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In this video we will demonstrate the proper way to check piston ring end gaps and also how to adjust this if needed. The only tools we are going need for this is our service manual and some feeler gauges and a small file. So the piston ring end gap is just the gap between the ring ends when the ring is installed in cylinder. It is important to make sure this in spec because if the gap is too small, the ring ends will butt together and it will cause damage to the ring, piston and cylinder. Ring end gaps should be checked whenever you are putting a top end back together. Whether it be new rings with the piston or freshly bored cylinder, it doesn’t hurt to check and make sure these are in spec. We are going to be working on a WR250F piston, but this method can be used for measuring ring end gaps on any two stroke as well. So after the cylinder has been prepared, we are going to slide the first string down in and then using the piston, go ahead and push the ring down at least ten millimeters making sure it sitting square with the cylinder wall. After that we can refer to our service manual for proper gap specifications. Find the appropriate feeler gauge and check to see if it fits in the ring end gap. You want a very light amount of resistance on the gauge and it looks like this one was gapped just fine so we will move on to the next ring. This is one of our oil rings, so it will have a different end gap limit than our top compression ring. So again, just use the piston to push it down and then using the correct feeler gauge, measure the end gap. We are going to repeat this process for each ring. The only ring that doesn’t need to be measured is the oil ring spacer which is the wave looking ring that rides in between both oil
scrapers. So if you measure the ring end gap and find the gap that is smaller than the specified limit, simply file one end of the piston ring
until the gap is within the specified range. Be sure not to leave any burrs or sharp edges that could potentially damage the cylinder. That is all there is to measuring ring end gaps. If you have any questions feel free to give us a call at 1-800-336-5437. Rocky Mountain carries everything you need to rebuild the top end on your machine. Be sure to check out our website www.rockymountainatvmc.com for a complete list of parts and accessories for your machine. Thanks for watching.

4 thoughts on “How To Measure Piston Ring End Gap on a Motorcycle or ATV

  1. If the gap is bigger than the specified service limit as listed in the service manual you either have wrong parts or your cylinder is worn causing the gap to be bigger.

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