Engineering solution sought!

Exmoor beast

Exmoor beast

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Minehead,Somerset, ENGLAND OF COURSE
On my old 750GT the sump plate had a stud missing but someone had added a 4mm stud/nut just to one side of the original hole. Now I thought if someone?s gone to the trouble of resiting the stud , there must be a good reason. I laid the bike over and sure enough there is a broken drill bit in the partially drilled failed stud- sunk about 5mm down. It?s fairly central but is stuck solid, hard as the hobbs and impossible to drill.
I can?t get a weld on it as it?s too low, the hole is blind so I can?t punch the bit out- the only option I can see is to strip motor and drill from the inside to punch the bit out and helicoil.
If anyone has any other method that doesn?t involve stripping the motor I would be very interested.
I probably won?t strip the motor straight away as I can use the extra stud that Erik the German fitted, as was ,but in time it looks like I will have to bite the bullet. Any sensible answers very much appreciated.
Many thanks ,Jason
 
There's a technique called spark erosion that I know nothing about but it may well be indicated in your predicament.

Paul
 
I had a snapped off bleed nipple with an Easi-Out snapped off inside the hole.
Took the sprocket cover to an engineering shop with a new bleed nipple, so they could determine the depth before hitting the taper, and they spark eroded it out, zero problems.
 
Apparantly it can be done with an acid called Alum. It disolves the steel , but not the Aliminium
Try googling it.
You have to strip the engine though..or turn it upside down.
 
I initially ruled this out but looking at the alternatives I might give it a go- nothing to lose.
The softer stud around the outside of the snapped drill should (?) dissolve more readily.
It?ll either work or it won?t, got to be worth a go! Thanks for the encouragement, Jason
 
Motor out, but no absolute need to strip it. Question is whether alum works in the tiny amount you'd get into the recessed broken bits. Electro eroding probably a better option with motor intact.
 
The Alum method is interesting. Never tried it myself, but would be interested to hear if anyone here has.

Here's an extract from Wikipedia on alum:
"Alum in the form of potassium aluminium sulphate or ammonium aluminium sulfate in a concentrated bath of hot water is regularly used by jewelers and machinists to dissolve hardened steel drill bits that have broken off in items made of aluminum, copper, brass, gold (any karat) and silver (both sterling and fine). This is because alum does not react chemically to any significant degree with any of these metals, but will corrode steel. When heat is applied to an alum mixture holding a piece of work that has a drill bit stuck in it, if the lost bit is small enough, it can sometimes be dissolved / removed within hours."

For your Guzzi I reckon you'd have to turn the engine upside down and build a little containment dam around the stud hole with some kind of material like auto body filler so you can get a reasonable volume of the alum solution for the drill bit to soak in. You would also need to figure out some way to keep it hot. A heat lamp placed close over the area might be enough. Certainly worth a try.

 
Thanks for that, Paul. I will put it back together and run him for a bit, then decide on partial or major strip down, I wasn?t sure if bottom case could come off . There are so many unknowns with this one I want to give it a good shakedown so I?m sure of clutch,gearbox, oil consumption etc.with bottom case off I have a lot more options. Thanks ,Jason
 
just take out the motor and strip the whole thing,

always a good idea to renew valve springs and piston rings even if you don't need them, and of course all seals o rings and gaskets, preventative maintenance! it provides a chance to look at everything, even if its low mileage, if it was a race bike you wouldn't think twice, so once in 40 years or more cant be a bad thing, the eyes can tell you a lot more than the feelings.

while its out, cut a lump out of the bottom case to include the offending corner, build up with weld, machine flat, drill and Timcert all four of them and any others on both cases even if  looking  slightly tired. Nice fresh threads, cleaned sludge traps, vapour blasted cases, spotless everywhere and no lurking shit, honed bores, new rings, valves lapped springs replaced and nothing to think of for 100,000 kilometres or maybe miles.
CLEM
 
I doubt you need to do the plug threads, because the heads have a cast in, iron skull, that includes a "nose" so that the plugs screw into iron, a tab of grease or drop of oil on the threads and they are god for decades, even if you don't do that they are still good for slightly less decades
CLEM
 
I doubt you need to do the plug threads, because the heads have a cast in, iron skull, that includes a "nose" so that the plugs screw into iron, a tab of grease or drop of oil on the threads and they are god for decades, even if you don't do that they are still good for slightly less decades
CLEM
Click to expand...

Why would you not do the plug threads? You already did the rings and valve springs and there was nothing wrong with them. :D
 
the rings and the springs have been compressed and in an unused, state not getting regular heat cycles, if the springs and rings had been kept in nice oily packets and boxes, and not under compression they would be good to go, springs that have been compressed and unmoved for 40 years have a tendency to offer little in the way of what they should, ie the ability to "extend" any spring, anywhere, piston rings are springs. The plug threads should be inspected carefully, torch and magnifier, and if in any way damaged, repair them, but of perfect why bother? they are not as stressed an item.
CLEM

ps I need a new rear suspension spring on my Mercedes estate, it was fine, and MOT tested last week, but I went shopping for fruit and veg last Saturday early am, and the car drove 100% perfect and looked fine on the very level car park where I left it, half an hour later, as I approached the rear of the car I could see that something was wrong, the spring had broken a coil off, and the car was sagging to one side, no major jolts took place in recent days, the spring snapped while the car was parked, it drove home OK but felt very weird and is now mothballed until Tuesday next when it will be repaired with new springs, both sides, just saying they break all by themselves, just sitting there, under the load of an empty car.
 
Finally got this one sorted- whilst the engine is in bits. Took the lower crankcase to Hamlins engineering in Bridgwater where they set the case up in a milling machine- not all plain sailing as they broke a tungsten carbide bit on the broken drill that has been in the blind hole for over thirty years! They persevered with another bit and cleared the hole and fitted an insert. Great company to deal with & had it done in a couple of days.
 
If it isn't causing any problems leave it until the engine has to be stripped for any other purpose and then get it fixed as a 'while I'm at it' job.
Just my two bobs worth ;).
 
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