Leak down test of dry engine on stand. What % is good?
Leak down test of dry engine on stand. What % is good? After getting 0 compression on my scrap yard engine, I decided to lap the valves to see if I would get any improvement. Now I only see about 12-17% leakage. My question is if this number would get better if the engine was warm and lubricated? Should I be doing some more work, or would you consider these numbers OK? I'm not going for perfection here, just want a properly running engine.
Thanks!
Thanks!
TECH Resident
Joined: Feb 2014
Posts: 954
Likes: 9
From: Encinitas CA
I had 30% leak down on a cold, dry engine and once running it had no compression once up and running .... while it did run, it had no power nor compression braking and hot gasses puffed out of the crankcase while it was idling. Once tore back down we found the rings were jammed in their lands (wrong rings) and more.
The builder did a poor job. In fact the rod bolts had also made contact with the case and he allowed that to clearance the case (this was a flat six Porsche engine with AL case).
How did the cylinders look when you had the heads off?
Doug
The builder did a poor job. In fact the rod bolts had also made contact with the case and he allowed that to clearance the case (this was a flat six Porsche engine with AL case).
How did the cylinders look when you had the heads off?
Doug
I had 30% leak down on a cold, dry engine and once running it had no compression once up and running .... while it did run, it had no power nor compression braking and hot gasses puffed out of the crankcase while it was idling. Once tore back down we found the rings were jammed in their lands (wrong rings) and more.
The builder did a poor job. In fact the rod bolts had also made contact with the case and he allowed that to clearance the case (this was a flat six Porsche engine with AL case).
How did the cylinders look when you had the heads off?
Doug
The builder did a poor job. In fact the rod bolts had also made contact with the case and he allowed that to clearance the case (this was a flat six Porsche engine with AL case).
How did the cylinders look when you had the heads off?
Doug
Suggest you put some oil in to the cyc.. cycle the piston up and down a few times and then do the Leak down test.
But what may be more important is the leakage and where it is coming from.. which is one of the reasons to be using a leak down tester. Once the compressed air is on, where is the air escaping from ?... sound like you fixed the air escaping from the valves.. is there much air escaping through the rings ?..
And also.. are the percentages close in each of the cyc..?... and what is the percentage of the high / low readings? but for a driver and cold.. 12-17% shouldn't be too bad.. but I would prefer to see single digit readings myself.
BC
But what may be more important is the leakage and where it is coming from.. which is one of the reasons to be using a leak down tester. Once the compressed air is on, where is the air escaping from ?... sound like you fixed the air escaping from the valves.. is there much air escaping through the rings ?..
And also.. are the percentages close in each of the cyc..?... and what is the percentage of the high / low readings? but for a driver and cold.. 12-17% shouldn't be too bad.. but I would prefer to see single digit readings myself.
BC
What bczee said. Single digits are better but yours isn't horrible if its dry. Oil it up and rotate it a few times to seal up the cylinder walls a little.
If its passing by the rings you would be able to hear air escaping through the oil fill cap.
If its passing by the rings you would be able to hear air escaping through the oil fill cap.
