[Jesse 1985]

My friend just bought a 93 fxr sport thats bored to 100 cu in , is that to much , is this engine a ticking time bomb?

 

[cwilks]

They all are if built and ridden correctly.

 

[Thermodyne]

100 inches is really pushing it if its on an oem case. Never actually heard of a setup that gave you 100 CI out of an evo case. A 103 EVO is 3 5/8 bore on a 5 inch stroke, and they were anything but reliable. Less so in a punched out MoCo case. And you can take a 96 inch side winder and bore it .040, but I'm thinking that will give you something like a 98.

Any chance the motor is off brand, like an El Bruto or Ultima. If so, then it sort of depends on when it was built. Old is bad, newer is better.

 

[Turboprop]

My friend just bought a 93 fxr sport thats bored to 100 cu in , is that to much , is this engine a ticking time bomb?

Simply being 100" does not make it a 'time bomb'. Back in the 90s, 3-13/16" bore was not uncommon on a set of harley cases. I rode a couple 106" evo engines (3-13/16" x 4-⅝") for many years. One was a semi drag engine, but I rode all over the east coast on the other one. Even rode it to the west coast and back. Twice.

Your post does not provide any really useful information. Bored to 100" does not make sense. Does this engine have harley or aftermarket cases? Almost impossible to get to 100" with just a bore on these cases, and it would be incredibly expensive. I suspect that there is more to this , perhaps an increase in stroke, possibly even special cases with an offset cam chest. You really should dig into this and flesh out what you have a bit more.