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MG MGB Technical Blown Head Gasket BBS discussion at MG-Cars.info
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MG MGB Technical - Blown Head Gasket
| I have a '72B / supercharged engine with a blown head gasket. Car had been running very slightly rough for awhile and this weekend I noticed the engine temp jump and engine compartment covered with coolant. Engine never over heated. I refilled radiator, cleaned engine, ran it for a bit in my driveway and I see a small trickle of coolant coming from right mid-gasket area. My question is how difficult is a head gasket repair - should it always be done "professionally". I am reasonably mechanical but it would be biggest job I have tackled thus far. Thanks for any advice. -Chris |
| Christian |
| Chris- You said that you saw "a small trickle of coolant coming from right mid-gasket area." I presume that you mean from the area above #2 & #3 cylinders. If that is the case, then your head (and possibly the deck of the block) suffers from warpage. At the very least, the head will have to be skimmed flat by a machine shop. Reassembly with a new head gasket (preferrably a Payen head gasket) is pretty straightforward affair. You'll need a good torque wrench, otherwise the head will warp again, and the head gasket will blow again. |
| Steve S. |
| IF the problem is the gasket, and not the head itself, this is pretty straight-forward. Mechanically, it's an easy job - pull the head, clean all surfaces, put in the new gasket and replace the head. But.... Pulling the head can be painful in a lot of ways. First, the head is HEAVY (~50 lbs.) and hard to lift at the best of times. Add in the fact that you're probably going to have old gasket sealant hanging on for dear life and the lifting gets harder. Then add in the fact that the studs may still be in place when you pull it (it's not always possible to remove one or more of them with the head in place), and you find yourself lifting all that weight straight upwards - no lateral movement available to loosen the aforementioned sealant. I'm living proof that IT CAN BE DONE, even without a lift or other niceties. But it can hurt. :) This is where the "Might As Well's" are going to take over your life - and wallet. None of the following is absolutely necessary, of course, but you know how that goes. Once you have the head off, you might as well have it inspected. Find a local mechanic or machine shop who will magnaflux it, looking for cracks, and will check the surface for deformation. Have the valves and guides inspected as well. Repair or replace as needed. Remember to follow the proper sequence and pressure when you retorque the head after re-installation; and remember to retorque after 500 miles then again after 1500. Once the head is off, you're going to find a lot of carbonized crud stuck to the top of your pistons. Leave it alone. It's ugly, and it may actually cost you some HP if it's left in place. But it's normal, and you can't remove it without causing more trouble for yourself. That is, unless you're just dying to rebuild your engine right now. ;) This is a hard job physically, but mechanically it's pretty simple. If you do any of the wrenching on your car you're definitely qualified to do it. Cheers! |
| Rick Stevens |
| Steve's note came in as I was typing mine, and I agree with him - and realize I didn't say that in my post. It does sound like warpage or a crack. |
| Rick Stevens |
| Thanks everyone. I think I will do the job myself - the engine was re-built three years ago so I am hoping the head will come off easily. Will have head Magnafluxed. Not sure why gasket blew after so little use but I suspect the SC may be to blame. Steve - what type of Payen gasket should I use? -Chris |
| Christian |
| Christian, If you are going to the time and expense of replacing the head gasket and cleaning up the head, I cannot stress enough the need of replacing the head studs with those made by ARP. This will greatly reduce the probability that you will be doing this procedure again in the not too distant future. Ray '67 SC Tourer |
| RAY |
| Christian- Payen only makes one head gasket for the MGB. These gaskets are resin-impregnated, have copper sealing rings to better resist excessive crush pressures, and require no additional sealing coatings. The resin softens when it gets hot and makes a better seal. Ray's suggestion that you replace the head studs with ARP items is a good one. When the engine is started and begins to heat up the cylinder head stud must stretch as the cylinder head grows in thickness. When the engine is stopped and allowed to cool the cylinder head stud must shrink to its original length in order to keep the cylinder head gasket sealing for the next cold engine start. When the stud has been submitted to months and years of repeated stretching and shrinking, it will eventually fail. If the bolt is removed for overhaul and reused, the re-torque procedure can further increase the chances of failure of the studs. When failure occurs and the cylinder head gasket allows antifreeze to enter the combustion chamber and lubricating oil serious engine damage will result. Stretched cylinder head studs will not hold their torque settings and will lead to a leaking or blown cylinder head gasket and possibly a warped and/or cracked cylinder head. Repeated retorquing of stretched cylinder head studs will likely result in a cracked cylinder head. Do not attempt to replace them with bolts. When a bolt to is torqued, it is reacting to two different forces simultaneously, stretching and twisting. This being the case, a torque reading does not accurately reflect the amount of stretch of the fastener. On the other hand, when torque is applied to the nut, a properly installed stud will stretch only along its vertical axis. The ARP cylinder head studs are made of 8740 steel. The ARP cylinder head stud kits include hardened steel washers and twelve-point nuts. Although the nuts may be smaller than the Original Equipment nuts, they are of much greater tensile strength. The ARP studs and nuts are rated at 190,000 PSI, which is considerably greater than a Grade 8 bolt, which is rated at 150,000 PSI. The nuts are of the twelve-point type so that a socket will hold on to them at much greater torque than is possible with a hex head nut, which will either round over or cam out of the socket. Do not make the common Beginner’s Mistake of presuming that because you have installed extra-strong cylinder head studs you can apply huge amounts of torque to their compression nuts in order to attain a more effective seal on the cylinder head gasket. This will most likely result in distortion of their mounting threads in the deck of the block. As a result, the clamping force will be reduced and the cylinder head studs will consequently loosen, leading in turn to a blown cylinder head gasket. In addition, over-torquing can crush the cylinder head gasket, also leading in turn to leakage of combustion gases and coolant, as well as a blown cylinder head gasket. Always use the torque values recommended by the manufacturer of the gasket. Steel studs have a different coefficient of expansion than that of a cast iron block and preloading them will aggravate this factor by increasing stress on the block. If they are bottomed out against their shanks in the block, the consequent preloading can cause the deck area around them to distort upwards as they expand more than the block, and that could lead to a blown gasket, or even a cracked deck of the block. When the block cools, being a casting, it will tend to return to its original flat shape if it has not cracked. Chamfer and retap the threads in the block prior to installing the cylinder head studs. Do not make the all-too-common mistake of attempting to torque the cylinder head studs down as this may lead to cracking of the mounting lugs inside of the block. Because the cylinder head studs extend into lugs that serve the secondary purpose of reinforcing the deck of the block inside the coolant jacket, any cracking of the lugs will allow coolant to leak past the cylinder head studs and undermine the sealing of the gasket. It is always possible that a previous owner may have already made this mistake, so coat the threads with a flexible sealer such as Fel-Pro Gray Bolt Prep immediately prior to the torquing of the cylinder head. Torquing of the cylinder head stud nuts to their specified 45-50 Ft-lbs will accomplish the task of securing the studs in the block just fine. Never use a thread locking compound as it will result in damage to the threads whenever the studs are removed, thus rendering them useless. Should the cylinder head stud spin or wobble in its threads when installed dry, check to be sure that the studs are not undersize. Be aware that it is not unknown for suppliers to accidentally ship the wrong cylinder head studs. The eleven cylinder head studs of B Series engines are 3/8” (.375”) in diameter with the upper sections of having 24 threads per inch and the lower sections having 16 threads per inch. Seven are 4 ½” (4.5”) in length while the remaining four are 6 ¼” (6.25”) in length. |
| Steve S. |
| Again, thank you all for your comments. So far I have removed head and was very pleased to find that it was not warped, and the block is OK too. May have, however, found a new problem. I removed the lifters for inspection and found that #6 has some pretty bad pitting. The cam lobe seems to be OK as far as I can tell by looking down the pushrod hole. Is it just a bad lifter that needs to be replaced or could it be a more significant problem? Thanks. -Chris |
| Christian |
| Chris- The camshaft lobe really should be given a careful visual inspection and be measured with a micrometer, but you might gamble on simply replacing the tappet and doing a careful run-in procedure. Drive for 100 miles and retorque the cylinder head stud compression nuts, change both the oil and the oil filter, then again at 500 miles to complete the bedding in of the new camshaft and lifters, let it cool and then retorque the cylinder head stud compression nuts using the proper sequence pattern. You will find some cylinder head stud compression nuts almost tight; some can take almost a quarter turn. Because retorquing the cylinder head will reduce the valve clearances, after every retorquing of the cylinder head you will need to reset the valve clearances. Run the car for another 100 miles again. You will find that this time the cylinder head stud compression nuts have not lost quite as much torque. Run an additional 500 miles and again retorque the cylinder head stud compression nuts. During this period do not exceed 4,000 RPM or 45 MPH, operate the engine at full throttle, or allow the engine to labor in any gear. Until the next 1,000 miles total has been completed, limit engine speeds to around 4,500 RPM when shifting gears. Cruising on the highway should be limited to no more than 3,500 RPM. Keep varying the throttle opening and engine speed. The secret is to constantly vary the speed and load without creating excess heat through full throttle laboring and high engine speed operation. After 1,000 miles of following this procedure, change the oil and oil filter and refill the sump with a quality oil such as Castrol 20W/50. After another 1,000 miles the engine will be properly broken in and ready for service. |
| Steve S. |
| As usual, Steve has left excellent advice, especially on the spaced, and graduated retorgues. And a minor clarification: If the lifter was pitted, then there's has to be some damage to the lobe, period. The matter is how much, and Steve shows how to mitigate and soldier on, giving you a routine to "season" the re-breakin of both the new hardened ( R_55 or so min) lifter/cam assembly along with the head gasket, and keep on going. Now , with your head off, might be the time to replace the cam and lifters for the supercharger though. Han's has a low-no overlap grind and the P-270 has proven to be a great improvement cam for the SC engine. My recall is with the pan/oil pump lossed, the cam is pullable with the engine in place on the 72 lumpy. Just a thought to really slow you down.* Cheerios, Vem * But a heck of a potential power add with a new billet P-270, or Han's grind, with Rockwell hardened new lifters, and the ARP head studs with Payean. Check Lawrie Alexander's wire trick to permanently seal the head gasket against coolant weeping between 2 and 3. |
| vem myers |
| I think the ARP studs and nuts are over-rated - and yes the pun is intended! Unless the studs are yielding, or failing in fatigue, which they clearly are not, then increasing the ultimate tensile strength isn't going to help. Nor do I follow the argument for 12-flat nuts; 50lbft is not a lot of torque and anybody having trouble with rounding needs to look at the quality of the socket or the calibration of the torque wrench! It is usual engineering practice to have nuts rated lower than studs/bolts. Sometimes in engineering, stuff 'just happens' - and blown cylinder head gaskets are a prime example. There must be thousands of us, perhaps tens of thousands, who have replaced a blown head gasket without any additional work for it to be fine for tens of thousands of miles thereafters? The stuff about running in is valid for new pistons/rings/bores but why would you run-in a new head gasket? N |
| Neil22 |
| Neil - I've just re-read these posts, and Steve's advice is not just for running-in of the new head gasket but also for the replacement tappet: New parts, unseasoned metal, break it in. As for the periodic re-torquing after gasket replacement, of course it's needed. Not every car may need it, every time - but the tens of thousands of us who have done it have in large part found that re-torquing is needed at least once, perhaps more. (And I'm not talking about backing off the nut and then re-torquing to spec. I mean doing it with the engine cold, from a standing start as it were.) |
| Rick Stevens |
| I think I can get the Cam out from underneath / front of engine. Currently, it is a 288 cam and I think I will stay with same grind. Power was very good. I have never indexed a cam so that step could be time consuming. I will go with nitrided lifters. C. |
| Christian |
| There were some dodgy head studs in early engines with a '22' on top. They should be replaced as they have a history of failure, but newer head studs should be fine - if it makes you happier, buy the APT parts, but it really is overkill. Get that head off and get a straight edge on the block and head to check for warpage, failing which you'll have to look to cracks. If you are lucky, it might be nothing more than a blown gasket - as long as you didn't run it that way long enough to etch the block or head...... |
| Bill Spohn |
| There have been problems with quality control even with the new Rover studs. Check the archives. If you are running a supercharger, you need the extra assurance of the ARP studs. Don't rely on 40 + year old studs that have been stretched uncountable times to give you an accurate torque reading and head clamping force. It's just not worth the risk for $150. Ray |
| RAY |
| steve i was very interrested to read your advice on cly head gasket tightening, i have never heard of it done like this before, where did you get this method from, do you have a lot of trouble with head gaskets blowing? andy |
| andy tilney |
| ps i forgot to add i agree with neil in somerset about running in head gaskets andy |
| andy tilney |
| Neil- Head gaskets compress (or "settle", if you prefer that term) as they break in. Thus the retorquing procedure. Yes, I am aware that Payen claims that their resin-impregnated gasket does not require retorquing after the intial running-in, but why take chances? Andy- No, I have no problems with head gaskets. I presume that the reason for this is that I use the break-in procedure that I described. |
| Steve S. |
| Composite gaskets need a special replacement process. First the head and block must be scrupulously clean. Fit and torque down in the normal stages. Set valve clearances. Then run the engine *without coolant* until the head gets quite warm (not red hot!) switch off and leave to cool right down (several hours ideally overnight). Then retorque, undoing each just a fraction first to break the stiction. Reset valve clearances. The fill with coolant to the correct level, but don't fit the radiator cap, and run the engine until the coolant starts expanding significantly and switch off. Again leave to cool right down then retorque as before, reset valve clearances, top up the coolant, refit the cap, and away you go. These gaskets seal by heat-bonding to the head and block. If the surfaces are greasy, or you put coolant and allow it to pressurise before it has fully bonded, it won't bond properly and subsequent leaks will be more likely. |
| Paul Hunt 2 |
| paul i was very interested to read your method of head gasket tightening, as it differs quite a bit from most of the others posted on here where did you get this method from or is something you devised from experience of doing these over the years |
| andy tilney |
| Paul- John Twist would challenge your re-torgue method. At his Tuning For Power Seminar last year, he completely withdrew the head stud, oiled it and spun it back in. Even Peter Burgess recommends a big "quarter" back off turn. Just snipping ol bud. Cheerios Vic |
| vem myers |
| vic i have just read your last post and i am sorry but i dont understand what you mean. i have been following this theam for quite a while, ihave also asked twice about these different methods of retorquing, but for some reason no one is willing to say where these methods come from i only ask this because i have never heard of any of them befor and i am interested to know if they are correct or if they are just something somebody thinks is a good way of doing them andy |
| andy tilney |
| Vic- Paul said "retorque, undoing each just a fraction first to break the stiction". After all, a quarter-turn is a fraction, right? Andy- I developed my method over time, starting with the sage advice of older mechanics back in the days when I was a beginner. My technique is more the end product of my own perfectionist tendencies than it is anything that is written in a manual. However, I think that most mechanics would agree that it is nothing radically different than those in general use. It's just more cautious, even if it is more time-consuming. |
| Steve S. |
| I was able to remove camshaft by easing steering cross-member forward and removing distributor drive gear. Also had to remove oil coiler. Two lobes quite bad. Now need to decide on whether to have camshaft plasma welded for repair or get a new one. Also, I would like to know root cause of failure. Camshaft failure, lifter failure, did I not break-in the engine properly after its recent rebuild, etc. Anyway, when I get it back in running order I will follow Steve S.' break-in advice. -Chris |
| Christian |
| Chris- The root cause of the failure is impossible to determine without having the engine at hand for examination. It could be that you got an inadequately hardened tappet. There's plenty of them around. Good ones can be had from Piper Camshafts, and even better ones can be had from Arrow Precision. I use the latter and swear by them. These are a worthwhile addition to any engine as they reduce wear on both the camshaft lobes and the faces of the tappets, as well as on the tappet bores and the load bearing lower end of the pushrods. While an Original Equipment bucket tappet weighs 47.5 grams, this high performance version weighs only 39.7 grams, adding an extra 50 RPM to the maximum safe speed of the engine. The wall thickness of the tappet has been wisely left at .050” in order to preclude breakage resulting from the high side thrust loadings incurred with high lift and/or long-duration camshaft lobe profiles. They are made of carburized low carbon steel, which is an ideal tappet material, providing a shock resistant inner core with an external “skin” that is much harder than normal in order to resist wear. This is the same technology used in the Original Equipment rocker arms. The hardening of the tappet is the last step in the manufacturing process, so testing for Rockwell hardness can only be done on the finished product. The oiling hole is drilled in the shank of the tappet after lathe turning, but before reaming and centerless grinding, and then the tappet is heat-treated in order to eliminate any stress risers that have resulted from the machining process. The tappet then emerges hardened as a result of the heat-treating process. Testing for Rockwell hardness is done by impacting the surface with a slender diamond-tipped punch-like bit, and then the resulting indentation measured for depth with a needle-like gauge. |
| Steve S. |
| steve thank you for your reply about the retorquing of cly heads, may i ask one last question, befor you came up with this method of doing them did you have problems with head gaskets on B series engins or any other engines with cast iron heads and blocks, again i only ask because i find these different methods interesting and what other methods did you try before you arrived at this one, thank you andy |
| andy tilney |
| As Steve S says. Any undoing movement enough to break stiction is all that is required, and a 1/4 turn comes into that category. Personally I wouldn't want to completely remove a stud or nut during retorqeuing. Whilst it is possible that an oiled thread may have 'dried out' when retorquing after a hundred miles or so, it shouldn't need re-oiling after the few minutes of running I mentioned. But yes, threads should be oiled before insertion, torque figures are generally quoted on that basis. |
| Paul Hunt 2 |
| Steve, How do you lose 15% of the weight of a tappet without changing the wall thickness? Also, heat treatment will not 'eliminate stress risers' - they are a function of the physical form not the material condition. Heat treatment can change the physical properties of the material, or reduce stresses induced by the maching process, that's all. Isn't carburisation a fancy term for 'case-hardening'? Whatever term you use, the process changes the chemical properties of the material on the outside. If the camshaft is worn (as the post says) then I would think the problem is unlikely to be a soft tappet - more likely a too-hard tappet, a lubrication problem, or excess load in the valve train (valve clearances, valve bounce, poor alignement, etc). I concur with retorquing the head nuts, just not doing it several times. Particularly since you'll need to recheck valve clearances every time. When I think about it though, the point of oiling the threads is to reduce friction and hence you'll get more preload into the stud for a given torque; a side-effect would be to reduce the difference between static friction (stiction) and dynamic friction so the backing off might be overkill too. Will still do it though. I agree with Andy inasmuch as there doesn't seem to be any problem with the 'original' method. Removing the studs doesn't make a lot of sense, if only for the reason that it must be tricky to put the studs back in tightly because there's not enough stud sticking out of the cylinder head to get two nuts on them (which you need to wind them in...). Not sure what is gained from doing that. N |
| Neil22 |
| Neil- You can reduce weight by using a lighter alloy. As a former Tool & Diemaker, I assure you that stress risers are an unavoidable result of machining. The cutter tears and compresses the metal, usually resulting in microscopic hills and valleys from which cracks can develop. In heat treating, the metal is brought up to a temperature whereat the crystals of which it is composed are able to reorient themselves in a more uniform manner, then cooled under controled circumstances so that the form of the resultant material is stabilized. You say that stress risers "are a function of the physical form not the material condition". Just what do you mean by the terms "form" and condition"? To me, the two are one and the same. |
| Steve S. |
| Steve, It won't be possible to get the weight savings you quoted via a change in alloy. Steels vary in density, depending on type, from 7.75g/cu. cm to 8.05g/cu. cm. That's a difference of 3.72% MAX. If factory lifters are 47.5g and the new ones are 39.7g, the difference is 16.42%. Can't happen without a change in part geometry. Besides, the higher density steel alloys tend to fall into the 'stainless steel' category which typically would not be used for an application like this. It used to be that MG lifters were chilled cast iron running on steel cams. Chilled cast iron (white iron) forms a very hard but brittle material. That's why only the face of the lifter was chilled, the balance of the part was left as grey iron. This was done in the casting of the lifter, not during post machining heat treatment. From memory, chilled cast iron is about 58-62 Rc (Rockwell C scale) hardness. That's awfully close to 'case hardened' (60-64 Rc (?)) hardness. Typically you don't want to run the same material against each other - steel on steel for example. The wear rate will be much higher and the parts will be subjected to galling. Generaly you don't want to run two materials of the same hardness either, rapid wear usually ensues. Longest life is typically achieved with different materials at different harnesses. Neil is correct that heat treatment - "stress releiving" will not eliminate stress risers. It will reduce (but not eliminate) stresses caused by machining, deformation (bending) and/or localised heating. Stress risers are geometry based. Good examples of typical stress risers are: sharp internal corners, keyways, splines, notches, etc. It's true effects depend on where they are and the stresses/forces that a part is put under. I'm sure what Neil meant by his statement is "physical form" = geometry and "material condition" = heat treatment. These are typical engineering descriptors. If a part has a feature that can potentially cause a failure under use, it is a legitimate concern. If the part is loaded so lightly that a failure is not foreseeable, it is generally not a concern from an engineering standpoint. However, from a GMP (good manufacturing practice) standpoint a part should be made the best way possible within the required cost / servicibility requirements. Tom |
| Tom Sotomayor |
| Steve- Yes, point absorbed, but what of Twist's tech ol son?. When Doug Jackson was building the cross flow 71 engine for me back in 1999, he mentioned that a recent batch of lifters-- supposed to be Rockwell hard at "55" --revealed a number of soft ones. I believe he has such a mention in his tech arts in site. If you happened to be the guy inadvertantly getting a "soft" one, and never knowing it, the cam lobe would soon suffer and you'd be scratching your head about like the gentleman above. So, Christian, whatcha going for on the cam? I'd urge a P270, new billet, from Peter B, or a grind to your specs at Elgin in California. Or, you could send him your recently withdrawn cam and he'll fix it. Lots of good options my boy. Vem PS- Any comments on Twist's withdrawl technique for retorgue, or is it just too mind blowing? |
| vem myers |
| Tom- I was aware that geometry-induced stresses (such as in keyways, splines, etc., are always refered to as Stress Risers. However, I have always been led to believe that deformations and compactions caused by machining were also refered to as such. Is there a separate engineering term for machining-induced stresses inside the metal? Or am I correct in also refering to them as Stress Risers? Vic- I think that John Twist simply removed the studs to oil both ends of them. Nothing mind-blowing about that! I like his perfectionistic, take-the-extra-time-to-do-it-right, leave-no-stone-unturned approach to doing things. A man after my own heart! You can bet that all warranty claims in his shop are from defective materials, never from defective workmanship. |
| Steve S. |
| Steve, Stress risers are strictly geometry based. Machining can introduce and relieve stresses on its own (That is why a piece of cold rolled steel - which is chock full of stresses from the rolling process - will usually warp badly when a milling cut is taken from one side). These are referred to as stresses rather than stress risers. Stresses are what are relieved/lessened by stress relieving. Stress risers remain after heat treating/stress relieving because the geometry has not changed. Now, if a ragged cut is taken and leaves a sharp edged groove then that is a potential stress riser. One of the easiest ways to explain stress risers is in cutting a piece of glass using a glass cutter. Without the use of the glass cutter if the piece of glass is flexed, it breaks randomly. When the glass cutter is applied the stress is 'concentrated' at the score mark. Cracks begin here and can propogate rapidly. Of course glass is not anywhere near as ductile as steel! Stress relieving can be accomplished with heat, cryogenic freezing and by vibration. Low level heat cycling can also stress relieve aluminum castings. That's why early alloy cylinder heads would typically warp after about 40-50K miles. This can get to be a very complex subject and there are a number of manufacturing engineers that spend their entire careers working on this very problem. Tom |
| Tom Sotomayor |
| i am sorry to ask this but who is jonh twist as i have never heard of him. and does he have yet another way of torquing down heads |
| andy tilney |
| Andy- John Twist is something of a living legend amongst MG owners on this side of the pond. He is a fellow enthusiast who owns his own shop where he maintenances, rebuilds, and restores MG's of all kinds. He also conducts workshops for owners so that they can learn how to do all of their own work, from overhauling their SU's to rebuiding their transmissions. Plus, he's a great guy to boot! |
| Steve S . |
| Andy; http://www.universitymotorsltd.com/information.html For more information about John Twist click on Employees. Clifton |
| Clifton Gordon |
| While Payen say it is not necessary to re tension the head studs it certainly does not hurt. With the modern gaskets like the payen it should be tightened in increments ie 30-40-50 then after final assembly thoroughly warmed up and checked again while hot. I must admit I leave my own cars over night and give a final hot check in the morning but it is always OK. While there are many people working on engines there will probably be as many ways to to do a job for the same result but the main things to remember are, free lubed nuts, correct tightening pattern, tighten in increments, and the final check with an iron head "hot" and an alloy head "cold" There is another thing to watch out for with worn lifters and cam lobes which I have come across several times in my many years of working on engines and that is a worn crankshaft thrust, shedding material "both thrust and crankshaft" onto an area of the cam. It is worth giving the crank pulley a push and pull while your at it. It does not happen often but it does happen. Remember in this case we are talking about a supercharged engine and you can talk all you like about tensile strength and get all technical but in most cases the OE studs have proved inadequate for the job and the ARP a good alternative. Denis |
| DENIS4 |
| denis you are the first person on this post who tightens up there cly heads the same way as i was told in the 60s just as a matter of interrest where did you get this method from i bet it was from the same place as me look forward to your reply andy |
| andy tilney |
| Andy I did my apprenticeship as an auto mechanic in 1953 which in those days was five years, then in 81 did a teaching degree and taught automotive technology till about 2000. The last several years part time as we also had a family dairy farm. Mechanics are still taught to do it this way. Denis |
| DENIS4 |
| i knew it same as me only mine was in late 60s and early 70s but still 5 years and 5years at colledge mine was at austin /morris/mg /wolsley main agents and lots of factory coarses on a b c series engined cars at BL only difference was we always ran them up with no water in then pulled the head down hot a good tip from the men who made the cars andy |
| andy tilney |
| Tom, Thanks, your interpretation is spot on. Experience is a fantastic thing, but some things are based in engineering theory. I still don't see the point in taking the studs out. To do so, you have to slacken off the relevant nut completely - so you're going to have to slacken off the whole lot in stages (as per Denis and Andy posts). And then you cannoot get most of the studs out anyway without taking the head off, which is a daft way to proceed! And what do you gain? What is the benefit of having oil on the threads that are already inside the block - particularly since you don't need to torque them in? Especially since you took them out and oiled them, presumably, when you had the head off the first time??? Hot torque will be different from cold torque because of expansion. You can check them hot of course, but the preload you get from the torque you apply will be reduced when the head contracts. So wouldn't it be better to check them cold? Last of all in this rant, the higher strength studs would reduce the chance of studs failing in fatigue... BUT the lower strength studs don't fail in fatigue anyway! Things fail in fatigue if the strain in service is enough to open up a microscopic crack which grows over time until the section is reduced, the stress rises above the strength of the material and the part fails. So stronger material might well last longer. But the stress is related to the strain in pretty much the same way for a particular material type. So stronger material will not necessarily see lower stress in service (it might even see higher stress). And either way, there doesn't seem to be much evidence of studs failing in service through fatigue, so the higher strength studs seem like overkill. If you're replacing studs anyway, then why not use the stronger ones. But £100 on studs makes a simple head gasket change a pretty expensive job! N |
| Neil22 |
| neil i think you must have missread what dennis and i have said we did not say slacken off the head nuts and as you quite rightly said there is no point in taking out the studs,infact that would not be a good idea atall, the reason for running these engines up with no water in was get them hot to soffen the varnish coat on the gasket ( on these copper gaskets the had DV stamped on them which stood for double varnish)which then formed a seal,, and shall we say stuck the gasket to the head and the block, and the reason for pulling down the head when hot was because of this the other reason for no water was if the seal was not perfect no water could get between the surfaces,untill the varnish had soffened and formed a seal, well this is what the men at the factory told me, and i do all my head gaskets this way and i have never had one leak so i think they must have been right these payen composite gaskets work just same as the old copper DV ones andy |
| andy tilney |
| Niel, Remember that this application is for a supercharged engine and that the stress load on the studs exceeds what the factory designed theese studs for. When running my supercharged B hard the head lifted just a bit and allowed oil to enter the radiator. When I replaced the head gasket I felt that the extra protection of the ARP studs was well worth the $150 price tag considering the $3,000 price of the supercharger. I didn't wont to be doing the job again in the near future. Ray '67 Tourer |
| RAY |
| Neil With an iron head the studs expand more than the head when hot so we tighten hot as the studs loosen off. On the other hand an alloy head expands more than the studs when hot and tightens up so we tighten cold. I also had the same trouble as Ray when I first fitted the supercharger. On full boost it would lift the head a fraction and pressurise the cooling system blowing water out the overflow. This was with a brand new set of standard head studs. I replaced the studs with ARP and have no further trouble even after increasing boost a couple of pounds. |
| DENIS4 |
| Bottomline here is experience over theory. The ARP, as Denis notes, have proven to be the durable choice in sc engines. And that is the end of that. Cheers, Vic |
| vem myers |
| Vic, Sorry to be an annoying pedant, but Steve S. was saying that the ARP studs are better because they have a higher tensile strength. And he was talking about failure of the studs in fatigue. I was saying that the bolts don't fail in fatigue in service, so the higher tensile strength is unnecessary. If the problem is with lifting of the head, and it's fixed with ARP studs, then the ARP studs must be *stiffer* - ie they are not stretching as much for the same load. I haven't thought this next bit through properly, but I would think that the same torque applied to stiffer studs/nuts would increase the clamping force and preload. So you 'might' get the same result by simply applying more torque (ie by applying more preload) to the OE studs. The stiffness and the ultimate strength of a material are two entirely different things. FWIW. Neil |
| Neil22 |
| Neil- You say that the Original Equipment cylinder head studs do not fail in service. Not so. So far the only type of fatigue failure that you've mentioned is the type that results in the stud snapping in two. However, there is another type of fatigue failure: stretching. Yes, that is also a form of fatigue failure. I never reuse the Original Equipment cylinder head studs because after 22 to 45 years of service, I just can't see the point in putting my trust in them. The financial cost of the implied mechanical complications of a blown cylinder head gasket and a possibly warped and/or cracked cylinder head, plus damaged pistons and maybe valves as well, just isn't worth the savings on the price of a set of new cylinder head studs. Vendors that sell what they claim is the equivalent of Original Equipment cylinder head studs never seem to be able to give any specifications on what they're selling, probably because they simply don't know and can't be bothered to find out if what they're selling is really equivalent to the Original Equipment item. That's why I use (and recommend) the ARP items, not just because of their tensile strength. |
| Steve S. |
| Steve, Stretching is not a form of fatigue failure.It occurs when the yield point of the steel has been exceeded, resulting in permanent elongation (ie plastic rather than elastic deformation). Some later cars require the studs to be torqued into this plastic range on assembly and then not retorqued. A strange feeling when I rebuilt a Toyota V6. Fatigue failure is the propagation of a crack by repeated cyclical stress, which in some cases may be below the yield stress particularly if stress raisers are present. David |
| David Overington |
| If they no longer do the job they are stuffed no matter what terms you use to describe the reason. |
| DENIS4 |
| David- When repeated cycles of stress such as heat-induced expansion and contraction result in the lowering of the yield point, the result can be described as fatigue-induced. The metal just flat gets tired and stretches under conditions under which it previously would not, such as in very old head studs. |
| Steve S. |
| I'm with David on this. When studs or bolts have stretched to their maximum specified limit (and on the K-series for example this is the criteria for using new) they are 'time expired', they haven't failed, any more than an oil filter 'fails' at 6000 miles. |
| Paul Hunt 2 |
| As a metallurgist I'm just a stickler for correct definitions! |
| David Overington |
This thread was discussed between 18/11/2007 and 11/12/2007
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