If the engine is vibrating within a certain rpm range, what is the likely cause?
3 answers
If the entire engine vibrates in a certain frequency range, then there may be a resonance between the exciting frequency which is the engine rpm/60 and one of the six natural frequencies of the engine on its mounts.
What do you mean by a "resonance"?
Oh, hummm
Well first of all google the words "Natural frequency" and "resonance".
The idea is that if something vibrates at a certain frequency it can be pushed at that frequency and the resulting motion will be large.
An example is pushing a swing. If you push it at the same frequency that it wants to swing, it moves a lot. If you push it too fast or too slow, it is more difficult to get it going.
Well first of all google the words "Natural frequency" and "resonance".
The idea is that if something vibrates at a certain frequency it can be pushed at that frequency and the resulting motion will be large.
An example is pushing a swing. If you push it at the same frequency that it wants to swing, it moves a lot. If you push it too fast or too slow, it is more difficult to get it going.