A How To / Diy repair damaged / stripped / cross-threaded bolt threads tutorial

[my67xr]

ok,
some of you may have seen my DS80 build/repair thread.
i took the bike up to our farm a month ago and tried it out.
it goes pretty well all in all, 5 speed gearbox is sweet and motor doesn't miss a beat.
pulls hard till it hits powerband then gives a fair bit more as the revs increase.
im very happy with it, especially for being pretty much a factory stocker bike.

on the last day we were there, i spent a few hours cutting a track with my father inlaws 4WD mini John Deere tractor, fitted with a bucket on the front.
the soil was very compacted etc, and a fair bit of weed around too, salt bush and native stuff.
i made a small track with a couple of straights, a few corners around the trees and a few hairpins corners too.
i will try and build it up each time i go, burms, jumps and extend it out longer too, we have plenty of room.
currently it is about 250 metres long.

i have done 20 or so laps on the DS80 on the track, but it came to an end.
i came off the bike a couple of times around the corners, trying to go too quick.
you get that i guess, :LolLolLolLol:
last lap i had my 11 yo son do a video for me on my phone, dodgy quality
i got half way around the track and as i was coming into the corner i head some cracking noises from the rear of the bike.
slowed down and the rear suddenly locked up, i layed the bike down.
got up started it, and went to take off and head back to the car.
the brake pedal was bent under the engines' side case.
i straightened it up and tried to take off again, still needed to bend the arm a bit more.
i got it free ,and slowly rode it back to the car.
the cracking noises were getting worse, i looked down and saw the rear sprocket bolts hanging out, and pussied it back to where we had parked.

we took the bike back to the workshop and pulled the back wheel off, i found that a previous owner had damaged the threads in the rear hub, where the sprocket bolted to.
then noticed the loose bolts had started chewing into the hub, hmm
and finally noticed the bolts they had used wer M8 x 1.25mm thread, no lock washers/tabs on them.
the thread in the hubs was M8 x 1mm.
that combination doesnt work for long at the best of times.

here's a pic of the damaged hub, i brought it back home to fix.
all the bolt holes were looking like the top one, hmm!

a month later i had a chance to look at it again, i went and bought some threaded insert repair kits from the local parts store.
i have used these plenty of times before fixing damaged threads.
i like them as the a drilled and tapped solid rod, not the Helicoil/Recoil
style wire thread inserts

they didn't have any in the finer thread i wanted, so i bought the slightly coarser ones to save mucking around/waiting etc.

these are very easy to fit, and are a cheap way of repairing things so they'll last for years.

you get a bolt, nut and 2 inserts for around $12, depending on size etc.
on the packaging it tells you what size drill to use to cut the new hole.
i drilled it out to 11.5mm as noted in the instructions.
drilling square to the hub face, and slightly deeper than the insert.

next step, screw the nut onto the bolt, most of the way on
and then screw the insert on as well, the bolt needs to go 2/3 of the way through the insert.
then wind the nut down tight onto the insert and lock it up.

i chose to use loctite on the thread to make sure it wouldnt come loose again.

sit the insert into the new hole and square it up.
next using an open end spanner to do the up via the nut (not the bolt),
some slight downward pressure is needed for the flutes to start cutting as you do it up.
the alloy cuts like cheese, hardly any force is needed to turn the spanner.
you only need to keep doing it up, as the swarf drops to the bottom of the hole, or in this case out the bottom of the hole.
you dont need to turn the nut back like when tapping a thread, just keep winding it in, the big cutting slots easily clear themselves
you know when you are done, as the nut will tighten up against the sprocket flange, or whatever it is going into.
once you have it tight it will look like this.

next grab another spanner and hold the bolt from moving, so the nut can be undone.
it only needs a little turn of the nut for the whole lot to become loose, and just unscrew the bolt from the insert.

once the bolt is out, you are left with this,

repeat the steps above for the other 3x remaining inserts and here it is,

being threaded all the way through this hub, i just ran a tap the rest of the way through.

here is a pic from the brake drum side, you can see the 2x cutting tabs in the bottom of the insert.
and the tapped thread continues now right the way through.

next i ran a fine file across the sprocket mounting face to deburr any of the damage, and make it smooth/square again.
i fitted a new bearing there too while i was at it, as the sprocket side of a wheel gets the most wear.

and a pic looking almost square to the face of the hub,
showing that there is none of the inserts sitting higher than the mounting surface of the sprocket.

so that's pretty much it, how to fit a new thread insert.


while im writing about rear hubs, here is another tip.
the rear sprocket bolts need to be a decent quality.
most of the china pit bikes come with some bad quality bolts as you would have found out.
i will be using some socket head cap screw bolts and high tensile washers to hold the sprocket on when i put it back together, and loctite too to stop this happening again.

here is a comparison of china and some decent bolts,
chigh *&%#!???!?***--- (haha) tensile bolt on the far left, this would be about a 4.8 tensile strength bolt
next a cheaper socket head high tensile bolt, rated at 8.8 tensile strength
then the bolts im using, 12.9 rated tensile strength.
and final bolt on the right, a 4.8 standard china chigh *&%#!???!?***--- (haha) tensile bolt, with a full guarantee that it will fail asap.....





hopefully this thread may help someone else out too,
and that i havent redone someone else thread??

now stop reading this, get outside and get yourself some thread inserts, and fix that damaged thread.
and jump on your bike and riiiiiiiiide haaaaaard!!!!! ........:scooter:


good luck and cheers,
craig

 

[westy465]

exelent work mate. diddnt know champion did them. if you wanna take it one step further, you can get the Heli-Coil or Re-Coil kits. expensive, but super high quality and strength.

 

[my67xr]

thanks westy ,
but I have thousands of thuse helicoils from M3 up to M18 thread sizes.
but prefer these over the wound stainless wire inserts, as you don't need special taps and tools to fit them either.
with helicoils /recoils you need to buy a specific length for what you need, these are 19mm long so you could always cut it down if need ed.

 

[GooseMan]

Great thead 67xr, glad to hear that the little 80 is still going hard and strong and I had never heard of these thread inserts before!! VERY interesting. These would work on the exhaust mounting bolts to the engine block wouldn't they? I still want to get my 80 going like new after seeing yours, its a shame Im limted by money so much

Good Job

 

[Shearer]

Good stuff.
I need to do the same thing to 82 z50r i have.

Some handy info & help full pictures , they sound think about make'n it "sticky"

 

[my67xr]

thanks gooseman,
yeah they would work on the heads exhaust stud threads too.
on one of my old 125's with a stripped thread for the M6 stud, i just drilled it out a touch larger and tapped it to M8 x 1mm pitch,
and got some new unbrako bolts (allen head) to match, the allen heads give you more room to move, beats trying to get a spanner in there.
also drilled out the flange plate on the exhaust header pipe to 8mm

here's my helicoil/recoil collection, M2.5 in the top left of the box, M18 on the bottom right

 

[my67xr]

thanks shearer,
they can if they want to, would need to edit most of the Suzuki DS 80 stuff from the first bit.

 

[my67xr]

the video of when the bolts come loose, and locked up on the swingarm,



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[rotn50]

very informative thread mate, very easy to fix an over tightened head stud on my pitty casing now.

 

[GooseMan]

Wow my 80 sounds so bad compared to that, have you upgraded the exhaust at all?? My'n has a horrible rattle but sounds alot more like a screaming child or something.

 

[my67xr]

the exhaust is just a standard expansion chamber, I cooked all the oil and carbon out of it on a gas powered camp stove while blowing compressed air through it.
I had to make the section from the head to the part where it starts expanding
surprisingly my neighbours didn't complain about the smoke and burning oil smell!
and it's also got a custom muffler that I made for it too.
sounds very tinny in that video .
I'll try and get a better video of the bike and how it sounds this weekend hopefully.

cheers

 

[my67xr]

and how's my 5yo dobbing me in, 'that's the second time'....lol
he sat on my lap when I was riding, he holds onto the bar pad so tight,lol, we got it up to about 60kph on the way down to that track.
did you guys hear the sprocket bolts ' cracking noises when they'd hit the swingarm when coming back from the stack,
in the last 20 seconds of the video?

 

[Shearer]

Dose sound mad! a. Ring ding ding
Sound don't hear much anymore in four stroke world

 

[my67xr]

20120930_135558.mp4 video by xrfairmont67 - Photobucket

20120930_133453.mp4 video by xrfairmont67 - Photobucket

 

[Cactus Jack]

Excellent info ... I've cleaned out several expansion chambers and exhausts the same way only I also filled them with small blue metal rocks and shook 'em around to literally sand the inside back to bare metal ... It's amazing what can be achieved when you think outside of the square !

 

[my67xr]

yeah,
lots of different ways.
heard of people doing them on the weber bbq
cooking them on campfires etc

I have a burner /torch and 1metre hose that connects up to my lpg bbq gas bottl,
I would have used it if the bottle wasn't empty.
I've heard of people using caustic soda too

you gotta watch out putting rocks/gravel kind of things in some expansion chambers though,
some have stainless mesh or stainless scourer type material in them.
the gravel can get caught in it and explode when heated, eg engine running at wot.
some expansion chambers are hollow too, so they'd be fine.

 

[Cordogs]

Dad fell over again. Can always count on your kids to dob you in ay! great post by the way mate, especially with all the photo's.

 

[GooseMan]

hey craig or anyone really, just wondering if you know if repco sell these thread repair kits, I've tried Mitre10 and supercheap but niether of them have one and repco is the only other place I can get to after work in time. Otherwise I'll have to send my bro out to fetch me one. Just wondering if you know is all.

 

[my67xr]

Sprint Auto parts sell them, there is one down near Target at Castle Plaza, cnr South rd and Edward st?
they keep them behind the counter.

 

[GooseMan]

oh ok then thanks, didn't realise there was one there, thats good cause I work at saint mary's, Detrac Diesel is the place. Thanks mate.