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Quote:
Originally Posted by chris_seven View Post
I can't find a description of how these parts work.

There is a 997 part described as a Garlock Ring and another hint at what sounds like an MLS system.

I am very interested to learn more
Basic description

Sealing System – performancedevelopments.com
Old 08-12-2017, 12:42 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #21 (permalink)
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Regardless of what sealing system you use; proper assembly procedures must be performed.

Head stud stretch and any collapsing of the cylinder head must be known and under control otherwise any sealing system is pointless. The integrity of the threaded bores in the engine case must be of the highest quality and any cleaning or repair work must be performed with care. This area is the foundation of holding the heads down to the cylinders. Any sort of thread reconditioning must be done with a straightening tap and never with a cutting tap.

Typically, the assembly procedure requires a torque on each head nut but if the stretch of whatever head stud used is unknown, the torque value is meaningless. Friction must be considered here and anything that will lower the friction must be performed. When buying any aftermarket stud, the supplier should be supplying the stretch value that stud will achieve to put the stud into its designed “tensile stress”.

The head stud must be put into “tensile stress” so under running conditions when the cylinder pressure tries to push the head and cylinder apart, the tensile stretch or elongation added to the stud must resist any lift. This puts the head and cylinder under compression with each other.

Air-cooled heads often soften over time and many are never checked when they are repaired. This is a quick and important test before any repair is started. Check that the platforms where the head washers sit are not collapsed inwards as this will affect the clamping forces applied to the head studs. We want all the force applied to go into the stud and not be lost in any movement within the case threads, the head collapsing under the washer or absorbed by friction.

If you assemble the heads and only use a torque value to tighten the head nuts, you are not compensating for any of these issues. If you do not want to measure the stretch, then an angle method should be used as it eliminates any friction.

Without any stretch value, you should do a dry test assembly and measure the stretch of the stud at various angles. In our tests with different studs, we have found that the typical stretch was between 0.006” – 0.008” to achieve successful clamping. Make sure in any testing the stud returns to its relaxed length. Stretch can be measured in thousands of an inch or hundreds of a millimeter so measuring can be achieved with simple measuring tools. The same tool (dial indicator) you use to do the cam timing (lift) can be used here. This method can give you an angle to use in assembly that will obtain an average desired stretch falling within the elongation desired. However, the best method is to measure each stud.

Making sure you have equal stretch on each stud will achieve an equal compression load on each corner of each head. This eliminates the probability of any leakage between the head and cylinder from poor assembly. If you continue to have any leakage issues, you will know it’s not from how you are assembling the engine. Now you can consider sealing systems and other solutions.
We recently did our sealing system for a customer and asked for the head stud used to be sent with the heads, so we could test the stretch of the stud for him and give him a stretch and angle value to use in the reassembly.

I tell customers that all this fancy work and fancy parts are worthless unless good assembly procedures are upheld. It is typically the basic’s that let us down.

“Nothing will humble a man more than an engine or an angry wife”.
Old 08-12-2017, 02:41 PM
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We had a similar issue with Coventry Climax Wet liner engines and using Coopers Rings. The precision of the machining work was essential to ensure sealing and in our case to avoid water leaks.

Have you measured the change in hardness of the heads? I would be interested to know how much change occurs as this would allow an estimate of the stress relaxation to made.

Do you measure the stretch of the head stud with an an Ultrasonic Gauge or have you made a mechanical fixture?

We have made a fixture to measure preload on an individual stud with a load cell and we have used this to determine a suitable 'torque + angle' relationship for preload but I am not sure about how much preload is needed to prevent the head from lifting with a Turbo engine.


Sadly this is a background task for us so it is not something we work on every day.

If you are using standard steel studs then a stretch of 0.008" would result in a preload of about 3700lbs per stud which is about what could be expected when using the standard 32Nm.

This would mean that at a peak cylinder pressure of around 1400psi on a 3.0 litre engine the head would tend lift clear.

I am not sure how much the preload needs to be relaxed before the head would shuffle but I would like to see preloads of about 6000lbs per stud which should allow a peak cylinder pressure of about 2200psi before lift occurs.

The later version of the workshop manual suggests a torque of 15Nm and an angle of 90 degrees.

This would suggest a 'stretch' of around 0.015".

When we make measurements using 15Nm and 90 degrees we see preload values of around 7000lbs.

This is significantly more preload than tightening to 32NNm which does produce a value of around 4000lbs an


Have you considered making studs with an increased thread size on the case end? This could then allow a larger shank diameter and increase the preload for a given stretch.

It would avoid the need to use a case saver or timesert and would remove all of the material that has been highly stressed and suffered from the effects of stress relaxation in the area of the case thread.

Last edited by chris_seven; 08-13-2017 at 02:58 AM..
Old 08-13-2017, 02:25 AM
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leakage

Just do what the factory did when they had leaks.Use electron I-Beam welding of the cylinder to the head.The later factory 3.6 head gasket works very well up to 1,2 bar.Weld them then run 2 bar and you will have new conditions to solve.Fred
Old 08-15-2017, 04:49 PM
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System installed and close to finishing run in. I have to say the quality of these items, the quality of machining and the no bull**** view from Performance Developments on what works and what does not and why, based on their extensive race engine preparation experience was a breath of fresh air.

Fist thing, they correct a multitude of errors my previous local West Australian machine shop did such as heads not perfectly matched for deck height, over the nose pressures for springs was way out, valve seat machining was very sloppy etc etc. Also, they corrected my misguided decision to use titanium retainers (that were part of a high flow 993 turbo valve kit I bought from a vendor). The titanium retainers were badly grooved by the spring after only a few thousand miles. With a properly set up spring / seat / lock system, there is no need for these on a turbo motor running around 7krpm on the street. I used a set of 962C retainers, spring seats and springs (with the very strong steel retainers). Absolutely no issues with float or anything at 7kprm but I know they will last.

Also, some dubious twin plug machining work was corrected. Heads / cylinders machined for the copper head gasket / fire ring. The tolerances on this work are extremely fine, with the copper parts being EDM.



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1988 930: 3.5L 100mm LN slipins, LN FFA rods, Supertec studs, GT3582R with T4 1.07A/R twin scroll housing, RarlyL8 equal length divided headers, dual Tial MVS 38mm WG's, Carrera 3.2 heads with 993 big valves. 964 Cams, full bay IC, KEP st1 clutch. PE3 sequential ECU with 750cc EV14 injectors, CoP twin plugs, J&S Safegaurd, Aquamist HSF3 water inj. Wavetrac LSD.
Old 11-19-2017, 01:36 AM
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Here are some shots of how it came apart with some obvious problems at the cylinder to head interface, you can see the oil stain patterns quite clearly, with oil trapped at the cylinder to head interface......

__________________
1988 930: 3.5L 100mm LN slipins, LN FFA rods, Supertec studs, GT3582R with T4 1.07A/R twin scroll housing, RarlyL8 equal length divided headers, dual Tial MVS 38mm WG's, Carrera 3.2 heads with 993 big valves. 964 Cams, full bay IC, KEP st1 clutch. PE3 sequential ECU with 750cc EV14 injectors, CoP twin plugs, J&S Safegaurd, Aquamist HSF3 water inj. Wavetrac LSD.
Old 11-19-2017, 01:39 AM
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So far its a dry as a bone running an easy 13-15 psi just to bed the motor in and recheck AFRs / knock patterns etc. Here is some information and the motor in action on its low boost setting.

https://youtu.be/e_lKnC0Hd1w

https://youtu.be/OVpB_4am6cE

I am really loving this 930 motor.......and finally starting to appreciate where all my money has gone
__________________
1988 930: 3.5L 100mm LN slipins, LN FFA rods, Supertec studs, GT3582R with T4 1.07A/R twin scroll housing, RarlyL8 equal length divided headers, dual Tial MVS 38mm WG's, Carrera 3.2 heads with 993 big valves. 964 Cams, full bay IC, KEP st1 clutch. PE3 sequential ECU with 750cc EV14 injectors, CoP twin plugs, J&S Safegaurd, Aquamist HSF3 water inj. Wavetrac LSD.
Old 11-19-2017, 01:43 AM
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Glad things have worked out for you. You bring up a really important point about the spring retainers. Titanium retainers are bought and sold as an upgrade, but often never told is the need for regular inspection.

Spring retainers have to be tight fitting to the springs. When left loose they will wear. When tight fitting the spring will over time dig into them. All very common. Titanium hates inclusions and nic's and will fail. Most Titanium retainers built by reputable manufacturers, used in racing are coated to help against wear. We use retainers built to our design by one the worlds leading valve train manufacturers, but the parts are life'ed out after so many hours. The retainers we saw in the above heads were badly worn and would have failed at some point.

My advice is to check them regularly and if you wish to use them, know that they will need to be changed out at some point. Or change back to steel and tool steel versions are the better of the two steels.
Old 11-19-2017, 04:25 PM
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How my titanium retainers looked...

Happier knowing I have tool steel retainers now.
Old 11-19-2017, 04:47 PM
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