Releasing a corroded stud (steel) passing through a casting (aluminium)

One of the problems of working on older IC engines is in removing the cylinder head where a steel stud passes through the head casting. There is a heavy tendency for the stud to corrode through galvanic action and this is not helped by the seepage of coolant into the stud passageway.

Recently we were removing a head from a Jaguar V12 engine and had to resort to sawing through 4 of the 14 studs on one of the cylinder banks when the head refused to lift more than an inch or so. We have at our disposal a 'head puller' which consists of two one inch thick steel plates which bolt onto the head in place of the cam carrier and this then uses rods to press down on the exposed stud ends, thereby lifting the head away from the cylinder block.

Thinking back to my time working at Triumph Cars we had similar problems with the Triumph Slant 4 and V8 Stag engines and I remembered one of the fitters made a tube saw which went over the stud and into the stud hole in the casting to remove the corrosion.

This led me to make a stud 'tube saw' which was made from a 12mm silver steel bar with a 7/16" hole drilled up it - leaving a ~0.5mm wall thickness! After re-sharpening the teeth several times we eventually cut through the crud on all 14 studs on the other cylinder bank and the head released easily.

I am now considering making another tool from a higher grade of tool steel (D2?) and also considering a diamond plating on the tip of the saw to replace the tooth form.

My question is - has anyone knowledge of a company that can diamond plate a tool? Is there any known supplier of D2 tool steel in tube form (it doesn't have to be exact sizes as we can machine to finish size )?

Martin

Might it be easier to adapt an existing tool, such as a diamond hole saw or Rotabroach, by cutting off the original shank and brazing the remaining cutting end onto the end of a piece of mild steel tubing etc?

EDM is a slow but less risky way to remove anything corroded into aluminum, and can be done with very basic equipment. With careful placement and an accurately turned copper electrode there is no damage to the aluminum at all, and the resulting hole will be ready to tap for a helicoil.

It should be possible to make a simple sleeve to fit over a plain exposed length of stud , with a suitable hole size to ensure a drill will start dead centre of the stud.

Enlarge to tapping size required.

Try these perhaps you can weld the end on to a tube shank.

Glass hole cutting diamond tubular bits.

David

When the museum inherited the workshop and tools a couple of years ago, there was a wallet of Pickavant tubular saws of several different sizes made to remove the corrosion products from between cylinder heads and the studs from the block. They are very thin wall, to pass over 3/8", 7/16", 1/2" 9/16" and 5/8" studs. I had never heard of them but they do seem a very good idea.

Over twenty years ago now but I used Diamant Boart, they seem to have moved to Leeds but may be worth a call. Another firm I looked at at that time was Major diamond supplies who are still going and in Northampton. They do make core bits.

Cheers

John

Edited By elanman on 18/02/2022 17:03:35

Thanks everyone for their inputs.

Just to clarify the studs are sliding fits through the head being screwed into the block at their lower portion and they hold the head down by way of nuts bearing down on the external upper head face. There is no threading involved (other than the nuts which remove with no problem and the lower end of the studs which thread into the block - and hopefully stay there! )

Old Mart - the studs are 7/16th dia (~11mm) and the nominal clearance hole in the head is just slightly over 12mm. I'd forgotten about Sykes Pickavant. Can you tell me what the o/d is on the 7/16th tube saw please?

Hopper - we did look at a Rotabroach and we purchased their 12mm o/d broach but the internal dia was just 6 mm! I considered grinding it out to 11mm but decided there would not be much left as the flutes would disappear leaving just 'legs' - the tube saw needs to be about 4 1/2" long to get through the head.so any Rotabroach would need mounting on an extension tube.

J Hancock - we do not want to remove the studs or damage them as they are hard to replace, both physically (extracting them from the block is precarious ) and purchase wise ( £11.50 per stud ).

Jeff Dayman - novel idea! Again I had considered EDM and water cutting but as there are 14 studs per bank we would have to make a multi tool to attack all 14 studs in one go. Will an EDM system work solely on the front end of the tool and not 'short out' as the sleeve goes deeper between stud and head?

Again thanks to all for responding to my question - all food for further thought.

Martin

David George - That sounds like a promising avenue to investigate. glass diamond hole cutter! Have you got a link please to a manufacturer / supplier?

If you can find some proper Plusgas and soak the area it will soften / disolve the corrosion . Its a lightly acidic solution so be careful not to get onto any paintwork as it will attack it . I dont know if the aerosol type Plus gas is as good as the old liquid variety. (tin wiyh a squirty spout) My tin has gotten me out of many a difficult situation .

You could also try squirting some phosphoric acid down the hole . It wont attack the alloy but will dissolve corrosion and turn any rust on the stud into a rust resistant phosphate .

Bit wary of Phosphoric Acid because it converts weak fluffy rust into a tough solid phosphate, which would make the joint even harder to break.

I'd try soaking in a 50:50 mix of Acetone and Automatic Transmission Fluid, longer the better! Several heat/cooling cycles are good at breaking up corrosion too.

Looking at the web, I found the pro advice is about preventing corrosion in the first place rather than getting rid of it. Otherwise a tube cutter, which Martin suggests himself. I don't think there's any need for the cutter to be diamond plated or even hardened because corrosion is softer than most metals. Teeth cut in the end of a thin-walled mild-steel tube should do if a commercial tube-drill can't be found. Plus lots of patience, clearing muck out of the hole, and resharpening. There doesn't seem to be a quick easy answer.

Dave

Someone who had the same problem with a Triumph Mayflower,

His solution was to make up a thin walled trepanning cutter and to use that to cut away the corrosion and possibly enlarge the holes through then head casting.

Probably greased the studs before replacing the head, to prevent a repeat problem..

Howard

I remembered some of the details of the tubular cutters. We only have the 7/16" and 1/2", the 3/8" is missing. The 7/16" has a bore of 0.442", od of 0.5" and the doameter at the tips of the teeth is about 0.513". The effective length is 2.95".

There is a trick - if you can get the right material.

Do this work out in the garden and away from livestock etc, as there will be fumes. The trick relies on the fact that aluminium will not dissolve in oxidising acids, as the process renews the Al2O3 coating which protects the aluminium. Nitric acid is the solvent, and it eats steel, cast iron, etc. The job should be immersed in the acid (which can be watered down a bit but not too much). It may take a few hours to eat through steel, but it does work. I have used this dodge ( back in 1975) to remove the corroded-in front engine stud from a V-twin Motor Guzzi engine. All that was left of the steel at the finish was a piece about 30mm long, with a tapered point on each end, which finally fell out as it no longer fitted the hole. And the Guzzi was rebuilt, and may well still be going.

So, all you need is an old crockery dish or aluminium pan, half a litre of HNO3, and some understanding neighbours.

Cheers, Tim

Edited By Tim Stevens on 20/02/2022 20:45:51

If making one, I would play safe and not use very hard steel for fear of it breaking or loosing some teeth. You could get away with only 3 teeth and sharpen them frequently with a swiss file. Every couple of turns the saw would have to be withdrawn and cleaned or risk clogging and jamming.

I have the same problem, in my case a Mk3 LeMans, but a lack of nitric acid.
I've tried most of the other obvious liquid options, but without success thus far.

Bill

OM - That SP tool looks just like mine! the saw has to go over 4" through the head and it is impossible to seal it against water (coolant) as the lower end of the stud is within the block waterways.

Here is a picture of the tool and the job it did:-

It broke during use at the point where the 7/16th" drill ended, so we silver soldered it back together after turning a register on the solid part of the shank. The teeth were reground about 4 times on a Clarkson T&C grinder, so it finished up about an inch shorter than it started out.

This is a picture of the block with two of the sawn studs showing (this is 'A' Bank - we didn't have to cut any studs on 'B' bank after using the saw ). We used penetrating oil, acid, heating and cooling - all to no avail. As you can see the studs 'live' in with the coolant which doesn't help matters any!

Thanks for all your suggestions guys.

Regards,

Martin

I have to get two sheared off screws out of a wooden guitar neck, in some ways a similar problem!

I was going to turn up a functionally identical tool from silver steel.

In the end I will be using a 6mm plug cutter, then making cross-grained mahogany replacement plugs using the next size up.

All good clean fun.

Neil