When you are running a project -especially with a small team- you will likely be required to complete some actual project work outside of your PM responsibilities (oh no!) This can be either a blessing or a curse depending on how you handle it.
The key here is to identify tasks that are not too large that you can't complete them in a reasonable time frame and, more importantly, are not part of the critical path.
Taking on work that is part of the critical path introduces unnecessary risk into your project. If you start working on something in the critical path and then suddenly get pulled away into another project related issue with higher priority you will either have to delay completion of your task or ramp up someone else to do it. Either way, this will introduce a major roadblock in the successful completion of your project and should be avoided whenever possible.
"How do I know if what I am planning to do is on the critical path?" You ask? Generally speaking, it is anything that will cause a delay in the project's schedule if it is not complete by a specific time, typically due to dependencies on other tasks.
I would argue that even if you are the subject matter expert in a given area, and feel that you must be the one to complete the task, you shouldn't if it is part of the critical path. This is a great opportunity to mentor another member of your team and let them step up to a new set of responsibilities and expertise. This way, you can provide integral oversight on the task while freeing yourself up to handle other project management related issues.
It is important for project managers to do actual project work in any industry in order to stay sharp and relevant. Staying off of the critical path allows you to remain productive and make a fair contribution to the project while giving you the flexibility to handle any high priority project-related issues that arise.
Poorly managed projects can be disastrous for everyone involved including the business, so it's important that we allocate enough of our time to ensure the project is run well. Part of this is the ability to identify tasks that you should not work on and delegate them to capable team members. Delegating effectively and avoiding the critical path will go a long way towards the successful delivery of your project.