leak down tester ..how does it work
Burning Brakes
Joined: Jul 2001
Posts: 853
Likes: 0
From: Foxfield, Co
Unless one can measure or do the calculations to determine the flow rate across the orifice, and compare it to the volume in the cylinder, it seems to me that the leakage "percentage" declarations are of little absolute value. And again, is the (volume) leakage percentage "per second", or "per millisecond", or what? Without any actual prior calibration of the tester, I can only picture this being somewhat accurate as a comparison tool when comparing an individual engine shortly after break-in, and then after a select number of street or track mileage. Otherwise it just seems like using an old torque wrench you find laying on the street. Sure, it will give a reading when you twist a bolt, but can you believe the readings? I prefer my measuring tools to be calibrated.
One of the main uses is not to just find the absolute accurate leak %, but to compare readings between cylinders, much like a compression tester. Its just that the leakdown tester gives you much more info on where the leakage is happening. It lets you pinpoint rings, intake valve exhaust valve, and head gasket leaks between cylinders.
Greg.
Melting Slicks
Joined: Sep 2004
Posts: 2,655
Likes: 19
Let me guess. Mechanical Engineering degree?
Unless one can measure or do the calculations to determine the flow rate across the orifice, and compare it to the volume in the cylinder, it seems to me that the leakage "percentage" declarations are of little absolute value. And again, is the (volume) leakage percentage "per second", or "per millisecond", or what? Without any actual prior calibration of the tester, I can only picture this being somewhat accurate as a comparison tool when comparing an individual engine shortly after break-in, and then after a select number of street or track mileage. Otherwise it just seems like using an old torque wrench you find laying on the street. Sure, it will give a reading when you twist a bolt, but can you believe the readings? I prefer my measuring tools to be calibrated.
Racer
Joined: Jan 2007
Posts: 325
Likes: 0
From: Ocala FL
One of the main uses is not to just find the absolute accurate leak %, but to compare readings between cylinders, much like a compression tester. Its just that the leakdown tester gives you much more info on where the leakage is happening. It lets you pinpoint rings, intake valve exhaust valve, and head gasket leaks between cylinders.
Greg.
Greg.
Crank it over a few revs then turn it over the last time using a breaker bar on the crank. Take a reading, then another in 5 minutes. Second reading shouldn't be more than 10% less than the first.
If it was, squirt some oile in on top of the piston (flat top) and crank it over a few times and then repeat the test.
If the second reading went up, the problem was rings, if it stayed low, the problem was head gasket or valves.
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
"Tom,
Maybe in the technique of how it is done. The three allen head countersunk bolts, spaced 120 degrees apart only prevents the possible slipping of the outer ring, not the function of the rubber damping. The bolts are not torqued down, just held ever so slightly snug in place with the use of nylocs. I don't think this is anything unheard of, I learned it working for an engine builder 25+ years ago who was buddies with guys like Keith Black, Nick Arias, Bill Hunt, Henry Velasco and Jack Engle, all a bunch of old timers today. Maybe this is considered old school today, but we would pin any 8" Hi Perf GM Nodular iron damper going onto an engine that would see 6,500 and above on a regular basis such as Nitrous and blown motors and I still do it today without ever having had a problem. I ran my blown 496 race boat for years this way along with my Nitrous 383 vette without any issues. I'm sure this was before we had all these other options available today."
There ya go... in the wording.
I took it literally as in "pinned" as opposed to retained.
Maybe in the technique of how it is done. The three allen head countersunk bolts, spaced 120 degrees apart only prevents the possible slipping of the outer ring, not the function of the rubber damping. The bolts are not torqued down, just held ever so slightly snug in place with the use of nylocs. I don't think this is anything unheard of, I learned it working for an engine builder 25+ years ago who was buddies with guys like Keith Black, Nick Arias, Bill Hunt, Henry Velasco and Jack Engle, all a bunch of old timers today. Maybe this is considered old school today, but we would pin any 8" Hi Perf GM Nodular iron damper going onto an engine that would see 6,500 and above on a regular basis such as Nitrous and blown motors and I still do it today without ever having had a problem. I ran my blown 496 race boat for years this way along with my Nitrous 383 vette without any issues. I'm sure this was before we had all these other options available today."
There ya go... in the wording.
I took it literally as in "pinned" as opposed to retained.
Last edited by Tom454; Apr 24, 2007 at 03:11 PM.
Race Director
Joined: Aug 1999
Posts: 18,126
Likes: 174
From: WI
...redvetracr
Le Mans Master
Joined: Apr 2005
Posts: 6,346
Likes: 418
From: Seattle Area WA
364709 is the one to use!
Symantec's will get you every time. OT but last year when I stopped in at Engle cams and was chatting with the Engle boys, old Jack came in, he turned 90 a while back and comes into the shop every single day.
Symantec's will get you every time. OT but last year when I stopped in at Engle cams and was chatting with the Engle boys, old Jack came in, he turned 90 a while back and comes into the shop every single day.
Last edited by Scott Marzahl; Apr 24, 2007 at 04:16 PM.
Tech Contributor
Joined: Jun 2004
Posts: 20,847
Likes: 959
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Thread Starter
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
ok boys the scoop is the Harmonic dampner does not line up with my index tab.... you know i bet it didn't slip....i bought the Harmonic balancer and a long style water pump to use this motor im my 37 ford...i bet the harmonic balancer was set up for an index tab that is up higher then the vettes one and that you can see through the long style water pump...
heres my home made TDC tool that Scott and I dreamed up......its a "sparkplug nonfouling" fitting that i drilled out and tapped to fit a 3/8x16 carraige bolt .
In any event the home made TDC locator confirmed exactly what the leak down tester with the vacuum plug told me...that the index tab and the timing tab were not aligned properly....
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heres my home made TDC tool that Scott and I dreamed up......its a "sparkplug nonfouling" fitting that i drilled out and tapped to fit a 3/8x16 carraige bolt .
In any event the home made TDC locator confirmed exactly what the leak down tester with the vacuum plug told me...that the index tab and the timing tab were not aligned properly....
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Le Mans Master
Joined: Apr 2005
Posts: 6,346
Likes: 418
From: Seattle Area WA
Bob, now you need a Tavia adjustable timing tab. This also might be a case of a pre '69 timing indicator which is a few degrees off from a later one tab. I don't recall if it's an earlier or later timing event at the moment.
Last edited by Scott Marzahl; Apr 24, 2007 at 09:47 PM.
Thread Starter
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
i seem to recall having to look in between the long style water pump on some cars to see the timing index tab.....and thats exactly where this index line is....i just painted a new white line....
