Hi Abraham,
Please find below link for your info on Equipment and Asset Integration.
Technical Structuring for Plant Maintenance Purposes - Asset Accounting (FI-AA) - SAP Library
As far as SAP PM is concerned, Diesel Generator is an equipment, Alternator is an equipment and engine is an equipment. If you have created fixed asset as Diesel Generator, the same asset number can be linked to all 3 equipment, so the cost can be group to asset.
Regards
Terence