The V8 Owners Forum -

I'm rebuilding my '72 P6 3500. I'm also a keen but totally inexperienced amateur! I've sheared off the long lower right bolt through the timing cover (now removed) which looks like it ends in a water passage. There's a bit less than an inch still stuck in the block, sheared flush to the surface. I center-punched it, started drilling with very small drill bits, working up in size, then got a reverse-threaded extractor in, then managed to snap that off as well. I tried drilling some more, but I'm worried that I'm going to damage the thread in the block. Gentlemen, who has some helpful advice?

Your kinda stuffed at this point specially since you broke the extractor which will be harder than a hard thing. If you have enough room you could maybe drill round it and finish the whole at the correct helicoil size. There is a process that I cant remember the name off but its something like spark erosion???? This will take the bolt out and leave the threads but you will have to ship your block to someone who can do it. Last but not least you can take it out to a large size and finish the whole off with a threaded plug that's tapped up the middle to take a new bolt.

Extrators are evil, it is suprising how many are broke in an attempt to remove studs and like kataman says drilling these out is even more difficult. I am told by others not to bother with extrators just drill out the sytd. I once sheared off an exhaust manifold stud, common occurance, and somehow managed to drill it that central that I managed to preserve the threads all that I had to do was remove the bit of the stud left in the thread with nose pliers, which looked like a spring, weird!

On my first RV8 I sheared both the top long bolt in the front cover. I had to work outside at that time. So I borrowed a right angle drill and drilled and tapped the holes to accept some 6mm studding. I have raced the car for 5 years since then and done 5 rebuilds due to various explosions. And the two 6mm studs are still fine with no front cover leaks. Everytime I take the engine out I think I should do them properly, but I cant be bothered as they wrok ok for me. Its only got to hold back about a bar anyway.

Mystic meg moment, I see two paths for you, the first is you trying to drill out the extractor and breaking the drill in the hole along with the extractor, meaning the whole thing is bolloxed, The second path is more daiunting but it makes more sense. The bolt is in the waterway so it corroded, they all do, you need to drill around the extractor and to hell with the damage to the threads, there gone now, you will throw the extractor set away (why do they come in multi packs, it is so you can continue this misery on 4 different size bolts rather then use it once and never again) If not to much damage tap the thread over size and have someone turn down a stainless rod that is the correct thread one end and a tapered chaft and use it like a stud. Or heilcoil. Bite the bullet and start drilling, it's fcuked so you have nothing to lose.

If it's looking like a 'drill oversize' type plan anyway, then may be worth trying to weld something onto the remains of the stud/extractor to try to unscrew it ?

I have welded a short bolt onto the end of a broken stud before, and often add a blob o weld to rounded nuts/bolt heads to give a socket something to bite on ...

The heat from the welding will often help free the threads up, and being steel in alu, you shouldn't have a problem with the mig wire sticking the wrong bits together, but you may make the odd hole

Just a thought.....

Over the years I have drilled out many broken bolts , studs, extracted both broken taps and easy outs,
If the bolt is a stuck as it seems to be and you have the extractor still stuck in there, Test the bit of the extractor that you have with a file to see how hard it is, If it seems reasonably soft, buy a NEW drill bit and see if you can drill out the extractor, Some cheap extractors are not worth the hassle, and are made of real poo metal, The last set of extractors I bought cost me nearly £60, and I havent broken any of them yet you can somtimes get away with Reverse Helix drills [Left handed] which need to be rotated in the opposite direction to normal drills to work, the Idea behind them is if they snag sometimes, not allways they will unscrew the broken item,
A way to ensure you allways drill along the centre of the bolt is to refit the cover, Next find a piece of tube, or machine up a piece of tube that fits into the bolt hole of the cover neatly, using a drill that fits the tube nicely, insert the tube into the cover use that as a drilling jig, that way you are fairly certain the drill will run down the centre of the broken bolt, see the link but you may have to sign on,
http://www.nsra.org.uk/forum/topic.asp?TOPIC_ID=42498
Short drills, if available are sometime a handy thing, as they are less prone to wandering and flexing in tight situations, If I find broken drills at work, I sometimes regrind them into shorties
Failing to get the extractor out,------- Really only leaves you 3 options. 1, Assess the situation a to see if you can get away without using it, and fix at a later date when it can correctly.
2, Take the block outand then take it to your local friendly engine rebuilders/engineers and ask them to spark erode the stud out.
3, Make a small hole cutter/hollow drill that is the same size as the O/D of the thread, using lots of oil drill the stud out, [This will need to be Jigged similar to the way described earlier, or make the cutter stepped so it would fit into the cover neatly and be self aligning,] next if you have drilled the hole out cleanly, you wont be far away from the helicoil size, and a repair would be easy from there, if, for any reason, the hole has come out to big, you will need to tap the hole to a suitably larger size andmake a screw in insert which can be either loctited into the block or scotched onto position with a grub screw or pin of some sort.

Ian

You only need to sign up if you want to post a reply, the forum is open to be read, damn fine article, the oly alterntive advice i can offer is a small grind stone on a deburring tool and see if that works, there just so dammed hard !!

Thanks very much gentlemen for all that instructive advice. Why indeed do extractor tools come in multi-packs!
I drilled out some more bolt material around the snapped-off extractor tip, but not enough to get a grip on the tip because the drill tips blunt so quickly.
I'll try using the timing cover as a guide. If I weld a tough drill bit to an extension (like the pics in the nsra link) only just smaller in diameter than the hole through the timing cover, that should ensure I'm drilling straight..? What drill bit(s) will cope with the sheared extractor. I just have to weld the drill bit on exactly straight...! I'm feeling challenged.
If your ingenuity and my inability don't get it out I'll continue stripping the motor and take the bare block to the specialists at the last resort.
My engine overhaul project is not as pressing as getting my rolling shell finished. It's my spare engine, I couldn't resist having a tinker, probably ought to have left it in the corner under a tarpaulin. Expect further novice questions the deeper I delve...