Replacing a broken stud - The HARD way

[OzFab]

As most of you know, I recently aquired a Marshin 150cc pitbike engine. Apart from the severely messed up wiring, the only problem (visually) with it was a broken exhaust stud.

I will now apologise in advance for the lack of before & early pics as I didn't know this would become as big an issue as it did.

So, I started out the usual way, drown the broken section in penetrant, centre punch & drill the centre with a 1/8" drill bit.

Then, after spraying even more penetrant, I hit it with the stud extractor. No joy, it wasn't budging. Worried that I would break the extractor (I've done that before) I drilled out the hole to the next size up. Unfortunately, I hadn't drilled deep enough so, I kept going: That's when it all went horribly wrong!

Instead of drilling straight, the drill went sideways towards the exhaust port. Worried that I would do irreparable damage, I stopped, rang a couple of mates for ideas/suggestions & rethunk the situation.

Here's what we came up with:

 

[OzFab]

It's a drill guide!

After measuring the dimensions of the now messy hole I hit the lathe. One end is an interference fit to the hole in the exhaust flange, the other end is larger (so it holds against the flange) & tapers down to the size & depth of the stud hole & is hollow through the centre.

Once I bolted the flange in place using the good stud, it gave me a perfect guide to drill the old stud out. Once I had a perfect base guide, the rest was easy

 

[OzFab]

Once I had the guide hole where I needed it, it was clear I'd need to increase th size of the thread; from 6mm it ended up at 10mm.

I did make up a stud 10mm on one end & 6mm on the other but, the 10mm end is too short & sinks into the head too far so, back to the drawing board

 

[realfast89gt]

Man, i know how that stuff goes. Last thing like that i had to fix was a spark plug in a ford v8 that broke and left only the threaded part. As long as you take your time and use a little brain power it normally goes well in the end.

 

[OzFab]

USUALLY! Only this time, Murphy's law kicked in

 

[HaM551]

New engine time ? you could probably get a new head off eBay

 

[Doc Sprocket]

No way! He'll get it- just give him time!

 

[realfast89gt]

I have seen amazing things first hand from JB Weld.

 

[OzFab]

New engine time ? you could probably get a new head off eBay

No way! He'll get it- just give him time!

I've pretty much got it, I just need to remake the stud a bit longer, loctite it in place & I'm done

 

[Doc Sprocket]

I got faith in you, brother!

 

[GoodWComputers]

This thread is giving me more, wait less... wait, more... confidence to try this?

 

[OzFab]

Done!

I got back on the lathe today & spun up another stud.

For those interested, I started with a length of 12mm round bar & cut 2" down to 10mm then the 1" on the end was cut down to 6mm. A 10* taper on the end & at the step to help start the dies, cut the threads &, finally, even out the taper at the step.

I made sure it was tooo long this time; it's easier to cut it off than add it on. A few trial fits, a bit of cutting & grinding & I'm done!

Who can pick it?

 

[landuse]

Nice job! We knew you would get it right.

 

[fowler]

good job
it certainly helps to have a good pool of resources and knowledge

dam these things are a real pain

i have gone though this with a D 10 dozer
started with a simple heat sheild change
found 4 brocken exhaust studs and the others were rusted to non existance

fixed them all then snapped the tap in the last hole
had to blow it out with an oxy

 

[Doc Sprocket]

Oh, FUDGE!

That's something that truly would wreck my day, breaking a tap off in a hole. I am not equipped to deal with a disaster like that...

Nice work, Tony- boy, you really cut it close with that one, didn't you? I just noticed the "hole in the wall".

 

[fowler]

Oh, FUDGE!

That's something that truly would wreck my day, breaking a tap off in a hole. I am not equipped to deal with a disaster like that...

Nice work, Tony- boy, you really cut it close with that one, didn't you? I just noticed the "hole in the wall".

Wow I see what u mean
Bloodly close
At least it's in the outside and not going to cause any sealing problems

Bet u were nervous when u tapped it

As for breaking a tap
I was only a 1st year and did it in a head worth 10s of thousands of $
I was s***ing my self alright

 

[cumminsbayou4x4]

i broke a tap off in my 3hp briggs crank shaft. i was doing it with no help and it was the first time id used one. when i did it i thought ill have to get a new crank shaft .then i thought why not weld a bolt to the end of the crank shaft and double nut the clutch on it. this worked great its straight and i have used it a lot with this system on it

 

[OzFab]

Nice work, Tony- boy, you really cut it close with that one, didn't you? I just noticed the "hole in the wall".

Yeah, that's why I had to go to 10mm & not 8; the drill slipped off the edge of the original stud. That's when I stopped & made the guide

 

[Rustydog2010]

Oh, FUDGE!

That's something that truly would wreck my day, breaking a tap off in a hole. I am not equipped to deal with a disaster like that...

Just on this. Have you heard about tap extractors? I found some in the W/S and had no idea what they were at first. When I used them they worked great. The flutes goes down beside the cutting edges, and you just unthread it.

Thats an awesome idea Fabroman. Making up that guide is what I call thinking outside the square. Might have to urmm... borrow it!

 

[fowler]

That's awesome

Where do they come from?