Are these case savers/timeserts?

[haasad]

Timeserts and Case savers are essentially very similar in function. If there is any doubt about capability for DIY have them done professionally. £280 seems a good price its not actually very hard to do with the right kit.
To drill exhaust studs make a drill jig from an old exhaust flange by welding a tube over one of the stud holes get the tube vertical. Bolt this flange / guide into position and use it to keep a drill centered on the damaged stud . Clearly the tube bore needs to be smaller than the stud diameter (8mm) . In an ideal world you would aim for a 6.2 mm (8mm tapping) drill on the stud center to allow you to re-tap or pick out the threaded remains. Another simpler option if enough broken stud is left is to mig a nut onto the stud and use that to undo it with heat and penetrant.
Same caveat applies if you don't have the neccesary tools and skills .

[fetuhoe]

There is a huge amount of debate on the subject of Timeserts or case savers and there are some detailed differences.

The story is that magnesium cases are prone to suffering from studs pulling out and stripping threads.

The reality is that the worst affected engines were the 2.7 litre motors using Nikasil barrels which expand more than the cast iron Biral and also for a while was fitted with thermal reactors.

These reactors run at an external temperature approaching 400 degC and do heat the engine case in the region of the lower head studs.

I believe that the issue is that over time die cast magnesium will suffer from Stress Relaxation and lose strength. As in all creep dominated mechanisms the impact will be dependent on time, temperature and stress.

These engines are now well past their basic design life and if they have accrued large mileages and are then rebuilt problems can occur.

In the VW Beetle world it was common practice to fit a low cost 'case saver' which is simply a coarse threaded insert used to replace a stripped thread.

They are not normally very well made and commonly have a much greater wall thickness than a timesert so is a once and for all fix. I would also question the class of thread fit in a case saver depending on the source. If the thread fit is poor the stud will not align vertically until after the thread locker has set and this can introduce a small bending moment into the stud.

The increased wall thickness also reduces the remaining section between the stud and the spigot in the engine case and as this is already marginal on a 2.7 I am not confident it is a good idea and cracking in the spigot is known to occur.

The Timeserts supplied by Wurth are manufactured to very high standards and are consistent and commonly used in Aerospace applications.

The other issue with case savers is that they don't have a locking feature and are commonly positioned using Loctite.

Timeserts are solid inserts and use the same STI tap as a helicoil. They locate positively in the axial plane unlike a helicoil and also have a locking feature.

If there is ever a problem then they can be removed and replaced by a 'Big Sert' so you do have a second try if there are issues.

It is better to fit timeserts using a vertical miller to ensure that the inserts are perpendicular to the case.

I have seen cases where either timeserts or case savers have been fitted to holes made using a pistol drill and when inserted the studs look like a porcupine.

There have been issues with timeserts when the wrong length of insert has been selected and in these circumstances they can pull out but there is a calculator on the Timesert website which should allow the correct selection.

The case saver does have a larger and coarser thread so is less likely to pull out but the other issues are equally as important.

In general I am not enthusiastic about case savers and prefer to use timeserts as I believe if correctly selected and used they are a better solution.

[Gary71]

Thanks for the detail, certainly not something I will be attempting myself.

So... if you were rebuilding a 3/4R Mag cased T engine back to T spec (with iron barrels) and all the head studs looked good and hadn't pulled would you leave them alone?

[fetuhoe]

I think it depends on the studs you are planning to use.

I did some calculations a few years ago during a debate about Dilavar Studs and other aftermarket studs and the results were interesting.

I estimate that the preload in a head stud is around 5000 lbs (the debate was on Pelican hence the units) when torqued to 24ftlbs.

With a Nikasil cylinder and a standard stud the increase in pull out force due to expansion for a Delta T of 120deg C is about 1500 lbs. (This would fall to around 700lbs for a cast iron cylinder)

Using a Dilavar Stud would reduce the increase in force from 1500lbs to around 400lbs (185 for Cast Iron Barrels)

Some of the aftermarket high priced studs have an increased cross-section in the shank - one brand uses 9.6mm diameter as opposed to the 7.6mm on the standard stud and this is why I started the debate.

A stud with this cross section would increase the pull out force from 1500lbs of the standard steel stud to 4300lbs and I think the impact of this on a magnesium case without a Timesert or case saver could be very damaging and not a risk I would take. The Aluminium case does, however, seem to survive.

I think a standard early T case with Steel Studs and cast iron cylinders will be OK as these are not hot engines and the expansion is relatively well controlled compared to Nikasil.

If, however, you use aftermarket studs with a large diameter shank I would install a Timesert. I would most likely use a standard steel stud.

I have noticed recently on EBay USA that there are some studs being offered at $15 each made from a material described as A286 and having the same expansion as Dilavar but a fraction of the price. Unlike Dilavar they are supposed to be Magnetic.

A286 is basically an Austenitic Precipitation Hardening Stainless Steel which is used in the hot section of fighter aircraft engines.

It is very well known, its properties are well understood and as it is normally sold to an AMS Specification it is eye-wateringly expensive.

It does have similar expansion characteristics to Dilavar and should be completely Non-Magnetic

There isn't any method that I am aware of that can produce an Iron based alloy with 25% Nickel and 15% Chromium and be magnetic - just not possible.

There is another problem with A286 - in its high strength condition it is susceptible to corrosion pitting in Chloride environments and if used on salty winter roads the corrosion can result in fatigue failures as we see commonly in early Dilavar studs.

A286 is used in marine environments but NACE recommend that only low/medium strength tempers are used in the presence of chlorides.

A 'fag packet' calculation would suggest that at this strength level the stud would be very close to its yield strength and I would not use them.

I have asked the manufacturer to clarify the magnetic/Non-Magnetic issue but as expected I have not received any reply.

Until we can understand what they are they may be very good value but I will need some convincing.

[Gary71]

Thanks. So leave the original steel studs alone then

[MikeS911]

Hi All.
I know this is not a new thread, but can anyone answer if it is visibly possible to identify a Timesert from a Casesaver already installed in a crank case? I understand and agree that the Timesert is the better solution but once installed is it possible to see a difference. With the Helicoil it is easy.
Thanks Mike

[911hillclimber]

Off google just, timesert is the bottom one so the shoulder is clear.

[fetuhoe]

I am sorry to say but I don't think that's a Timesert.

I think it is a Spark Plug Thread Repair insert.

Timeserts are a little different and have a much smaller flange.

[911hillclimber]

Stand corrected, but the difference in the two are much the same iirc, timesert is more a tube with outside and inside threads, helicoil is a special section wire and thought to be weaker of the two.

Iirc they are detailed in the Anderson tuning book for head stud repairs.

[fetuhoe]

These are VW type case savers commonly used in air cooled Beetle engines.

They tend to be a larger diameter than a Timesert and don't have any locking features so are normally installed with a high strength thread locker.

In general they are a 'last resort' solution and if there are subsequent problems the case will have to be scrapped.

Timeserts generally have a thinner wall, they have a locking feature so they are not normally installed with a thread locker.

If there are subsequent issues it is often possible to replace them with either a Big Sert or a Case Saver.

I would tend to install studs into Timeserts or case savers using a lower strength 'Blue' Loctite rather than Red or Green.