Looking into rebuilding an engine I have with a damaged crank; everything else appears to be in good shape.
Reviewing the factory service manual I noticed some tight tolerances for a factory motor:
For example piston ring end gap:
Maximum end gap
No. 1 0.20 to 0.25 mm (0.00787 to 0.00984 in.)
No. 2 0.60 to 0.70 mm (0.02362 to 0.02756 in.)
Oil ring 0.10 to 0.35 mm (0.00394 to 0.01378 in.)
Main Bearing Clearance
Standard clearance: 0.013 to 0.031 mm (0.00051 to 0.00122 in.)
Rod Bearing Clearance
Standard oil clearance: 0.025 to 0.055 mm (0.00098 to 0.00217 in.)
Looking at a couple aftermarket forged piston manufacturers I noticed depending on application there is quite a bit more gap being requested.
I did find that someone had posted an IAG Extreme Stage 3 block clearances which is a good reference point for example gaps.
Piston End Gap JE 86.25mm 3.396" 10.5:1
Top .020
2nd .023
Oil .015+
If I was guessing it looks like they used 3.396 * .0060 = .020376 for the top ring per JE blown race only recommendation.
However for the second ring 3.396 * .0063 = .0213948 isn't the recommendation for blown race only but closer to the minimum factory gap.
Main bearing clearance .0012 XPG STD
Rod bearing clearance .0018 ACL H STD
I thought it was interesting that their main bearing clearance is the loosest OEM and the rod bearing clearance was within factory spec also but toward the looser side as well.
Anyone have experience with the amount of blow-by that could be expected with this much end gap on the piston rings? Any builders out there with example clearances that would be a good rule of thumb or any additional modifications that should be done to support the motor?
edit:
DarkPira7e was able to get a copy of his IAG Stage 1 clearances:
I conclude that they aim for the loose side of main bearing clearance, rod bearing clearance is *slightly* loose, and the end gap is identical on the piston rings.
Thanks for the help guys, hopefully this information helps someone out in the future.