Leak down testing?

[Steve.k]

What do you guys consider a good leak down on good engine(new). We did leak down on fresh build while chasing a lifter gremlin. It ended up in 5-6% range.

[hondo383]

Temperature of engine at test time?
What brand tester/what type/orifice size?

[engineguyBill]

5 - 6% range is considered good results. Was the engine warmed up to operating temperature before the test?

[Steve.k]

Yes engine warm. Snap on tester of dyno guy. We chasing a gremlin that ended up hyd lifters bleeding off. We did leak down to confirm we never had bad cylinder(s)

[MadBill]

4-6% is very good for conventional rings; zero to 2% for Gapless*. (*Not looking for a debate on the merits or otherwise of same, just reporting my results.)

[piston guy]

+1 4,5,6 % is plenty good , 10 is still acceptable IMHO. I agree with MadBill on the gapless numbers.

[statsystems]

4-6% is very good for conventional rings; zero to 2% for Gapless*. (*Not looking for a debate on the merits or otherwise of same, just reporting my results.)

In your younger days you would have been open for debate lol. That's one of the few things about getting old I don't mind!

[Belgian1979]

4-6% is very good for conventional rings; zero to 2% for Gapless*. (*Not looking for a debate on the merits or otherwise of same, just reporting my results.)

In your younger days you would have been open for debate lol. That's one of the few things about getting old I don't mind!

[Steve.k]

Thanks guys. I've personally never tested one. If it seemed bad i tore it apart without checking. We did this on advice of dyno owner so I was curious.

[PackardV8]

Piston-to-wall clearance and end gap can make race engine leak down a bit higher. On good stock engines with hypereutectics, it's not unusual to see 2%-3% after a lot of miles.

[Steve.k]

Packardv8 thats good to know. Ive done a few engines with the kb hyper pistons and for the dollar they made excellent power. I never did leak down with these pistons but was always surprised by the way they ran. I tore two down after about 4yrs running and was pleasantly surprised how well everything looked. Basically no scuffing on skirts which is typically seen With forged.

[hoodeng]

Cylinder leak down tests as a lot of guys know can pinpoint a leakage path to be further investigated ,as in listening to the inlet ,exhaust and crankcase to isolate the path and obviously the lowest number is the best . With an early race engine we were instructed by the supplier to when doing a leak test to tap the valves and observe if the leakage improved and incrementally rock the crank back and forth on TDC ,if it improved go with the lowest number recorded ,the explanation was that engines are dynamic and not static and that valves belt the seat when they shut and that rings shuffle and seat in grooves.
On the race data with another engine 22" of pan vac was the ideal to the manufacturer , any trailing in pan vac through the pass indicated rings not standing up ,yet when a leak test was done the rings showed fine,fresh rings went in [bores had to be observed as perfect].
We were also instructed to do a cranking pressure test at the same time on a new build ,if the leakage was pretty even and the pressures variable indicated cam timing variance or comp variance ,that could be investigated further at that point.
As usual a simple question throws up a number of perspectives, some related ,some peripheral ,but relevant none the less in their own way.

Cheers.

[DaveMcLain]

Cylinder leakdown testing can be good to use to find problems but the numbers are mostly meaningless.

[MadBill]

Cylinder leakdown testing can be good to use to find problems but the numbers are mostly meaningless.

Unless the equipment is built, and better yet certified, to the applicable FAA spec...

[MadBill]

All anyone needs to know (and more!) about leak down testers: http://www.musicanddesign.com/Ferrari/L ... esting.pdf
Note, if you stop reading after the second page you'll have a solid grasp of the subject but if you carry on to the end you're on your own; don't say you weren't warned!