Unsettling discovery on transfer case housing

If this is not a "through" threaded hole, i would buy the appropriate helicoil repair kit and install it. If the hole is "through"' that is goes into the lubricated housing, i would pull the outer housing so i could clean out any tapping debris, install the helicoil, clean it up and reinstall it with a bit of locktight on the threads. Maybe use an o ring washer under the bolt head.

hth,
chris

 

If it is stripped, a helicoil is a perfect, and perfectly acceptable, fix. I have done it myself in the exact location. Still have the helicoil kit left.

 

When I was in my transfer cover I stripped out a stud. On closer inspection I found that two other holes were already Helicoiled. I think that perhaps I wasn't as heavy handed as I thought and someone previously was a bit stonger than he thought and maybe loosened it all up for me and/or stripping these is really easy to do. Anyway it was no big deal to helicoil it. I got my kit from McMaster.com, M8 x 1.25mm.

 

I understand that it is standard practice in the aerospace industry to helicoil all threaded holes in light weight alloy parts from the start. The repair will be better than new. The contact area of the threads to the weakest material will be increased making the joint much stronger.

 

BEFORE YOU PUT A HELICOIL IN IT:

Is the thickness of the casting around the hole enough that a helicoil won't be significant?

There might be a Standard diameter and pitch that is similar to the metric one and only slightly larger in diameter, and you might be able to tap it to that while barely removing any metal at all. Or if the next metric size up is smaller than what you would have to tap it to to insert a helicoil, you might just want to go to that. Make a note in the service manual of that particular hole/bolt, and put the original bolt into a ziploc baggie and save it.

The point is to be as uninvasive as possible. You can always take more metal away.

If you do go with a helicoil, consider buying a TimeSert (I think that's what they're called). They expand at the bottom when you screw the bolt in, so they stay put permanently in the hole.


- T

 

Yes, you need the whole kit. It has the correct size drill bit, an insertion tool and a special tap in addition to the inserts. You will also need a tap wrench in most cases, but I believe that I had to carefully use a wrench because of clearance issues to surrounding parts. Don't get that tap in crooked!

I have heard good things about the Timeserts, and the fact that they don't back out is always given, but I've never had any issues with a Helicoil moving, nor heard of anyone with direct experience of one moving.

I went to McMaster.com and typed in Helicoil and clicked through the choices and came up with these two kits for 8mm x 1.25:

Insert Length
12 mm 91732A952 $36.84 per Kit

8 mm, 16 mm 91732A951 39.83 per Kit

M8 1.25 mm 8 mm, 12 mm, 16 mm 10.35 mm 91732A951 39.83 per Kit


I don't remember how deep the holes are. I think I bought the last one just for the variety. I know I have three different lengths. My first Helicoil was scary to do (on my Guzzi's sump) but it goes real easy. You do have an accurate pre-drilled hole from the factory.

 

Hey look, I even took pictures when I did it.
A picture of the hole with stripped threads. Note that there are more threads down deeper. Perhaps you could just use a longer stud/bolt.

#1 A picture of the tap, but also includes the mask I constructed on the car with gaffers tape and paper to keep chips and swarf out of the tranny.

#2 Helicoil installed, the tang is still visible in the bottom. Note that there is plenty of meat for the larger hole and Helicoil, I have no concerns about that in this application.

#3 Cover cleaned and replaced.

I have had the cover off twice now, once because I dropped a nut down the timing hole in the bellhousing (#$%##@#!!!) and once to remove the fuel tank.
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Good job . . done a few here myself . .. one thing that makes me very nervous on a part like this is getting the tap straight . . . I take the time to make a tool to start the tap . . . nothing worse than putting a nice new helicoil in and finding you can't get the cover on 'cause the studs crooked . . .. not happened first hand on Ferrari but other hurried repairs have been victim .

Sean

 

For those that don't know, the easiest way to get a tap started straight is a "tapping block". To make one you just drill a hole in a piece of scap matel thats at least as thick as the tap OD, 2 time the OD is best. Drill it on a drill press so the hole is straight and square to the face. then just hold the block over the hole you want to tap and it will guide the tap in perfectly straight.

 

Mark,

Brilliant ! Brilliant..!
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You don't just whack the stud with a hammer until they line up? The guy who showed me the secret about oiling my squeaky brakes taught me that trick as well.
I've never used a tapping block, but next time I will. That is one of those things that is obvious once someone tells you about it! I've even made similar jigs for hand drilling holes, but never even thought about it for a tap. The flat surface available on the case is pretty narrow, it might not be very easy, but it seems like your chances of accuracy are greatly increased.

BTW the kit I bought was Helicoil part number 5403-8, and it looks like I used the 16mm length.

 

I overkilled it and picked up the two adjacent studs to hold the tapping block in the right place . .. one of those things where you only get one chance to do it right and the right tool/block only takes a few minutes . ..

In case you get them crooked, there's an added benefit of straightening them with the hammer which is that the nut becomes self locking on the disorted thread unless you're dumb enough to protect it .

 

Mike,

Alignment block - very cool idea.

A nut on the stud before you whack it with a hammer - f*cking priceless.

I knew there was an overwhelming reason why i study this forum morning and night.

Don't hurt the car.

loving it,
chris

 

Hi All
To look into some very slight external lubrication issues, I’ve had my transfer cover off for the first time and when I came to replace it, two of the ten nuts wouldn’t torque. Clearly my PO either didn’t possess, or didn’t use, a torque wrench. Needless to say, he didn’t choose to strip any of the eight that would have been easy to helicoil. Does anyone have any experience of repairing the two hollow dowelled threads at 12:00 noon and six o’clock positions? I’ve tried gently warming up the bell housing up with a blow torch, but haven’t managed even to get the dowel sleeves out yet…. Also the O/D of the helicoil tap looks to be about the same as the dowel O/D and I’m concerned about losing the outer cover location features.
Advice gratefully received!
Thanks
Paul

 

OK, answering my own question - I put an 8.2mm drill bit down into the dowel to support it and then used (purists please avert your eyes) grips to gently extract them. The PO’s copious use of Araldite around the various dowels and threads didn’t seem to be helping, but they are out now. Helicoils now inserted and a pair of new dowels on order.