Why is the CE ring facing the wrong way?

[VFR750]

Why did Porsche specify the CE cylinder head seal ring with the open side facing outward?

Since the high pressure is inside, trying to get out, the proper direction should have the open end facing inward, not outward.

If you don't believe me, go to Parker-Hanifin website. They make them, and they say the open portion faces the high pressure side for the best sealing.

The only thing may be the fear of broken spring bits going inward. Based on my limited experience the broken spring bits get pushed outward.

Anyone ever spec out CE rings facing inward, for better sealing?

[chris_seven]

I am not sure that I would agree that they face the wrong way but I can understand the argument.

This type of seal is predominantly used for 'static' applications where there is a fairly continuous internal pressure and the ring would then be 'energised' by the internal pressure being applied through the ring and generating a force on the mating faces.

This could mean that the energising spring could be removed making the seal cost even lower.

If you use a sealing ring which is energised using an gas pressure which fluctuates dynamically it is quite likely that the faces of the seal will 'fret' against the mating faces which could cause real problems.

If you calculate the change in force that occurs at peak cylinder pressure and the cyclic nature of the pressure change you would have an ideal wear regime at the interfaces should you change the seal orientation.

By using the sealing ring in, what I agree seems to be, the wrong direction and using a spring to energise the seal then you maintain a relatively static force on the sealing race which reduces the tendency for fretting.

Fretting still occurs but this is likely to be due to general vibration rather than dynamic pressure fluctuation.

The CE Ring used by Porsche is a relatively cheap solution and if you are worried that the seal is not good enough it could be replaced by a Wills Ring which is a circular ring that is internally pressurised with Nitrogen and does provide a much greater level of sealing force. They are made in a range of materials including Inconel and do maintain much higher sealing forces than spring energised solutions.

[racing97]

I used some HelioFlex gas filled rings in some 102 mm barrels years ago and the wide bolt spacing and lack of material on the sides of the 3.8 993 based cylinder heads did not have the ability to preload the ring at all. They were from the Nissan GTP projects of the 80's which had a more robust head and were able to preload the ring and were quite sucessful in running tremendous boost levels.
The 3.8 heads were hard to seal no matter what you would do but the engines kept running and eventually they came up with the 993TT and a completely satisfactory design.

regards

[VFR750]

What got me thinking about this was looking at a Parker catlouge. They list similar sized CE rings and I was a litte surprised at the force needed to crush them to their seating height.

I'm not entirely sure the four head studs can do it at 24ft-lbs torque. Which means the heads might not be fully seated to the cylinders during new assembly.

Then I looked at thier recommended usage and they recognize cylinder fire rings as one use. They suggest the c should be facing inward.

Since they make them for practically everyone in the world involved in high pressure sealing, I kind of think maybe there is a better CE ring.

Just wondering out loud....

[racing97]

What size are you looking for?

[VFR750]

I'm not looking to buy; I have a set for my 95mm cylinders.

Just wondering why they are what they are.

[racing97]

I wasn't looking to sell but to give but the diamentions are for 102's anyway, I never could use them as they would not not give me the crush and kept the parts apart.

regards

[chris_seven]

The figures in the Parker guide may not be entirely relevant as they seem to be for a much higher duty. I worried about this issue about 5 years ago and spent some time looking at the detail.

The clamping force generated by four 911 head studs torqued to 24 lbsft should be around 16 000 lbs and for a 95mm dia ring this translates to a seating force of about 1300 lbs per inch of circumference.

With seating forces at this level I would expect to see a 3/32" spring energised ring being able to seal at least 30 000psi, if not more.

I would be surprised if an IC engine ever produces peak cylinder pressures of more than 3000pis and this would be a Turbo charged unit suffering from some detonation.

High performance NA engines are unlikely to be much more than 1500psi.

I believe that the rings used by Porsche may be manufactured by Elring and without measuring them in detail it is hard to say how much crush they need but in general providing the mating faces are in good shape they seem to work well.

The mating surfaces need to meet the required spec in terms of RA and flatness and the depth needs to be correct but this is easy to check.

The only issues I have seen have been as a result of head stud problems causing a loss of preload and the resulting hot gas leakage burnt the rings.

Effectively the sealing force maximises at about the elastic limit of the C ring and this is why a gas pressurised Will ring seal to a higher level.

The down size is that they are more costly and need more clamping so the groove design may need to change.


The RSR and 3.2 eliminated this ring completely and run happily on an aluminium/aluminium joint.

I suppose the ultimate solution would be to follow Porsche's lead and EB weld the head to the cylinder

I still don't think fitting the ring with the open face seeing cylinder pressure will provide any substantial benefit for this application and the resulting opening will be a trap for collecting carbon based debris that could ultimately cause problems.