lilngineer
Well-Known Member
I have a 96 787 that I rebuilt top and bottom.
I first built the motor with the same 82.25mm cylinder jugs (re-honed) and new pistons, rings, pins, bearings, & crank.
I got about 5hrs into the break-in and I found compression was only 125/140. It ran ok, but I figured I would repair the top end while I was ahead.
Today, I swapped my jugs for a new set machined to the same .25mm over. I did reuse my 5hr pistons/rings. I checked compression cold before starting and found it to be 140/~152. I also did not have the throttle wide open when testing.
Is this acceptable for a top end rebuild? I find it hard to believe my previous 5hrs wore down the rings to account for the pressure difference.
Could this be because the pistons/cylinders were not specifically matched? How important is this in reality?
I appreciate any help/insight you can provide. Not too crazy about ripping it apart yet again.
I first built the motor with the same 82.25mm cylinder jugs (re-honed) and new pistons, rings, pins, bearings, & crank.
I got about 5hrs into the break-in and I found compression was only 125/140. It ran ok, but I figured I would repair the top end while I was ahead.
Today, I swapped my jugs for a new set machined to the same .25mm over. I did reuse my 5hr pistons/rings. I checked compression cold before starting and found it to be 140/~152. I also did not have the throttle wide open when testing.
Is this acceptable for a top end rebuild? I find it hard to believe my previous 5hrs wore down the rings to account for the pressure difference.
Could this be because the pistons/cylinders were not specifically matched? How important is this in reality?
I appreciate any help/insight you can provide. Not too crazy about ripping it apart yet again.