Dirty Little Secret - Time-Certs are no good for rebuilds...

[Wayne 962]

Well, one of the things that I've learned writing this book, is that Time-Certs are really not a good insert to use in the mag cases for the head studs holes. Here's an except from the book:

Case-Savers - Perhaps the most common upgrade/repair that you can perform on your case is the addition of case-savers. The soft magnesium material used to manufacture the early cases has a tendency to let the studs pull out of the case when the case is stressed. This is most prevalent with the cylinder head studs, although other studs in the case also have a tendency to pull out. As mentioned in Chapter One, if you have a case with pulled head studs, it basically requires a full rebuild. Aluminum cases are strong enough that they don’t suffer from the same head-stud pullout problem. However, the magnesium cases manufactured from 1969 through 1977 will encounter these problems at one time or another. Particularly as the case ages and is exposed to an increased quantity of temperature cycles, the magnesium will weaken and the studs will pull.

The most widely accepted solution for repairing pulled studs, is to insert what are known as Time-Certs into the case. These are threaded inserts that are larger than the diameter of the original studs, and are manufactured out of steel. The hole in the case is first tapped with a tap, and the insert is installed into the case using a special insert tool. The tool helps to expand and press the Time-Cert into the case so that it will not back out if you try to remove a stud from a Time-Certed hole in the case.

However, there is an inherent problem using Time-Certs with a magnesium case. The method in which the Time-Cert is actually installed can damage and warp the case. Since the Time-Cert creates an interference fit, it actually pushes out into the case to maintain its ‘grip.’ Since the magnesium material is weak, there is a tendency to deform the material around the case. This actually makes the case weaker, and increasingly prone to having the studs pull out. As shown in Figure X, you can see that a properly installed Time-Cert has been pulled out of the case.

Instead of using Time-Certs to repair your case, I recommend that you use what are known as case-savers. Competition Engineering uses these steel inserts that are specially manufactured for installation into 911 engine cases. The inserts are not an interference fit, and install into the case without damaging the material. They have a larger outer diameter than the Time-Certs, so they can even be installed on a case that has had Time-Certs pull out of the case.

The case-savers have a very coarse, thread pitch on their outer threads. As most engineering books will tell you, a fine thread will give you greater strength than a coarse thread. However, this is not the case with weaker materials like magnesium. The coarser threads actually maintain a stronger grip in the magnesium because there is more material to grab onto. A fine threaded case-saver would pull out very easily, whereas the coarse thread ones don’t. The opposite is true with aluminum, because the material is much stronger.

Every cylinder head stud should have the case-savers installed, along with the long stud that is close to the intermediate shaft on the inside of the case. In addition, it’s sometimes wise to have the studs that hold the engine to the transmission reinforced as well. If you really want to treat your case right, you can have all the studs removed, all of the holes replaced with helicoil inserts, and have brand new studs installed. It’s very difficult to pull a case-saver out of the magnesium – with the added strength, you should be able to put together a high-compression high-performance engine.

At the same time that you are checking all of the threads on your case, make sure that the cam oil line threads are checked as well. These sometimes have a habit of becoming galled or cross-threaded, and may need to have an insert or case-saver installed in their bore.

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The folks in the know seem to really be against using Time-certs. People like them because they are cheap and easy (good things to like), but they don't do the job. Use case-savers, and have them professionally installed on a Bridgeport or similar milling machine...

-Wayne

[Wayne 962]

P.S. Every week or so, I will let the carrot out of the bag a little more on the engine book. I've got a lot of interesting stuff that I'm really eager to share!!!



-Wayne

[J P Stein]

Ayup, got em'.

[Wayne 962]

Whoops, let me clarify this statement:

"If you really want to treat your case right, you can have all the small outer case studs removed, all of the holes replaced with helicoil inserts, and have brand new studs installed."

The case-savers are generally too big for the smaller outer case studs - helicoils work well there...

-Wayne

[Keith S]

Hay wayne, slightly OT but remember the signed copy of your '101 Projects' book you gave me at the toy show in February? Some b*****d (a quaint olde english term) stole it at the airport! Any chance of another (pleeeeeeaaaaaasssse?)?

[Bob Goding]

Wayne---what have you done !!!!!--------------I have my 7R case halves all cleaned up and ready for the timeserts !! I was concerned about pushing out the side of the Cyl.hole with the inserts so I have machined up a steel disc from 3/4 plate .Its a snug fit in the case cylinder hole and should hold the pushout and save having to rebore the cylinder holes afterwards. it should tap out after the inserts are in. I am just trying to arrange access to a suitable mill, now I dont know what to do. Looked up the Competition Engineering site but seems they want to do the job.
Are Pelican supplying these casesavers and the tooling?---
Since I have all the timecerts and tools, etc, I will probably go ahead and use these. Everything I ever read about these mag cases said that timeserts were the thing but when you actually see a case , the studs sure dont have much edge distance. I am amazed that even bigger cylinders can be installed for 2.8 or larger

[Wayne 962]

Bob, unless you have a milling machine in your basement, I don't recommend that you do this task yourself. There are somethings that you can do at home, and others that you really can't unless you have the proper experience and tooling.

Put it this way - I have about 1000 hours of machine shop experience (from school / summer jobs), and this is definitely not a task I would attempt without my trusty Bridgeport. Even if I had a Bridgeport, I would double and triple check the alignment of the table. I remember those things used to get off when someone else used them.

Machining is tricky - this is something that is better left to a professional.

As for your cylinder head insert, it might help, but I doubt it. In all likelihood, the tool will get stuck in there when you install the inserts. When you pull the tool out, you will then have an out-of-round cylinder spigot. There is no way to get around reboring the cylinder spigots - it's just something that needs to be done in order to do the job properly.

Do the right thing...

-Wayne

[Jim Sims]

For internal (female) threads of a given size there is about a 3% stripping area advantage of coarse threads over fine threads however I believe the "stronger grip" of the case-savers is due to the fact they have a larger outer diameter and hence are engaging more case material in shear. The coarse thread explanation is at odds with fastener compliance theory and experience: a big coarse stiff steel thread will pass most of the joint load to the first matching thread in the magnesium and can lead to a failure of that magnesium thread. When the first thread fails the load is passed to the second thread and it fails and so on. I strongly suspect that if fine threads were used at the larger diameter of the case-savers the joint would be stronger still as long as the thread size doesn't approach the magnesium grain structure size. Were there any pull tests done to compare the stength of the case-savers versus Time-Certs? Have the case-savers been in service long enough to demonstrate their long term superiority or possible flaws? Cheers, Jim

[pwd72s]

Wayne, when's the book coming out? You have a sale here...

[island911]

I thought everyone knew.
Over the past 40+ years, rebuilders of VW and aircraft engines have been preferentially using case-savers.

Aside: I believe the courser threads perform better in the cast magnesium by minimizing the length of the thread (stress riser).
Also, the idea of pulling on just the first few threads first works fine when both the stud and hole are of similar material or have the same strain-rate and strain to failure.
If I were writing a book with this, I would simply recommended case-savers over time-certs as a proven solution; and leave the thread failure mechanism theories out of it.

[J P Stein]

The case savers are not (apparenty) as easy to install as time certs.
On a 2.7L, they come mighty close to eliminating the spigot land.
Eyeballing the installation done by a local machine shop, showed approx .100 land on 23 places......unfortumately, there are 24 places. The 24th had broken out about .04 of the land on the case saver side of the land.
With the spigots decked and squared, this left approx .06 width
for a sealing surface at that point........that'll get the sweat rolling down the crack of ones..........

I put it together and have not had any signs of leakage.....Real close to having a scrap case, tho.

[Wayne 962]

Using the fine thread in magnesium -

A good comparison would be like using a machine screw in wood. Fine threads theoretically give a stronger joint. However, that doesn't work for all material properties. You use a very coarse screw in wood to grab the edges of the material. If you used a fine screw, the material wouldn't grip.

It's not exactly the same, but it's similar...

-Wayne

[boyo]

Hmm, that other guy's book still says Timecerts - guess it needs to be revised now?

Actually I think Bruce's book has some good generalities, but Wayne if the rest of your book is like this, sign me up for a copy!

So where can I pick up a milling machine cheap? Any recommendations on how to become an expert machinist? I'm trying to plan my next career, for when I retire 16 years from now. I've got time, just need the skills...

-Boyo

[Wayne 962]

Apprentice. Good choice, as computers really suck...

-Wayne

[TimT]

timeserts work just fine on magnesium cases, I know....... my 2.2 race motor ( built from a '69) regularly sees 7800+ rpm and the "timeserts-steel stud-raceware nut" combo has been flawless for going on 4 years now.

The whole idea behind timeserts, case savers ,or whatever ( except heli-coils) is to distribute loads to a greater area, lessening the overall stress on the receiving (weaker) metal.

The tool used to install the timesert kinda swages the insert into the case, no catastrophic changes in dimensions are seen.

Also it would be nice to have a bridgeport to install them, the timesert kit comes with a jig to plumb your drill and tap. I did a DIY install when I built my engine nice and easy.

You will really need to clarify the differences between the 3 popular tread repair/reinforcing systems:

i.e. timeserts, case savers, heli-coils.....

I wouldnt think twice about putting timeserts into a magnesium case

[Jamesking]

Originally posted by TimT
timeserts work just fine on magnesium cases, I know....... my 2.2 race motor ( built from a '69) regularly sees 7800+ rpm and the "timeserts-steel stud-raceware nut" combo has been flawless for going on 4 years now.

The whole idea behind timeserts, case savers ,or whatever ( except heli-coils) is to distribute loads to a greater area, lessening the overall stress on the receiving (weaker) metal.

The tool used to install the timesert kinda swages the insert into the case, no catastrophic changes in dimensions are seen.

Also it would be nice to have a bridgeport to install them, the timesert kit comes with a jig to plumb your drill and tap. I did a DIY install when I built my engine nice and easy.

You will really need to clarify the differences between the 3 popular tread repair/reinforcing systems:

i.e. timeserts, case savers, heli-coils.....

I wouldnt think twice about putting timeserts into a magnesium case

Agreed:
One thing that everyone should know it that the method used to install time-sert inserts is practiced every day in ALL cases manufactured. This is called roll threading. It will not "warp/deform" a case in anyway, as Wayne states.
If it did then the automotive world would not be using this method to create the thread in the first place.
The amount of metal the driver tool is cold rolling is insignificant.
Yes all threads in the automotive world are roll formed there are no chips and the thread strength is much greater than a traditionally cut thead.
I have used time-serts and the installation went smooth and easy.

Just my 2 cents.

Oh and btw Wayne it is called time-sert not time-cert.
If i was calling helicoil , heliFoil i would expect people to think i may not quite know what i'm talking about...

[IROC]

I'm actually unfamiliar with what a "Time-sert" actually is, but we have to install threads in relatively soft materials (mostly aluminum) all the time in my industry (aerospace) and we almost exclusively use threaded inserts (Carr-Lane calls them "Keenserts"). The mil spec for the most common ones (that I use) are MS51830.

Helicoils are generally bad because the strength of the joint ends up being a function of the skill of the guy installing the Helicoil. Threaded inserts are much better.

Also, like Jamesking mentions, cut threads stink. Very large hoops have to jumped through in my industry to use something with cut threads.

Just some miscellaneous rambling.

Mike

[RickM]

Quote: "As most engineering books will tell you, a fine thread will give you greater strength than a coarse thread. However, this is not the case with weaker materials like magnesium. The coarser threads actually maintain a stronger grip in the magnesium because there is more material to grab onto. A fine threaded case-saver would pull out very easily, whereas the coarse thread ones don’t. The opposite is true with aluminum, because the material is much stronger."

I'm not an engineer but would it be more accurate to say that the more contact area between the case and the threads the stronger the grip? It seems to me that a coarser thread is typically a deeper thread. So the depth of bite affords greater securing power....just in a different way from fine (more) threads.

[1fastredsc]

I believe that depends on how fine the threads are. The more threads there are then the more contact there is given more circumferential distance of thread now present (the more threads the more contact there is wrapping around the bolt/stud). But if there is less significantly less area to contact per circumference of thread with the finer thread than maybe there's less contact (for every thread that wrapps around the bolt/stud is much smaller, than the increase in threads may not matter).
To IROC:
A time sert is a threaded insert. The only thing that makes it special is that the bottom of the insert is rolled inward. This way when using there tool to thread in the insert, once the insert is flush with the chamfer that is cut into the new thread you tapped, the insert stops threading in and the tool pushes through the rolled bottom making it expand and lock into place. This makes it insanely hard to take the damn thing out if it's in a strong metal.

[Grady Clay]

Time-Sert info:
"
"
None of these pages have copyright notice but I assume (C) Time-Sert

I'll scan the Heli-Coil stuff tomorrow. and post links.

Can someone post "Case Saver" technical info? The guys at CE are great.

Best,
Grady