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

[crazyal]

With careful installation and use they are a strong and viable repair. They demonstrate well in the lab and other situations where assembly is well controlled. Their nature of "no inherent structural form" is much more demanding of this than are threads in parent metal.

Working during assembly and disassembly with slight offsets, misalignments, dirt, dings in the bolt, etc can easily damage the 1st thread or two, or cause binding at some point down in the hole to spin and unseat the threadform. The repaired hole is then in jeopardy and very likely to surprise you later - maybe trying to go out or in with the bolt. The helicoil needs replacement and youre likely working thru a hole that is too small to replace it thru. A conventional bolting situation into parent metal is more durable, tolerant of much greater damage, and easier to correct promptly [often by just firmly enforcing the original correct lead in with an undamaged hi grade bolt lubed with moly].

Preserving this real world advantage, even greatly widening it is often easier than you might think. Making use of pitch crossovers within or between sizes in the US or metric, or the US and metric systems can allow this. Just go to the next bigger bolt with same pitch. Between system conversions match ~ exactly at 20tpi [1.25], 16 [1.5], 10 [2.5]. ... So you can find cases that allow you to pilot into the original helix with a slightly larger std tap. Some are; #] 1/2 x 20 into 12 x 1.25M, #] 7/6 x 20 into 10 x 1.25, #] 3/4 x10 into 18 x 2.5M, #]12 x1.25M into 7/16 x 20, #] 10 x 1.5 into 3/8 x 16 ...

Going larger, and hence more rigid is good as a rule in the service we are dealing with here. Some cases, such as where thermal expansion affects preload, you do not want to force rigidity in place of compliance offered by the original bolt size. Here, use of a helicoil into a usually softer more mobile metal like aluminum preserves compliance and extends the threadform to engage enuf of the parent metal for good strength. If helicoils ever can be universally deemed good it is in this type of application involving weaker metals.
larry

Nice to know.

 

[crazyal]

The reamer and tap for preparing a hole to receive a helicoil is several inches long and is generally not suitable for blind holes. A common application for helicoils is renewing spark plug threads, which are through-holes. A sizing reamer first pilots on what's left of the old threads, and reams out the hole. The next section of the tool taps the new threads using the end of the reamer flutes to guide and center the tap. All of this takes a tool that for a 16-19mm bolt size would be about 4" or 5" long, too much for a blind hole that's likely only 2-1/2" deep, if that.

Here's a slightly different idea that builds on other posts here:

To take full advantage of the existing holes, the threads can usually be extended somewhat. This is because the original threads are not fully formed for the full depth of the hole. Taps are tapered so in blind holes they leave a full diameter or more of incomplete threads. Machinist have a special tool called a "bottoming tap" that can be turned into a threaded hole to finish the incomplete threads at the bottom of the hole. Then a full length bolt can use all the threads, helping solve the problem. The bottoming tap may need to be guided and/or carefully advanced, but it will work much better than trying to oversize the whole thing from scratch. Best to have a machinist look at this with you.

Another thing I'd mention - be real sure of the diameter and thread pitch of any taps and/or new bolts you use. Take a bolt out that hasn't given any problems and carefully compare the size and thread pitch. Some bolts on my tractors are 1.25 mm pitch, others are 1.5 mm, even though they are the same diameter. They look the same at first glance and can create a real mess if mixed up. You might even find that someone has forced a mismatched bolt into a hole already.

90% of the heli-coil inserts we use are in blind holes. Normally we just have a local machine shop come in and install them since we are too busy and but all of our repair kits come with bottoming taps. The biggest problem we have with blind holes are people using bolts too long and when they tighten them up it mushrooms the end making it very hard to remove.

 

[nvr-enuf]

Thanks everyone.

My bolts are only 1.75" long, I took a picture but at my work I am not allowed to access tinypic or sites to upload pictures. The threads in the center of the bolt are flattened.

The bolts are also 8.8 which I am told by my ex-kubota dealer are grade 5 bolts, not grade 8.

I agree with your comments, longer bolts could and should have been used from the start.
I will try the tap / hardened bolt idea first for the M16 by 1.5 and see if I can save what I have with out having to drill out to M18 size.

The holes are not thru holes, looks to me like the loader bolts to the engine or a large casting that is bolted to the engine.

Thanks everyone.

 

[nvr-enuf]

I tried uploading picture of the bolt that I took out - this one is not as bad as the others.

 

[IslandTractor]

I had a similar experience with my Kioti DK40/KL401 loader. Discovered one bolt missing and another one or two very loose. The loose bolts had some thread damage as I recall. I got a few replacement bolts from the dealer then gently retapped the threads in the block. I think mine was M18. I then simply reinserted the new bolts, torqued to spec and used medium strength Loctite. No problem in the past three years.

Pretty sure the problem was related to installation and my failure to check tightness each year. It is now part of my oil change drill.

 

[SPYDERLK]

View attachment 323614

I tried uploading picture of the bolt that I took out - this one is not as bad as the others.

New looking bolt with lots of motion. We really need to identify the problem with your loader setup. If it was only that it was never tightened then putting back everything truly tight will cure it unless parts have been bent because of it. If its poor fitment or missing braces it could be an entirely different or only a compounding problem source. Poor fitment adds up to the same thing as not tightening. The interfaces must fit to each other neutrally so that they are clamped by all the bolt tension rather than squeezed toward each other for the 1st portion of tension. Your assembly may have been hanging on the bolts instead of being clamped by them. -- It looks new. Who did the assembly and how many hrs is on it? If a dealer, or Kubota, did that a few hrs ago you should be dealing with them.

Unfortunately, going up to 18mm is a huge change from your 16mm. 11/16 x 16 and M17 x 1.5 are standard threads but there doesnt seem any demand for bolts so not readily available.
larry

 

[rbargeron]

.......If helicoils ever can be universally deemed good it is in this type of application involving weaker metals.....

I believe Porsche routinely used helicoils (or similar threaded inserts) for the spark plugs in their aluminum heads for years - maybe still?

 

[rScotty]

View attachment 323614

I tried uploading picture of the bolt that I took out - this one is not as bad as the others.

Much better than I'd hoped.... Movement of the loader mount but not much damage from the engaged portion of the thread. And it looks like the bolt didn't even back out much - which is what I'd feared. This is very good so far. From the looks of that bolt you may have caught the problem in time and maybe no lasting damage. If the others don't look too much work just clean out the threads in the block (see previous message), install new bolts, torque well, and continue.
rScotty

 

[SPYDERLK]

I believe Porsche routinely used helicoils (or similar threaded inserts) for the spark plugs in their aluminum heads for years - maybe still?

Wouldnt doubt it. Plugs threaded into aluminum should be done with a coating of anti sieze on threads. Cant trust everbody to do it so put a steel insert in. I thot case serts/keen serts/time serts were used for this mostly because they have a solid wall and are more difficult to damage when installing the plug. May not be room for the "serts" in Porsche heads. Helicoils are smaller OD. :confused3:
larry

 

[RFB]

Heli coil repair is not suitable for threads in that type of service

Sir,

What about this system: http://www.timesert.com/

Is this sufficiently different to be efficacious?