High leak down on fresh build before break in

[BILL-C]

Is there a recognized “standard” orifice on leakdown testers? I know that in the past I have gotten different readings with different brand gauges at the same test pressure.

[jdperform]

Then doesn’t this mean the head is cracked somewhere.

Maybe I’ve been guilty of using to much press on seat rings and rolling a burr .
Soft parent metal behind seat. To little press and ring will move before perhaps falling out. I only do alum race heads. We see leaking behind seats more than a guy would think

[naukkis79]

If valves aren't lapped by hand they won't seal right after installation. Seat and valve face are ground at different angle, eg. to 45 and 46 degrees which will self lapping valves to seats at first few rounds of engine running. But just after assembling you can't expect them to seal properly.

GSX-R valves are coated so valve lapping isn't allowed if intention is to keep valve coating intact.

[hoodeng]

All proposals are worthy of investigation ,but i don't think they would collectively add up to 60-65%,but they may if every point made was a leakage path, that figure suggests something more intrusive.

Cheers.

[MadBill]

Is there a recognized “standard” orifice on leakdown testers? I know that in the past I have gotten different readings with different brand gauges at the same test pressure.

The FAA standard for engines up to 1,000 c.i. (yes, I know, why not a cylinder displacement spec.?) is a 0.040" orifice 0.250" long, with a 60° approach angle and 60-80 psi test pressure, but most general purpose testers don't reference a standard and could differ. A lot of guys test at 100 psi, which makes the leakage percentage calculation pretty simple.

[user-23911]

If valves aren't lapped by hand they won't seal right after installation.

Really?

Valves refaced on refacing machine.
Seats cut on seat cutting machine.
Assemble.
Vacuum test.
Test OK.
When they leak, you did it wrong.


Standard procedure in this part of the world.
Hand lapping went out with the invention of machines.

[hoodeng]

Agreed , why would you scratch up a perfectly good seat? especially if its done on a Contour.

Cheers,

[rebelrouser]

I leak test every engine I build, for 30 years. I teach automotive at a technical college and teach my students to do the same thing. Regular rings with .004 per inch of ring gap and good seal on the heads before firing I get 30 to 10 percent leak on average. Nitrous or blown engines with bigger end gap I usually get 30 to 40 percent leak. Gapless rings 10 to 0 percent are normal in my experience. I write down the numbers on the ticket for the build, and have customers check leak after break-in, numbers always get better. Using a leakdown has found many issues that needed fixing, and in my opinion is a great way to check your work before you fire the engine. Not claiming to be an engine guru, been a automotive technician since 1974, teaching for the last 25, build 10 or so performance engines a year. If I build one and it leaks a lot, I always find an issue if I take it back apart.

[wombat58]

I bought a Moroso leak down tester years ago and it read 40% leak on an engine that read 4% against another brand leak tester. Pulled it apart to find that the reference orifice was full of sealant that they used during manufacture. Cleared the orifice with a jet drill and it read within 2% of the other leak tester, and has been reliable since. Measurements are only as good as the quality of the tools used.

[Schurkey]

Is there a recognized “standard” orifice on leakdown testers? I know that in the past I have gotten different readings with different brand gauges at the same test pressure.

The FAA standard for engines up to 1,000 c.i. (yes, I know, why not a cylinder displacement spec.?) is a 0.040" orifice 0.250" long, with a 60° approach angle and 60-80 psi test pressure, but most general purpose testers don't reference a standard and could differ. A lot of guys test at 100 psi, which makes the leakage percentage calculation pretty simple.

Far as I know, there's no cubic-inch limits, but rather a bore-diameter limit. Less than 5" bore, .040 orifice as described. 5" bore or larger, 060 orifice.

The text of the FAA regulations requires a 60 degree approach angle, but the included diagram has a 60 degree taper on the exit as well.

https://www.faasafety.gov/SPANS/noticeV ... x?nid=3416
There's a link at the bottom to the full text of the regulation. FAA calls it a "Differential Compression Test", and the description starts on Page 6 (Section 8-14)

I used a Snap-On single-gauge leakdown tester for decades. Seemed to be hugely sensitive--indicated lots of leakage. I supplemented that with a leakdown tester using a Master Orifice as required by Teledyne/Continental. The Master Orifice is a way of checking the leakdown tester, and calibrating your expectations via a "test" leakage. WONDERFUL CONCEPT, but the test (Master) orifice included with the tool is too large for performance automotive work, Someday, I'm going to replace it with a smaller orifice.
https://www.amazon.com/Aircraft-Tool-Su ... ter+master
They supply the leakdown tester with an 18mm spark plug adapter unless you tell them you want 14mm.

[naukkis79]

Really?

Valves refaced on refacing machine.
Seats cut on seat cutting machine.
Assemble.
Vacuum test.
Test OK.
When they leak, you did it wrong.


Standard procedure in this part of the world.
Hand lapping went out with the invention of machines.

After cutting valves could seal fine, but nobody could guarantee that. Specially on bike engine with hard steel seats, very hard valve coatings, very tight valve stem clearances and very light seat pressures. After running engine valve clearance will tighten up few hundreds and valves stop leaking.

http://www.suzukigsxr.org/valve_seat_repair-293.html

It's a fact that valve seal is not achieved after assembly but only after engine running which seems to be original posters problem.

[Tuner]

Link is to a YB post about the calibration orifice in the tester, between the regulator and the gauge in a single gauge tester and between the gauges in a two-gauge tester. I prefer the two-gauge type because you can set and maintain a constant test pressure upstream of the restriction.

https://www.yellowbullet.com/forum/show ... stcount=11

[tresi]

Is there a recognized “standard” orifice on leakdown testers? I know that in the past I have gotten different readings with different brand gauges at the same test pressure.

The FAA standard for engines up to 1,000 c.i. (yes, I know, why not a cylinder displacement spec.?) is a 0.040" orifice 0.250" long, with a 60° approach angle and 60-80 psi test pressure, but most general purpose testers don't reference a standard and could differ. A lot of guys test at 100 psi, which makes the leakage percentage calculation pretty simple.

Far as I know, there's no cubic-inch limits, but rather a bore-diameter limit. Less than 5" bore, .040 orifice as described. 5" bore or larger, 060 orifice.

The text of the FAA regulations requires a 60 degree approach angle, but the included diagram has a 60 degree taper on the exit as well.

https://www.faasafety.gov/SPANS/noticeV ... x?nid=3416
There's a link at the bottom to the full text of the regulation. FAA calls it a "Differential Compression Test", and the description starts on Page 6 (Section 8-14)

I used a Snap-On single-gauge leakdown tester for decades. Seemed to be hugely sensitive--indicated lots of leakage. I supplemented that with a leakdown tester using a Master Orifice as required by Teledyne/Continental. The Master Orifice is a way of checking the leakdown tester, and calibrating your expectations via a "test" leakage. WONDERFUL CONCEPT, but the test (Master) orifice included with the tool is too large for performance automotive work, Someday, I'm going to replace it with a smaller orifice.
https://www.amazon.com/Aircraft-Tool-Su ... ter+master
They supply the leakdown tester with an 18mm spark plug adapter unless you tell them you want 14mm.

I made a leak down testers I/A/W AC43-13 and I too wondered about the need for a smaller oriface. My oriface my be a bit too long, a 41 caliber bullet swedged into a pipe nipple nicely and added a bit of locktite to make sure the lead sealed to the pipe. What would you suggest for an oriface for automotive work? Mine seemed to be a bit low. I've had several motors read 2-4% leakage after break in. This was with convention moly rings with the gaps on the tight side.

[naukkis79]

Agreed , why would you scratch up a perfectly good seat? especially if its done on a Contour.

If you want to check valve job before installation you need to lap valves. If you don't want to scratch seat and valve you could use red lead. I prefer checking valve contact before assembling, if there's something wrong it saves a lot of work.

But main point was that GSX-R valve job isn't even supposed to seal after assembling, final sealing is achieved after engine running.

[hoodeng]

Hi Naukkis79, i don't know if you are familiar with the 'Newen Contour' machine , these give among'st the best most accurate seat finishes achievable in capable hands .
Blueing the seat to confirm required width and location is all you would want to do, lapping would compromise the finish.

Can you explain why a GSXR would not even seal after a head service , and would need to be run to achieve correct valve seating? This is new to me.
As for how and what type of leakage tester is used ,zero is zero and minimal leakage after assembly is paramount , 60-65% is either a test equipment miss use or incorrect, or an engine fault.
My previous post gave the procedure to isolate the leakage path.

Cheers.