niklas 1 Posted February 16, 2006 I've just got my 84 mm forged pistons and I've measured the current ring gaps to be about 0.008" (0.2mm) for the top rings and about 0.016" (0.4mm) for the 2nd rings. In a thread on here the recommendation was 0.003" (0.076mm). And in the spec supplied by Wiseco it said 0.004" / inch bore, which ends up being 0.013" (0.336mm). What should I aim for? Regarding the difference between the top and 2nd rings, I've stumbled across this: I received a new set of 4-Stroke Piston Rings from Wiseco and the second ring gap is quite a bit larger then the top ring gap. Do I have the correct rings? Yes. The second ring gap being larger then the top gap was an upgrade and improvement to a select number of our 4-Stroke ring packages. As the piston moves down on the power stroke, combustion pressure accumulates in the land area of the piston between the top ring and the second ring. This accumulation of pressure can cause the top ring to unseat from its sealing area at the bottom of the ring groove. This is addressed by increasing the gap area of the second ring. This affords a controlled release of the inter-land pressure, and keeps the top ring seated on its lower sealing surface for improved performance. Please remember this gap difference is not present on all of our ring packages, but just a select number of 4-Stroke applications. So I guess the 2nd rings should have a larger gap whatever the final gaps will be. But should it be about 0.008" larger or some other value which depends on the top ring gap?? Any suggestions? Share this post Link to post Share on other sites
petert 555 Posted February 17, 2006 12-13 thou. on the 2nd ring and 15-18 thou. on the top ring will be fine. Share this post Link to post Share on other sites
niklas 1 Posted February 18, 2006 12-13 thou. on the 2nd ring and 15-18 thou. on the top ring will be fine. Hrmmm.. not the other way around? 12-13 (0.30-0.33mm) on the top ring and 15-18 (0.38-0.46mm) on the 2nd ring? Share this post Link to post Share on other sites
B1ack_Mi16 67 Posted February 18, 2006 Just go for wiseco's specs. My top-rings (also wiseco) were spot on on the clearance, and the second rings were a bit wider, so I didn't have to grind anything. You'll have to grind your top ones just a little bit, and leave the others alone. Share this post Link to post Share on other sites
petert 555 Posted February 18, 2006 (edited) If you read the FAQ's on the Wiseco site, they certainly say that SOME of their pistons should have more clearance on the 2nd ring. If so, you should be aiming for 17-19 thou. on the bottom ring. Edited February 18, 2006 by petert Share this post Link to post Share on other sites
Pierre_b 3 Posted February 21, 2006 Hello, If you read the FAQ's on the Wiseco site, they certainly say that SOME of their pistons should have more clearance on the 2nd ring. If so, you should be aiming for 17-19 thou. on the bottom ring. I have no experience in engine building so this is just based on my various readings . I have never heard/read about second ring gap larger. I thought that the first ring must be wider because the first ring receive more heat and then expand more, and the second ring should be smaller, because the ring expand less. I thought that the aim was to have the smallest ring gap possible on first and second ring to obtain maximum power (without having ring end butting on each other). Is this wrong? What do you think of this theory of pressure between the two ring? Why only "some" engine require this particular setup ? Thanks, Pierre Share this post Link to post Share on other sites
