Stripped cylinder head stud...

[Hambo]

...or rather the thread in the crankcase to which the stud locates. Started off with a routine 10,000Km service on my '94 GS11; checking the tappets, when I noticed the cylinder head nut on the LHS bottom exhaust side was only finger tight. Gentle torque on a 15mm socket only resulted in extracting the stud. After a few blue words, I removed head and barrel in order to remedy the situation.

The question is, what's the best way? Drill and tap casing to M12, and then have the respective repacement stud made up? Stick with the original stud and go for a M10 Heli-coil? Any experiences, comments gratefully received.

Thanks, Hambo

 

[Possu]

Heli-coil or similar is the best way to go, far easier than getting a decent stud made.

 

[Paul Young]

This happened to my R80GS & always seems to happen to the same stud (L/hand cylinder, lower front stud).

Check that the stud isn't part of an oilway as the airheads used the lower front studs as part of the oil feed to the c/heads with the return route being via the pushrod tubes.

When it happened to mine, I had the hole taken out to M12 & had a s/s stud made up for a cost of about £20 - M12 at one end then M10 at the other. I filed a "v" through the M12 end to create the oilway & fitted the stud before fitting the cylinder & c/head over it. That way, the stud pulled against its own base as well as the threads.

 

[Hambo]

Thread repair

Thanks for the response, decided to do down the helicoil route to repair the threads in the crankcase in which the cylinder head studs locate.

After stripping down the cylinder assembly and measuring the depth of thread required (20mm), I drilled out the old thread with the corresponding M10 Helicoil drill bit (10.4mm). With the girlfriend shouting alignment instructions (up! down!) and my heart in my mouth, in we went. (Please note the importance of using soiled boxer shorts to cover crankcase mouth!)

In order to ensure the tap went in true, I drilled out the respective hole in the old head gasket to match the diameter of the socket extention used to turn the tap. I then attached the old head gasket to the end of the studs, using plastic pipes as spacers, passing the socket extention through the pre-drilled hole.

After tapping down to the same depth drilled (25mm from crankcase surface, inclusive of 5mm recess), I used compressed air to clean out the swarf, before feeding in the helicoil. As I used a tapered tap, the helicoil locked itself at the end of the taper, in this case the correct depth required.

I then screwed in the old stud and as a result of the taper, the stud locked in the correct position and on the newly formed thread, not the back of the casing, which is important. Hey presto, repair complete!

Now I just have to put the rest back together.

 

[Noddy]

Well done that man, nice report and photos.

 

[Pukmeister]

Nice one, glad to see you found an ingenious way to solve it, including a cable tie on the cam chain / pulley to keep it aligned. That old gasket trick to keep the threads square is a good one, I'll try and remember that.