Hello everybody, A little history; I have been working on a customers 1999 456 MGTA, 9100 miles, never had Timing belts replaced, but nice car (just purchased). When the car came in it had the "Slow Down" light on, many trouble codes, burning oil, etc. Thanks to this forum we figured out that this could be from failed Valve guides. After checking the spark plugs, compression, etc it was confirmed. I removed the heads, new custom made Manganese Bronze guides were installed, valve job and the heads were Ported while apart. Anyway, as you know, the Factory Shop Manual is terrible, I would like to confirm the Cylinder head bolt (actually stud) torque with a Ferrari Tech. B.T.W. All studs/nuts were replaced. I have done the first stage of 60Nm, but what is the 74Nm/min 38 degrees, 104Nm/max 131 degrees? Also, we have 2 Factory Shop manuals for this car, does Ferrari have any other books that detail disassembly/reassembly? Thanks, Mike Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Can you post a scan of the page where/how these are mentioned in the text? The "degrees" refer to the amount of rotation of the nut during tightening. On modern production lines, they measure both the torque on the head bolt/nut and the amount of rotation needed to achieve that torque and check that both are within certain boundaries (this confirms the bolted connection has the expected stiffness). Just guessing here, but it seems like they are trying to describe something like "the required rotation required to reach 74 Nm should not be less than 38 degrees, and the torque should rise to 104 Nm before reaching 131 degrees of rotation. Just a guess...
I agree that most new engines use TTY bolts (Torque To Yield). Usually they call for 1-2 pre-torques and then 1 final rotation of so many degrees. I figured that these head studs were TTY, that is why I replaced them. The torque specs that I listed are only for some special tool, which they call a S.P.S. Unbraco, mod Sensor 1. Besides these expensive factory manuals we also bought a Ebay 456 Service Manual on CD. I just looked through that (some of the sections are older) and it has a couple of different paragraphs that are not in this paper book. In the CD, the Torque is 60Nm pre-torque and then 90 degrees (TTY), if you do not have that above mentioned S.P.S. tool. Can a Ferrari Tech confirm this? Thank you, Mike
Mike, The factory tool they refer to is a digital torque wrench which will give the actual torque reading, at a specific angle before and after the initial pre-load torque was set. So, in simpler terms...it enables you to read the actual torque, while the stud "is in yield" at a specific angle. Pretty cool...and a very accurate way of doing things. In the same breath, the new Snap-on digital torque wrenches (Techwrench) do the same thing. With torque to yield, bolts or studs, there is a specific, but often fairly wide "safe" torque zone, before "permanent" elongation occurs; hence the detailed specs given by Ferrari. However, if you don't have the special tools, if you use the 90 degree (TTY) figue after you've pre-loaded the stud, you'll fall in the "safe" zone, in terms of applied torque. Regards, David
Thanks David for your reply. I have seen the Snap-On tool that you mentioned, I never thought of the Ferrari tool doing the same thing. I will get back on this car today and see how much I can get done. Cheers, Mike
On the Snap-On tools, the "Atech" version does the torque angle calculation. I'm not 100% on their other digital torque wrench. The biggest difference between the two is that one of, poddibly the model you refer to, has a "stand-alone" digital display box. Torque is torque.... Good luck, David
I know this is mainly about torque, but since you brought it up, I have a '95 456 with 30K+ miles and NO valve guide problems. Since you now are more experienced with the 456, what can you say about the fact this later model with less miles has failed guides, when many of us, me in particular, have not? thanks rik
I would assume that this particular car had many "dry starts" based on its low mileage. I believe that is why you see some with low miles with bad guides. The exhaust guides on this car were very bad, some with .030" clearance to the valve stem. It had misfire codes (along with a few other codes) for cyl's 4,5,6. Those were probably the worst, but all of the exhaust guides had a lot of wear. From what I have read, all of the "M" series had inadequate valve guides, but one would think that the 550 would also have the same problem? My "theory" is that all of these guides were based on the same Copper Alloy Bronze formula, but obviously made in different batches. This coupled with different driving methods, fuels, climates, etc, accelerates the wear. Maybe the different Tuning from a 456 to 550 also makes a difference? One good thing on this car with its low miles, is that it did not require any new valves. My machinist usually has his valve guides made for other vehicles and that is what we did on this car. The cost is about the same for these custom Manganese Bronze guides when compared to the replacement Ferrari guides. Mike
thanks, will look over this concept One thing is, your custom replacements are better than the replacement 'improved' valve guides from OEM
We contacted the Ferrari Dealer and asked the Parts Dept what the replacement guides were made of, nobody knew and nobody really wanted to find out. According to this forum the replacement guides are Iron. If that is the case we would not install them. Nobody uses iron/steel guides on late model cars. So, instead of gambling on a $2K worth of Ferrari mystery guides, we opted to have them made for us out of Manganese Bronze. That is the material that everybody is switching to for guides. The price was the same, but we knew they were the best, only downside was waiting another 2 weeks. Mike
other 456M valve guide discussions: http://ferrarichat.com/forum/showthread.php?p=138134603#post138134603 and look here for another update link : http://ferrarichat.com/forum/showthread.php?t=131243&highlight=456+valve+guide another top end: http://ferrarichat.com/forum/showthread.php?t=134185&highlight=456+valve+guide Not much good, but a discussion anyway: http://ferrarichat.com/forum/showthread.php?t=139444&highlight=456+valve+guide http://ferrarichat.com/forum/showthread.php?t=136728&highlight=456+valve+guide
Mike, they probably meant Cast Iron, not just iron. I would agree with you that Manganese Bronze is a better choice.
The new guides are sintered iron and it is a very good quality material for that use. Iron in various forms has been used for valve guides quite successfully in more cars than any other material and is still being used with very good results in a good many cars. The Ferrari guides however are quite expensive, and not terribly consistant dimensionally. Several of the bronze alloys are a very good choice. The 456's do have occasional valve guide problems. I have a client whose car while not having a great deal of mileage was in use almost every day and it has bad guides. They have not been replaced yet. He has replaced it with a 430 for a daily driver. We also did one recently, used intermittantly with about 20k miles and it used more oil than gas... No real pattern to valve guide problems to them yet, just like the 355. The electronic torque wrench that Ferrari shoved down our throats was $10,000. Real POS. I have the Snap On and it is a very good piece of equipment.
