that may not be the best approach.   I agree you should call some of these people and get their opinions, but they're also trying to sell, so you have to judge the info.  Maybe just remove damaged insert and reinstall is the least resistance path, assuming the internal threads stripped, not the external.
I'm concerned that you did not give a reason, for retorquing, like it was leaking, etc. and may have simply overtightened a good connection.   If it wasn't leaking, for instance, it may not have needed retorque.
A thread is only so efficient and coarse is less so than fine.   When there's two of them(heli-coil) that reduces it even further but they're different size.
So the tightening has to be evaluated compared to a new thread which the factory torque is based on.   I have put a drill to a block before, but always ultimately defer to the engine machinists in a case like this, over DIY, if I'm not certain of my success.   No guarantee, but they may have better technique or equipment.

[gary griffin]

Thanks for all of the great ideas everyone.  I will tike the time to sort out and figure the best way for me. Preferably it would not include removing the engine from the car.

I figure the jig to be they key factor for repair at this point.  I have an extra left head that I could possibly use for a jig. My engine was changed out to a 1941 engine when the army owned it. I found and good used  a 1942-1948 head for the left side as the 41 head was incorrect. 

Jim,  I always re-torque after a run in.

[harvey b]

Would a screw in stud work?,you could install a stud and use a nut to torque it down,might save some movement when it is finally tightened up? might be worth a try. harvey

[Janousek]

I measured the O.D. of a 7/16 helicoil at .545"

McmasterCarr list a large keysert or 7/16" that uses a 37/64 drill bit which measures .580".
On paper you should be good to use a keysert if the block isn't to rusty from the backside.

Your head will make a good template if you have a bushing made to tighten the 37/64 drill into the head bolt hole. 

Another option is to borrow a magnetic drill and use a go/no gauge to align the hole if you think the current hole is aligned good enough.   I used a magenetic drill to install helicoils for 27 headbolts in our Auburn engine last summer.   Worked like a charm.  You just have to know someone that has one and is willing to lend it. 

Good luck.   Brad