TLDR:
Observation is that the Athena/SCE Vulcan (think SCE Vulcan is equivalent in other markets) Cut ring gasket on my 1.8 VVT BP engine presents consistent increased valve leakage with clamping torque. Potentially the head is deforming around the hard stainless fire rings affecting the outer cylinder’s valve sealing the worst.
Valve leakage on outer cylinders increased c. 13-14% at 80Nm head clamping torque from initial valve leakage of 2% on a cold engine.
On a warm engine this valve leakage issue is further increased up to c.29% increased valve leakage on the worst cylinder.
No issue was observed with the same head using a standard Mazda MLS head gasket in back to back tests. The Mazda MLS gasket was tested last.
This is a test sample of one. Potentially may help someone chasing a high valve leakage issue that is not obvious. I know of a record breaking tuner in the VW scene which had the same observations with a cut ring gasket.
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The horribly long version:
Brief history: built my engine 2 seasons ago. Initial build had high valve leakage on initial build in the outer cylinders with cylinder Nr4 the worst. Engine runs Apex studs and nuts and Athena/vulcan cut ring head gasket.
Ran it for the first season as the car still ran well at c.370hp fly/ 315whp.
Removed head end of first season and sent for refresh with focus requested on good valve sealing.
On rebuilding the engine this spring with a fresh Athena cut ring gasket the engine still had high valve leakage on outer cylinders. C.40% on cylinder 4.
I ran it again for the summer season at c.370hp again. No issues operational all summer.
I’ve removed the cylinder head recently and did a ton of tests on it before I planned to send it off to investigate the valve leakage.
1st test: I sealed the combustion chambers with a plastic plate and neoprene gasket to test valve leakage only without the bottom end having an influence. Leakage was c.2-3% on each cylinder.
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I then fitted the cylinder head back onto bottom end in car with Athena cut ring gasket and apex head studs and nuts:
Athena cut ring gasket torqued at 30Nm:
Cylinder 1: TDC 15% leakage sounds like bottom end.
Cyl 4: TDC 14% majority of leakage sound from bottom end.
Cyl 2 TDC 8%
Cyl 3 TDC 7%
Cyl 1 TDC 15%
Cyl 3: BDC 8%
Cyl 2: BDC 7%
Cyl 1: BDC 15%
Cyl 4: BDC 14%
Increase head clamp to 50Nm:
Cyl 4 TDC: 15%. Nr 8 inlet leakage loud, Nr 7 inlet low, Nr 8 exhaust loud, Nr7 low. Bottom end.
Cyl 1 TDC: 16%. Nr 2 exh valve, Nr 1 inlet valve, bottom end.
Cyl 3 BDC: 10%
Cyl 2 BDC: 7%
Cyl 4 BDC: 13%
Cyl 1 BDC: 17%
Increase head clamp to 70Nm
Cyl 4 TDC: 21% . in8 loud, in7 medium, ex8 loud, ex7 medium. Bottom end.
Cyl 1 TDC: 20%. inlet 1 loud, ex2 loud, ex1 noise. Bottom end.
Cyl 3 BDC: 11%
Cyl 2 BDC: 8 %
Increase head clamp torque to 80nm:
Cyl 4 TDC: 25% In8 loud, In7 medium, Ex8 loud, ex7 medium, bottom end not increased.
Cyl 1 TDC: 25% In1 loud, ex2 loud, ex1 medium. Bottom end not increased.
Cyl 3 BDC: 13% In6 loud, in 5 medium, ex5 low, bottom end low.
Cyl2 BDC: 10% In 4 medium, bottom end not increased.
Increase head clamp torque to 90nm:
Cyl 4 TDC: 30%
Cyl 1 TDC: 27%
Cyl3 BDC 16%
Cyl 2 BDC 9%
I then loosened the torque off with tester still connected. Cylinder 4 leakage returned back down to 10-12% as torque loosened off.
Loosened off readings:
Cyl 4 11% little to zero notable noise from the valves.
Cyl 1 14%
Cyl 3 14%
Cyl 2 10%
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I then tried Athena cut ring gasket and std head bolts at 30Nm, 60Nm, 80nm:
30Nm:
Cyl3 TDC 13% in7 low, bottom end.
2: tdc 8%. Ex3 v low. Bottom end
4 TDC 15% In8 medium, Ex7 v low. Bottom end
1: TDC 16% In1 med, ex2 med, bottom end.
60Nm
Cyl1 TDC 20%
Cyl4 TDC 17%
80Nm
4: TDC 20% in8 hi, in7 med, ex7 low, ex8 high. Bottom end
2: TDC 25% In1 hi, ex1 med, ex2 high. Bottom end.
3: 14%
2: 11%
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I then removed the head and changed the gasket to a standard Mazda MLS on std head bolts at 30, 60, 80Nm:
30Nm:
4: TDC 9%. In8 low, bottom end.
1: TDC 14% Ex2 med, bottom end
3: BDC 12% In6 med, bottom end.
2: BDC 8 % Ex 3 tiny amount. Bottom end
60Nm
3: 16% In6 med to hi, bottom end.
2: 8% ex3 low. Bottom end.
1: 14% ex2 med. Bottom end
4: 12% In8 med, ex7 low, bottom end
80Nm
4: 13% In8med, ex2 low to med. Bottom end.
1: 14%
2: 8%
3: 15%
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I then changed the std head bolts out to the Apex studs and nuts on the std Mazda MLS gasket:
30Nm
Cyl 4: 12%
60Nm
Cyl 4: 13%
80Nm
Cyl 4: 14%. In8 med, ex7 med, bottom end
Cyl 1: 14%. Ex 2 med, bottom end
Cyl 3: 15%. In6 med, bottom end
Cyl 2: 8%. bottom end only.
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Then to double check the bottom end I fitted a cylinder head with RTV sealed valves and the Mazda MLS gasket and head bolts. This isolated the bottom end leakage for testing:
Cyl 1 TDC 13%
Cyl 4 TDC 11%
Cyl 1 BDC 12%
Cyl 2 BDC 6%
Cyl 3 BDC 13%
Cyl 4 BDC 11%
I then calculated the valve only leakage on the different gaskets from my previous results by removing the bottom end leakage:
Cut ring gasket with Apex Studs at 80Nm:
1: 13% valve leakage.
2: 4%
3: 3%
4: 14%
Standard Mazda MLS with Apex studs at 80Nm:
1: 2%
2: 2%
3: 2%
4: 3%
Observation is that the Athena Cut ring gasket in this configuration appears to cause increased valve leakage results. Potentially the head deforming around the hard stainless rings affecting the outer cylinders worst.
No issue observed on the standard Mazda MLS head gasket.
No issue observed on the head at resurfacing earlier this year - it was flat as a pancake and required minimal decking to remove the previous seasons indents from the first cut ring gasket.
I've to check valve sealing margin width and position on the valve seat to ensure it is best practice.

 

Damn that's a really interesting post. I use a cut ring hg same as that one since I think it was 2021 I've had that cut ring hg on my car. Admittedly I have not checked for valve leakage but my car runs great and have had zero issues over the last 5 years. Are you going back to the MLS to resolve this issue on your car? I wonder if I'm getting any extra valve leakage on mine.... Honestly I'm not even gonna check bc I don't want to know bc it runs great lol

 

My car also ran great both seasons with this valve leakage issue so I'd say don't look just in case!

I've not decided on next approach yet. This could be related to my setup only, the condition of my head, my valve job, valve seats blah blah etc etc.

Thought it worth publishing so people can consider should they end up down a rabbit hole like me, with me chasing valve leakage and thinking I simply have a compromised valve job. I'll be checking the valve job closer on full disassembly to ensure it presents as best practice as a final check. Head flatness will be checked again when having the fire ring indents removed. The deck presented flat at the start of the year and has presented no symptoms of being porous etc.