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Old 12-11-2017, 03:16 PM   #1
Snowphun
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Question Leakdown issue on one cylinder - what will happen if I keep running this engine?

I have a hybrid (ej205 heads, ej255 block) with forged pistons, sadly the shop who built it put it together poorly and has been pushing some amount of oil into the turbo inlet since I installed it (with IAG AOS). Once every 30 or so start up I get a smoke cloud out the exhaust, otherwise it doesn't burn much oil between changes. Did a warm leak down test and compression test last week, issues are clearly with cylinder #4:

Leak down/compression
1 6% - 161 psi
2 19% - 151 psi
3 10% - 163 psi
4 44% - 136 psi

Doesn't look good, but it drives fine and for all I know the numbers have been this bad since I installed it. Engine has 8000 miles on it, this is the first set of tests I have so no other numbers to compare it to.

What will happen if I continue to run this engine? I intend to do leak down and comp tests again in a month and a few times after that to see if the numbers change. My goal is to use this engine through the winter and resolve when I have more time in the spring.
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Old 12-11-2017, 03:38 PM   #2
rtv900
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just run it

who did the leak down test?
and what psi was it done at?
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Old 12-11-2017, 03:42 PM   #3
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I did the leak down test, totally open to some user error but I got consistent results and had a spare engine to get comfortable with the process. Was done at 100 psi and was still finger burning warm.
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Old 12-11-2017, 05:28 PM   #4
rtv900
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Quote:
Originally Posted by Snowphun View Post
I did the leak down test, totally open to some user error but I got consistent results and had a spare engine to get comfortable with the process. Was done at 100 psi and was still finger burning warm.
ok, well at least you know what psi you did it at and stayed consistent because that makes a huge difference.
If you dialed it down to say, 80psi for just one cylinder that cylinder would show a WAY higher leakdown than the rest.

Put air to #4 and try to find out where it's leaking down. Like out the intake, or out the exhaust, or into the crankcase.
That will at least give you an indication how big a job you have coming your way.
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Old 12-11-2017, 05:57 PM   #5
Snowphun
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Originally Posted by rtv900 View Post
Put air to #4 and try to find out where it's leaking down. Like out the intake, or out the exhaust, or into the crankcase.
That will at least give you an indication how big a job you have coming your way.
No question there, air is coming out the oil filler tube and the AOS returns into the turbo inlet hose. So it seems to be pushing past the rings.
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Old 12-11-2017, 07:21 PM   #6
Charlie-III
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Quote:
Originally Posted by rtv900 View Post
ok, well at least you know what psi you did it at and stayed consistent because that makes a huge difference.
If you dialed it down to say, 80psi for just one cylinder that cylinder would show a WAY higher leakdown than the rest.

Put air to #4 and try to find out where it's leaking down. Like out the intake, or out the exhaust, or into the crankcase.
That will at least give you an indication how big a job you have coming your way.
Why would a lower test pressure show a lower leakdown rate?
Typically, the higher you go, the more issues it shows.

Just trying to understand your post.
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Old 12-12-2017, 05:29 PM   #7
rtv900
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Quote:
Originally Posted by Charlie-III View Post
Why would a lower test pressure show a lower leakdown rate?
lower pressure shows a HIGHER leakdown, not lower.
as a percentage of course, not total volume, but that's what leakdown shows, a percentage.

only so much air can get past a finite space. So if you are twiddling 20 psi into a cylinder with a bad ring practically all of it can easily go past, say 90%.
If you put 120 psi to that same space then yes, more volume will pass, but as a percentage it will be more like 15%.
Put 500 psi to that same one and it will be 2%

And then run the engine WOT, putting say 2000 psi to that cylinder. Obviously his crankcase would explode if 15% of that 2000 psi was blowing by every stroke right? That total gas volume would be insane.
But at 2000 psi the percent leakdown is probably a fraction of a percent.
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Old 12-12-2017, 07:54 PM   #8
Max Capacity
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So where in central CT are you ? There are a few great places to have your car worked on the tuned, even a great machine shop. Most are in north central CT, Vernon (one of the best Tuners) and Somersville (great machine shop and trusted mechanic) area.

www.tuningalliance.com and http://eastwoodsautomachine.com/

Eastwoods assembled my ej257 short block and LegacyGT heads back in May 2012, 94,000 miles later at 21psi, the engine still runs great.
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Old 12-13-2017, 08:07 AM   #9
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Originally Posted by Max Capacity View Post
Eastwoods assembled my ej257 short block and LegacyGT heads back in May 2012, 94,000 miles later at 21psi, the engine still runs great.
Thanks, I'll need a good machine shop to figure out if what I have is salvageable. I'll check them out, all set with a tuner.
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Old 12-13-2017, 03:37 PM   #10
Max Capacity
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Quote:
Originally Posted by Snowphun View Post
Thanks, I'll need a good machine shop to figure out if what I have is salvageable. I'll check them out, all set with a tuner.
I was at Eastwoods yesterday, I stop by every few months to chat. They are old family friends. But don't take my word for it... I have been at auto parts stores in other towns and get talking to the older guy's behind the counter and get around to mentioning Eastwoods and the common reply is, "they are without a doubt the best shop in the area". That's coming from more then one place too.

You can tell them I sent you. If you go there, as you walk in the door look to your right, you'll see at picture there of a yellow Honda civic in the winners circle at a NHRA event. Just tell them that's who sent you to them.
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