Kubota L4330 - Loader bolts missing / threads mashed / stripped threads

[Coyote machine]

The damaged bolt pictured may not be representative of the more damaged bolts, BUT it does present the possibility that threads furthest into the holes may not have been in use with the current length of bolts used from the factory.
So, again I would want to know what is the maximum bolt length is that would fit the existing holes and see if that length bolt will screw into EACH hole until it has reached maximum or very close to max depth. I would do this without the loader bracket being in the way while 'testing' your easiest fix.
I would put aside all the theory about helicoils, machinists, etc., and focus on what exists to work with on the machine. Bottoming taps are a useful tool for this situation.
If using the existing holes with longer bolts of the same diameter, pitch, etc. becomes unrealistic, THEN I'd look at the myriad options presented in this thread.
I'd spray each hole with something like Brakleen and then dry with compressed air, inspect each hole and access the damage on an individual basis, then proceed, working my way up from easiest to most damaged to give you practice in technique. Clean the tap frequently and check progress. Oil the tap threads frequently too.

 

[SPYDERLK]

Sir,

What about this system: ++ TIME-SERT Threaded inserts for stripped threads, threaded inserts, thread repair stripped sparkplug's, Ford sparkplug blowouts, threaded inserts threaded, repair stripped threads, stripped threads, inserts threaded inserts, Ford spark plug repair,

Is this sufficiently different to be efficacious?

Yeah. Thats the kind of insert Id go to if there was not a close upsize bolt I could rethread the casting to take directly. ... Those solid wall inserts are not generally a high grade steel. Not really necessary even with a Gr8 bolt if you have 5 or 6 [coarse] or 7 or 8 [fine] threads engaged, but Id sure like to see em in Grade 5 equivalent steel.
larry

 

[crazyal]

I would buy the correct size tap and try to repair the threads. Make sure you get a bottoming tap. When you run it into the hole you can see how deep the threads go so you'll be able to tell if you can go with a longer bolt.

 

[SPYDERLK]

I would buy the correct size tap and try to repair the threads. Make sure you get a bottoming tap. When you run it into the hole you can see how deep the threads go so you'll be able to tell if you can go with a longer bolt.

While a bottoming tap will be needed to get full threads close to the bottom of the hole you usually will go with a plug or spiral point tap first. These have a more tapered tip to spare the tap stress of cutting the full thread abruptly. Then you follow that with the bottoming tap to complete the last partially cut threads left by the tapered tap. Best to use high speed steel taps. They are agood bit tougher to make breakage much less likely.

Scottys method of chasing and reforming damaged threads is meant to avoid cutting excessive metal from the deformed threads, leaving a more original hole. A strength class 12.9 socket head capscrew would be applicable here. Regardless -- taps or thread reforming -- a good feel for the job variables is priceless and unfortunately is near impossible to impart to one who has little or no experience. Tapping with good taps is the most straightforward.
larry

 

[rScotty]

........ Regardless -- taps or thread reforming -- a good feel for the job variables is priceless and unfortunately is near impossible to impart to one who has little or no experience. .....
larry

I agree. This thread seems to have given birth to two different conversations. One is on how "Nvr-Enuf" should best go about repairing his loader mount, and the other conversation is on the best way to repair internal threads damaged beyond repair. Judging from the picture of the bolt in message # 24, I'd say that the original loader bracket mounting problem seems near to be solved.

But we still have a ways to go on the subject of tapping and thread inserts. No matter which insert is chosen, it seems that tapping is the skill that is needed most. So I've been thinking about how to teach tapping. Hopefully without all the mistakes it took me to learn it.

I also agree with Spyderlk that tapping it is all about "feel"; after some 50 years I've messed up enough threads to finally almost become passable with my tapping. Although I messed up one hole in a batch of custom seat brackets in 1/2" mild steel just a week ago. Still learning, and at the same time struggling with how to teach it. Best way is probably to watch someone who knows how. Better make that someone other than me... /

Lacking a handy teacher, if it were me trying to teach myself I'd try tapping some coarse-threaded through-holes first into some aluminum, then into mild steel, and finally into hi-nickle cast iron block material. That would be very easy material progressing do darn hard. Using material as thick as the tap will do. Then go back and do the same three metals again but with blind holes....always feeling for the importance of keeping it straight, lubed, and how often to backing out & clean chips.

To start I'd stay under 1/2" diameter thread just because that size is about the upper limit for easy enough hand tapping in hard material while still being able to learning to "feel". And I'd do my learning with the tap vertical and maybe use some sort of guide to hold things perpendicular. A square block with a tap-diameter size clearance hole drilled through it is priceless for that.

After a go at those threads and materials, I'd either do the same with fine threads, or more likely get impatient and move directly to doing the same materials but with bigger taps in the 3/4 & 1" diameter range - those being sizes most likely to be used to mount loader frames to engine blocks. These big taps require a whole different feel because of the pure muscle needed to turn 'em.
Luck, rScotty

 

[IslandTractor]

I agree. This thread seems to have given birth to two different conversations. One is on how "Nvr-Enuf" should best go about repairing his loader mount, and the other conversation is on the best way to repair internal threads damaged beyond repair. Judging from the picture of the bolt in message # 24, I'd say that the original loader bracket mounting problem seems near to be solved.

But we still have a ways to go on the subject of tapping and thread inserts. No matter which insert is chosen, it seems that tapping is the skill that is needed most. So I've been thinking about how to teach tapping. Hopefully without all the mistakes it took me to learn it.

I also agree with Spyderlk that tapping it is all about "feel"; after some 50 years I've messed up enough threads to finally almost become passable with my tapping. Although I messed up one hole in a batch of custom seat brackets in 1/2" mild steel just a week ago. Still learning, and at the same time struggling with how to teach it. Best way is probably to watch someone who knows how. Better make that someone other than me... /

Lacking a handy teacher, if it were me trying to teach myself I'd try tapping some coarse-threaded through-holes first into some aluminum, then into mild steel, and finally into hi-nickle cast iron block material. That would be very easy material progressing do darn hard. Using material as thick as the tap will do. Then go back and do the same three metals again but with blind holes....always feeling for the importance of keeping it straight, lubed, and how often to backing out & clean chips.

To start I'd stay under 1/2" diameter thread just because that size is about the upper limit for easy enough hand tapping in hard material while still being able to learning to "feel". And I'd do my learning with the tap vertical and maybe use some sort of guide to hold things perpendicular. A square block with a tap-diameter size clearance hole drilled through it is priceless for that.

After a go at those threads and materials, I'd either do the same with fine threads, or more likely get impatient and move directly to doing the same materials but with bigger taps in the 3/4 & 1" diameter range - those being sizes most likely to be used to mount loader frames to engine blocks. These big taps require a whole different feel because of the pure muscle needed to turn 'em.
Luck, rScotty

Some of you guys are obviously very experienced machinists. Most of us however are simply guys with tractors, not machine shops, and we are limited pretty much to field repairs unless we turn over the project to a dealer. My experience with the almost identical bolt backing out problem on my loader was that a good enough repair could be made with Harbor Freight metric taps, a new OEM bolt and a few dabs of Loctite.

While that equivalent of a bailing wire repair may be scoffed at in water cooler discussions by trained machinists, I do think it is important to let the OP (and others) know that "good enough" fixes are possible without prior experience (I had to go out and buy the metric taps and blue Loctite in my case). Even more important, it is critical to publicize the root cause of these problems: failing to check bolts regularly.

You machinists are helping to educate us but it can be a bit intimidating to think that one needs to spend a week or two practicing before trying to clean out a simple bolt hole with a tap. Common sense and using limited force would seem perfectly adequate preparation IMO. And of course, an ounce of prevention....

 

[rScotty]

SNIP.........You machinists are helping to educate us but it can be a bit intimidating to think that one needs to spend a week or two practicing before trying to clean out a simple bolt hole with a tap. Common sense and using limited force would seem perfectly adequate preparation IMO. And of course, an ounce of prevention....

Well said. That's just the point I was trying to make....although you made it much better and thanks for being so forceful.
I agree completely that cleaning out a simple bolt hole with either a new tap or using a hardened bolt with some slots cut into it is easy and usually good enough. It's also always the first thing to try. I do that most times too. Check my back messages here.

It's a completely different thing when we start talking about drilling out existing threads so that we can tap an oversize - horizontally into a cast steel! - that I gotta point out doing that is not trivial. In fact, there is a chance it won't be any improvement. At least not the first time done.
rScotty

 

[SPYDERLK]

I agree. ... I also agree with Spyderlk that tapping it is all about "feel"; after some 50 years I've messed up enough threads to finally almost become passable with my tapping. Although I messed up one hole in a batch of custom seat brackets in 1/2" mild steel just a week ago. Still learning, and at the same time struggling with how to teach it. Best way is probably to watch someone who knows how. Better make that someone other than me... /

Lacking a handy teacher, if it were me trying to teach myself I'd try tapping some coarse-threaded through-holes first into some aluminum, then into mild steel, and finally into hi-nickle cast iron block material. That would be very easy material progressing do darn hard. Using material as thick as the tap will do. Then go back and do the same three metals again but with blind holes....always feeling for the importance of keeping it straight, lubed, and how often to backing out & clean chips.

Luck, rScotty

:thumbsup: Yeah. And then we have the issue of retapping a damaged hole. This can range from trivial to catastrophic. Getting a fluted tap to start in the old thread can be a challenge - a good hard bolt may "find" the thread more easily and reform the beginning so the tap just falls into it correctly. Then youre home free? ? ... Not if there is a section in the hole that has broken free but sorta stayed in position. If it moves as the fluted tap crosses it it can jam the tap to be stuck in the hole. Inspect the hole very carefully for this before risking a tap into it. Asymetrical distortions also become an issue as they interact unequally with fluting. A fluteless tap would be much less risky. That, or a hard bolt using a moly lube. A "fix" in that chipless way also makes the very most of whats remains of the original. Unfortunately thread forming/fluteless/chipless taps in large sizes are uncommon.
... And all of this stuf [except the hard bolt] is expensive proportional to degrees of escalation.
larry

 

[IslandTractor]

:thumbsup: Yeah. And then we have the issue of retapping a damaged hole. This can range from trivial to catastrophic. Getting a fluted tap to start in the old thread can be a challenge - a good hard bolt may "find" the thread more easily and reform the beginning so the tap just falls into it correctly. Then youre home free? ? ... Not if there is a section in the hole that has broken free but sorta stayed in position. If it moves as the fluted tap crosses it it can jam the tap to be stuck in the hole. Inspect the hole very carefully for this before risking a tap into it. Asymetrical distortions also become an issue as they interact unequally with fluting. A fluteless tap would be much less risky. That, or a hard bolt using a moly lube. A "fix" in that chipless way also makes the very most of whats remains of the original. Unfortunately thread forming/fluteless/chipless taps in large sizes are uncommon.
... And all of this stuf [except the hard bolt] is expensive proportional to degrees of escalation.
larry

I know you are trying to be helpful and to pass on your considerable knowledge but sometimes vast experience with difficult cases can overpower the simple situation faced by most of us in common situations where retapping is necessary. Reading you guys is a bit like asking a neurosurgeon how he manages headache and then hear a reply on the technical challenges of difficult brain surgery cases. Sometimes the best answer is "take two aspirin and call me in the morning"!!!

 

[nvr-enuf]

I have removed the loader brackets on both sides of the tractor, cleaned the threads, blown out with compressed air. The right side is worse than the left side. There are 4 holes that bolt the bracket to engine. I have drilled and re-tapped two of the 4 with M18 using a bottom tap. Even with a bottom tap, you still can not tap 1/4" from the bottom of the hole based on the taper of the tap. The other two holes will be a challenge since there is a large brace that will not allow me to get my 90 degree drill in between in order to drill out the existing holes. The brace did not obstruct the upper holes. I trying to get my hands on a smaller 90 degree drill.

I think the main reason why I had this issue was because I added the sub frame connector brackets and likely did not get the bolts that were long enough. That being said, I have a wide variety of the stock size for the holes I do not need to drill out and M18 bolts for the holes I did drill and re-tap.

Torque specs - what is the ft lb torque that I should apply to the loader bracket bolts? I will use loctite and torque that kubota states for the M16 and use that same torque for the M18. If anyone has this torque spec, please respond - thanks.