Topic: Need help now - exhaust screw stripped. Results....

[oldbiker]

You may not want to hear this, but I recommend that if you cannot get the remains of the stud out, you take the head to a decent machine shop and get them to remove it. Over the years I have made several attempts to drill and clear a broken stud and have found it almost impossible to keep the drilling central. This results in a damaged off centre hole which then has to be repaired with either a helicoil or timesert insert. A good shop will clamp the item down and use machinery to stay dead central so they either clear the tapped hole or put in an insert. Easy out are hardened and have a habit of breaking off leaving a hard center that you CANNOT drill through.

[johnny-from-bel]

Well, it seems that this bugger isn't coming out.  I am now thinking of cutting off the exhaust flange to see if I can get a better bite on the remaining screw head.  So far, every indication of this stuck bolt/screw is lending itself to drill and tap.  What size would/should I tap it if I must?  Do you recommend the use of a Helicoil?

Thanks.

A very frustrated,
Sparty

I think you are not giving it enough time. I have spent up to three weeks heating, WD20, tapping, etc...

Now if you are determined to drill it out.
Helicoil is very good. I have used it before.

I believe these bolts are M8, please correct me if I am wrong.

Start drilling out the hole using a 4mm drill. Make shure you drill straight and not to deep.After you drilled the hole put a 4mm rod in the hole and check that you have 90 degees in every direction. Now Increase drill size with 1mm until you are at 6mm. You may now be able to pry out what is left of the bolt. If not drill a 6.8 mm hole (7mm if you do not have 6.8mm). Now you can try to recut the M8 thread. Pry out as much as you can at the top to get a good starting point.
If that fails drill the hole with the drill that came with the helicoil, cut thread, insert helicoil and done.

Patience is the key to success

[spitfire]

I recently had a similar experience with my 76 750F, though the exhaust attachment is different the principle is the same. when I removed the exhaust system one stud broke leaving about 1/2" protruding. Following advise from people on this forum I spent 2 - 3 alternatively soaking the stud with WD40, spraying it with a freezing penetrating spray, heating it with a torch and giving it a sharp whack with a hammer to try and jar the threads loose. I then used a roller type extracter which broke the stud revealing that nothing at all had penetrated.
I had been toying with the idea of checking the pistons and rings on the bike as it had not been fired up in 12 years, the broken stud made up my mind so out came the engine and off came the head and cylinder barrels. Rather than butcher the head myself I took it to a car engine shop for a small amount of money they drilled the head and fitted an insert, while it was there they soaked it in a bath for two days to clean it. If I had not wanted to check the pistons and rings I could have taken the whole bike for the work.

[spitfire]

Whoops, should have read 2-3 weeks

[sparty]

Two hours of tapping, spraying, heating, tapping, tapping, tapping, and repeating.  A broken back, stiff neck, scuffed knuckles, and one extracted screw!  What a wonderful day to be alive!  I got the SOB of a screw out about 20 minutes ago.  Here is a picture of what I had to deal with.  Guess which screw wouldn’t come out?

Now I can install the new exhaust.  This part of Nightmare CB750 is over.


Sparty

[johnny-from-bel]

Congratulations !!

[750goes]

Be gentle with the new screw, and clean the existing thread hole out with a wash of wd40 or some lubricating fluid, and make sure you can screw it all the way in easily before putting on the exhaust.

As i mentioned mine came out ok, but screwing it in I had to clean out the old thread- and that took a while to do as well.

did you put new exhaust gaskets on the head

[sparty]

Be gentle with the new screw, and clean the existing thread hole out with a wash of wd40 or some lubricating fluid, and make sure you can screw it all the way in easily before putting on the exhaust.

As i mentioned mine came out ok, but screwing it in I had to clean out the old thread- and that took a while to do as well.

did you put new exhaust gaskets on the head

I will no longer be using screws for the exhaust.  I am going with stainless bolts and anti-seize on the threads.  I will be cleaning out all of the bolt holes first, that is for sure.  And YES, I will be installing new copper exhaust gaskets.  I never take shortcuts with my mechanical repairs/modifications.  If something is wrong, I usually over-fix it.  I have also been updating the bike to make it safer (ex. new sportbike MC with braded lines, rebuilt front fork, and new rear shocks).

Sparty

[oldbiker]

Well done Sparty. I admire your perseverance.

[sparty]

Well done Sparty. I admire your perseverance.

Not really perseverance, but rather desperation - I want to ride the damn thing...

I learned or re-learned a very valuable lesson in patience.  I have never had to spend eight hours extracting a screw/bolt before.  However, my celebratory beers afterward never tasted so good.

Sparty

[spitfire]

Great news, glad it worked out for you.

Cheers

Dennis