Just replaced the 1-4 head on my 348 after having 2 burnt valves replaced and the head serviced. Have torqued the head down using the procedure in the WSM but it seems quite a bizarre procedure, I know there must be a very good reason for it and was wondering if someone knows why? I have done a search on f-chat but cant find an explanation. Tightening starts in the centre and moves to the outside thats all fine. All studs go straight down to 60nm then they are turned a further 90 deg? Why not just say 65nm or so and be done with it? Does anyone know the reason for this? Also to confirm it is ok, you do a pressure test on the water system at 8-10atm (110-145psi) for 15 min seems horrendously high considering the operating pressure is probably never more than 20psi? I have not pressure tested it yet but plan to in the next couple of days and get it finished off.
I had this procedure elaborately explained to me at one time (I will try my best to reproduce the information w/out embarrassing myself) Step one will evenly load and compress the head gasket as well as apply equal pressure across the length of the head minimizing distortion. Step two gives you the pressure required to contain combustion and seal your water jacket. The pressure test value does seem a bit excessive...I could see the value of SLIGHTLY exceeding the operating pressure. Good luck!
a further 90 degrees result in much higher than an additional 5 Nm. Would likely be in the 90Nm or more. This is an alternative method of torquing that is independent of the the lubrication on the fastener. It basically ensures the correct stretch on the studs to hold the head tight. Although, you do have a point that after torquing to 60Nm, what is the point of calling out degrees? Why not just say 90 Nm as a final step and be done. Porsche flops back and forth on this a lot.
No, but I just ran up against something similar... I twisted off the crank pulley bolt in a Honda Civic - very lucky for me the piece was easy to extract by hand from the crank. I was on the way to 181 ft.-lbs and it twisted off before my calibrated torque wrench released. I went to the dealer to get a new bolt and complain and was given a printout with the following torque instructions: 1) oil the threads 2) torque to 145 ft-lb, then fully loosen 3) torque to 20 ft-lb 4) turn bolt an additional 60 degrees 5) tighten accessory belts, start engine, idle 3 minutes, turn off engine 6) turn bolt an additional 30 degrees I'm curious as well. What's going on here? Is this supposed to insure proper stretching of the bolt, based on empirical evidence from the factory?
Its not as bizzare as you think as dodge intrepids have the same procedure. Probably many more. As to why, my guess would be every bolt has different stretch , friction etc so one torque for all wont cut it.
Tightening spec with torque value alone is unreliable due variable friction from oil or rust on thread and seat. Measuring bolt stretch is the most accurate way, because metal strech is very predictable to the tensile load. This is often done on race engine con rod bolts, but obviously impossible to do in a head stud situation as you can't put a micrometer on there to measure stud stretch. So the theory is that a preload torque is applied to remove the slack and get you half way there so to speak, where factors affecting friction is less critical, then the last critical bit is precise linear stretch as determined by angle and thread pitch. I believe it's also related to the design of the bolts and studs so that optimal clamping force is at on set of some plastic yield in the metal. 360 con rod bolts are such one use only designs.
As bolts tighten, they tend to sieze at different spots due to friction within the threads. When they do this it takes a greater amount of torque to get them moving. And as torque increases, so does thread friction. Often, when tightening head bolts with a beam type torque wrench you will see what is called "judder". The bolt is stopping and starting and makes the pointer flex back and forth. What happens then is that you may have some bolts that exceed the torque, and others that arent anywhere near the limit. By stopping recorded torque readings at a lower point that is about 90 degrees before an average bolt would meet full torque, you can usually stay below the point where bolts start juddering. Now when you rotate the bolt 90 degrees further, you can be confident all the bolts are at full and even torque simply because the bolt was rotated far enough to put the proper load on it. And with stretch bolts this becomes even more critical. If you surpass the limit too far the bolt will yield and torque will actually fall below spec, or the bolt could actually fail. I believe all stretch bolts use 90 degree final rotation to reach full torque. In any event it is always best to follow a manufacturers workshop manual to the letter with critical assemblies. It is also important to know if a bolt is supposed to be oiled or dry. Generally, engine bolts are oiled, wheels bolts never are. But always refer to the written information.
One point not mentioned is, when it says 'oil the thread' it means a smear of oil. If you get surplus oil or water down a blind hole, you'll be tightening the bolt against the hydraulic pressure and likely sheer the bolt before even the face of the bolt head is in contact with the head. Fortunately I've now erased from my memory how I know this !!!
Many many cars use the 'degree' torque method. Ive lost count at how many different makes and models reccommend doing it that way. Also, a smear of oil on the bolts is more than enough alright. And I am glad you WONT be testing the cooling system at 140 psi! You wouldnt have much of a heater core or radiators left!
The procedure is to presure test just the engine, so heater cores and radiator do not come into it, agree 140 psi in the heater core would make a beauuuutiful explosion...... You are right .8 -1.0 atm seems more reasonable possibly a little higher maybe 2 atm I would be happy with but I am sure it reads 8-10 atm. Maybe my crappy scan of the manual is to blame I would be interested if someone else has a better copy. Every time it fires the cylinder puts thousands of pounds pressure on the seal to the water jacket but other parts of the water system, (water pump seal etc) never see anything like that presure? Image Unavailable, Please Login Image Unavailable, Please Login
NO this torque spec is not bizzare at all. It was designed from a "torque angle signature analysis". This is the best way to torque a bolt. You can do it with torque with a torque wrench, bolt stretch, and torque angle. Torque angle is the most accurate because it takes into account more parameters of who a bolt fatigues, yields etc... If you do a google search on "torque angle signature analysis" and look at a graph of bolt tightening you will instantly see how superior a method it is. In aerospace on critical fasners it is the only way it is done. If someone like ARP on a con rod bolts specifies a specific stretch you have to do it their way unless you do your own TASA.
Ok, never HEARD of that before! Ah, ok. Sorry mate, for some reason I was thinking you had the engine back in the car already! I just looked in my WSM and it also says 8-10 atm for 15 mins. Must have forgot the decimal place when they printed it!
Thanks FBB makes sence now looked up article http://www.hexagon.de/tasignat.htm My interpretation would be that 60nm takes the bolt to the top end of the elastic clamping zone just prior to the yeild point, then the aditional 90deg takes it past the yeld point to somewhere, that after the bolt relaxes will still ensure that probaly?? 45 degress or so tighteneing angle is still available. Because torque increases very slightly past the yield point we are mainly looking for available tightening angle not aditional clamping presure.... So the 60nm will stay constant through the cycles of warm up and cool down not all of a sudden loose it's clamping presure.
Just been looking at this again I wounder if this is meant to be read as 8 "divided by" 10 so 0.8 does not seem to make sence but if someone may have seen this before in Italian/English translations???
You are basically correct around 20psi. Test at 1 atm which at standard temperature and pressure (rememmber that from chem 101?) is 14.7 psi. You are really looking for leaks not testing to a burst pressure.
Yeah, f*cks me mate. I wouldnt have bothered pressure testing it at all, so you are 'one up' over me there! Well, thats what one would think. You wouldnt have to go more than 20psi, so buggers me what the WSM is talking about. Unless they DID forget the decimal place and it is 0.8 and 1.0 as Brian already stated earlier? That sounds right.
I have all the blanking plugs and presure tester so will only take 10 mins or so to do the test and it would be a pain in the a$$ to find a problem when the motor is back in and have to pull it out again.... I can understand 140psi to check the seal on the headgasket as cylinders generate thousands of pounds presure and 20-30psi probaly would not find something that would leak at 500psi. My main concern is probaly the waterpump seal letting go. Hopefully someone out there has either done the test or has seen Italian/English translations like this?
Was curious, so here is the info from the 360 manual 5 bar = 72 psi. Are you confused now?? Image Unavailable, Please Login
You guys are all under the impression Ferrari manuals are good and the information contained in them are correct. You're wrong. They are ***** and full of bad information. If you actually try and repair their cars using the information in them as gospel you will make some serious and very expensive mistakes. You have to KNOW how to fix these cars because those books are not going to get you there. If you need them you are in over your head. Use your heads. Why would anyone pressure test a cooling system to a couple of hundred pounds? Do you really like buying waterpumps? Not to mention any one of a number of gaskets. Nothing in that cooling system is designed for that pressure, not even the water jacket portion of the head gaskets. Use your head and do it the right way. If that is not good enough information put down the wrenches and back away from the car because you have no business working on it. Quit relying on Ferrari for anything besides building cars because they are incapable of doing ANYTHING else.
I totally understand mate. Its only a 10 min job, but I have NEVER torqued down a head or done a head job that has leaked after re-assembley. So thats why I probably wouldnt bother with it. Thats just me though. Probably not. Well, ya never know?? How much pressure can they handle?? Im sure you can find out what the seal is good for. You know, if its a lip seal, double lip seal. Im sure there is a chart that tells you how much pressure they can handle before they push past the lip or blow out.
