Dilavar - more questions

[motogman]

The Dilavar head stud problem is well documented in many threads and I am in the process of replacing 6 broken studs in a 3L motor. But working to remove the broken remnants has raised some questions that I do not readily find guidance in my searches.

1) I am down to drilling out the broken studs after defeating my various clamp devices to get a hold of it. (Other options are to weld a nut on which I have been told does not often work or going to EDM which is my last resort). But my question is - what drill bits work on Dilavar? I thought I had some reasonably good bits but after about 4-5mm the bits I have give up and no longer cut the stud. This has happened with several.


2) A more technical question... What is the metallurgy of Dilavar? My understanding is that is is an iron based alloy which is non-magnetic and has a coefficient of thermal expansion similar to aluminum. The expansion was the property that made it desirable for the application. The propensity for corrosion pitting and notch sensitive for fracture are what cause them to fail (as I understand). I have been unable to find technical metallurgy references to the alloy content and other properties (i.e. hardness etc.). Any metallurgist out there with more insight?

[walt]

Have you tried to heat the base material surrounding the stud. I used a MAP gas to free mine, acetylene would have been faster but it did job

Don't know much about Dilavar but it's obviously high chromium or nickel content so yeah, it's going to be very tough to drill.

[30westrob]

I used a pipe wrench on long studs, and welded nut on short. Per Walt’s guidance you must heat the aluminum around the stud. I use a plumbers acetylene torch. this has always work for me.
Your drilling idea is wrought with risk. Drill slightly off center and you have a damaged thread hole.
Rob

[walt]

An alternative to welding a nut on is to get yourself a stud extractor. You don't indicate but hopefully the stud didn't break off flush.

[porsche930dude]

Just an idea but if youve got something to grab onto I would grind two flats on it and use vice grips.

[Dpmulvan]

Originally Posted by motogman

The Dilavar head stud problem is well documented in many threads and I am in the process of replacing 6 broken studs in a 3L motor. But working to remove the broken remnants has raised some questions that I do not readily find guidance in my searches.

1) I am down to drilling out the broken studs after defeating my various clamp devices to get a hold of it. (Other options are to weld a nut on which I have been told does not often work or going to EDM which is my last resort). But my question is - what drill bits work on Dilavar? I thought I had some reasonably good bits but after about 4-5mm the bits I have give up and no longer cut the stud. This has happened with several.


2) A more technical question... What is the metallurgy of Dilavar? My understanding is that is is an iron based alloy which is non-magnetic and has a coefficient of thermal expansion similar to aluminum. The expansion was the property that made it desirable for the application. The propensity for corrosion pitting and notch sensitive for fracture are what cause them to fail (as I understand). I have been unable to find technical metallurgy references to the alloy content and other properties (i.e. hardness etc.). Any metallurgist out there with more insight?

Try some two flute carbide bits use a slow speed and some tap magic. Helps to have a milling machine.

[$yncro]

Originally Posted by walt

An alternative to welding a nut on is to get yourself a stud extractor. You don't indicate but hopefully the stud didn't break off flush.

This is exactly how I pulled mine off..
Got me a set of bolt extractor.
I used it on one headstud that broke off
1/4 inch off the case. It came off with no
Damage to the case. Try it first before drilling.
Good luck

I have a pic but won't let me upload it.

[SCadaddle]

We removed the dilivar head studs from my SC engine by:

1) heating the area of the case with a torch around the head stud to 300-350F as per an infrared heat sensing gun

2)At which point while applying a rotational force with the heat still applied at 300-350F touched the base of the stud at the case with a chap stik size applicator of Burts Bees Wax--peppermint flavor (as my research indicated it contained the most bees wax of all of Burts Bees products sold at the local Walgreens!) ---- and as the bees wax flowed in and gave off a very minty smell, the stud gave loose and rotated right on out only as long as we kept the heat on it. Removing the heat and she would tighten right back up!

Good Luck!

[proporsche]

as mentioned above..in order the brake off(burn it off) the loctite on the threads use torch - that is propane gas not a torch which is in England flashlight;-)
Then, it will come out very easy...using whatever technique you like
do not be afraid to use the flame...


Ivan

[Walt Fricke]

For drilling, try cobalt bits.

[theiceman]

how about a pic of what you are dealing with ?? there is no doubt its not coming out without the blue wrench though.

[Steam Driver]

Two things worked for me on my SC:

1. Get a proper stud extractor, one that applies the torque on the centerline of the stud, so you aren’t applying any side loads on it while twisting it out. The latter situation worked against you by loading the threads against themselves and also increases your chances of breaking the stud off.

2. The AL case is a huge heat sink and radiator. I use a trick I learned taking big studs out of really big heat sinks. Heat the stud, not the case. Heat it to just red hot (don’t overdo this!) then let it cool off. What this does is expand the stud in the hole as well as breaking the thread locker bond and any corrosion that may be present. Perhaps more importantly when the expanded stud cools off the surrounding material doesn’t quite shrink back to its original size. This helps to loosen the stud also. This has worked great for me on the head studs, exhaust studs, etc.

This trick comes from restoring steam locomotives. They have lots of big studs (for mounting appliances and accessories) screwed into the boiler shell, which is quite thick. Obviously one can’t heat that easily to remove a stud (which may have been rusted in place for 50-75 years), so we heat the stud instead. We generally use new stud replacements, but they are of standard size and the pressure vessel isn’t compromised at all. So it shouldn’t hurt a 911 case or heads.

[Dpmulvan]

Read the guys post he’s beyond a stud extractor.

[motogman]

Yes. Unfortunately I am past the point of a stud extractor. The stud extractor worked well for the ones that had some length left but the ones broken at the case are the problem.

Some good ideas here - I have ordered some left hand drill bits and will try those with heat.


My questions about the metallurgy and properties of Dilavar arise from my experience trying to drill these out and having Ti and Cobalt drill bits give up after a few millimeters of progress. It seems this Dilavar is bad ass stuff.

[Henry Schmidt]

Electrical discharge machining (EDM)
Quick, easy, no case damage and generally reasonably priced.

[motogman]

I like the idea of EDM for removal. There is a good post about building and EDM apparatus and DIY.

Can anyone provide the name of a shop where I can get EDM done in the Detroit area?

[gomezoneill]

Originally Posted by motogman

I like the idea of EDM for removal. There is a good post about building and EDM apparatus and DIY.

Can anyone provide the name of a shop where I can get EDM done in the Detroit area?

Electrical discharge machining (EDM)https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjS4cTT3s3tAhUCB50JHQspDSgQFjAAegQIARAC&url=https%3A%2F%2Fmetalmite.com%2Fmachining-services%2Fwire-edm%2F&usg=AOvVaw0JQM_E-n4tEFlsV6kQ_jGp

[safe]

Originally Posted by motogman

I like the idea of EDM for removal. There is a good post about building and EDM apparatus and DIY.

Can anyone provide the name of a shop where I can get EDM done in the Detroit area?

There is nothing left to grab on to?
If you heat the case until the loctite lets go they spin out pretty easy.