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Old 06-02-2023, 01:38 AM   #1
03NA-TS
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Member#: 534410
Join Date: May 2023
Location: Greater Vancouver
Vehicle:
2003 Impreza 2.5 NA

Default Engine Knock (Con Rod?)

Hi all,
I rebuilt my 03 2.5l NA motor, because it had piston slap. So I had crank polished, block honed at 0.020" over, new pistons, rings, bearings, seals, block and heads decked, new timing components, and I lapped my valves.
It is making a knock, varies with RPM and is silent, (or at least mostly) when there is light to no load on engine. So high idle seems to be decently silent, put in reverse or drive instantly knocks..
My diagnostics so far include;
Bore scope cyl 4 as when I unplug that injector sound vanished, engine builder said the walls looked good.
Double checked tensioner, not the cause.
Ignition pack not the issue.
Swapped injectors with number 2 but still only when #4 unplugged does the sound go away. So the injector isn't the issue.
I made sure to be picky with valve lash when heads were back on the block, so that shouldn't be an issue, (always the slight possibility...)
Seems to me that it would be a rod bearing issue???
Please tell me if there is still something I need to check before jumping to this conclusion! I haven't checked compression, but I'm planning on doing that before going at the bearing. I'm linking a video of the car running at a lower idle.
Thanks for all the time you take to help me!!
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Old 06-02-2023, 06:59 AM   #2
arse_sidewards
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Member#: 532328
Join Date: Dec 2022
Default

Does it change with warm/cold?

Dump some 20w50 in there and see if that makes a change.
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Old 06-02-2023, 06:59 AM   #3
arse_sidewards
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Does it change with warm/cold?

Dump some 20w50 in there and see if that makes a change.
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Old 06-02-2023, 10:35 AM   #4
03NA-TS
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Member#: 534410
Join Date: May 2023
Location: Greater Vancouver
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2003 Impreza 2.5 NA

Default

Don't really hear a change between warm and cold.
Is 15w40 sufficient, my shop stocks that. How much would you swap out?
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Old 06-02-2023, 11:30 AM   #5
arse_sidewards
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I mean, 20w50 will be a better test and it's all the same price on the shelf of your local big box store.

Why aren't you doing the oil change yourself. It's just an oil change? Also gives you a chance to cut open the filter and look for glitter.
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