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| Manxmodder:
Hi Tom, I have made flywheels for 2 stroke cranks in the past(about 4.75 inches dia) and my method was to bolt the 2 flywheels together and machine the crankpin holes right through as one. I have also seen other guys tack weld the flywheels together and then separate them after all the main pin and crankpin boring was completeed . These methods guarantee alignment of the pin bores.....OZ. |
| billmac:
Hi Tom. A TIR of .030" for the crank pin is way too much unfortunately (as I am sure you appreciate) regardless of the type of bearing you intend to use. The suggestion to bore the flywheels together should help, but you obviously can't do the taper turning right through that way. A tapered fit crank pin is traditional, but not all engines were made like that. Some had parallel pins and were a press fit in both flywheels. This makes lining up the flywheels to get the mainshafts running concentric more of a challenge of course. With a taper fit you can pull them up on the nuts lightly then 'bump' the flywheels on a big lump of wood or a chunk of brass or lead until you get them true, then pull them up tight. It is best to use lathe centres (or bench centres) to test for this alignment. Just a thought that might give you a way forward - Villiers engines used a parallel fit crank pin that was a light press fit. This allowed for alignment adjustment. The crankpin was bored at each end and after alignment you pressed in a plug in each end, a good press fit. This caused the ends of the crankpin to expand minutely and increase the strength of the overall fit in the flywheels. The Villiers design perhaps was not the best, but they made them in the tens of thousands so might be worth investigating this method, since it would allow you to bore out your flywheels together and in one setting, which should give you much better alignment. You might be able to rescue your existing flywheels this way, but you would obviously need a new crankpin. Watching progress with interest. |
| tom osselton:
So I'm scratching my head what does "tir" stand for? |
| Bluechip:
Total Included / Indicated Runout or similar ... :thumbup: Dave |
| tom osselton:
Ok thanks, I was just wondering I'm going to have to make one of these soon for a twin. |
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