First Engine drop - nasty surprise.

[neilca]

Walt has already stated what I would do next. If it is stuck try heating the area with a propane torch. The magnesium expands more that the steel bolt and a little movement could help break it free. Easy does it.

[greasemonkey]

Hmm, looks as though I've got more to think about than the stud in the first picture,..




In total there are 5 broken head studs - all lower. I'm not sure of the material yet but all the lower studs have a very feint golden colour (color ?) to them. All of the top row studs look like standard steel. Both types have very - mild surface corrosion.

Fortunately, they all seem to have broken off with 10mm or more stud poking out of the block. I intend to mig weld a nut onto the remaining piece, wait 10 seconds, then undo them with a spanner,....

I'll report on the success (or not!).

This being my first engine rebuild, I have not found it that hard and certainly not too daunting so far. The possible exception being the 46mm can nut - needed a friends help with this due to 4 hands being needed and the 46mm tool.

Yesterday saw me using a standard valve spring compressor to remove all the valves and springs (all bagged up individually). Fortunately no nasty surprises there. with 122K miles all the seats looked fine. Naturally the guides were a little floppy - about 0.5mm wobble. These will be replaced anyway.

I intend to drill the guides out to within about 1mm of the guide edge and 80% of the length. I then intend to bang them out with a drift as they will be weak by then.

I have read that putting the guides in can be a DIY job;
1, remove old guides
2, clean heads thoroughly
3, freeze guides in domestic freezer - heat heads to 200 dec C in oven.
4, make brass drift to bang the hot guides in.

Your thoughts please,...

Greasemonkey.

[piggdekk]

Greasemonkey,
even if You pull the guides yourself You'll need to properly machine the ID of the new ones afterwards and do the seats. Why not taking them to a machine shop and have all done by them?
luca

[zelrik911]

Originally Posted by greasemonkey

Hmm, looks as though I've got more to think about than the stud in the first picture,..




In total there are 5 broken head studs - all lower.
Your thoughts please,...

Greasemonkey.

OH Dear - this is my SC 3 Ltr nightmare! TWO studs broken on that middle jug.

Please keep posting your progress - as I may have to go through that myself in the near future.

With your heads I would think again about getting a pro &/or shop to do it. If its easy for you it would be very easy for them and if there is a problem they can deal with it.

For example, during the job a valve seat may loosen up or some valve springs may be soft & its second nature for a shop to remedy.
Anyway good luck & hope there are no more hidden surprises.
Peter in Melbourne Australia
( Sweltering in 100+ degree heat!)

[Walt Fricke]

I'd consider pulling worn guides myself. There is also a technique which calls for drilling, but I think maybe not the full 11mm, and tapping and screwing in a bolt, whose head is used for pressing the old guide out.

But not installing new ones, as making sure the new ones are just the right interference fit OD for the holes (which probably are a bit larger due to pulling the old guides) calls for careful measurement, and having a lathe to turn new guides to just the right size, hole by hole, is what you need. New guides typically come oversize, as they are intended to be turned down as needed. Not like over/under sized bearings which come at the needed size already.

My understanding is that you want to hone the installed guides to just the right ID. The reamers I purchased, with stuff like this in mind - and because they weren't expensive - are not the right tool. And the guide ID needs attention, as again it isn't necessarily the right size, and is going to be smaller after the guide is pressed into place.

A lot of shops, even those with the tools and mechanics with general machining skills, tend to farm out this kind of head work.

[Walt Fricke]

Peter - I've never heard of a 911 valve seat coming loose as a result of a valve job. Even in swealtering heat. Plenty else which may be tough to deal with on a one time basis, though.

Having a valve spring checker is quite an expense for a guy just doing work on his own engine, I'll grant you. Though I wonder how often one finds a soft spring in a stock 911 which wasn't raced or overheated? The stock springs are pretty stout.

If you have the specialized tools, refacing valves and seats isn't out of home reach. Setting installed height not that tricky, though it is good to have some extra shims on hand.

But here also I know a number of shops with competent guys who find it cost effective to send heads out for at least the valve/seat facing part. Or the whole shebang - my spring compressor is marginal, so it is often a bit of a rodeo, and in my wildest dreams I see a hydraulic one dancing around.

[Lapkritis]

Yikes and wow.

[irobertson]

A friend of mine who runs a machine shop will take out a busted stud for $50.
Or $100 if you have tried to do it yourself first.
At some point you are probably going to get your case halves either cleaned or looked at by a professional.
Why not let them dig the broken bolt out for you?
If it needs to be opened up and rethreaded for a time-sert, it's best to do it on a mill and NOT by hand.

[greasemonkey]

OK, a quick update.

Taking the guides out is easy. drill them out for about 90% of the length. use two drills of increasing size to get to within 1mm of the outside diameter. I used some tape on the drill bits as a marker for the depth. Then tap them out, using the ledge you have created, with a drift. Takes about 1hr to do the 12 holes and whack them out. I used a pillar drill with an adjustable bed.

I've taken all the cylinders off of the pistons and disconnected the pistons from the rods. A very easy job, but needs two people, as you need to support the piston while you tap the gudgeon pin out. Thx Cheryl! With the exception of a score mark along the length of the bore of No 1, all the pistons, rings and cylinders seem fine so far (pre-measurement).

I'm now trying to remove the head studs. Even the whole ones that you can get tools on are VERY tight. So I'm going to have to get a machine shop with oxy to heat them up a little. I'm a fairly stong guy but JEEEZ they are tight. Whilst they have the block, I'll get them to do the broken stud too.

Interestingly, I've had a number of people try to drill out or weld to the flippin' stud to try and get it out - nothing so far,.... All their cobalt drills do nothing and MIG weld doesnt seem to 'stick' to the stud.

Onwards.

[turbo nut]

If the broken studs stick out. Drill the threads out of a nut so that it will fit over the broken stud. Then TIG weld the nut to the stud. Heat the case up to release the Locktite, The stud will normally come out. If it broke of flush sharpen a bolt to a blunt point and TIG weld that to the end of the stud heat the case and remove.

[trond]

you can not weld dilvar studs. I think. It is not steel

You need a map gas torch to warm up the locktite. keep warming until there it releases a tiny puff of smoke. Get the best and most expensive stud puller you can get.

[fred cook]

Get a propane or mapp gas torch. Use it to heat the block inside the hole for the cylinder and next to the stud. When you can feel the warmth on the opposite side of the stud, try turning with a collet stud remover or an adjustable pipe wrench. It may take more than one application of heat. Once the block is properly heated, the studs will be fairly easy to remove. It only took me a few minutes to remove the 12 dilivar studs from my SC block once I learned the technique. By the way, my engine had 3 broken studs and one that had been replaced some years ago! Good luck!

[iiXii]

Do not stress. This is a classic on these engines. Mine had 4 studs broke. The first valve adjustment has been very hard on morale. € 2,000 pieces (ARP studs, etc.) and € 2,000 for labor.
Good luck!

[911pcars]

Originally Posted by trond

you can not weld dilvar studs. I think. It is not steel

You need a map gas torch to warm up the locktite. keep warming until there it releases a tiny puff of smoke. Get the best and most expensive stud puller you can get.

Not sure about the "dilvar" base material, but real Porsche Dilavar studs are steel and thus should be weldable.

Let me know if anyone wants to buy the most expensive stud puller you can get.

Sherwood

[turbo nut]

They weld just use alittle stainless filler rod.

[greasemonkey]

Thanks for all the replies.

I took it to a motor engineering company this morning. I asked them to do all the head studs, the one on the first thread and remove the flywheel (lazy I know,..).

These guys have been going for 40+ years and have an average age of 60 years! They are used by all the local mechanics when the going gets tough,...

I got a call mid morning to say 21 out of 24 head studs are removed, the flywheel is off and the one in the first picture of this thread is out! They used an air impact drill to get the original stud out. Never heard of one of those,... (bull$,..?)

I asked about the 3 remaining head studs to see if they had tried welding a nut to the remaining bit (at least an inch showing for all 3), and was told I need to find somewhere that does Spark Erosion. Trying my nut/welding technique "would make it worse". Thanks.

So that's £140 +VAT and the saga continues,...

[Walt Fricke]

Spark Erosion must be what those of you in Blighty call electron discharge machining or EDM. It is really magic, as the arc burns its way down the stubborn stud. By the time it gets out to the threads, so little is left that, if they won't just screw out, you can pick them out with a bent scribe tool.

I think of it as being used on a stud broken off flush.


With all due respect for the years of experience these guys have, welding on a nut isn't going to make things worse. The most it might do is to break off the rest of the protruding stud. Which I think is what the EDM shop would do anyway to get started. No need to burn off anything sticking out. With the heat applied in welding, the corrosion or adhesive which is making the stud not want to turn is likely going to be reduced in strength so the stud can be screwed out.

And if, by chance, using an impact gun on a welded nut damages the case threads, they are pretty easy to repair with TimeCerts or other case savers.

I'd find an EDM or whatnot shop, and then ask this shop to humor you and do the weld nut thing. And that you won't hold them accountable if somehow the results involve even more expense.

[keynsham1]

Thread insert or case saver, solid unit, not the coil.
Bruce

Why not thread inserts? They are used as standard on aircraft engines after all as opposed to other types of insert. Solid inserts require a larger oversized hole which removes future reparability. Just a thought!

[911pcars]

Originally Posted by keynsham1

Why not thread inserts? They are used as standard on aircraft engines after all as opposed to other types of insert. Solid inserts require a larger oversized hole which removes future reparability. Just a thought!

Numerous rebuilds confirm what currently works and what didn't work as well (Heli-coil and equiv.). History doesn't have to repeat itself unless there's new technology to learn about.

Sherwood

[keynsham1]

Maybe heli-coils are more difficult to install correctly. I have used them in many applications in the past with no problems.