Cylinder leakage test

[Kirk Morgan]

Will a gas ported piston and ring package leak the same as a conventional piston and ring package?

[Henrys Toy]

Originally Posted by Kirk Morgan

Will a gas ported piston and ring package leak the same as a conventional piston and ring package?

Good morning Kirk and to all,
Are you using a leak down tester to quantify this ? A cylinder pressure transducer would probably be the best choice to be sure. What dynamics that actually happens during combustion and the resulting pressures will be much different then we can simulate with a compressed air leak down tester.
The leak down testers vary for tester to tester, the various temperatures while the test is being done and other factors will lead to variation.
If you use the same leak down tester the same way, might give you a reasonable answer, but it will still vary.
If someone on here has a better solution for testing this, I hope you will chime in here.

Respectfully,
Henry Kunz 1534 H/SA

[Lenny5160_v2]

While not an answer to the question, when I use a leak-down tester I'm mainly looking for consistent results from all cylinders.

[Ralph A Powell]

You can also listen for intake and exhaust valve leakage. When I tested at TDC then I would let the piston roll over to BDC and with a long beaker bar pull the piston toward TDC and watch tester to see if it is holding pressure.

[Kirk Morgan]

Here is some detail to my findings. This is a Nitrous engine which was chirping out of the left bank after a run. Iam not a Nitrous person but a N/A engine person. Ran the valves all was good. Ran a compression test not good. The compression was a roller coaster from 200 PSI to 50 PSI. Un adjusted all the valves and removed the rocker arms. The 50 PSI was a exhaust valve leak with 80% leakage and the 200 PSI is 20% leakage. I have a cylinder leakage tester and they way i use it i turn the pressure on one side to 100PSI and read the other gauge to see how much leakage there is. To me the 20% leakage on the 200 PSI cylinder is to much i was always trying to get in the 10% or less leakage range on engines i have built. I have never built a engine with gas ported pistons. BTW i always spin the engine over 5 revolutions when checking static compression.
Thanks

[Jeff Stout]

Exhaust valves leaking I wonder why, they run away from each other. Low valve spring pressure or broken spring.Any of the low

cylinders measurements next to each other? What did plugs look
like? Asking as I have had all these problems on nitrous plus more.

[Henrys Toy]

Originally Posted by Jeff Stout

Exhaust valves leaking I wonder why, they run away from each other. Low valve spring pressure or broken spring.Any of the low

cylinders measurements next to each other? What did plugs look
like? Asking as I have had all these problems on nitrous plus more.

Good morning Jeff, Kirk and all,
I'm not a nitrous user, but I'm thinking the EGT's might be on the extreme high end and could cause exhaust valve face and seat erosion. Exhaust valve guide wear or loose clearances could be contributing factors. Like a " stacking of clearances " and the possibility of the valve springs fatigue and pressure loss causing the exhaust valves to bounce once they are trying to seat I would think should all be taken into account.
What condition was the engine in when the customer started using N20?
If it was " seasoned / used " there may have been underlining conditions that were exasperated once the "bottle" was used. The quality of the exhaust valves themselves can also be a factor.
No definitive answer, just food for thought, I hope this helps.

Respectfully,
Henry Kunz 1534 H/SA

[Mike Pearson]

A leak down checker is just a tool. It is mostly used to diagnose an issue in the cylinders of the engine. its a comparison tool. If you have a baseline for the engine when it is performing properly then you have something to compare it to down the road if you are having issues with performance. Typically anything better than 10 percent is considered good. Leakage by the intake valve is the worst and even a small leakage past the intake valve will effect the performance of the engine. The exhaust is typically not as sensitive.

[Jeff Stout]

Originally Posted by Henrys Toy

Good morning Jeff, Kirk and all,
I'm not a nitrous user, but I'm thinking the EGT's might be on the extreme high end and could cause exhaust valve face and seat erosion. Exhaust valve guide wear or loose clearances could be contributing factors. Like a " stacking of clearances " and the possibility of the valve springs fatigue and pressure loss causing the exhaust valves to bounce once they are trying to seat I would think should all be taken into account.
What condition was the engine in when the customer started using N20?
If it was " seasoned / used " there may have been underlining conditions that were exasperated once the "bottle" was used. The quality of the exhaust valves themselves can also be a factor.
No definitive answer, just food for thought, I hope this helps.

Respectfully,
Henry Kunz 1534 H/SA

I would never read egts, they would naturally show hot. Spark plug reading is your friend. Like you said used motor and maybe had underlying issues. Nitrous always finds the weak link. Hope it's not internally.

[Jeff Stout]

Also if motor would be built for nitrous more ring gap is required and I would expect 10 or more leakage.