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CaseyCreek 
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 Topic: Best way to repair stripped out 7/8" threads
Posted: 05 Sep 2020 at 9:01pm |
(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.
[TUBE]dY9oXtih_5g[/TUBE]
(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?
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steve(ill)
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Posted: 05 Sep 2020 at 9:27pm |
One common fix is to use a thread insert repair kit... I have done a couple on the B final drive case that you mount the draw bar loop to.
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.
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steve(ill)
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Posted: 05 Sep 2020 at 9:29pm |
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Like them all, but love the "B"s.
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CaseyCreek
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Posted: 05 Sep 2020 at 9:44pm |
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.
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Tracy Martin TN
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Posted: 05 Sep 2020 at 10:22pm |
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Casey, Helicoil is the route to go. I don't know which bolt hole it is. Can it be drilled using a magnetic base drill? I have done hundreds of them of various sizes and locations. Post a pic of hole and its location. Thanks Tracy
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shameless dude
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Posted: 05 Sep 2020 at 10:28pm |
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get sum dog chain and a short tarp strap, wrap it around the lower lift arms, when hooking up something the tarp strap will stretch enough to hook up. have used this on most all my tractors for years.
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jaybmiller
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Posted: 06 Sep 2020 at 6:33am |
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
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Jim.ME
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Posted: 06 Sep 2020 at 6:54am |
7/8" is the tap drill for 1"-8 NC thread. 59/64" tap drill for 1"-12 NF.
Here is a Starrett chart.
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DougG
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Posted: 06 Sep 2020 at 7:18am |
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If that metal is as easy as drilling on an Allis it will be a breese, seems it's low grade stuff, I'd be careful not to go to deep as Jay mentioned but I think back there it's out of the oil housing
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DrAllis
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Posted: 06 Sep 2020 at 7:57am |
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There are several thread repairs of different designs available to do this good. Trouble is, most of them need a lot of meat around the hole to work. Drill the hole oversize and install a one inch bolt and Loctite it.
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desertjoe
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Posted: 06 Sep 2020 at 8:24am |
Hey Jim.ME,,,I made me a copy of your link to post above my lathe,,,, THANKS,,!!! 
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steve(ill)
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Posted: 06 Sep 2020 at 8:37am |
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If your 7/8 bolt is stripped out , your not too far from the root diameter of a 1 inch NC bolt.. Use a small drill with very little horse power.. Get a drill bit turned down on the end to fit the smaller drill ( 3/8 inch)... Just go slow and round out the hole.. 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.
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steve(ill)
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Posted: 06 Sep 2020 at 8:40am |
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you could even take a 1 inch stud and turn the outside part back to 7/8 NC and thread it... Screw the 1 inch stud in 1-1/2 inch with loctite, and let the 7/8 end outside be the original size.
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Like them all, but love the "B"s.
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CaseyCreek
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Posted: 06 Sep 2020 at 9:21am |
 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.
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thendrix
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Posted: 06 Sep 2020 at 12:45pm |
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Easy way to figure trap drill size is OD - thread pitch. For example, 1"-8 the has a .125 (1/8") thread pitch. You figure this by 1" divided by 8 thread which equals .125. 1 minus .125 equals .875 or 7/8. Works the same for metric but metric threads give you the pitch without having to divided 1 by the threads per inch.
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jaybmiller
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Posted: 06 Sep 2020 at 3:50pm |
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 ??
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DiyDave
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Posted: 06 Sep 2020 at 7:09pm |
jaybmiller wrote:
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 ??
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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!
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steve(ill)
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Posted: 06 Sep 2020 at 9:11pm |
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im starting to wonder if you could take a 7/8 stud and smear JB weld all over one end and screw / pound it into the hole and let it dry..... If the load is not that great, the stud sticking out should be able to anchor the chain with no problem... i think epoxy or JB weld should hold that load.
Edited by steve(ill) - 06 Sep 2020 at 9:16pm
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Fred in Pa
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Posted: 07 Sep 2020 at 6:35am |
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I would never even think of JB Weld for a repair like this .Fix it right.
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Sugarmaker
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Posted: 07 Sep 2020 at 7:03am |
my two cents also, I would carefully drill the damaged hole out with a hand held drill to the 1 inch coarse thread size. You will need a stepped down bit for that. You local shop may have the tooling. Going the full 3 inches deep to clean up. Hand tap the 1 inch thread. Drill the mating component clearance hole out to 1 1/16 inch, Get a good Grade 5 bolt to replace the 7/8 fastener that broke pulled out the thread. 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
Edited by Sugarmaker - 07 Sep 2020 at 7:07am
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Clay
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Posted: 07 Sep 2020 at 8:26am |
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One of the best heli-coil type inserts are the ones sold by CAT.
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ocharry
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Posted: 07 Sep 2020 at 9:21am |
hi Casey,,,hey im pretty sure i have a 7/8 drill with a 1/2 shank,,,that is the tap drill for a 1" bolt,,,,and i am also pretty sure i have a 1"-8 tap ,,,
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
Edited by ocharry - 07 Sep 2020 at 9:23am
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chaskaduo
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Posted: 07 Sep 2020 at 11:04am |
You're a mighty fine man Oil Can. 
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CaseyCreek
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Posted: 07 Sep 2020 at 3:53pm |
ocharry wrote:
hi Casey,,,hey im pretty sure i have a 7/8 drill with a 1/2 shank,,,that is the tap drill for a 1" bolt,,,,and i am also pretty sure i have a 1"-8 tap ,,,
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 |
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.
Edited by CaseyCreek - 07 Sep 2020 at 4:02pm
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DougG
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Posted: 07 Sep 2020 at 3:54pm |
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That JB Weld fix comment was way out there- gotta wonder what thoughts are elsewhere
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Tbone95
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Posted: 07 Sep 2020 at 4:59pm |
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I somewhat support Steve’s jb weld suggestion, though I would use ....I can’t remember the number...it’s a green loctite industrial adhesive. We use it at work to bond a workpiece to an arbor for hi precision high torque specialized machining processes. You can snap the steel driver off before that stuff breaks loose in the hole / arbor.
If it should happen to fail, the option to fix it with a drill and tap is still there.
Edited by Tbone95 - 07 Sep 2020 at 5:02pm
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steve(ill)
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Posted: 07 Sep 2020 at 5:24pm |
i posted the JB weld comment to get some discussion and more input... I do not know the EXACT purpose of that bolt, but i though he said it was to hold the side movement plate and chain.. I dont know why the bolt would be 7/8 inch diameter. Maybe the load is greater than i think....
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 ?
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steve(ill)
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Posted: 07 Sep 2020 at 5:26pm |
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I have used high strength epoxy to glue 1/2 inch studs into concrete holes drilled 4 inches deep.... if you put a puller on that stud and pull, you will bust a chunk of concrete 6 inches in diameter out ( a couple TONS load), before the epoxy will let go.
Edited by steve(ill) - 07 Sep 2020 at 5:27pm
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Like them all, but love the "B"s.
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DiyDave
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Posted: 07 Sep 2020 at 5:38pm |
Common problem, with all bolts that point up, is that they tend to loosen, from side loading. Now you have a chain attached to it, connected to the lower 3 point arms, you get a swing, an impact, and viola, the bolt starts loosening. In any case, I'd put lock-tite on it, no matter what/how you replace it. A perfect example of this movement is AC's D-series factory 3 point hitches, which install with 3 up-threading bolts, they loosen, then shear the bolt(s) off, if not watched...
Remember, also, don't turn with a rigidly mounted implement, in the down position... |
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tadams(OH)
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Posted: 08 Sep 2020 at 2:15pm |
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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.
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