Exhaust Bolt holes on 78GS1000

[salty_monk]

How much meat is there on the bolt holes for the GS1000?

I have a snapped bolt in the lower outside on cylinder 3. I'm going to drill it out & Helicoil, not much room because of the frame.... I've got a pilot in there, seems to be pretty straight & I think I can stay fairly straight but it might angle a bit because of the frame as I go deeper.

I can measure they are just under 25mm deep (with a caliper) but I wanted to know if there is anything around them? Presumably you can only hit an oil line if you go too deep not off to the side???

Like an idiot I put a torque wrench on this one but hadn't checked the setting properly & so when I pull on it the bolt twisted (because the torque setting was too high) & has been held on "by a thread" ever since!

Teach me to rush putting the exhaust on late at night... (a friend had just flown in & we wanted to go riding so I needed both bikes operational!)

Dan

[Pete Logan]

I think I can stay fairly straight but it might angle a bit because of the frame as I go deeper.

Not sure on the meat, but that right there doesn't sound like a good idea. If you can get a longer bit to avoid the drill kicking out against the frame that would be better.

Aside from anything else, if the hole is off, the recoil prolly won't hold.

[FlyingSteve]

5 of the exhaust bolts snapped on me because they were severely rusted and they just snapped like twigs when I tried to take them out. I was able to get 3 of them out by using a TIG welder to get them nice and hot and weld little "blobs" on and then weld nuts on to the blobs... Took a lot of doing though... I welded and re-welded on them like 5x each till they finally broke loose and I was able to spin them out. The other 2 just would not budge and so I had to drill them and use a helicoil. I didn't drill them out perfectly, was slightly off center, but the drill went through fairly easily and then on the one I was able to weld a blob to the remainder of the bolt and get it out but the other bolt I had to completely drill out. There is a fair bit of meat on the '80 550 head. As long as you don't go and really oval the hell out of the hole, you should be fine.

[Nessism]

Dan - there is NOT much meat on the sides of the threaded bosses so red flag if the hole is not dead nuts on center. I have some chunks of aluminum, and drill bushings, so you can make a drill guide if you are not comfortable with the results you have achieved so far. At the very least I'd stick a bolt into the good hole, your drill bit into the pilot hole you have drilled and eyeball the two so see if your going in at the same angle.

BTW, the hole from the factory is much longer than common helicoils so you don't have to go full depth unless you want to use two helicoils or get some special long ones.

[salty_monk]

Was planning just to go depth of one Helicoil which I think is 12mm plus clearance for the end of the tap (unless those kits come with a plug tap??)

At this stage I have "taken a pause" as I don't want to screw it up. I believe I am pretty central & straight so far but I am only in about 6mm.

The pilot I drilled was with a left handed bit & I stop as soon as it started to go off centre because of the frame & then used one of those Dewalt bits with a pilot tip on it which appears to have gone in straight.

What's the drill size for the helicoil? Possible that I may have to go pick up an extended one.

Dan

[first timer]

Dan, had this happen on my Kat, if you value the head pull it and take to machine shop so they can do it nice and square. If you insisted on doing it pull the head or engine to get a straight shot. The frame will really mess with you when drilling. And once you get off center it gets worse exponential.

[salty_monk]

No time for that mate... bike is going to Reno next month

I know what you're saying though. I think I can get a straight enough shot to get a helicoil in there with the right length of drill bit.

Seems like the drill size for Helicoil is 21/64" (about 8.35mm, I thought it would be bigger than that but I guess the tap cuts it out to about 9mm or so.

Dan

[FlyingSteve]

Take your bike to a machine shop or weld shop and let them extract the bolt using a TIG welder like I did with a few of mine.

[salty_monk]

Managed to successfully drill & helicoil with the engine still in the frame. Just took it easy & bought an extra long pilot drill.

I also plugged the front of the hole smooth with JB weld & poked a punch in it central to give me a good starting point on a nice flat surface, seemed to work well. (I was worried about hitting the rough edge of the snapped bolt & skating off centre.)

Dan

[simon kuether]

I had a similar thing .
I've just rebuilt the engine so while I was at it , I got the head drilled , helicoiled and studs fitted so no more bolts .
I was a bit suss of the frame /angle thing as well and decided against it and just put up with it until now .

Glad to hear it all worked out old mate .

Cheers , Simon .

[salty_monk]

I just bought a stud kit from Napa that was recommended on here. They seem like a good bit of kit, 10 studs & nuts for $14. Looks like they are right on the lower length limit for aftermarket pipes but should work out ok.

I have one on my 750 that is going to need the same treatment as the threads are very sloppy from 30 years of removing & replacing the Bassani for oil changes no doubt. When I put it back together I actually had to search for a bolt on the upper end of the thread dia tolerance in order to get it to bite.

Dan