Hey guys is it fine if my freewheel bike which is single speed is not that straight with its chain line, because my cogs and crank arent that straight but it is also not that far, im thinking if it is already safe to use given that im using a chain tensioner? I have measured the space between them and it is most likely 0.73cm apart, i have a 1by 38t crank and 16t cogs and my bottom bracket is 107mm,my frame is an old style mtb LeRun brand
Derailleur bicycles are regularly ridden with more than twice the misalignment of what you have. They have to be ridden this way, because you can't fit N cogs into the space of 1 cog, well unless N=1. So some cogs have non-straight chainline.
Usually you can even backpedal these bikes with no ill effect.
If you have a chain tensioner, your bicycle differs from a derailleur bicycle only by having N=1. The only possible problem I see that if the chain tensioner does not have a clutch or the front chainwheel is not of the narrow-wide type, it's possible to drop the chain from the 38-tooth chainwheel.
So I'd classify it as safe. I'd not classify it as convenient (unless there's a clutch and narrow/wide chainwheel) since it's likely the chain drops someday forcing you to get your hands dirty in dirty black chain oil.