[alfa] Camshaft bearing stud problem

[Jon Pike <jhpike@xxxxxxx>]

Well..  this is turning into a bit of a saga..

I had the second stud pull loose while doing my last R&R of the cams, 
(to put on fresh locktabs) and decided to do it myself, since I had 
everything back together at that point, manifolds, Spica, air pump 
bracket, etc... and didn't want to pull the head again.

So I buy a Timesert kit, for 8 x 1.25mm..  $45.  I measure out 
everything,  realizing that tapping a blind hole requires some 
overdrilling, since taps have incomeplete threads at the end for easy 
starting into the hole.

I try to get a definitive "how much deeper do I need to go" answer, but 
nobody who really knows is still there, the day before Christmas..  
Seems they say .300"  Measuring,  I get someplace between .250-.300"  I 
decide splitting the difference is an idea,  .275" is pretty close to 7mm.

I finally get one of the guys I had some machine work done,  he says "oh 
yeah,  there's a lot of room under the studs".

So,  I measure things out.  The hole from the top deck (top of head) to 
bottom side (ignoring the rounded bottom of hole) is about 17.4 mm 
deep,  with about a 6 mm deep wider countersink area.  The Timesert is 
about 11.7 mm from top to bottom.  I want to add 7mm extra depth for the 
nose of the tap,  which comes to a total hole depth of 24.4 mm.

Here's something neat I found out about the Timeserts..  The drill is 
very close to the inside diameter of the cam bearing cap!  I was told of 
the trick of using a junk cam bearing cap, drill it out on a drill press 
for a square hole, then use the cap to guide your drilling of the head.  
I was even given a cap to use the first time around..  but this drill 
was much smaller than the drilled out cap.  Maybe that's the Helicoil 
diameter?  Anyway,  the Timesert drill is about .035" smaller than the 
stock cap's hole,  no drilling or damage and it guides pretty well. I 
measure and mark the depth to the top of the cap on the drill with 
tape.  Great...

Here's where I start to screw things up.  First off,  I didn't pull the 
exhaust cam. I was going to save a bit of time and hassle by leaving it 
in there.  If I had.. I probably would have noticed the oil passage 
coming up at a 45deg angle,  you guessed it, from under the inboard side 
cam stud I was about to drill out.  Yes,  as I hand drilled down with my 
tap twister, very near the end I feel a change, and sure enough, I'm 
breaking out into air down there!!!

Words were said..  Then some more words...  I went away for a while to 
relax, then re-assesed the situation.  Yup, I drilled into a passage,  
Yup, it was oil, not water.  I pulled the cam, and could see light, and 
some chips.  Got the shop vac and a piece of 1/2" hose, a rag for a 
cork,  and sucked out all the chips,  used Q-tips to budge resistant 
ones, etc.  Apparently no chips farther down the oil passage.

Did some measurements.. found out that just about 20.0mm is how far down 
you could drill before you hit oil passage on an inside cam stud.  This 
is my advancement of Alfa knowlege, since we don't have blueprints for 
heads available.  Uh, better assume that for the inner exhaust side of 
the center cam bearing cap.. no guarentees on the others,  but it likely 
is the same.  Check where that passage goes and at what angle...

So...  I thought that I might as well finish the job.. slowly did the 
tapping..  It looks like the countersink normally done with a Timesert 
isn't needed,  since there is a natural countersink,  and the tool 
dosen't work with it.. designed for flat surfaces, which this is not.  
So I tapped it out, with a trimmed down Q-tip stuck farther down the 
gallery so new chips wouldn't migrate farther, and many breaks for chip 
removal and suction.  Inserting the Timesert went easy,  and looking at 
it seems to show that I could have "fudged" the expected overdrill 
somewhat less.  I did put a little bit of penetrating green locktite on 
the outer edge.

That might have been my second mistake,  not waiting to call the 
Timesert guys for a better opinion on how deep,  though they might have 
said "go .300" deeper" after all..  We'll see tomorrow...

I'm debating on what to do on the inner threads, one of the thread 
sealing compounds or red high strength locker?
After I calmed down,  I realized that an oil passage is better than a 
water passage,  if a bit of oil leaks past the threads, it's just going 
to drain back like the flow from the bearing, but water leaking would be 
a disaster.  And I'm looking pretty clean,  so I don't have to pull the 
head and clean all oil galleries.. (I hope!)  Is anyone sure of the 
oiling layout in the head?  I would think that nearly all chips made 
would be only in that bearing's gallery,  and not be able to go to 
others?  Do each of the six oil holes in the block go only to each 
bearing,  or is there cross porting farther up?  Am I safe to assume 
that I could run the engine for a little bit, and pull the cam  to find 
whatever leftover stuff right there in the oil port ready for easy 
removal?  Or is any little bit of something, even aluminum, going to do 
damage very fast?

I'm leaving the penetrating lock stuff overnight,  haven't installed the 
stud for the time being. I'll get some opinions,  and be looking to hear 
a few from the more serious engine builders and folk who have been thru 
this one before.

Thanks, and don't drill too deep!!!

Jon
77  Spider
Irvine, CA
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