WR450 2008 model
The threads have stripped on the left hand oil drain bolt, which drains the oil from the integral tank - the bolt has always been tight and wouldn't freely rotate by hand. When I had a look and started poking around, the thread peaks just starting breaking away from the crankcase main section. It hasn't been over tightened as I use a torque wrench and tighten it to the factory spec of 20Nm, but this seems a little high now, especially and the other drain bolt which is M10 (this bolt is M8) and that is 20Nm as well!
I am getting ready to repair it by tapping it out to M10x1.25, so it is the same as the other drain drain bolt.
There appears to be plenty of metal in the area to support the larger diameter bolt.
I have decided against helicoiling it back to the original M8 sie as I'm concerned about breaking the tang off the helicoil and it going into the oil tank and not being able to get it out, and also how to stop swarf getting into the tank when drilling and tapping the new thread (I know the trick about putting grease on the tap so the swarf sticks to it, but this isn't 100% effective and some swarf always escapes) and hence getting sucked down into the oil pump and possibly blocking an oil way.
To prevent swarf getting into the oil tank, I have made a little plug, from an M8 bolt, which I have filed a screwdriver slot into, and inserted it into the few remaining threads that are left - this blocks up the hole and will prevent swarf getting in to the oil tank. It is nothing more than 4.5mm of threaded portion from a normal bolt, screwed into the drain hole - you can just see it in the photo below. I can then drill and tap the hole knowing no swarf can get into the tank. The plug will then unscrew and as its M8 (ie has an OD of 8mm, and the minor dia of an M10 fine pitch internal thread is 8.80mm), it will come out easily past the new threads. Depth to this plug is 14.5mm which is just under the length of the new bolt (which is another bolt as fitted the the other drain hole), which I can shorten slightly so it will tighten up against the copper washer and make an oil tight seal
My question, is what is that little hole in the threads, circled in red?
I've tried poking a wire into it, and it appears to be a blind hole, so may be a bit of porosity in the original crank case casting, but I can't be certain.
Does anyone, who has split one of these engines, know if this hole goes anywhere?
Edited by GuyGraham, May 06, 2014 - 12:10 PM.