170VAC is too high. Disconnect the output wires from the generator breaker to get a good measurement of the voltage between the common and neutral connections at the breaker while the generator is running. If this is more than 132 VAC, generator issues need to be resolved before continuing.
The next step is to isolate the wire past the generator. So with the generator off, leave the output wires from the breaker disconnected and disconnect the generator input wires at the automatic transfer switch (ATS), or unplug the shore power from the generator receptacle. Now measure resistance between the common and neutral wires and common and ground wires. If anything other than an open circuit is measured, there is a short in the wire between the generator and ATS or receptacle that needs to be corrected. Best guess is, because of age, there is a generator receptacle and something inside that box has giggled loose and is shorting.
