Unofficial Royal Enfield Community Forum
General Discussion => Tech Tips => Topic started by: papadacus on February 17, 2013, 10:12:44 pm
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Hello,
I am rebuilding a 58 Constellation motor and don't know how to set the timing up after I've taken it all apart.
It is a 700cc twin. How do I set it up so that it is timed correctly?
Any resources or input would help, Thanks.
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Your best bet is to download a manual or buy one from CMW or Hitchcocks. ERC
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Should I take my cylinders to a machine shop, tell them the bore of the model, and ask them to re-bore it to a +20, then purchase the +20 piston rings?
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Should I take my cylinders to a machine shop, tell them the bore of the model, and ask them to re-bore it to a +20, then purchase the +20 piston rings?
No, you measure the cylinders to see if their oversize already.
Then you buy the pistons (usually 20 over), measure them and bore the cylinders to the correct dimension depending on the piston manufactures spec.
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How do I get a measurement that precise?
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I don't know if they are available where you live but in the U.S., inexpensive dial or digital calipers can be found.
http://www.harborfreight.com/hand-tools/measuring-tools.html
These can measure inside dimensions, outside dimensions and depths to an accuracy of .001 inches (0.0254mm).
Given a choice, I recommend the dial type because they are accurate and they always work.
The digital type are easy to read and very accurate but the small battery usually is dead every time I want to use mine.
As for measuring the new piston, whoever is going to do the reboreing should have the measuring tools to do the job.
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Take them to whoever is going to bore it. Have him measure them. The standard bore is 70mm- 69.874" actual. You can go .040" over size. You can get a rough bore size with a set of digital calipers. Your best bet is to have them checked by a machine shop before you order anything. ERC
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After you figure out where you are going with the bore, buy the pistons first so the machinist can use it to do the bore correctly. He will make up for manufacturing differences and there are some.
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I was planning on getting only the piston rings. When hitchcocks says the piston rings are +20, are they saying that they will fit the stock pistons and a bore of 70mm +20, or that those piston rings will fit an oversized piston?
Typically with car engines you use the stock pistons and just buy oversized rings when doing an overhaul, so this is the knowledge im going off of. Is it different in this situation? As I said, i'm new to engine work on bikes, so I'm unfamiliar with the process.
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Those rings will only fit the .020"over piston. The land size will be the same so they will fit the groove. But diameter wise they will be too big. They aren't really made to fit a standard bore. ERC
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If your standard bore checks out OK and you don't need a bore job or new pistons, and you can't find standard bore rings, I think you could get away with removing an extra few thou off the end gap to get to the stock bore size with no problems.
Bare