Just removed this from an engine with noisy worn bearings with a view to saving it for another motor as it looked pretty free of scoring when I took a peek. There are fine scoring marks visible but are they quite passable or should they be rubbed away? Another question is what's the best method to remove the carbon of the crown as I've never done this before and don't want to scratch the aluminium?
Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Probably the wear on the piston skirt after checking it's size with a micrometer is more important than the slight scoring , but if you're going to spend $15 on new rings then another $25. isn't much for a new piston.
I'd just use some steelo to get the carbon off the piston crown.
You wouldn't want the piston skirt to be any smaller than 2.413 .but that would be with a standard bore with no wear, once the bore is worn total clearance between piston skirt and bore should be no greater than 8 thou.
If your bore is worn 3 thou a new piston would be at maximum clearance but won't last as long as a rebore.
I dissolve the carbon with a spray product. The vast majority comes straight off, the remainder I find needs a bit more persuasion and I use a nylon scraper.
The stuff I currently use is a Penrite product and it’s very good (just can’t remember the name) but I used to just use oven cleaner for the same job years ago. I helped rebuild a few fancy racing engines and got a bit of stick for using oven cleaner earlier on so changed to something more automotive. It did the job without the “toxic” alkaline stink of oven cleaner so I’ve stuck with that range of things since.
Some people go to a lot of trouble polishing the piston and so forth but so long as it’s clean and free of defects it won’t make a scrap of difference.
If you’re using digital calipers check their accuracy and repeatability. I don’t own any because most of my gear was bought before they came in but I had a colleague measure a bolt using his and I made a replacement based on his measurements and it was oversized because his calipers weren’t accurate. To check them a relatively inexpensive set of gauge blocks will work fine.
