Help! Stripped a thread in the crankcase

[pete]

Yep, I did, not good.

Started reassembling my engine yesterday, and got as far as the second bolt before striking trouble.

I put in the gear selector drum, put on the arm that holds it in place and the first bolt no problems.

I then put in the selector arm and the pivot bolt for that is where I got into trouble.

It tightened up, but the torque wrench didn't click, so I kept going, then it got loose, then I realised what was going on

The manual says torque of 11 - 16.5 foot pounds, I set the torque wrench to 13 which I figured was safe.

I'm not really sure how I managed to overtighten due to the torque wrench, but with my luck, I'm not surprised.

It's the bolt circled below:



It's number 12:



So, what can I do?

It looks like there's a few more mm's of thread depth below where it's stripped in the hole, so I figure a longer bolt will solve it for me hopefully.

Only catch there is that under the head of the bolt is a little pivot shaft for the arm, so it's not just a straight forward bolt.

I suppose I might be able to find a tube of the right diameter to fit over a bolt and perform the same function though...

Anyone else have any other ideas?

[Dogma]

Aw, crap.

#12? You probably can't find a shoulder screw with longer threads. The threaded portion is a consistent length, while the length of the shoulder portion can vary for any given nominal diameter. Your only hope for a longer version is to get one with a longer shoulder and have a machinist grind the shoulder back to a shorter length. But you don't know if the case will hold it. If you can get a screw in with a hard tube over it and reach the right torque, it might be OK. It would make me nervous though.

If you have a helicoil installed in the case, the screw may not stop at the same place it used to. Which would result in your shifter mechanism binding.

I think you probably need some combination of thread repair and a new screw. The new screw will need to be heat treated so it won't wear out. I don't know if an automotive machine shop will have that capability. A TIG welding wiz might be able to fill the stripped hole with aluminum to be re-tapped (without warping the case).

I think you'll need to take all the relevant parts to a machine shop and see what they say.

A new case might be cheaper, if you can find one.

Maybe that will knock some ideas loose, or maybe someone around here who's been around the block a few more times might have a clever idea.

[pete]

Bugger, they're all the sorts of things that have been running around my head.

A new case... well... that's something also that crossed my mind but I tossed it out straight away as I spent a hell of a lot of time trying to get the POR 15 Black Velvet paint to stick and cure, so don't fancy doing that again...

I'm still thinking talk to a bolt shop first, but only because that's the most straight forward option and it will probably lead to nothing, but of course if I did fluke it, then it would be such a simple solution...

Machine shop would be next then I would think.

Thanks for the quick reply too... this is gonna bug me 'til I get it sorted.

[SqDancerLynn1]

Should be easy to re-thread it with a helicoil, just make sure to use locktite. Get a new bolt.

edit You could just use a threaded rod, figure out how long you need it and Drill the spacer part to fit over the new stud & put a nut on the end if there is room

[pete]

Hadn't thought of a helicoil, probably because I've never had a need to use one before or look into them, so I'll have to see what the go is there.

The threaded rod is a good idea actually, I wondered about something like that but the way you put it definitely sounds more feasible, another alternative.

Thanks guys, keep the ideas coming, I'm sure something will work out and it will all be good again

[tatu]

Helicoil
Quick, cheap, easy and a proper repair

Just to add it is an imporant one to get right as it is the gear detent as you don't want any enexpected gear shifts.

[spchips]

+1 on Helicoil, or actually I prefer the Autozone kits, can't remember the brand at the moment, but I like them better. All basically the same thing, I just prefer these. They give you a different tool to thread in the insert.

It usually happens naturally, but make certain in this case that the alignment is correct. Also, you might have to cut or grind the insert shorter so it doesn't stick out. Usually the "thread inserts" are about the same depth as the bolt diameter, or a little longer.

[pete]

Thanks again guys, I will definitely start looking for a helicoil.

One thing though, as a complete noob (knob?) at this sort of thing, how easy/hard is it for me to stuff it up and make it worse?

I'm assuming just take my time, don't rush, and take care will be all the things I really need for it... is there anything else to be careful of with helicoils?

[gearhead13]

Any of the bolts that go into the soft aluminum should be torqued down on the conservative side. The spec in the manual should be the absolute MAX torque that you apply.

[tatu]

Thanks again guys, I will definitely start looking for a helicoil.

One thing though, as a complete noob (knob?) at this sort of thing, how easy/hard is it for me to stuff it up and make it worse?

I'm assuming just take my time, don't rush, and take care will be all the things I really need for it... is there anything else to be careful of with helicoils?

I'm sure its a 6mm thread and I think its straight in with the supplied tap on that one, no drilling, Gently, bently, but a firm hand keeping it straight. Dead simple.

[pete]

Ok cool, that *sounds* nice and easy, so let's hope it really is!

I'll commence my search for a helicoil and tap etc. tonight, but not sure when I'll get time to go and procure them at the moment.

Will let you all know how I go...

[pete]

Rightio, first port of call is where I've got my polishing stuff from and other odds and ends.

If I read the info on BassCliff's site right about threads and part numbers, then I'm looking at a 6 x 1.0 x 16mm bolt. Does that look right? I'm getting that from the fact that number 13 is the same size and thread as 12, just without the shoulder.

So, if that's the case, then I need to find a helicoil that gives me a 6 x 1.0 thread in a standard metric pitch.

This kit appears to be what I'm looking for, does it look right to others also? If I buy it from these guys, I can buy it online which will save me trying to take a day off to go find something...

https://www.bolt.com.au/product_info.php?cPath=296_348_349&products_id=2958

[tatu]

I'm not sure of the pitch, best thing is establish if the bolt thread is ok, as mentioned ealier in this thread it might be goosed if it is ok, or you have a replacement wind on a nut of known thread and pitch and that is your answer.
(My experience is that 12 / 13mm spanner sizes are on 8mm threads)
Somebody else here might know?

[KC1908]

Pete,

I would say it is 6mm. I will have a look tomorrow after work but I think I would have a helicoil kit in the shed. I live at Anstead in the western suburbs of Brisbane and work in Roma Street if you wanted to borrow the kit. I will make sure I still have some coils left and let me know if you want to use it and we could meet up somewhere.

Ken

[pete]

Thanks Ken, I may take you up on that yet, although I'm happy to fork out the $$$ to buy my own.

I work in the valley so just a couple of train stops away if we do...