attleej Posted October 6, 2019 Share Posted October 6, 2019 Dear All, Meteor tank engines (and later Merlins) are prone to snapping their 'corner' cylinder studs that hold the cylinder head /cylinder block onto the crankcase. The studs appear to snap in service and not just when being tightened up. It is thought to be a stress corrosion problem. The studs are an interference fit in the crank case and are very difficult to unscrew even when complete and with the possibility of have two nuts secured on the top of the stud. About 16" of leverage is required to get them to unscrew. Unfortunately, the snapped studs can leave only a 7/16" diameter stud only 3/4" high or less! The engineering solution that I have devised is to drill and tap the remains of the stud 1/2" UNF Left Hand. (Thanks to TSB for that idea). Then a left hand threaded bolt can be screwed in and the remains of the original stud will unscrew. I found that the remains of the stud unscrewed quite easily. This probably because the threaded remains of the stud 'relax' slightly. If the remains of the stud does not unscrew, the replacement stud can be turned down and threaded 1/2" UNF, LH , and screwed in place with Locktite to stop it from unscrewing when the cylinder head nuts are torqued up. I made up a range of special jigs to facilitate drilling the remains of the stud absolutely square and concentric. This is essential in case the stud will not unscrew and a turned down stud has to be resorted to. The manual makes it clear that the studs cannot be bent even slightly. Photos of the tooling can be seen on other posts of mine on the HMVF forum. John 3 Quote Link to comment Share on other sites More sharing options...
sexton Posted October 30, 2019 Share Posted October 30, 2019 Very interesting, John. Sounds exactly like stress corrosion cracking, which is surprisingly common for high tensile bolting under a lot of stress and seeing moisture and heat. I guess studs were larger diameter below broken 7/16" section since you drilled and tapped for 1/2"? What is the torque on these studs? Malcolm Malcolm Quote Link to comment Share on other sites More sharing options...
attleej Posted October 30, 2019 Author Share Posted October 30, 2019 Malcolm, I believe that you are right in suggesting that it is a combination of stress, moisture and heat. All three. The studs other than the corner studs are running covered in oil from the rockers and do not suffer from this problem. The studs are much larger diameter where they are screwed into the crankcase 11/16 BSF or maybe bigger still. The cylinder stud nuts are torqued to 115 ft lbs. The studs are necked down so that they are quite small dia for most of their length. This means that the stretch and stress will remain constant even though the aluminium cylinder block has expanded with the heat. John Quote Link to comment Share on other sites More sharing options...
sexton Posted October 31, 2019 Share Posted October 31, 2019 John, i worked at a nuclear plant, so steam, heat, and highly stressed bolting. We had a very good metallurgical department who identified failure causes and we saw our fair share of bolting SSC. 115 ft-lb on a 7/16" stud is 140,000 psi stress in the stud. High quality grade 8 bolting has an ultimate tensile stress of 150,000 psi. So those studs are extremely high tensile material. No wonder they were susceptible to SCC. And no wonder you had difficulty drilling and tapping it! 1 Quote Link to comment Share on other sites More sharing options...
attleej Posted November 4, 2019 Author Share Posted November 4, 2019 Malcolm, Not only did I have to use HSS cobalt drills I also needed to use an HSSE tap which is HSS cobalt apparently. Even so, the tap could only manage about three tappings before it lost its edge. Initially it was like going through EN1A with lots of lead! Even so, if the tap can solve the problem at £35 a time it is worth it. Most of the studs are covered in oil passing back from the valve gear. The corner studs in question are "dry". They are sealed at the bottom and there is a special washer at the top. I doubt that the temp would exceed 100 degrees C. Coatings on the stud do not appear to be successful. I was wondering about filling the void with engine oil and grinding a groove in the top washer to relieve any pressure. That way the air would be excluded so the studs would not be in a corrosive environment.. What do you think? John Quote Link to comment Share on other sites More sharing options...
David Herbert Posted November 4, 2019 Share Posted November 4, 2019 1 hour ago, attleej said: I was wondering about filling the void with engine oil and grinding a groove in the top washer to relieve any pressure. That way the air would be excluded so the studs would not be in a corrosive environment.. What do you think? John John, I think that that is an excellent idea, it is certainly very hard to see that it could do any harm. The worst that could happen is that the oil oozes out and then you are no worse off than the standard arrangement. David Quote Link to comment Share on other sites More sharing options...
radiomike7 Posted November 4, 2019 Share Posted November 4, 2019 Hi John, Have you spoken to the likes of Flight Engineering to see how they address the problem? Quote Link to comment Share on other sites More sharing options...
attleej Posted November 4, 2019 Author Share Posted November 4, 2019 Yes indeed. I am in close touch with Peter and have discussed this problem. That is why I know that it is common to both Meteor and Merlin engines. I am very keen to share the techniques that I have developed. That is the beauty of a forum like this. John 1 Quote Link to comment Share on other sites More sharing options...
ruxy Posted November 4, 2019 Share Posted November 4, 2019 (edited) 6 hours ago, attleej said: Malcolm, Not only did I have to use HSS cobalt drills I also needed to use an HSSE tap which is HSS cobalt apparently. Even so, the tap could only manage about three tappings before it lost its edge. Initially it was like going through EN1A with lots of lead! Even so, if the tap can solve the problem at £35 a time it is worth it. Most of the studs are covered in oil passing back from the valve gear. The corner studs in question are "dry". They are sealed at the bottom and there is a special washer at the top. I doubt that the temp would exceed 100 degrees C. Coatings on the stud do not appear to be successful. I was wondering about filling the void with engine oil and grinding a groove in the top washer to relieve any pressure. That way the air would be excluded so the studs would not be in a corrosive environment.. What do you think? John Cobalt drills or OK'ish but more easily broken than a standard HSS drill. A few years ago I had to drill many holes , only abt. 3/6" dia. and then C'sk them. I had no long lasting luck with Cobalt . I had been off the tools twenty + years and had never used TiN. I happened to be going to a specialist coater who did for cutting tool manufacturers (as well as gold coloured SS urinals for residents of Saudi Arabia - their motor yachts , apparently crew quarters) . Explaining the problem - I was given a stash of misc. sizes . No need for Rocol cutting paste (RTD) - a single stubby did hundreds of holes dry. Then I used a 'gold' TIN drill to countersink. The drills were at a production stage not marked with makers name of size. The ones I have used since for difficult jobs are the ones grey or purple finished - I believe these must be TiAlN Coated Drill Bits Edited November 4, 2019 by ruxy spelin Quote Link to comment Share on other sites More sharing options...
sexton Posted November 5, 2019 Share Posted November 5, 2019 (edited) 18 hours ago, attleej said: Malcolm, Not only did I have to use HSS cobalt drills I also needed to use an HSSE tap which is HSS cobalt apparently. Even so, the tap could only manage about three tappings before it lost its edge. Initially it was like going through EN1A with lots of lead! Even so, if the tap can solve the problem at £35 a time it is worth it. Most of the studs are covered in oil passing back from the valve gear. The corner studs in question are "dry". They are sealed at the bottom and there is a special washer at the top. I doubt that the temp would exceed 100 degrees C. Coatings on the stud do not appear to be successful. I was wondering about filling the void with engine oil and grinding a groove in the top washer to relieve any pressure. That way the air would be excluded so the studs would not be in a corrosive environment.. What do you think? John John, the metallurgists told me the factors in SCC were bolt material, bolt stress, temperature, and environment. You're stuck with bolt material, bolt stress, and temperature. So the only variable,you have any control over is bolt environment. Surrounding the studs with a protective layer of oil to keep moisture and halides out has to help. Malcolm Edited November 5, 2019 by sexton Quote Link to comment Share on other sites More sharing options...
Stuartarmytank Posted November 27, 2019 Share Posted November 27, 2019 The corner studs break due corrosion . Getting them in and out requires heat on the base with the banks off . There was a mod that had a seal between the bank and the block ... that made the situation worse as it trapped any moisture CB in . Best apply a thixotropic wax from time to time to prevent corrosion . other studs don’t have the problem as they are the return path for rocker gear oil . I used specialized drills to make a hole and inserted a stud remover . With heat apply pressure to remover ... when temp right it will crack and come out easily . if you don’t use heat when replacing you will never get it down to the correct height ... bloc the to top of stud . Quote Link to comment Share on other sites More sharing options...
attleej Posted November 28, 2019 Author Share Posted November 28, 2019 There are two problems with heating up the crank case. The first is that the EMER says to use an oven which I do not have access to. To use localised heat is to risk distortion. The second is that even with heat the stud might not come out. I had a scrap crank case which I could afford to heat up very hot and local to the stud. Nevertheless, the stud still would not come out! I also made a special tool for undoing the studs. It consisted of a tube with a bi-hex socket at the top for engaging with the double nuts locked together at the top. At the bottom it was hex so that I could use a large FO combination ring spanner. This avoided the problem of the stud tending to bend all over the place under the load. A really good point about the risk of the stud not screwing all the way down. I will be careful. If necessary, I have a suitable tap and something that was not available in the 1930s when the engine was designed- Locktite! I think I will fill the corner stud voids with OC 600 worm gear oil. If it leaks past the seals it will only do so slowly. I will grind a pressure relief slot in the washer at the top which will also allow the void to stay 'topped up' with engine oil. John Quote Link to comment Share on other sites More sharing options...
sexton Posted November 29, 2019 Share Posted November 29, 2019 John, the guys at the nuke plant used to bring in an electrical discharge machining contractor when they broke a stud on a critical piece of equipment. Don't know the price but it didn't seem to be too expensive. Malcolm Quote Link to comment Share on other sites More sharing options...
Stuartarmytank Posted November 29, 2019 Share Posted November 29, 2019 Atleej I and my friend have done quite a few engines. We use Oxy on the casting bulge inside the crank case . While one is applying pressure to the stud extractor the other should heat the crank case. It does not require so much heat so that it would damage the crankcase or change the alloy properties. You will need heat to refit the stud or you will never get it down. If you use lock tile the next poor soul will have even more trouble than you getting it out. No need to seal it with anything as the corner studs are not a return path for oil . If they are left without anything but a little thixotropic wax of some sort ( Ardrox) they are easy to have a look at on a regular basis. I you grind a slot then the oil on the rocker gear will leak out through the corner studs...I don't think that is a good idea. Best just paint the studs and brush them down with preservative. Seriously when you get the temp right they crack and come out easily . Quote Link to comment Share on other sites More sharing options...
Stuartarmytank Posted November 29, 2019 Share Posted November 29, 2019 (edited) forget the last picture ...I put it in by mistake and cant figure out how to get rid of it Edited November 29, 2019 by Stuartarmytank Quote Link to comment Share on other sites More sharing options...
Stuartarmytank Posted November 29, 2019 Share Posted November 29, 2019 the studs I removed and the finished engine 3 Quote Link to comment Share on other sites More sharing options...
attleej Posted February 2, 2020 Author Share Posted February 2, 2020 Dear All, First Q is does anyone know how to edit the subject of this thread. It does not search on google as well as I would like. It might be better to call it "Meteor and Merlin"..... rather than "Meteor / Merlin". If a moderator can do it, just do it please. We have now started to fit the cylinder blocks onto the pistons and crankcase. I had to make four of the piston ring compressors in the photo. They are made from a scrap Merlin cylinder liner. In reality, it is a bracelet that can be threaded out from between the piston and the cylinder studs. The liner is cut into 6 segments and they are held together with a strip made from a paint tin. In order that it works properly the tapped holes in the liner and the tin strips were drilled precisely on the milling machine. The segments from the liner are, of course, precisely the right radius to suit the piston. The forks were used to lift the block into position over the engine turning rig and were left in position for convenience. The block is actually lowered by means of the M20 nut on top of the cross member. Under the nut is a cheap thrust washer to reduce the turning effort. It is not very convenient using a 30 mm ring spanner and I need to make some sort of hand wheel arrangement. The system works well except that the pistons are apt to tilt and jam in the bores, especially when the relevant crank is not at TDC or BDC. I am minded to make a packing piece that will spigot into the cylinder's bore in the crank case and the bottom of the piston. Thus the piston would not be able to tilt and would be dead in line with the cylinder bore. It might pay to tighten the piston ring compressors a bit more than hand tight. The device in the end of the crankshaft is a turning tool. Photos were by Andy A who helped me do it. John Quote Link to comment Share on other sites More sharing options...
john1950 Posted February 2, 2020 Share Posted February 2, 2020 If you want to edit your content there is an edit click next to quote at the bottom of the item. I just click that then click to put a cursor in the area I want to edit with a left click, then just add content or delete. Quote Link to comment Share on other sites More sharing options...
radiomike7 Posted February 3, 2020 Share Posted February 3, 2020 Why can a Merlin/Meteor not be assembled in the conventional manner, are the big ends too large to pass down the bores? Quote Link to comment Share on other sites More sharing options...
john1950 Posted February 3, 2020 Share Posted February 3, 2020 On RR Merlin it is a one piece head and cylinder block. Same as later Leyland 500 fixed head diesel engine. Unlike Packard Merlin engines. Quote Link to comment Share on other sites More sharing options...
attleej Posted February 3, 2020 Author Share Posted February 3, 2020 Not quite! The heads are only removed from the block if essential, say to change a liner. I don't know anything about the Packard Merlin engines. I think that there are two reasons why RR went this way. First, the EMER says that the block assembly should be pressure tested by immersion in a tank of hot water. This is done by applying air pressure to the cooling system. Obviously this is impractical if the block is already on the crank case! The second point is that the EMER says to assemble the rods onto the crankshaft before fitting it to the crank case. Presumably this is to allow checks to be made for no binding on the journals. In short, doing this way means that more inspection and checking can be done thus reducing risk. John Quote Link to comment Share on other sites More sharing options...
john1950 Posted February 3, 2020 Share Posted February 3, 2020 I was only going of a very old memory in the grey matter. Quote Link to comment Share on other sites More sharing options...
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