View Full Version : Wrong headbolts

Harry Yarnell
08-14-07, 01:23 PM
I should have known. The warning signs were there, but I didn't pick them up in time.
I'm doing a headgasket job on a '93 STS, and have gotten to the point of drilling and tapping the block for inserts. I've attempted to drill two holes. The bit goes easily for the first inch, then gets increasingly difficult to drill. The last 1/2" refuses to drill. WTF? Drill looks fine.
Back up a minute. As I was tearing the engine down for this proceedure, I noticed someone had written REAR and FRONT on the heads. Oh, oh, someone's been in here before.
Trying to remove the headbolts with a 10mm tool, won't fit; the bolt took a 3/8" hex. Odd.
When the heads came off, I tried to see if it had inserts. Hard to see in that hole. Tried a thin magnet down the hole looking for the tele tale 'stick' of steel (Timeserts are steel). Nothing.
Tried to install the new headbolts to check fit; they wouldn't go, just thought the thread holes were badly messed up. But no.
Bottom line, someone has installed stainless inserts for a 4.9, which uses 12 mm threads, not 11.
Can't reuse the 12mm bolts as at least two of the bolts won't hold torque.
Not sure what to do now...

08-14-07, 01:32 PM
Would this be a candidate for a Timesert "Bigsert" kit for the Northstar?

Or are you saying that now that the 4.9L inserts are installed, you can't get them back out to re-use the hole?

Harry Yarnell
08-14-07, 02:59 PM
Exactly. Don't know how to get the inserts out.
I've got a spare '93 motor in the back of the shop I may use, but this one (the one with the 12mm inserts) is so clean; not even a hint of top cylinder ridge...

08-14-07, 03:19 PM
Just shooting from the hip here, but any chance of putting the old bolts back in about 3/4 and then mig welding them to the insert. Then use the bolt to turn out the insert.

08-14-07, 03:43 PM
Drilling stainless steel is a tricky proposition because if the drill stops cutting it quickly work hardens the surface and you might as well be trying to drill hardened tool steel. Use sharp carbide drill bits with lots of cutting fluid and at a reduced drilling speed. Apply enough pressure to keep the drill bit cutting.

08-14-07, 05:40 PM
Do they make screw extractors that big?

08-14-07, 09:41 PM
I've seen screw extractors as big as your fist.

08-15-07, 03:24 AM
Do they make screw extractors that big?

Just use a reverse drill bit (left fluted). It will dig in if it's sharp enough... Run the drill really slowly (<100 RPM!) and use lots of downward pressure.

Harry Yarnell
08-15-07, 10:54 AM
Great idea!! (screw extractor)....but didn't work.
Not sure about the reverse drill, will consider that, but the Timesert drill
wouldn't cut it.