I have some questions about boring a 2 stroke cylinder.
Is it common for a cylinder to wear more down towards the skirt area?
The piston is tapered, the top is smaller to allow for more expansion because it runs hotter than the skirt area. So lets imagine a new bore and a new piston. The bore, of course should be square, that is the same diameter top to bottom. (?) Lets say the clearance should be .0055"
Measuring clearance at the top and bottom would give different values because of the piston taper. WHERE exactly should one measure when looking for the proper clearance?
If one shot for the proper clearance at the top of the bore, then the skirt would be tight if it fit at all. If one targeted the skirt, the top of the piston would have excess clearance, which I know it is supposed to have hence the larger diameter at the crown. As I am typing this, that seems to make sense. (I find that if I try and write out my questions as if to ask others then sometimes it comes together in my mind.)
Measure the skirt of the piston an inch up, and then an inch down into the bore of the cylinder and use those numbers to target the clearance? I suppose that would give the desired clearance at the skirt and would show some excess at the top.
In the process of boring, I would say it would still be important to measure both areas of the cylinder to check for holding square...I am waiting for my upper area to catch up to the skirt area, there is still a greater measurement in the skirt area but i am assuming that is because the cylinder had worn that way. I am going a very little at a time and tracking the measurements so I can see the trend between the skirt area and the top cylinder measurements.
This is the first time I have attempted to bore a cylinder. It is one of those things that I have been burned on before sending them out and I have been doing some machine work at my new (4 years so far) job. I finished up a 40 hour class on precision measurement and alignment they sent me to a couple months back. My method is fairly crude--I am using a lisle hone. If the result is not perfect, I can live with that. As little at a time that this is going, I feel confident about not overshooting it, thats for sure. I have access to a nice lathe and a bridgeport at work but for the amount of time I would fret over the process, it would be a little stressful to try and pull that off there. heheh... I cant afford a boring machine or even a used bridgeport. I have seen some vintage jig hole borers go by for sale, I am thinking I could probably modify one of those to work fairly well at some point. Basically, i am experimenting here, knowing that my methods are not what they "should" be, but that is the story of my life, and I enjoy the process as much as the results or even in spite of them. I have done a whole lot in my life that the "Internet says cant be done". Of course I had my start turning a wrench about 38 years ago so there was no Youtube to run to to figure out why my SL70 wasn't getting 2nd gear.
Thanks for any input!
_________________ 1972 S2 350, 1972 F9 350 Bighorn, 1975 KX400, 1981 YZ465, 1980 XT500 (Built for MX) , 1987 KD80, 1995 MZ Skorpion, TTR 125, 1994 KDX200 , 1978 Mobylette, 1985 KX350R-F91m (Frankenstein) and a Doodle Bug
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