If your diesel generator is cranking but not starting, there are a number of potential issues that could be the cause. Here are a few things to check:

1. Fuel: A lack of fuel is a common cause of a diesel engine that won't start. Check the fuel tank to make sure it has enough fuel and look for any signs of leaks in the fuel lines.

2. Fuel filter: A clogged or dirty fuel filter can prevent fuel from reaching the engine. Check the filter and replace it if needed.

3. Air intake: A diesel engine requires a certain amount of air to mix with the fuel to create combustion. Check the air filter to make sure it's clean and not clogged.

4. Battery: A weak or dead battery can cause the engine to crank but not start. Check the battery and make sure it's fully charged.

5. Glow plugs: Although you mentioned that your generator does not have a glow plug, if it did have one, a faulty glow plug can cause starting issues in a diesel engine.

6. Injectors: Faulty or clogged fuel injectors can also prevent a diesel engine from starting. Check the injectors and clean or replace them if necessary.

7. Compression: Finally, low compression can also cause a diesel engine to crank but not start. Check the compression levels and make sure they are within the manufacturer's recommended range.