Cylinder leakage test

[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

[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.

[Terry Drinkwater]

I was fortunate to travel with Johnny Pilcher and his family to a lot of Pro Mod races, including ADRL and many local events. There was a lot of teardown in between rounds at the larger events due to excessive cylinder leakage. In all of our mid-race repairs, the problem seemed to be detonation and/or excessive cylinder temps, which would lock up the top ring.

[Adger Smith]

As with most instrumentation the end user is usually looking for a specific number rather than using the instrument as a diagnostic tool.
I have always used a leakdown to diagnose conditions. As said earlier Valve leakage, ring leakage and even head gasket condition.
All engines are not the same due to various clearance diffenences in cylinder wall and ring lands and end gaps for the specific aplication.
I remember when EGT gauges became the vogue.
I had customers telling me that EGT "Had to Be" XXXX number because the instructions sais so.
Put the engine on our dyno and tune it and the number didn't match what they said. Do a re tune to try to achieve their numbers and the power was way off...
I always leaked a fresh engine as I built it.. then re leak after a short run on the Dyno...
For the question about gas ports. I have never done a back to back, but it would seem they might leak a little more. However with ring seal being aided by the air pressure pressing the ring out against the cylinder wall and down against the ring land it might help static ring seal.

[Dan Bennett]

Probably stating the obvious, and may not apply to some racers but the years I worked with teams running Jenkins engines he had two things that he concentrated on. Yes, he was known for reading spark plugs - a lot of teams would send somebody over to our trailer so he could give an opinion on their plugs but first and foremost he had two things he insisted on.

First, the amount of leakage. He insisted on very low numbers. Second, on variation between cylinders. If he didn't like what he saw, he always asked for the engine back for a refresh. I remember other teams thinking he was being excessive (or maybe being too cheap or just didn't have the money) ignoring the request. And of course, they'd cry real tears when they started having problems qualifying.

This was not troubleshooting if the car had lost performance, It was checked regularly. We used to talk about a lot of things, but he would never discuss the hone finish he had come up with.


Came back to edit to include another example of how much he thought of keeping things where he wanted them. He told me that shortly after starting to use the ZL1 aluminum block, he found that heat cycles would quickly take the bores out of round. He then set up a system so he could keep a block heater running 24/7, even when in the trailer (or maybe ramp truck at the time, don't remember}.