repair of bolt threads on block or weld repair

[72chevy4x4]

I have a tractor which has a subframe assembly which bolts to the front of the lower portion of the engine block. The front axle, FEL, bonnet, and a few other pieces mount to this subframe.

The bolts holding the subframe onto the block have all sheared or wallowed out. Drilling and extracting is not going well, so I'm looking for suggestions. The depth of the existing 'wallowed' out holes is approximately 1". Three of six holes per side, are sheared, which doesn't leave a lot to work with.

#1 I could helicoil the existing holes-can they take enough torque to provide the lost strength if I can't drill out the other 3 holes?

#2 welding on the block: could I arc weld using a cast iron stick? If so, I would open up the existing holes through the subframe and weld the subframe onto the block. My guess, IF it's allowable, I could only do one shot at a time, then let it cool for a considerable amount of time so as not to heat up the block too much (of which oil pan is nearby). The other concern is will the weld hold through out the years?

If anyone has some ideas, please share

 

[ray66v]

What if you drilled the studs out, had the holes from drilling them welded closed, used the remaining holes to bolt up the sub frame. Then used the sub frame to guide your drill and redrill the welded holes and tap them. Welding cast is not for beginners, so if you have not done it, I would get a qualified welder. I realize this means you still have to do a lot of drilling. But, maybe someone else has a way around that.

 

[ToadHill]

I helicoiled many race components on my racecar for years. If done right they will hold up as well or better than the factory. Remember you'll be replacing the cast iron threads with steel coil threads and you should actually have better threads than you started with.

 

[Renze]

The solution that gives you most strength is to drill out the holes (if that's even necessary) and tap them one size bigger. I dont know how many meat is around the thread holes, but that would be a 100% solution.
I know helicoils, though never used one myself, so i have no idea if they are as strong as a "real" tapped hole.

 

[72chevy4x4]

I've been working on the extracting the broken bolts, and even after drilling out enough of one side of the stud (didn't start drilling in the center...), the remaining stud still won't come out and I'm breaking my tools :-(

I just tapped one of the wallowed openings 12x1.50, and the threads are not clean, so I'll go out and buy a larger tap-maybe 13 or 14x1.50.

Over the years, the loose fitting bolts had slightly wallowed out the holes on the subframe-I was planning on welding on a grade 8 washer at time of reassembly. Might be able to find a sleeve at TSC, but not positive about that course of action.

thanks for the info thus far

 

[PILOON]

Helicoils are a permissable repair even on aircraft engins, as a matter of fact I believe that is where the system was developed.

Once a helicoil is inserted, the attachement is better than origional as you now have steel against steel rather than cast iron.

On aircraft a very common use was for 'rethreading' sparkplug holes and there you are looking at some pretty high PSI's due to compression, not counting the temperature ranges due to combustion (typically CHT's= 500 deg's).

One problem is that each thread size calls for a different insertion tool and a different tap.

I vote for helicoils!

 

[Soundguy]

My vote is to do the hard work and extract ALL the sheard off bolts... it's hard work.. and we have all had to do it.

On the holes that are wallowed out.. .. MY choice would be to oversize and retap to next standard size.. if there is not enough meat there.. then helicoil is the next choice.

soundguy

 

[Wayne County Hose]

Aircraft are also held together with rivets and don't move dirt. I wouldn't hold my tractor together with rivets. Heli-coil's are an absolute last resort. You have to drill oversize for a heli-coil anyway, so why not just drill for a larger bolt? If you are having a hard time drilling the holes on center, go rent an electromagnetic drill. They are worth their weight in gold, and they are heavy! While you are at it, you could drill out the wallowed holes with this drill press and insert a steel bushing and weld it. It would be better than new.

There is also what I consider a helicoil on steroids. It is an actual threaded insert that is more like a nut with threads on the outside too. If I had to do a repair like this and needed an insert, it's what I would use. I have had a new helicoil kit in my toolbox for over 15 years and have never used it. I got it for nothing and just keep it around for my friends to use, and it looks nice. I've seen too many come out. Don't know if it was improper installation or not, but I would avoid them at all costs.

 

[rankrank1]

I would vote drill and tap oversize. When tapping things oversize I always look at both metric and standard SAE size bolts and pick the one that is the minimum oversize that will correct for the stripped hole. That way the minumum amount of material is removed from the structure. Also, if the hole is shallow, I will pick a finer thread over a courser thread for more threads.

 

[bjcsc]

I'm with Wayne County Hose. The inserts I think he is talking about are Keyserts. I've used the stainless ones to repair wallowed out holes quite a few times. Around here you can buy them from industrial fastener companies. You'll notice the description reads: "especially suitable for use in heavy wear and high vibration situations such as mining and earth moving equipment".