Hi all, I'm new to the site, but have been lurking around here occasionally picking up tips while I shopped for a new saw. That ended the other day when a friend handed me a stihl MS390 that needed a new top end and said, "It's yours if you want it". Since this is my first saw rebuild (I've got a few dozen assorted other stock and modded engine builds under my belt), I'm hoping to get a couple questions answered.
1) Are there any "must do" or "must check" items that I should address while the engine is apart? The bottom end looks and feels fine, but I'm not sure if there are any critical measurements or inspection points.
2) This saw is a non-decompression model. I live at 7K ft altitude, and cut wood anywhere from about 6K to 9K ft, so obviously the performance is going to take a hit. It appears that nobody makes a high compression piston, but since I need a new cylinder anyway, I'd like to find out if there's any compression or performance advantage to either the decompression vs. non-decompression head so I can shop appropriately.
3) Considering the altitude, is there anything outside of the muff mod that you all would recommend to help the performance. I'm not building a hot saw by any means, but 25% power loss makes one think twice about modding, and it's not like I have anything to lose in this case....
Thanks everyone
1) Are there any "must do" or "must check" items that I should address while the engine is apart? The bottom end looks and feels fine, but I'm not sure if there are any critical measurements or inspection points.
2) This saw is a non-decompression model. I live at 7K ft altitude, and cut wood anywhere from about 6K to 9K ft, so obviously the performance is going to take a hit. It appears that nobody makes a high compression piston, but since I need a new cylinder anyway, I'd like to find out if there's any compression or performance advantage to either the decompression vs. non-decompression head so I can shop appropriately.
3) Considering the altitude, is there anything outside of the muff mod that you all would recommend to help the performance. I'm not building a hot saw by any means, but 25% power loss makes one think twice about modding, and it's not like I have anything to lose in this case....
Thanks everyone