Fixing Pulled Stud Without Engine Disassembly -- Possible?

[Rich911E]

I have a magnesium case engine with a pulled head stud that I would like to fix and start using again. It seems that there should be some way to use a long drill to drill out the magnesium case and insert a case saver without disassembling the engine. I was thinking that a long gun drill (or something similar) in a fixture would be sufficiently accurate to drill out the case and use an extended tap to prepare it for the case saver(s). I realize that there might be some chips from the drilling that might work their way down into the case but it would seem that these could be washed or cleaned through removal of the oil pan/screen. The gun drill is sort of a half-round drill that collects the majority of the chips in the drill itself.

There are a lot of people on this board with machining experience and I wonder if this is possible.

Rich



PS: Took the GT3 on a drive last weekend -- a 550 Maranello and a 360 Challenge Stradale showed-up to challenge. The GT3 acquitted itself quite well -- the Stradale wasn't keeping up.

[sammyg2]

You would have to remove the old head stud, drill the case to a larger diameter (which may be too large for the holes in the heads), then tap the threads in the case, then insert the case saver or time-cert, what ever they are called today, then re-install the head stud.

I usually say anything is possible but if you pull this one off I owe you a beer. I'd say it would be darn near impossible.

[john walker's workshop]

one pulls, then another, etc. it's a loosing battle. i suppose it could be done, but the head and cylinder would have to be drilled oversize to get the timesert/helicoil/casesaver thru as well as the installation tool.

[speeder]

I dunno, they always told me, "no machine work while it's running", but this might fall under some kind of exception.

Seriously, this doesn't sound like a very smart plan of attack. I have seen someone here do a simple extraction of a broken stud *stump* and screw in a new one w/o disassembly once, but it's in the Pelican "DIY Hall of Fame/Don't try this at home" archives. Drilling would be a whole 'nother kettle of fish, lots of chips.

[Rich911E]

I have been looking at some pictures of the assembly and didn't consider the drilling through cylinder head (which could probably be sleeved to compensate) but then also the fins of the cylinder barrels. I didn't remember that they were so close fitting to the studs themselves. I suppose the small amount of materials removed would not make much of a difference, but it is certainly not optimal.

I did find a place called "tight fit tools" on the web that makes drill extensions and what are called stub step-drills. In other words a short drill that steps up from the shaft size to a larger diameter that is then threaded onto the shaft. If you could allow the shaft to come through the head and cylinder barrel fins and then thread it onto the stub drill (remember, we are just drilling into soft magnesium here), drill out the hole to a size to accept the insert, thread the insert into place, and reinsert a stud, it might work.

This may be more work than its worth, but if we could come up with a system that works, I think it might make some people happy. I'll probably just have to pull it apart and do it right.

Thanks for the thoughts though.

Rich

[techweenie]

I heard about someone doing this last year. It requires disassembly of the 'top end.' Using air pressue and rags, you have to create overpressure in the case so that any shavings from drilling will go out; not in.

Allegedly, this was done by a shop, but I consider that kind of work about on the level of putting sawdust in a transmission to quiet it down.

[William Miller]

Rich,
I like your idea along with the presurized case. I'm sure a skilled machine shop could modify a drill bit and tap to work with an extension.
The bore of the stud hole in the cylinder, head etc. may actually work very well as a drill guide. I know they make some long extensions for cordless drills with hex heads (For drywall bits) They are now making drill bits that fit into these extensions. (See Dewalt.com) I haven't seen one this large, but see no reason it's not possible. Taps could also be machined to fit the hex extensions. I think one limititation would be if the skirt on the cylinder barrel partially covers the larger hole needed for the insert. If so, game over!
Good luck and I hope for all of us that it works!

[techweenie]

You simply can't do it with the head & cylinder in place.

The cylinder fin clearances around the stud are smaller than the hole you need to drill in the case for a 'case saver.' So not only can't you get the bit in there, you can't get the insert in, either.

[sammyg2]

In order to get a larger diameter drill or tool or whatever in there you will have to drill the holes in the heads larger. That simply will not do.
Those holes have shoulders around them that the head barrel nut washers seat against. If you remove material from those shoulders by drilling the holes in the head larger you will probably not have enough material left to hold the torque on the barrel nuts. I'd venture to guess that the OD of the inserts are at least as large as the OD of the barrel nuts so if you go that big the chances of the washers getting distorted goes way up. The more shoulder the better, the less shoulder the worse. By the time you get a drill and tap and installation tool in there to install the inserts you woulds have to have a pretty big hole. The washers are fairly strong but with constant compression and countless heat cycles I'd be really surprised if they would stay flat.
I don't have a head or threaded insert in front of me right now so I can't measure the diameter of the holes or the insert, maybe someone else can offer up some numbers?

If you remove the heads you "might" be able to get away with drilling the holes through the cylinder fins large enough but if you have the heads off, why not go all the way?
If you have a team of Nasa schientists working on this project with a million dollar budget you could come up with a way to do it, but otherwise color me doubtful.

[wastintime]

I know one person who went against advice and tried... 3 years later his motor ran again.