(Details.  The actual question is at the bottom.)

I didn't start this problem, but I have to admit that I finished the damage.  I bought a Ford 7700 and I have used it for about five years.  Great tractor, even if it isn't orange.  The problem is that one of the bolts which hold in the sway blocks pulled out and took the threads with it.  There is no way to just screw the bolt back in to the original hole.

The bolt is 7/8"-9 x 3" and it goes up in to the chassis of the tractor.  I don't have a picture of the bolt location, but in the video I am posting, the bolt is just behind the play button on the link.  On my tractor, the bolts attach to chains which prevent the lift arms from swinging around.  One of the bolts is still attached and giving no problems.

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(The question)

Basically, what is the pilot hole size for the next size up from a 7/8"-9 thread? Should I punt on this one and let a local machine shop do the work? 

You drill out the hole to ( lets say) 1-1/8 inch and thread it.... then you LOCITITE a threaded sleeve into the hole that is 1-1/8 OD and 7/8 inch ID... Back to original size... 

another way is to rethread the 7/8 hole to 1 inch and use a NEW bolt.

https://www.amazon.com/V-Coil-8-inch-UNC-Thread-Repair/dp/B00EO4NULO" rel="nofollow - https://www.amazon.com/V-Coil-8-inch-UNC-Thread-Repair/dp/B00EO4NULO

I had looked up a helicoil repair kit and it was going to set me back over $200.  For that much money, I thought I could probably take it to a local machine shop.  We are lucky enough to have a good one a few miles away.

I looked at the repair kit you posted with the link from amazon.  At $95, the price is now getting within range of trying it myself.  Thanks. 

As to drilling out a 3" deep hole to 1" in solid metal with a hand-held drill, I don't trust myself to do that yet.  If I could pull that off, the end product would probably be stronger than new, though.

hmm... does this bolt hole go INTO the casting far ? drilling it ,might go too far , and oopsy... you found gold, black gold, Texas tea ?????

I KNOW what happens to D14 rockshaft PTO cover holes if bolts are too long....

maybe you could just weld/braze a nut onto the casting? It seems there wouldn't be a lot of stress on it( sway chain ) ??

just trying to think of options not seeing it in person.

Jay

Here is a Starrett chart.

uploads/16335/tap_chart.pdf" rel="nofollow - uploads/16335/tap_chart.pdf

 Hey Jim.ME,,,I made me a copy of your link to post above my lathe,,,,

 THANKS,,!!!

steve(ill) wrote: Your only taking out 1/16 of an inch or so.... Why 3 inches deep?  A 1 inch bolt only needs to go in 1-1/4 inch to get strength.

The three inches is the current depth of the bolt hole.  I was just duplicating the factory measurements.  I really do appreciate the help on this, btw.  I have rethreaded stuff for years, but this one is outside of my experience.

yeesh, 3" deep thread hole !! If it's ONLY used for the sway chain, maybe fill with JBWeld ,then drill and tap. I just can't see a sway chain needing 3" x 7/8" bolt to secure it.

Maybe I'm missing something ??

Don't matter how big the bolt is, there is always the loose nut behind the wheel, that can break an anvil with a feather...

You've already got a 7/8" hole drilled, 3" deep.  Just take the right sized bit, for the thread you want to make, and hand drill it, with an old slow speed 1/2" drill, and the proper sized bit for the bolt or heli-coil you are putting in.  Most taps have the size of the drill you need, printed right on the side.  With a Heli-coil, the bit is usually included in the kit!  If you get it a degree or 2 off  true, it aint that critical, to make any kind of difference, anyway!

For some reason this threaded connection failed? was it over loaded or was it loose and wore out from use? 

Good luck with your repair.

That is a good tractor, Having this repaired will allow you to sleep better too!

Regards,

 Chris

so if i do,,, i could send them to you to use,,,,and when you are finished you could send them back to me,,,,i probably also have a fine thread set too,,,but i need to look and see,,,,pretty sure i do have the 1"-8 tap and i know i have a short 7/8 with a 1/2" shank drill

reason i mentioned fine thread it will be easier to turn and make threads in the hole,,,,a 1" tap will need a big wrench

that hole is already to size mostly,,,just needs cleaned up and made some kind of round again,,,then put a tap in there and threads will be back but next size up

and old trick is to use good old crisko (showing my age here,,,lol),,for lube on the tap,,,,but if you have or can find some stuff called tap-ezz it works good too,,,im sure there are other specialty tapping lubes out there too

just me trying to help out some

ocharry

I can't thank you enough for the offer, but I have a decent set of drills and a tap and die set.  I just haven't ever worked anything this big before where I couldn't put it what I am working with on a bench.

I think I am going to try and drill the hole out for a 1" bolt instead of using a heli coil. 

Look at it this way... The hole is now about 1 inch diameter.. or about 3 inch circumference.. He said the hole is 3 inches deep... Lets assume we shove the stud in 2 inches... 2 inches x 3 inches is 6 SQUARE INCHES of surface area between the stud and the hole bore... if the Epoxy or JB weld has a SHEER strength of 2000 psi, then 2000 x 6 is 12,000 POUNDS that the stud could hold before the epoxy RIPPED out..

Is there 12,000 pounds of load on that bolt ?  I though maybe NO.. but again, why is the bolt 7/8 inch diameter ?  My "guess" would be that a 5/8 inch bolt would be enough to hold the chain and block ?   What did i miss ?

Remember, also, don't turn with a rigidly mounted implement, in the down position...

tadams(OH) wrote: Was the bolt 3" long that went in it ? If the hole is 3" deep and the bolt was there is probably good threads still in there that if a guy ran a tap in and cleaned up you could put a longer bolt in and not have to redrill.

Been there, done that.  When I bought the tractor in 2015, someone had already put the current bolts in.  My belief is that they had been slipping out before I bought the tractor.  I kept torquing the bolts down (no Loctite, I'm going to fix that this time) and they kept loosening up.  This time when they loosened up there wasn't anything left to grab on to.

What I haven't made clear enough is that these bolts take a beating.  I use this on a loader tractor.  I keep an 1,100 lb stump grinder on the back to keep by back wheels on the ground.  Oh, and I work on hillsides.  What ends up happening is that the stump grinder is always working back and forth.

The picture is of the last treetop that I cleared this season.  I have been clearing trees of this field for almost ten years.  I still have about three to go.  There are over 3,000 stump holes that I periodically drive over in this field.  It pays to go slowly.   The whole field is terraced so I am constantly swinging everything back and forth.

Probably a lot more detail than you wanted, but I am sure that a lot of people are wondering why I couldn't have just done what you suggested.  I really appreciate the help offered on this forum.  I was completely out of my element on this one.

Tbone, on an Allis, I would have sway blocks.  Here is the way Ford did it.

So, my drill size is 7/8" and I only have one (cobalt).  If I understand what I have been reading, I need to get a cheaper drill and reduce the size of the to fit inside the hole, then make a pilot hole before drilling the hole which will hold the threads?    To do fine threads, I need a 59/64 drill?

If the fine threads would be stronger in the cast housing I would think the manufacturer would have used fine.  Coarse is usually found in cast materials from what I've seen.

If the bolts were 7/8"-9 NC originally I would use 1"-8 NC.  Clean, degrease, and use the primer for the thread locker on the threads (tapped holes and the capscrews) after tapping.  Use red thread locker.

I believe Ken (MI) was suggesting grinding about 1 inch of the end of the drill smaller in diameter to act as a pilot in your existing stripped out hole.

 Another point about cast iron to go with Ken's point on no cutting oil needed for drilling.  When doing work on old Allis Chalmers Hydro Turbines, Voith (holds the rights to most of them now) said not to use anti-seize or other lube on fasteners threaded into cast iron for the same reason, the carbon/graphite in it provides its own lubricant.  Thread lockers do provide some lubrication so don't over torque.

You know this but you only have check chains to stop the arms from hitting the tires.  The sway/ stabilizer set up Tbone95 mentioned was an option, there were no blocks on the sides of the case for the arms to hit limiting sway.

but Ken and Jim brought up a good point about this being cast iron,,,,duuuuuhhh,,,never even thought about it being cast iron,,,,(was thinking cast steel)but if it is,,,skip all the stuff i said about using a lube,,,,you wont need it

and it will tap WAY easier than steel,,,,not that it will be easy,,,,but a tap will cut easier in the cast iron,,,and if it is,, it is more than likely a good cast

also,, if it is cast iron,,, thats probably why the hole is 3" deep,,,cast isnt as strong as steel so it needs a little more purchase ,,,hence more thread contact

also Ken's idea about a piloted drill is a good idea,,,it will help keep the drill from jumping around,,,kinda like the drill in a hole saw,,,,ever try using a hole saw without the drill to keep it centered 

anyway,,,,go slow and careful and you can do it

ocharry 

Given the amount of help I received on this topic, I wanted to post some pictures of how things turned out.  I went ahead and tapped both holes to 1" (7/8" drill bit) so that they would match.  Then, I used blue Loctite when I put the bolts back in.  I had a local machine shop drill out the holes in the steel plate to 1 1/16".  The twenty dollars they charged was less than the cost of a new drill bit of that size.  I thought things turned out pretty well.

This was actually working well, but I kept thinking about the parts diagram from Jim.ME which seemed to show a stabilizer.  So, I started looking online for one of those.  What I found out surprised me quite a bit.  The Ford 7710 which replaced the 7700 used a very slick adjustable part on the outside of the lift arms.  Even better, the 7700 was fully drilled and ready for the system on the 7710.  So, I ordered two of those stabilizers and wound up with the situation you see below.  I had to order knock-offs because I couldn't find any original Ford parts in the salvage yards I contacted.  That being said, it works really well and I don't worry about the bolts getting pulled out again.