Hi.  Just put new piston and rings on my 68 YG5T.  It starts up and runs great, but I discovered that one of the bosses on the inside of the tank that center it over the frame is weeping gas.  I think one of the spotwelds that holds the boss to the tank has broken loose. 

I was thinking of using some POR15 patch in a bead around the boss to seal the leak and then possibly make a plastic collar that is slightly larger than the boss to take any pressure off it - meaning remove the rubber bumper and no longer have the boss press on the frame.  This all seems sketchy though - considering if the leak gets bad.. well.. fire.

Just a shot in the dark out there in case anyone has a workable tank for one of these waiting for a home?  I know.. doubtful.  Or, has anyone had experience and a possible workable repair with a spot weld on one of those bosses breaking free?  Ideally, it would be a braze/weld repair followed by a tank seal, etc.  Sadly, I have a ride in mid May and this might be the show stopper for that.

P.S.  I don't know if a YG5T counts as a badge bike.  My tank badges are gone, anyway.

Thanks for any ideas.
-Adam

It might be helpful if you were to post up some photos of the tank and the area of concern. That way others could think about what needed to be repaired and how they might approach it. I would suspect that however you do eventually affect a mechanical repair, that you would want also to then seal the tank after.

I have been contemplating some repairs on a early '68 DT1 tank that had been repaired a few times before, apparently with braze. The tank holds liquid, but looks terrible. Not quite sure how I will tackle that. I suspect if your tank is otherwise original, that might be damaging to the original finish.

Snap a couple of pics and let us see what you are up against.

Thanks for the ideas.  Yeah, this bike is really beat up - definitely nothing cosmetically good about it.  I ended up using POR15 Patch, which worked really well.  I've used POR before and found it to be essentially indestructible.  I agree, I should seal the tank, but will likely wait until next winter to do it.  There are not any other leaks and generally the metal seems solid (enough). I made a separate rubber standoff, and removed the rubber plug from the boss that was leaking, so now the area that was leaking is not a stressed part (i.e. Just in air - not resting on the frame.)Now the bad news.. 2 miles after a fresh piston and rings, the engine seized again.  This was light riding and just re-timed the engine.  I suspect the injector pump.  It did restart and I'm going to try premix and see how that goes.  Geez. 

 
 

POR15 is pretty good stuff, I know several members here have used in many areas and on many things other than Yamaha enduros with success.

Sorry to hear of the engine seizure, but with only a couple of miles hopefully it will not have done too much damage. You indicate suspicion of the oil pump, and that is always a possibility. May I suggest that if it is not too onerous for you to maybe take a peek into the cylinder, maybe through a port, and do a visual check for damage? You have a new piston and rings, but (probably a dumb question) were the ports chamfered just a bit by whoever did that task? This would not be the first 2-stroke engine that had that step missed. Probably not the issue with the small bore like it is with larger, to be sure.

If you are suspicious of the pump, after you have bled it (you did, right....??), you could do an output test by temporarily removing the output line and letting it drip into a small measuring cup (I use a Nyquil cup), rigging the throttle so the pump is at maximum (engine is not running), and spin the wheel 200 times and see what you get. If you get around 5cc/ml, that should be enough. That would tell you the pump was giving sufficient oil. (pump output for a 125 at max throttle should be around 4.6-5.1ml, per a note I have from DEET)

I can tell stories about forgetting to flush the oil tank of all old gunk, filling it with fresh Yamalube, bleeding the pump, and discovering a few miles later there was water in the oil tank ( ICK!!!), but that's a thread for another time.