Okay so the starter has been in place almost 30 years, held in place with stainless steel bolts. Bolts that have been heated and cooled a few thousand times. Bastards both sheared off when I removed the starter! 

My question is how deep do the threads go into the housing? Do they go past the bottom of the raised mounting on the gearbox?

I don't want to drill them out to find I have made it into the gearbox and dumped swarf in there.

All advice appreciated, except the obvious advice that I should have taken a couple of hours to gently get them out in first place 

The holes are 22mm deep on the housings I have.
You will need a nice sharp drill for stainless and keep it lubricated while drilling. If it stops cutting don't push harder or you will work harden the metal and make it even more difficult to drill. Remove the drill and resharpen or use a new drill to continue.
Mix some acetone and auto trans fluid 50-50 and use that as a penetrating oil, let it soak for a few hours at least then try to remove the bolt remnants with an easy out or similar.

Always use copperslip or some sort of anti seize on the thread of a steel bolt into aluminium. I realize you didn't put those bolts in but it is good advice anyway.

best of luck.

Thanks Rick!

I have not had a lot of luck with easy outs and there is enough material used for the starter mount for me to drill it out oversize and re thread it.

I will try the easy out, but the last time I used one it broke off and man those buggers are hard to drill out!

They should be called not very easy out, I have some success and one of the good things on the market is left hand turning drills that tend to help as you drill the stud. I have seen them on fleabay but can't find any now.
I have RIGID brand stud extractors and they are a parallel insert that bites all the way down the hole and work well but at $150 a set its big money for 1 stud.

RicK G wrote:They should be called not very easy out, I have some success and one of the good things on the market is left hand turning drills that tend to help as you drill the stud. I have seen them on fleabay but can't find any now.
I have RIGID brand stud extractors and they are a parallel insert that bites all the way down the hole and work well but at $150 a set its big money for 1 stud.

Not the sort of tool you lend out!

Forgot about left turning bits, I will check local suppliers before I start.

Thanks again Rick, always sage advise (well almost always:D)

A piece of advice I received from a toolmaker friend when I had problems getting a bolt out of a caliper. I'd seriously work-hardened it to the point where even a good-quality HSS drill blunted within seconds and it just laughed at titanium-coated ones. He said 'use cobalt drills, drill slowly and keep the pressure on. Don't let it skid'.

So I put my hand in my pocket and bought an 8mm cobalt drill just for that job. I had to resharpen it once but basically the bolt came out almost like I was drilling mild steel. I now have a set of cobalt drills that are kept just for drilling stainless steel.

Yeah stainless is fun stuff to drill. One of my first jobs as an apprentice fitter was to drill 1/4" holes in a 6x4 sheet of 316 stainless. Holes at 1" intervals on a grid over the whole sheet. I sure knew how to sharpen drills when I finished.

Dai wrote:A piece of advice I received from a toolmaker friend when I had problems getting a bolt out of a caliper. I'd seriously work-hardened it to the point where even a good-quality HSS drill blunted within seconds and it just laughed at titanium-coated ones. He said 'use cobalt drills, drill slowly and keep the pressure on. Don't let it skid'.

So I put my hand in my pocket and bought an 8mm cobalt drill just for that job. I had to resharpen it once but basically the bolt came out almost like I was drilling mild steel. I now have a set of cobalt drills that are kept just for drilling stainless steel.

 great in a drill press dai

but my experience in hand drilling is not good with cobalt drills ...they do seem extremely susceptible to any sideways distortions whilst drilling

not that in this case you would want that to happen

I have found that with stainless all the above rules applied about drill without slip etc ...I use short bursts of a fairly low speed drill  with some time for heat dissipation ...seems to work for me on the thousands of stainless rivets I have extracted  during my work requirements ...young apprentice snuffed all our stock (5 which I expected to do 100- 150  rivets or more )  on just about  30 rivets patience and constant pressure  are the key ...I agree


I have found ...( and don't know if they are available over there ) the "Sutton " "blue " hss drill is extremely good for stainless in all forms
the drill is actually black in colour but exceeds all others for the task by about 3 to 1 ....or just what I think in any case


cheers

charlie99 wrote:
I have found that with stainless all the above rules applied about drill without slip etc ...I use short bursts of a fairly low speed drill  with some time for heat dissipation ...seems to work for me on the thousands of stainless rivets I have extracted  during my work requirements

You've noted the real problem there Charlie - heat dissipation. Also; thanks for the warning on cobalt drills.

Thanks to all who contributed.

I purchased a left hand turning drill bit . I also purchased a pack of 5 normal drill bits and a bit sharpener.

I could not seem to prevent the drill from wandering off centre resulting in about 15% of the hole being into the aluminium casting.

Drilling out stainless is a nightmare!

The left turning bit was not much help, probably because I was off centre. Took the best part of a couple of hours to drill out and re tap one stud.

I had had a guts full of it and decided to put the old girl back together with just one stud holding the starter. The starter exchange is only one of several attempts to sort my electrical problems anyway and I figured if it was not the answer I would sell her off to a wrecker and take up skateboarding!

So far so good. A couple of hundred kilometres and the battery seems to be holding most of its charge. 

I have had a couple of times that the starter seems to be a bit sluggish to turn but I think I have probably done in the battery with all the mucking about I have been doing. I will put on trickle charge and take it to my battery shop for them to test it.

If all it needs now is a new battery I will strip it down again and drill and tap the other stud holding the starter. When I have forgotten the about how tough it was.

As I started my professional life as a machinist/toolmaker, I learned few little tricks.
First one, is to use a center drill to pre-drill the bolt. Even when applying a lot of pressure it doesn't flex and your drilling keeps straight.


In the case of the starter screws, I would have reinstalled the starter on the engine and had a bushing made to fit tight in the screw holes. This bushing should be drilled to a size smaller than the screw (ie: 5mm for a 6mm screw) and will serve as a guide for the drill bit.
This way, the drill bit stays centered and if you don't apply too much pressure, you will drill straight.

This solution can be applied to any broken screw. You can take a thick plate of metal, drill a hole and securely attach the plate to the part where the broken screw has to be removed.

Sorry for the late advise.

CF