Well has anyone heard of the bolt for hell , i found out about it last week when im finally on holidays so decided to investigate why my xr400 lacked the power it used to have.... so decided to take the engine out , and conserve the frame while at it. after 4 days it finally came out here are some tips: 5Kg Hammer, SOLID steel bar very heavy duty with a big diameter so you can hit it hard with out a miss. Penetrating oil. took me 3 days missed a one blow and smashed my clutch case too .... but on the fourth day it started to come out slowly... i also stuffed up the bolt face. but welded another one on it and it finally was better grip and turned, also make sure the other side (bolt face) is supported by wood or metal , otherwise the bolt does go out slowly from the nut side of the frame, but incorrectly as the frame starts to stretch! one engine was out started the leak down test. found my right exhaust valve leaking and put some soapy water around the head and notice some bubbles coming out deep inside the fins from the intake side.... This is weird not sure what caused this: 1. Head gasket leaking and making its way through one of the vent holes into the area where its leaking 2. crack inside the intake valve chamber... but took the intake valves off and there is a hair line like a scratch . BUt both sides have something similar do not sure if its a crack.... here our some pics where leak came out from; Ok made the pics where the air was hissing out off. now in each intake port there are this lines as you can see, and right next to the valve lip this line looks sharper... could this be a crack hence leaking from other side ? but since the intake valves are closed the air could not have escaped to that crack, unless i have leaking valves but then i would of felt air at the intake port which i did not... So this leads me to think head gasket..... what do you Xr specialists think?