abyssmaltailgate
Greenhorn Mechanic
Certainly not a new topic, but I'm trying to appraise the condition of my pistons, piston rings, and cylinders.
First, I want to replace my piston rings, but am unsure what size/dimensions I need. The local Yamaha dealer wasn't much help since their computer database archives nominal sizes i.e. "standard," "1st oversize," "2nd oversize," etc. Based on the info outlined in the Haynes manual and that stamped on my engine's parts, the diameter of my pistons are 74.954mm, and the diameter of my cylinders bore is 75.007mm, which means there is a 0.053mm clearance. This isn't much help since Haynes doesn't indicate if this is standard bore or not. I assume it is but I want to know for sure. Hopefully someone out there can help me clear this up?
Additionally, I did the poor man's test and shined an LED light upwards from the bottom of my cylinders with the pistons and rings in place in pretty much total darkness. No light shone through. What's more, the rings were within the measured tolerances outlined in the Haynes manual. Based on these findings, everything should be in good, running condition; however, this is a 40+ year old engine with unknown mileage, and I believe most of the internal components to be original. I also removed the rings to polish the piston heads. I figure I should replace them anyway as a measure of cheap insurance.
As far as the pistons and cylinders are concerned, they all seem to be in good condition more or less. One piston has two, small, shallow scratches on the dome since I dropped it while polishing it by hand. I can't imagine this would create any problems, but then again, I really don't know. Finally, the cylinders all feel smooth on the inside but have some transverse staining (probably from the pistons sitting in place since it was last ran) and what is potentially light scoring. Will someone please appraise the condition of these parts and point me in the right direction?
I've considered having the cylinders bored and honed to 750cc, but I also want to get this Yammie back on the road before the end of the season. This will obviously increase my spending and the time the bike spends off the road, but if the the rings and pistons need to be replaced and the cylinders honed anyway, maybe it's worthwhile since the engine is completely disassembled now?
First, I want to replace my piston rings, but am unsure what size/dimensions I need. The local Yamaha dealer wasn't much help since their computer database archives nominal sizes i.e. "standard," "1st oversize," "2nd oversize," etc. Based on the info outlined in the Haynes manual and that stamped on my engine's parts, the diameter of my pistons are 74.954mm, and the diameter of my cylinders bore is 75.007mm, which means there is a 0.053mm clearance. This isn't much help since Haynes doesn't indicate if this is standard bore or not. I assume it is but I want to know for sure. Hopefully someone out there can help me clear this up?
Additionally, I did the poor man's test and shined an LED light upwards from the bottom of my cylinders with the pistons and rings in place in pretty much total darkness. No light shone through. What's more, the rings were within the measured tolerances outlined in the Haynes manual. Based on these findings, everything should be in good, running condition; however, this is a 40+ year old engine with unknown mileage, and I believe most of the internal components to be original. I also removed the rings to polish the piston heads. I figure I should replace them anyway as a measure of cheap insurance.
As far as the pistons and cylinders are concerned, they all seem to be in good condition more or less. One piston has two, small, shallow scratches on the dome since I dropped it while polishing it by hand. I can't imagine this would create any problems, but then again, I really don't know. Finally, the cylinders all feel smooth on the inside but have some transverse staining (probably from the pistons sitting in place since it was last ran) and what is potentially light scoring. Will someone please appraise the condition of these parts and point me in the right direction?
I've considered having the cylinders bored and honed to 750cc, but I also want to get this Yammie back on the road before the end of the season. This will obviously increase my spending and the time the bike spends off the road, but if the the rings and pistons need to be replaced and the cylinders honed anyway, maybe it's worthwhile since the engine is completely disassembled now?