Piston slap or rod knock?

_Broken_WRX_

New member
So I recently bought a built 08 wrx hatch. The engine only has 7k on it since it was rebuilt and is a fairly mild setup. (Just over 300 wheel) The engine sounds fine after its warmed up but there is a distinct high pitch ticking that depends on rpm on startup. It lasts for about 10-20 seconds before fading away. Im thinking it could be rod knock until the engine gets oil pressure. Its got forged pistons and is bored to 99.75. (Manley Pistons) Could this just be piston slap or something worse? The car also needs a new tune. It hasnt been retuned since it got a new certicooler and headers. Also it burns a good bit of oil on startup as well. Im new to subarus as well so anything helps. Im also not sure if im doing cooldowns correctly or not after driving it hard.


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Eagleye

Tinkerer
Post a video if you can. Have you changed the oil since having it? Curious if it has any bearing material in it.
 

_Broken_WRX_

New member
Yes I changed almost as soon as I got it the oil was clear. The catch cans seemed to have normal catch can things in them too. Bot that I know what should be in them. I have a video but Im not sure how to post it on here.


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Alin

Diehard Car Enthusiast!
 

Eagleye

Tinkerer
When you did the rebuild did you install a new timing belt and tensioner? Personally I think that is too loud for piston slap but it could just be the way the video was taken. If the tensioner and belt were replaced I would have the oil pan dropped to check for damage. Not all that time consuming or difficult for peace of mind.
 
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_Broken_WRX_

New member
When you did the rebuild did you install a new timing belt and tensioner? Personally I think that is too loud for piston slap but it could just be the way the video was taken. If the tensioner and belt were replaced I would have the oil pan dropped to check for damage. Not all that time consuming or difficult for peace of mind.

I bought the car once it was already rebuilt. The timing belt was replaced but im not sure about the tensioner. Dropping the pan is a good idea. The car is in a shop right now for a new transmission right now anyways so I will ask them to do that for me. (The center diff busted on the way home)


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Eagleye

Tinkerer
Given that it is already in the shop, I would agree that having them drop the pan to inspect everything would be a good idea. If I recall correctly you can go so far as removing 2-4 rods to inspect more closely before pulling the motor and cracking it open. #1 requires the block to be split to remove. You should know what you are dealing with just from dropping the pan though. While that is dropped you could see what kind of oil pick up they put in for the rebuild. If it is stock you may want to go ahead and replace that with a Killer B just for insurance. Around $150 is worth it if the stock one would have ever broken in the future. Unless you are racing the car/doing parking lot donuts a windage tray or new pan are unnecessary (and they add about $500 to the cost...yikes).
 

_Broken_WRX_

New member
Given that it is already in the shop, I would agree that having them drop the pan to inspect everything would be a good idea. If I recall correctly you can go so far as removing 2-4 rods to inspect more closely before pulling the motor and cracking it open. #1 requires the block to be split to remove. You should know what you are dealing with just from dropping the pan though. While that is dropped you could see what kind of oil pick up they put in for the rebuild. If it is stock you may want to go ahead and replace that with a Killer B just for insurance. Around $150 is worth it if the stock one would have ever broken in the future. Unless you are racing the car/doing parking lot donuts a windage tray or new pan are unnecessary (and they add about $500 to the cost...yikes).

Its got a tigworks oil pickup in it now. Atleast thats what he said... Ill cal the shop today and ask them to do that for me. Thanks


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Eagleye

Tinkerer
Its got a tigworks oil pickup in it now. Atleast thats what he said... Ill cal the shop today and ask them to do that for me. Thanks


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If they can, ask them for pictures. That way you can be sure of what oil pickup is in there and how everything looks. I don't really see how it could be internal damage causing the sound since it fades away so quickly. Rod knock is going to be pretty constant and get louder upon revving. My injectors use to tick something fierce with my built STi, but that remained pretty constant too. Does it seem better when it is a short time period between start-ups (as in the car is already warm and oil was moving around the engine)? Good luck, keep us posted.
 

_Broken_WRX_

New member
If they can, ask them for pictures. That way you can be sure of what oil pickup is in there and how everything looks. I don't really see how it could be internal damage causing the sound since it fades away so quickly. Rod knock is going to be pretty constant and get louder upon revving. My injectors use to tick something fierce with my built STi, but that remained pretty constant too. Does it seem better when it is a short time period between start-ups (as in the car is already warm and oil was moving around the engine)? Good luck, keep us posted.

Yea if its already warm when I start it it doesent make the noise at all.


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Eagleye

Tinkerer
Yea if its already warm when I start it it doesent make the noise at all.


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Gotcha, given that I would suspect at worse it could need a tensioner if it was not already replaced with the build. If it was, then I would chalk it up to owning a Subaru.
 

sniperkill

New member
You could also try putting some thicker oil in her? Amsoil or Magul 20w50 should quiet that noisy lifter right up?


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