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Old 07-30-2010, 12:25 AM   #1
salvator_rizzo
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Member#: 112713
Join Date: Apr 2006
Chapter/Region: RMIC
Location: Boulder, CO
Vehicle:
2005 LGT, CBR Race
Blue/Red

Default Bad Compression Numbers after Rebuild EJ251

So I was having a noise problem after I finished rebuilding the motor.

Pretty much everything was done to the motor- resurface heads, full valve and seat surface, new valve stem seals, hone cylinders, recondition rod bearing bores, polish and grind crankshaft, new main and rod bearings, new piston rings, new head gaskets, new timing belt etc etc. A lot of work.

So i had a noise coming from what sounded like the head around cylinder 2 area. I was advised to do a compression test to see if I had a problem with valves or something so I did.

Numbers came back as follows (checked each cylinder twice for consistency):

Cyl #1: 70 psi (not expected at all)
Cyl #2: 100 psi <-- what i thought was the source of noise
Cyl #3: 100 psi
Cyl #4: 130 psi

So... what could possibly be going on? I was expecting cylinder 2 to be maybe around that 90-100 mark based on noise, but 1 and 3 as well?

timing problem maybe? pictures of sprockets :

passenger


driver's (the green spot is marking the alignment mark, ignore marker thats nothing)


crank


please help, this car is driving me crazy
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Old 07-30-2010, 01:59 PM   #2
yarrgh
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Location: Aurora, CO
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2001 2.5RS
Black Diamond Pearl

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did you set the valve lash correctly? Are the rockers torqued down all the way/correctly? You can squirt some oil into the cylinder that is low and do another compression test, it it's different....that points to something. I forget exactly what, search on it.
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Old 07-30-2010, 10:05 PM   #3
salvator_rizzo
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2005 LGT, CBR Race
Blue/Red

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yea I adjusted the valves just the other day to within spec, so that should be good. Everything was torqued in accordance with the FSM, so I'm pretty sure thats good there. i've heard of putting some oil in the cylinder to check compression, I've give that a shot
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Old 07-31-2010, 03:04 AM   #4
rhino6303
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Location: SW Washington
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2005 Impreza OBS SRR
05 Legacy GT RBP

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If you add oil and the compression goes up in that cylinder, it means the rings are shot and didn't seat properly.
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Old 08-06-2010, 12:43 PM   #5
nasty_beer
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adding oil to a cylinder only shoots the comression tester full of oil. What you really need to do is a leak down test to find where your loosing compression.
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Old 08-09-2010, 12:18 AM   #6
SeeMonkey
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Did you break it in with non synthetic oil? I would think you would get some smoke if your rings aren't right.
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