OP
OP
KWIKNVA
TYF Newbie
- Joined
- Jan 20, 2012
- Posts
- 21
- Reaction score
- 0
Actually I just got the yukon back from the dealer. Never a good place to take a vehicle for warranty work if you ask me. Took 3 weeks and they actually did nothing but let the truck idle. At first they said no noise. I had to tell them to drive it! Then the tech and ext. warranty adjuster agreed there was a knock. I didn't get a full detail explanation on why there was a knock but the adjuster just referenced the TSB on cold engine starts and it was normal. Basically said ok to drive until it fails. Svc rep didn't see it being cost effective to tear down the motor to see normal wear and then have to bill me for the labor as the warranty would not cover the labor for diagnostic and not find a issue.
jagi0966 has explained this knock and symptoms the best which lead me to look at Hypereutectic Pistons. Just looking at Wiki you will read
The average temperature of a piston crown in a gasoline engine during normal operation is typically about 300 °C (570 °F), and the coolant that runs through the engine block is usually regulated at approximately 90 °C (190 °F). Aluminum expands more than iron at this temperature range, so for the piston to fit the cylinder properly when at a normal operating temperature, the piston must have a loose fit when cold.
"piston slap" which is when the piston rocks in the cylinder and it causes an audible tapping noise that continues until the engine has warmed to operational temperatures. These engines (even more so than normal engines) should not be revved when cold, or excessive scuffing can occur.
I think the only thing I can do at this point is go with a full synthetic oil and allow the motor to warm up properly in cold temps. I've notice that around 200-205 degrees the knock goes away. At 0-199 it will knock. Wife pulled off to go to the store and it sound awwful. Came home sounding like a Singer sewing machine.
If I've read everything correct, Forged possibly is the only way to get rid of the piston knock. I hate the knock and I like lots of hp so I may be looking at build in the future.
jagi0966 has explained this knock and symptoms the best which lead me to look at Hypereutectic Pistons. Just looking at Wiki you will read
The average temperature of a piston crown in a gasoline engine during normal operation is typically about 300 °C (570 °F), and the coolant that runs through the engine block is usually regulated at approximately 90 °C (190 °F). Aluminum expands more than iron at this temperature range, so for the piston to fit the cylinder properly when at a normal operating temperature, the piston must have a loose fit when cold.
"piston slap" which is when the piston rocks in the cylinder and it causes an audible tapping noise that continues until the engine has warmed to operational temperatures. These engines (even more so than normal engines) should not be revved when cold, or excessive scuffing can occur.
I think the only thing I can do at this point is go with a full synthetic oil and allow the motor to warm up properly in cold temps. I've notice that around 200-205 degrees the knock goes away. At 0-199 it will knock. Wife pulled off to go to the store and it sound awwful. Came home sounding like a Singer sewing machine.
If I've read everything correct, Forged possibly is the only way to get rid of the piston knock. I hate the knock and I like lots of hp so I may be looking at build in the future.
