430 build Part II...this time a 455!

I look at the list of parts in your signature, and you're balking about a hundred- or hundred and thirty-dollar tool?

Yes, I'd expect that somebody rents these. May depend on your geographical market, they're more likely rented in NYC or LA than West Podunk, Wy.

Keep in mind that for automotive use, there's no requirement to market the tester with a certain-size main orifice; the orifice makes as much difference in the indicated results as the actual cylinder leakage. A small orifice makes the tester more sensitive, a large orifice makes the indicated results appear better. Only "aircraft" leakdown testers are guaranteed to have the correct size and shape main orifice (.040, with inlet and outlet tapers) and only then when the tester is intended for engines with a bore of 5" or smaller. (Larger-bore aircraft engines get a tester with a larger orifice)

The master orifice allows you to "test the tester", VERY helpful if you don't use the tester often. Otherwise you'll need to test a few "good" engines, to see how your tester reacts with an "unknown" engine.

 

I agree a leak down tester is the best. But with both valves closed { rockers off } There should be no leak at #6 exhaust valve. Were the OLD heads reworked for the rebuild ? You posted they cam off a engine that blew up. The heads should be reworked on a rebuild. No oil to the heads before it blew. Not good. Just my '02. Also, I looked over the post and unless I missed it what were the compression readings dry and wet for the other 7 cylinders.

 

I agree there should be no leaking through the valves, but it was as I described so I'm assumign the valve head or seat or both are jacked. The heads were no reworked. I honestly forgot about them as i was getting the machine work done to the block becuase i thought theyd be okay to reuse. Obviously, a big mistake.
The compression numbers were in one of the pics i attached but for reference:
1-157 2-143
3-150 4-145
5-140 6-0
7-149 8-146
The compression numbers were much lower than with my 430 build (upper 170s-mid 180s) but I have much thicker head gaskets and deeper dish pistons in this motor. The spread i think is fairly even (when i took the readings on cylinders 2 and 4 yesterday just to compare both came out at 150 so im assuming atmospherics play a part) and the test was done on a cold engine. Not sure what you mean by dry or wet.

 

Well, I went and bought a Habor Freight leak down tester...probably not the best option but i figured it would at least give me an idea. So far i've done cylinders 2 and4 and got similar readings. The video shows number 4 test. Now, as stated in the video the leak down shows either 65 or 55% leak down on both cylinders depending on how i set the gage before i hook it up. Pretty high leak down according to this gage but so far between the two cylinders ive tested they're consistent. And yes both pistons were at TDC during the test.


I had a thought about the possible high leak down numbers and low compression number...these are speed pro forged pistons which are known to expand a bit when hot. All these tests have ben on a cold engine so might all this be an exercise in futility?

[video=youtube;Aay6Qz3AdoE]http://www.youtube.com/watch?v=Aay6Qz3AdoE&feature=youtu.be[/video]

 

Your readings mean NOTHING, and I mean N-O-T-H-I-N-G, until you've tested a few known-good engines to compare to.

When you apply inlet air pressure to that leakdown tester, do both gauges read the same when the hose to the engine isn't plugged in?

Piston expansion doesn't mean much since the pistons don't seal the combustion chamber. More a factor of the rings, and they'll be at whatever temperature the cylinder walls are soon after shutting off the engine.

The way I see the second gauge, up to 70% leakage is considered "moderate". Must have a very tiny/non-standard orifice in that unit. Can you still return it?

[EDIT]Aww, hell. I finally looked at your video. That unit is totally fukked-up. You're leakdown testing with ten pounds of pressure instead of 60 psi+. (OR--one or both gauges don't read right!) My single-gauge Snap-On tests at 60. FAA standard is 80 psi. Most folks test at 100 psi, because the math is easier. Read the instructions that came with that leakdown tester, verify that you have the procedure correct--and if you do, tell Harbor Freight to kiss your ass, that thing is junk. When not plugged into the engine, so there's no air flow through the unit, those gauge needles should move together--they should hit the 100 psi (left gauge) and 0 leakage (right gauge) at the same time. Typical Communists and Communist Collaborators. They've wasted our time. I told you to buy "aircraft quality".[/EDIT]

---------- Post added at 12:25 PM ---------- Previous post was at 12:00 PM ----------



Both gauges should move simultaneously.

 

STILL more info.

Dug around on the search engines, and got reminded of this thread from a couple of years ago.

http://speedtalk.com/forum/viewtopic.php?f=1&t=26822

The Harbor Fright leakdown tester is designed to be defective. It is DELIBERATELY screwed-up. The second gauge is calibrated to test at ~15 psi. See the sixth post in the thread I linked to, especially.

First Guess: Harbor Fright thinks you are a moron, so they build the tester to use only 15 psi in order to not push the piston down the bore--turning the crank and the engine fan in the process--to avoid injury lawsuits from negligent users who are too stupid to accurately put the piston at TDC, or who don't have enough sense to lock the crankshaft in position before testing at other-than-TDC.

Whether this 15-psi leakdown test is still useful is a question I'm not prepared to answer. I don't own one of those testers. I don't see any advantage to owning one when equipment built to FAA standards is readily available, and for practical purposes is directly comparable to pressures and procedures that are essentially "industry standard"--except, of course, for keeping tighter tolerance on the actual tool used.

 

LOL, thanks for all that. I'll order a proper leak down tester and go from there.

 

One thing I probably haven't made clear--If you're ordering one of the two units I've suggested, be sure to tell them you want the 14mm automotive adapter rather than the 18mm one they ship with for aircraft use. If you're buying a leakdown tester from some other source, it will "probably" come with the typical 14mm adapter, or an assortment of adapters.

There's a few auto engines that used the big 18mm thread, but they're pretty rare nowadays. Typical is 14mm; but the trend is smaller--12 and 10mm stuff, and crazy crap like the Ford Modular non-industry-standard spark-plugs. MOST (I won't say "all"!) leakdown testers use the same style of quick-disconnect plugs, so for example I can use all my Snap-On leakdown or compression-tester spark-plug adapters with the ATS leakdown tester. (Gotta unscrew the Schrader valve out of a compression-tester adapter to use with a leakdown tester.)

 

Alright, I got the aircraft leak down tester and the results are as follows:

Plugged the compressor into the inlet of the tester.
Then adjusted the pressure to 80psi (both gages wen to 80 at the same time)
Plugged the tester into the spark plug hole and held the crank to keep it at TDC
I then released the valve to let the pressure in.

Primary gage went to 70psi and the 2nd gage went to 30 and stayed there. I could definitely feel the piston trying to turn over but i could hear the air escaping into the crankcase. I felt a litle air out of both the intake and exhaust but most of it was down in the case.

Now when i closed the valve and open the master oriface and the leak down gage went to 40 while the pressure gage stayed at 80. What does that mean.

Also, does it matter that the engine isnt warm?

 

It is normal for the first guage to drop a little when the air is flowing into the cylinder. You can turn up the air pressure regulator a bit to compensate...or not. Your choice.

Second gauge goes to 30 is bad. Very high leakage. NO leakage out of the valves is acceptable. SOME leakage past the rings can be acceptable. The standard for "acceptable" varies depending on the application. For Continental aircraft engines, you're ten psi below the minimum. That engine would be repaired before it flew again. For automotive engines, the standards are arguably TIGHTER/LESS TOLERANT. Some folks demand less than ten percent leakage for race engines, perhaps 20--25% for a "grocery getter". What is important here is that the leakage indicated on your engine is WAY EXCESSIVE; and unacceptable also based on valve sealing problems.

Your engine is releasing more pressure than the master orifice. The engine is wounded.

Not really. Some folks make a big deal about warming the engine. It may make some difference...but not enough in your case.

 

Guess i shouldve read the directions...it says to compare the reading off the master valave pressure. Now according to the inst anythimg less "than the mv reading means your rings are bad but i tested two cyli nders and got 30 and 34. How do i know if thos is "acceptable leakage? A lot of the reading ive done says upwards or 20-30% is normal so how do i get that percentage off this test?

Plus, if the valves are leaking slightly im sure that scewing the test. Ugh, anyone have a good head i could borrow? Lol

 

The simple way is to test at 100 psi. Then whatever the second gauge reads is your percentage of sealing. So 100 psi regulated pressure, and let's say you have 50 psi on the second gauge, you have 50% sealing or 50% leakage. You have 100 psi on the first gauge, and 80 on the second gauge, you have 80% sealing, or 20% leakage. You have 100 psi on the first gauge, and 30% on the second, you have 30% sealing, 70% leakage. You get the idea.

Testing at 80 psi in accordance with the FAA procedure, you need to work some math to figure out the percentage of leakage; and I'm not in a position to deal with that right now. Most folks just test at 100 psi and read the second gauge for sealing.

 

Am I wrong? I'm thinking that your math is correct, but incomplete. There is 42.8% SEALING, which means 57.2% leakage.
The total leakage is WAY high, we already know that the valves don't seal, but we can't be sure how much of the remainder is going past the rings. I'm guessing that he didn't pull the rad cap to check for pressure loss into the cooling system.

 

I see what you guys are saying but i do'nt know if that's how this gage works. The instructions say to take the master valve pressure and base the differential off of that. No granted, it also says anything below that pressure inidicates an engine that needs rebuilt (for airplanes).

When the master valve is open there is a regualted amount of air being forced though the valve orifice, basically a regulated leak. So, when i did that the left valve stayed at 80 and the right gage read 40. So, i closed the master orifice valve and connected the tester to the engine. When i opened the air valve it read 30...so in my mind 30/40 = 25%. Right?es? No?

 

No. The Master Orifice is the maximum amount of leakage allowed. You have lower pressure on the second gauge when connected to the engine than when the Master Orifice is open. The engine leaks MORE air than the Master Orifice. The engine is faulty.

If the engine leaked LESS air than the master orifice, Continental Engines says the cylinder is OK. But automotive standards--and Non-Continental aircraft engines use a tighter standard still. Continental Engines allows a larger leakage than general FAA guidelines, and your engine is worse still.

The only question here is how much is going past the rings, and how much is going out the two valves.

I would test the remaining seven cylinders.

 

Ok, i understand now. Unfortunately, my results are from two other cylinders than the one that was faulty. I just don't see how the leakage can be that bad on a brand new engine especially when the engine ran as well as it did even minus one cylinder. I guess I'm screwed then and at this point i dont think im up for building another Buick motor.

 

The valves don't seal.

1. If the rocker arms and pushrods are in place, the lifters may need time to bleed down. On some engines, the valve adjustment could be too tight.

2. The guy who did the valve job needs to re-do his work.

Get the valves to seal, reinstall the heads using the gaskets you have now, test again to see what the leakage past the rings is. If it's acceptable, you can try to run the engine with the re-used head gaskets, or you can install fresh head gaskets and see how the engine runs.

 

The rockers are off and it wasnt the machinists fault as the head worked great on the 430 before i blew it up. I guess what ill do is take one head and have it completely re-done and use it on both sides. If it tests ok, then ill get the other one done and put her back together. if not...well, i could always take the block and have it bored and get new pistons....but honestly, at this point im leaning more towards an LS swap if this engine doesnt pan out.