andrewc
XS650 Enthusiast
im writing to ask for your guys opinion on what my head stud issue im having could be caused by. the motor i have is a 72. ive built it with "Forgetrue" 80mm pistons,(must be close to 10:1 compression, they have a pretty big dome on them) 3 angle valve job and recut valves, (stock valves), new valve seals, new rings, re-honed cylinders, mild port wok in the head, and a stock cam. i got the motor not knowing it had the sleeves and the big pistons in it. first time i went to fire it, i found it had a blown head gasket. i took the top end off and found it was blown from the left side back (outer rear stud on the shifting side) stud which as you know has one of the oil returns encasing it. i bought a new big bore base gasket from mikes, a cometic head gasket, and did all the head work at that time. put it back together and it started to stretch that one (and only that one) stud which caused the head gasket to blow in the same spot again, ultimately letting oil and exhaust up and out of the top nut on the valve cover. (it made a horrible sound that sounded like a bad exhaust leak and i could feel air coming from under the acorn nut) i tried re-torquing it, a regular shouldered nut (thought maybe the nut was bottoming out inside before torquing properly on the brass washer ), and it ultimately snapped as i was in one of my re-torque cycles, due to it stretching. so i figured it was a weak head stud that over time caused the studs to get weak and that one gave out first. (but still, it was the only one that gave me an issue) i then found 8 NOS studs and replaced all 8 with the NOS ones. i just fired up the bike today after getting it all back together, and everything seemed great. i made it maybe 5 miles from my shop and it started leaking again, i could see the acorn nut shaking and could feel exhaust coming out again. (as well as see oil and exhaust staining around the washer/nut on the valve cover) it doesn't seem as the bolt has broken because it will re-torque, but im almost positive that this caused the head gasket to blow again. the head gasket ive been using (ive gone through 2 now) is a cometic 80.5mm, and the base gasket i made from aluminum. do you know why this one stud would be causing issues over and over again? i dont have any issues with the other 7, just the outer left backside. (closest to carb on shifter side) i put the head on a surface table and it was flat, no warping or play. have you ever heard of this before? im starting to think this motor is jinxed or has some sort of voodoo on it haha. i apologize for the short novel, i just wanted to explain my situation in detail. any help, tips, advice, or solutions are greatly appreciate. im almost at the point of just buying another stock motor and swapping my charging system and hand made ignition and wiping my hands of the whole "hopped-up" engine nightmare. thank you in advance.