Piston Ring Clearances
Don't Forget To Check!!
When you are putting together your engine, you should NEVER assume that the rings are within tolerance just because they are "new". I've found that most rings ARE manufactured within the factory tolerances for the given application. But there have been a few instances where the rings were too tight. This may seem like a good thing, but if your rings are too tight you risk having NO clearance when your engine warms to normal operating temperature. This condition will cause excessive friction/wear on the rings and cylinder walls.
To check the ring END GAP, simply slip each ring one at a time into the cylinder and use the bare piston to push it down about 5mm down into the cylinder's inner wall.
Use your feeler gauge to check the gap between the two ends of the ring. Do this same procedure on ALL the rings for each cylinder (including the 2 thin oil rings). The factory end gap tolerance for NEW pistons/rings for 1600cc based air-cooled engines is as follows :
UPPER Compression Ring ...... 0.30 - 0.45mm / .012" - .018"
LOWER Compression Ring ..... 0.30 - 0.45mm / .012" - .018"
Oil Scraper ............................. 0.25 - 0.40mm / .010" - .016"
Most likely if an adjustment has to be made, it will be because the ring is too tight. In that case, you would need to VERY CAREFULLY & SLOWLY file the ends with a jewelers file, to increase the end gap. Just make one pass with the file at a time and then re-check the gap. You DO NOT want your gap too big. If your gap gets too big, you'll have to get a new ring, or possibly a new complete set of rings of your supplier does not sell individual rings.
Now it's time to check the side clearance of each ring in it's respective piston groove.
Again, use you feeler gauge to check this. The factory side clearance tolerance for NEW pistons/rings for 1600cc based air-cooled engines is as follows :
UPPER Compression Ring ...... 0.07 - 0.10mm / .003" - .004"
LOWER Compression Ring ..... 0.05 - 0.07mm / .002" - .0027"
Oil Scraper ............................. 0.03 - 0.05mm / .001" - .002"
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Revised: August 29, 2003 .