Boxerworks.com

I have a stripped case thread, one of three bolts that hold an oil filter cover that seals with an O ring. The bolt is M6 with a 1mm thread pitch and is about 3 1/8 inches long measured under the bolt head. The thread runs about an inch from the tip of the bolt. I'd like to install a helicoil but the hole is too deep for that. The tap is no where near long enough. I was thinking I could use a shorter bolt and install a helicoil closer to the surface of the engine case. The helicoil requires a 1/4 inch hole to be tapped for the coil. The existing hole fits a 1/4 in drill bit with a slight amount of wiggle. There is not much material around the bolt shaft so I would like to use a M6 bolt again. The bolt torque is 7 ft/pds. How tight would that existing hole need to be to correctly tap the hole for the coil? Or I'm all ears on some other solution.

If interested you can see the part on the link below. The case is marked RH and the numbers 25 are on that part. I'd hate to have to replace the entire case on this old but reliable machine. That bolt has always felt a little rough coming out and this time when attempting to gingerly tighten it, the thread failed and came out with the bolt. Shit happens....sometimes it happens to me.

http://www.yamahapartsnation.com/oempar ... case-cover

ewww! There is Japanese residue all over my BMW forum!

There can be a number of reasons why a bolt would reach way down like that before it hits threads.

1. (most obvious) The threads are in a different part than the unthreaded hole, and the part with the unthreaded hole is actually sandwiched between the cover and the part with the thread.

2. The area with no threads is too thin to support threading

3. The threads are deeper in the part because the metal down there is thicker and the part would flex/warp if the threads were in closer to the mating surface.

4. The unthreaded part of the bolt is serving some other purpose (I don't know what) between the mating surface and the threaded section.

5. The enlarged hole above the threads is an oil passage, and the bolt threads in below where the hole carries oil.

I'm sure there's others that haven't dawned on me. I can't imagine any reason they would put the threads that deep in there that wouldn't get screwed up if you threaded it up closer to the mating surface. The most obvious solution is to find a long reach tap (may take some searching on the web), but, since that will require a bigger bolt, I don't know if that's possible. Also, a bigger bolt could screw up numbers 4 and 5. Regardless, tapping up higher in the hole will face the same issue.

The main thing I'd do before I tried anything is determine exactly why that hole is threaded so deep in that hole.

I worked on a Honda CB200 for a while. It's case covers had varying lengths of fasteners quite long.
http://www.ebay.com/itm/50-NEW-HONDA-6M ... 46&vxp=mtr

I think the Major has it, though. The screws probably pass through the side cover and thread into the block.

And looking at that diagram closer, I don't even see a "oil filter cover" pictured or listed in the parts list.

Do you have a picture of the actual part/engine?

I have checked the availability of tap extenders and they are really expensive, so that is out. From looking at your diagram, you have to remove the side case to get to the area that requires the heli-coil. The area that the threads are located is in the main case. I would go that route for ease of repair and a chance to check out the other mounting holes.
You may have to get another heli-coil tap and make it a bottoming model as the standard one may bottom out before it makes threads deep enough to fully insert the heli-coil.

Major Softie wrote:
5. The enlarged hole above the threads is an oil passage, and the bolt threads in below where the hole carries oil.

The top hole on the filter cover is a bleed hole used when changing the oil. That is, if ZM's bike is like my '83 TT600
So the bolt is going through the oil filter cover, and then through the rh engine side cover and into the rh engine case.
It isn't a huge job to remove the side cover, and then perhaps clean, prepare and fill the threaded hole with JB and drill and tap a new whole.
I don't think/know if the threaded section actually passes oil through it. If it does, then JB's prolly out.

There would also be about 9,000,000 rh engine cases out there somewhere.

Edit, you're a smart guy Major.

ME 109 wrote:prepare and fill the threaded hole with JB and drill and tap a new whole.

JBWeld for thread repair? Never tried it. How does it hold up?

The bottom two bolts on my XTE filter cover are stripped - so the problem is not uncommon'.

On my bike there is sufficient hole/thread depth to take a longer bolt / piece of threaded rod / stud so it can be botched temporary till the clutch /side cover can be removed and a helicoil inserted.

Like sometime next year,if/ when the clutch needs replacing----.

The cover seals with an O ring so it doesnt need a lot of torque.

There was talk on the XT forum that bottoming out a stud might obstruct an oilway at the bottom of the hole, on some models , but if it does it will probably be the feed to the air bleed on the top bolt so it will be immediately obvious if it does.

The bolt does go through to the crank case, so it holds the oil filter cover and the clutch cover a the same time. There are a lot of bolts on that clutch cover. I guess I could attach the filter cover to the side case as a simple fix and if I have to do the clutch then deal with the better fix. I just need to figure out how to attach the filter cover directly. I don't believe the stripped chamber serves any other purpose.

Thank you for your opinions. I know this won't satisfy Robs quest for conformity, but I have not posted this elsewhere.

ME 109 wrote:

Major Softie wrote:

There would also be about 9,000,000 rh engine cases out there somewhere.

Not where I live. I've never seen another one like it in Canada. Not much on Ebay.