Open hole on top of case??? + mystery knocking noise

[Cafebrat]

Hey guys,
New member to the forum here, but I've been finding all my Suzuki info for the last couple months here and it's been suuuuper helpful. Anyways, I recently bought a 1972 Suzuki T500. The engine had a random and intermittent knock after the bike warmed up about 3-5 min into riding. So I pulled my cylinders off expecting to see a crap show but everything was clean, tight and as it should be. However I did notice that my right side head gasket (the metal one) was a much smaller diameter than my piston, and is bent/pressed upward on the inside edge. When I put in back on the top of the cylinder there is a very apparent overhang indstead of fitting flush with the cylinder bore like the left side does. so I'm assuming this is my noise, the piston making contact with the small gasket diameter. Does that make sense to anyone else?? Idk I'm pretty novice when it comes to mechanics. Anyways, I ordered a new gasket set and new rings to re-assemble and I'll see where that leaves me.

My real head scratcher is that I noticed a small hole in the top of the top case. If your looking at the engine as if you were on it, on the back side of the cyliders, where the cylinders meet the case, there's a fin dividing the area into two, and on the right side I have about a 1/4" hole that goes right into my gear case. Is this supposed to have a hose or filter on it?!?! I'm really confused why there's an open hole to allow crap to get in there. I'm assuming it's a crankcase breather but it should have a filter right?

Thanks in advance guys!

[GT750Battleship]

Very hard to know...without photos..could you upload some ?
Cheers,
Roger

[Rocket350]

I couldn't say on the head gasket but I'd say its possible. Its obviously incorrect so I'd install a new one and see. As far as the hole, I came across it on mine after a pressure washing. I think its nothing more than a drain so gas water or whatever won't puddle up there in that valley. Look under the bike and you'll see where it comes out. I still Ned to get something in there and clean mine out.

[ConnerVT]

I believe you will find that this is a drain hole, which passes through to the bottom of the motor. It allows water to not collect on top of the case when it rains.

[sbaugz]

Yup, it's a drain hole that goes all the way thru crankcase and comes out underneath.

[Cafebrat]

Thanks guys, I went down and stuck a wire down through the hole and hit the wood board it's sitting on. When I realized it, I felt like a complete idiot I hadn't just stuck a wire in there right off the bat. If anyone's interested in hearing the outcome of the engine I'll follow up. And if all goes well maybe youll see my T500 in a build thread on its transformation to a cafe