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Old 06-14-2019, 03:33 PM   #1
smoothdurban
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Default Another compression test results Thread

Guys

I recently had a b230FT rebuilt and I just completed my second oil change after a 300 mile break in.


Out of curiosity I decided to do a compression test and check the conditions of the plugs.

Plugs all look good as I expected as I wasn't encountering any performance issues. So I figured I would do a compression test.

I did the test hot with the fuel pump relay disconnected, and the throttle open.

I did the compression test from cylinders 4 to 1

My numbers are (1 - 4)

149, 148, 148, 121 :(

I was a bit surprised by the 121 on cylinder #4 so I decided to do a leak down test.

theses are my leak down numbers (1 - 4)

100 - 97, 100 - 94, 100 - 96, 100 - 95

During the leak down test I did here some hissing noise in the crank case via oil dip stick tube as well as when removing the the valve cover cap but the hissing was minor

The audible hissing was the same for all cylinders.

What gets me is how low the compression on cylinder #4 is compared to the other three cylinders.

Any ideas what else I should check or is it to early to consider the break in done?
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Last edited by smoothdurban; 06-14-2019 at 05:45 PM..
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Old 06-14-2019, 06:48 PM   #2
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Make sure you pull all the plugs before the test. Block the throttle open. Also, put a charger on the battery for the test. It’s common to see the last cylinders down on compression as the battery voltage drops after repeated cranking.
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Old 06-14-2019, 07:25 PM   #3
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Quote:
Originally Posted by MikeSr. View Post
Make sure you pull all the plugs before the test. Block the throttle open. Also, put a charger on the battery for the test. It’s common to see the last cylinders down on compression as the battery voltage drops after repeated cranking.
As stated in OP I started with #4 with the throttle wide open. All the plugs were out but the battery could of gottten weaker by the time I got to cyl #1.

I plan to grab a borescope and check the cross hatch in Cyl #4. I was thinking it may not be broken in yet, to keep an eye on it and see if it increases in the next hundred miles or so.

Last edited by smoothdurban; 06-14-2019 at 07:38 PM..
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Old 06-14-2019, 07:47 PM   #4
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Try a running compression test.
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Old 06-14-2019, 08:38 PM   #5
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Check the valve lash. You may have a tight one.

What was done to the engine during the rebuild? Was it bored with new pistons or honed with new rings? What was done to the head?
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Old 06-15-2019, 07:46 AM   #6
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We set the lash off the engine without the hushers installed. Is it possible a valve is not full closing at the correct time during the transition of the compression stroke but it does close fully which is why I am seeing 6% loss on my leak down test? Essentially it is closed to give me a good leak down test result but may be slightly open during compression stroke transition, but seals fully at TDC.

The engine was completely cleaned. New 0.024" oversized Mahle pistons. New rods as well. The head was cleaned and found to be true enough so we did not machine it. We added new standard dia I&E valves, new guides, seals, and springs.

Below is my lash when we finished assembly of the head

Cyl 1 Intake / Exhaust Cyl 2 Intake / Exhaust Cyl 3 Intake / Exhaust Cyl 4 Intake / Exhaust
lash .016 / .015 .014 / .015 .014 / .015 .015 / .014

Shim 4-10 / .155 4-10 / .155 .160 / .1535 .158 / 4-10

where 4-10 = .161
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Old 06-15-2019, 10:13 AM   #7
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Head true enough, did not cut, hmmmm, sounds like you might have a Trump liar head.
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Old 06-15-2019, 10:22 AM   #8
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Quote:
Originally Posted by VB242 View Post
Head true enough, did not cut, hmmmm, sounds like you might have a Trump liar head.
I don’t see how it could be warped enough to throw compression off by 25+ psi on one cylinder with only 6% leakage
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Old 06-15-2019, 12:48 PM   #9
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Rings?
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Old 06-15-2019, 12:50 PM   #10
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Next time do compression test stating at the other end.
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Old 06-15-2019, 01:12 PM   #11
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The cranking compression is a little low, but the leakdown rate is definitely in the okay range for cyl #4.
If while doing the leakdown, you didn’t hear anything come g from the intake or the exhaust, it’s most likely not the valves leaking.
Have you gone full throttle/ full boost on the engine yet?
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Old 06-15-2019, 03:19 PM   #12
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Quote:
Originally Posted by lummert View Post
Next time do compression test stating at the other end.

I originally did the test from 1 to 4

Cylinder 4 yielded 105 when I did it that way the other cylinders were the same


Quote:
Originally Posted by culberro View Post
The cranking compression is a little low, but the leakdown rate is definitely in the okay range for cyl #4.
If while doing the leakdown, you didn’t hear anything come g from the intake or the exhaust, it’s most likely not the valves leaking.
Have you gone full throttle/ full boost on the engine yet?
No WOT’s yet and boost is set to 7psi.
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Old 06-15-2019, 08:36 PM   #13
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Give it some beans and seat those rings!
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Old 06-15-2019, 09:02 PM   #14
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I upped it to 10 and gave her a little bit harder then normal. Got a few nice 5k pulls in both second and third gear. I will check the results tomorrow.
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Old 06-17-2019, 02:01 AM   #15
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And try to double check the valve clearances while you’re at it. They may have tightened up a bit with all the new components.
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Old 06-17-2019, 06:09 AM   #16
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Quote:
Originally Posted by klr142 View Post
And try to double check the valve clearances while you’re at it. They may have tightened up a bit with all the new components.
Will do. Just need to order another valve cover gasket before I open things up. Hopefully I wont need it.

Right now I am trying to find what keep throwing code 1-4-3. Got a newer knock sensor and my harness is new as well so unless the wire routing near my coil pack is causing the problem I may need to run a shielded wire to the EZK from the sensor.
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Old 06-20-2019, 10:12 AM   #17
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make a note of it, and go beat on it some, maybe come back and check it in 3000 miles if it's doing something odd.

the wire going to the knocksensor from the ezk is already shielded unless you did something special. sensor does not need to be really tight on the engine block, I think the tq spec is between 10 and 14 ft/lbs (off the top of my head). I don't think there's a whole lot of difference between any of the knock sensors, since they're wide-band resonant devices (i.e. they're not tuned to a specific frequency themselves unlike say.... GM sensors), and going .024 over on the bore size is unlikely to change the resonant frequency enough to throw things off there either. Over-tightening them however is said to cause issues.
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Old 06-23-2019, 04:46 PM   #18
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Spec call out for 0.012 - 0.016" cold. Do you guys recommend tighter or looser side of that spec?

From an earlier post we set lash to;

Cyl 1 Intake / Exhaust Cyl 2 Intake / Exhaust Cyl 3 Intake / Exhaust Cyl 4 Intake / Exhaust
lash .016 / .015 .014 / .015 .014 / .015 .015 / .014
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Old 06-24-2019, 02:23 AM   #19
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What camshaft are you running, what are your goals with this setup, do you have to pass emissions and do you care about your idle quality?

In a turbo car, I would recommend running no tighter than .016” for most situations. Where did you see the .012-.016” spec posted?
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Old 06-24-2019, 03:19 AM   #20
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I have the IPD turbo cam. The car is a Weekend cruiser. No emissions but I prefer it to idle well which it does.

I pulled those numbers from my Chilton manual
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Old 06-24-2019, 12:20 PM   #21
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Nice, that's a good cam for all around use. The .012"-.016" range is ok when cold for checking, supposedly, but if you look underhood on your car it most likely says .016"-.018" is the desired setting.

In any case, I would just recheck them to make sure all is well and rule it out as the potential cause of your low compression. If any are .014" or tighter, I would loosen them up at least one shim thickness, or two on the exhaust side.
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