Checking cylinder bore, 1985 2.5 Iron Duke (Page 2/2)
82-T/A [At Work] JAN 14, 07:01 PM
I feel like I need to get a degree in this so I can totally understand it. I ran the numbers with my daughter, and they seemed really excessive (yet the car ran and drove fine). So again, I went out to the garage myself, and this time I did it in inches, and I'm trying to compare the information in the service manual with my numbers.

First - I measured the top ring (haven't reamed the ridge yet) and got a perfect 4"s with my micrometer, just to double-check.
Second - I then zeroed out my digital bore gauge on the ridge to get a 4" baseline.

Third, I measured each cyl bore, doing three measurements at the top (one at the 12:00, then 2:00, and then 4:00 location). I did this DIRECTLY under the ridge, and then measured it again three more times in the same positions about half-way down from the cyl bore, and these are my measurements in inches:

Cyl 1 -
Top / .006, .005, .0035
Mid / .0005, .0, .0015

Cyl 2 -
Top / .0065, .004, .003
Mid / .001, .001, .002

Cyl 3 -
Top / .0055, .0045, .002
Mid / .001, .001, .0015

Cyl 4 -
Top / .006, .007, .006
Mid / .001, .0005, .001


This is what the Service Manual mentions for acceptable variance for bore:
Out of Round = .001
Taper = .005


So when I do the "maths" for my out of round and taper (from mid to top), by cyl...

Cyl 1 -
OOR: .0025
Taper: .006

Cyl 2 -
OOR: .0035
Taper: .0055

Cyl 3 -
OOR: .0035
Taper: .004

Cyl 4 -
OOR: .001
Taper: .0055


So, I know I wasn't expecting a different result, but I wanted to make sure that I did this right. I'm committed to a .040 overbore, and already bought the pistons and the rings.

With the measurements (this time in inches) above... does that look like I did the measurements properly? The motor ran well... but I never really pushed it. It did smoke some... but it ran well to say the least, no clattering. I just want to make sure I did my math right and did these measurements right, because it's driving me nuts thinking maybe I didn't do it properly.

My .040 overbore should be more than enough... but any thoughts?


Thanks!
jelly2m8 JAN 15, 01:58 AM
82-T/A, you got Discord?

[This message has been edited by jelly2m8 (edited 01-15-2024).]