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« on: December 20, 2006, 03:03:38 PM »
Hi folks, just joined the site. My early model CB750 smokes badly under load from the exhausts and engine breather. The cylinders have been rebored to +25 and has pattern pistons (ART?) and genuine honda rings. The bores look good, the pistons are a close fit and the ring gap is within tolerance. The rings were fitted with the N25 stamping facing up and spaced with the gaps at 120 degrees. I tried fitting new valve guide seals, but that did not help. The next step will be to take the valves out and check the guides. One thing I noticed is that there are two types of scraper ring in each set. One is stepped on the underside and the other is plain. There is no mention in the workshop manual of which grooves to fit them in. I don't see that it would make much difference anyway, but I would appreciate any info on this, or the smoking problem generally.