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Building Integrity
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Date: 10-27-2019
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Number of Hours: 8.00
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Manual Reference: Section 2
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Brief Description: 20 days later
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You gotta love those performance shops that tell you in a "week" they will be done and end up taking almost 3. Ugh. Well the cylinders are back and honed for a finished bore of 4.157 which is .002 larger than what UL claims to bore them to. I've seen UL's cylinder bores all over the map on a handful of cylinders I've analyzed. Either way, the guys at Kennedy Performance matched them all with clean cross hatch patterns, ready for installation.
Take a look at pic #2. The difference in quality is immense when looking at a Wiseco vs KB Piston. KB cast CRAP. Still can't believe UL uses them. Pic 3 shows the hand selected 6 forged pistons from Wiseco all measuring EXACTLY 4.1515 and within a gram of each other. This piston was made for a 4.155 bore so with the added .002 they should have plenty of room for expansion vs. the KB Pistons that truthfully didn't expand enough causing the slap. I even called Wiseco and confirmed the bore clearances to .0055 as sufficient for an air cooled cylinder operating at WOT. If anything it still may be too much as liquid cooled applications call for .0035. We shall see.
Here is where UL has everyone sweating. UL uses, and I confirmed, a .014 top compression ring clearance and .018 oil ring clearance. Using the standard .004 per in. of bore dia. this is really pushing the limits of the clearance before the rings close up. Which, by the way, could very well be a reason for wide spread cylinder wall scoring. On the advise of Wiseco, and multiple professional engine shops, I decided to be conservative and use .017 for the compression ring, and .019 for the oil ring. My last UL re-build had .018 and .020 which worked just fine but only made 76/80 on a leakdown test. Either way, each ring set was gapped for a specific cylinder. Best of luck to me :)
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KB Pistons removed
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Crap on the left. Wiseco on the right
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6 paired pistons ready for install
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