The last bike engine was with my best mate holding it in place in the garden with no headers on and kicking it
We had a frame for beetle engines as where Iv worked we specialised in those a long time back
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Ours was to go in a sidecar and made out of three unknown engines so needed it as a spare but needed to know the bottom wasn’t knocking or head rattlingWhile there's an undoubted visceral delight in firing up a rebuilt engine.... But unless you've radically modified it, I'm not sure what you'd learn. Think Flight of the Phoenix.