I have an 87 TRX 250R with a 4ml 310 stroker and while out riding recently all but one of the four head bolts sheard off and the head came loose. I have taken the head off and everything seems to be perfectly ok other then the head bolts. Has this ever happened to anyone else? Any idea as to why the bolts broke in the first place?

 

the extra compression probably did the damage. They prob stretched and then broke the bolts off???