As an immigrant without a work visa, you shouldn't be taking income away from other shops. There are lots of ways to set up a business entity. Those other shops are trying to feed their kids and keep a roof over their families' heads. If you want a semi-business hobby, teach some local kids. Pass your knowledge on. The community will love you. Good luck. You'll figure it out.

You can't work without an Alien Employment Permit and the matching work visa. It's not worth the hassle for 1 US dollar an hour. A better idea: get a Special Work Permit and volunteer through a church or another organization, fixing things for people who can't afford it. Done right, that might eventually qualify you for an SRRV Courtesy Visa (if you're not already ex-military).

Here's a suggestion. First, look up PEZA. https://www.peza.gov.ph/ If you can produce something (anything) that can be exported, you can own 100% of the business, import tools and equipment for it without any fees, and qualify for a lot of other perks. Example: import broken outboard boat motors, hire locals to rebuild them, and ship them right back to the US, where new outboard prices have made this profitable. I'm a US manufacturer living in the Philippines, and I plan to replicate my US business here to tap the markets in this part of the world. PEZA is also a one-stop shop for permits and licenses, so you don't have to deal with local governments and the headaches that come with them. Why compete with locals when you can employ them?

Better come fix all those Vietnam War–era helicopters the US donated to the Philippine Air Force and make them airworthy again.

Cente, that sounds like a perfect retirement hobby, especially with your mechanical background. If you're only working on your own scooters or helping friends now and then, that's very different from openly running a repair shop. But once you start taking paying customers regularly, even by word of mouth, the local barangay or LGU may treat it as a business. Then you could run into requirements like a barangay clearance, a mayor's/business permit, BIR registration, and possibly zoning or neighborhood restrictions. As a foreigner, there may also be separate rules about actually working or running a business. My suggestion: build the detached garage/workshop for personal use first, and check with the barangay and the city/municipal business permit office before taking regular paid repair jobs. That way you can enjoy tinkering with scooters and motorcycles without creating unnecessary legal problems.