It looks like a pin to hold the engine in the up position for service that someone built or it's just the end of the factory tilt lock without the handle on it.
It doesn't look like a home built thingie, more like OEM. It has a spring and detent feel. You can push it in and she'll bounce back. Pull it out and it stays there.
It's tough to look something like that up with no model or serial number as there are may variations of V/6 engines, you might tale both to the BAM Marine site and look at the parts break downs for help.
Trelos, the "duh" was on me, not you. I should have given that info from the git go. Couldn't get the serial before, boat was in my storage.
But here's the unit's info.
1984 Blackmax 150
Sn#6439912
Is there a site with blow up parts diagrams anywhere?
Eric
that's what it is... my '82 V150 has the same thing. I wasn't sure if it was supposed to be a lock for trailering, but I thought it was too flimsy for that and never used it.