Pistons what is the acceptable movement?

Tiny
CHRISDONNO
  • MEMBER
  • 2008 FORD F-450
  • 6.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 191,000 MILES
I bought a remanufactured long block to replace the existing engine because of a broken piston. The new engine had several valve train issues, and I went round and round with the warranty company and they decided to send 2 new heads and claimed they would reimburse me on gaskets and valve train parts If I purchase them and send them the bad parts. While I was cleaning the block for the new gaskets, I wiped off the pistons and noticed they move. I don't know what the acceptable movement is, but it looks excessive. I checked the bore at the top of the cylinder and IF the pistons are new and I am reading the numbers right they should be fine. I only drove the truck about 26 miles with the new engine and the warranty company is giving me trouble and I don't know if removing the piston to measure the skirt would void the warranty but maybe you can tell from this video if it's an acceptable amount of wiggle.
Monday, December 4th, 2023 AT 11:39 AM

9 Replies

Tiny
CHRISDONNO
  • MEMBER
  • 6 POSTS
Trouble sending video I think. Here it is.
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Monday, December 4th, 2023 AT 11:44 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 44,198 POSTS
Hello, and thanks for the video. I don't know if taking the engine apart will void the warranty, you will need to call them for that information. Since this is a diesel, the piston to wall clearance is more excess than gasoline engines. Here are the piston wall clearance specs:

Clearance to cylinder bore. 0.045-0.095 mm (0.0018-0.0037 inch)

I would use a round feeler gauge to measure the clearance to be sure, but it looks okay to me from the video.
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Monday, December 4th, 2023 AT 2:53 PM
Tiny
CHRISDONNO
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I'm not sure how I would get a feeler gauge past the piston rings but if.03 inches of side-to-side movement looks normal for the crown then I guess it's not an indication of excessive clearance at the skirt?
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Monday, December 4th, 2023 AT 4:17 PM
Tiny
CHRISDONNO
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  • 6 POSTS
In other words, is it normal for the piston wiggle/clearance at the crown to be 10 times greater than the clearance at the skirt?
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Tuesday, December 5th, 2023 AT 3:59 AM
Tiny
KEN L
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"At the crown"? You mean at the top of the bore? Also, you don't need to measure past the piston rings just at the top of the piston. The piston does not vary its measurement from top to bottom, the bore will not as well. Can you load another video of what you are talking about?
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Tuesday, December 5th, 2023 AT 10:28 AM
Tiny
CHRISDONNO
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In picture 1 I slid the piston to one side and zeroed the caliper.
In picture 2 I slid the piston to the other side for a negative measurement.
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Tuesday, December 5th, 2023 AT 11:30 AM
Tiny
KEN L
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Yep, that is within spec, to be sure you can call the engine manufacturer and they can help confirm the issue as well.
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+1
Friday, December 8th, 2023 AT 8:26 AM
Tiny
CHRISDONNO
  • MEMBER
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Thank you for your help. I did remove the piston and measure it, the ring gap and the bore and found that it was just outside of spec. But I had a mechanic who has worked on lots of 6.4l engines look at it and he said it is normal to go a little over spec. On piston clearance when rebuilding these.
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Monday, December 11th, 2023 AT 3:43 AM
Tiny
KEN L
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Good job, I am glad you got to the bottom of the problem. I don't like to tell people that outside of spec is okay due to the manual recommendations but personally I do agree with the extended clearances in some cases. Use 2CarPros anytime, we are here to help. Please tell a friend.
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Monday, December 11th, 2023 AT 10:25 AM

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