Piston to deck measurement variation
Posted: January 18th, 2019, 3:20 pm
I could use some help on my stroker build. I am seeing variation in measurements that is not what I expected.
Short block info:
- 2003 block
- New bearings
- New rods
- New pistons (60 over)
- Crankshaft polished undersized 0.020
- Bores honed to spec for the new pistons.
- Block was line honed ~1000 miles ago. My machinist checked to see if it needed to be redone. He said no.
- Block was decked ~1000 miles ago. My machinist checked to see if it needed to be re-flattened and re-squared to the bore. He said no.
- I bought this engine from somebody else because the price was really good. The engine had an "issue". I discovered a cam bearing failure, #6 piston scuffing, and bad rod bearings. My machinist checked everything for me due to that discovery. We think the cam bearing failed for improper valve lash (it was a solid lift and the previous owner never adjusted lash) which caused the bad rod bearings. We think the #6 piston scuffing was caused by piston to bore tolerance being too tight. My machinist measured it and it was under 2 thou.
- Pistons are above the deck at TDC.
Crankshaft main and rod bearing tolerances were right on target per plastigauge.
Piston to deck measurement above the wrist pin. I measured here as I understand it is the "ideal" location.
- All holes are the same measurement within 1 thou
- I can repeat this measurement over and over again and the measurements vary less than 1/2 a thou.
-
This makes me think that the deck and crank are parallel to each other.
Piston to deck measurements at the 3 and 9 o'clock positions and 1/4 inch in from the edge of the piston. I measured here as it should show the worst case variation.
- The left sides measured ~6 thou (average) higher than the center measurement.
- The right sides measured ~6 thou (average) lower than the center measurement.
- The left to right variation per hole was greater at #5 compared to #1.
Question #1: Is piston rock causing this? I did not expect piston rock to cause a 6 thou error like that.
Question #2: Is this okay?
Short block info:
- 2003 block
- New bearings
- New rods
- New pistons (60 over)
- Crankshaft polished undersized 0.020
- Bores honed to spec for the new pistons.
- Block was line honed ~1000 miles ago. My machinist checked to see if it needed to be redone. He said no.
- Block was decked ~1000 miles ago. My machinist checked to see if it needed to be re-flattened and re-squared to the bore. He said no.
- I bought this engine from somebody else because the price was really good. The engine had an "issue". I discovered a cam bearing failure, #6 piston scuffing, and bad rod bearings. My machinist checked everything for me due to that discovery. We think the cam bearing failed for improper valve lash (it was a solid lift and the previous owner never adjusted lash) which caused the bad rod bearings. We think the #6 piston scuffing was caused by piston to bore tolerance being too tight. My machinist measured it and it was under 2 thou.
- Pistons are above the deck at TDC.
Crankshaft main and rod bearing tolerances were right on target per plastigauge.
Piston to deck measurement above the wrist pin. I measured here as I understand it is the "ideal" location.
- All holes are the same measurement within 1 thou
- I can repeat this measurement over and over again and the measurements vary less than 1/2 a thou.
-
This makes me think that the deck and crank are parallel to each other.Piston to deck measurements at the 3 and 9 o'clock positions and 1/4 inch in from the edge of the piston. I measured here as it should show the worst case variation.
- The left sides measured ~6 thou (average) higher than the center measurement.
- The right sides measured ~6 thou (average) lower than the center measurement.
- The left to right variation per hole was greater at #5 compared to #1.
Question #1: Is piston rock causing this? I did not expect piston rock to cause a 6 thou error like that.
Question #2: Is this okay?