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?
Piston to deck measurement variation
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- Noob
- Posts: 15
- Joined: December 19th, 2017, 12:04 pm
- Stroker Displacement: 4.7
- Vehicle Year: 1990
- Vehicle Make: Jeep
- Vehicle Model: Wrangler
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- Strong Poster
- Posts: 896
- Joined: August 15th, 2009, 1:27 am
- Stroker Displacement: 4.7
- Vehicle Year: 2000
- Vehicle Make: Jeep
- Vehicle Model: Cherokee
Re: Piston to deck measurement variation
Your measuring normal piston rock.
Get your pair of pistons up to TDC. Square the piston up in the cylinder the best you can. Add up your 4 corner measurements and divided by four and that’s your number.
Get your pair of pistons up to TDC. Square the piston up in the cylinder the best you can. Add up your 4 corner measurements and divided by four and that’s your number.
-
- Noob
- Posts: 15
- Joined: December 19th, 2017, 12:04 pm
- Stroker Displacement: 4.7
- Vehicle Year: 1990
- Vehicle Make: Jeep
- Vehicle Model: Wrangler
Re: Piston to deck measurement variation
Thanks Russ.
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