Engine covers

[baylensman]

So when I did my slave cylinder I had to take off the left hand rear finned cover. Evidently I did something wrong putting it back on. I noticed the other day the center or lower bolt of the three has fallen out. I have several spares of various lengths in my tool box. I tried to put one in, it never tightens up! It feels as if there are threads because the bolt feeds inward as I turn it, but never bottoms out. I'm guessing the threads are stripped in the head, but there is just enough left to allow the bolt to suck inwards? I was wondering should I drill our and retap and helicoil it, or just tap one size bigger and use a different bolt? if I go from and 8 to a 9 will I have to open up the hole in the cover?

The cover feels snug and doesn't vibrate at all, but it does hold the freeze plug in place doesn't it?

[Flyinfool]

First make sure the bolt you are putting in is really a metric bolt of the correct size.

If the threads are stripped I would put in a heli coil so that you are still using the correct screw. I hate going up a size and having one oddball screw. That oddball will just make things more difficult for as long as you own it.

[M61A1MECH]

[cowpuc]

If it were mine, the first thing I would do is clean out the hole real well where the supposively bad threads are. Then I would measure the depth of that hole. Then, if I didnt know what size of metric thread I was dealing with, I would remove one of the other screws holding the cover on to help me determine thread size when looking at other screws. I would then dig around in my vast metric screw supply or head down to ACE Hardware or the local bike shop and find a screw to replace the lost one that is 1/2 mm or 1 mm short of hitting the bottom of the measured depth of the hole.. Once I found the new screw, I would carefully screw it into the hole and, by feel as I screwed it in the hole, I would determine whether or not I had cross threaded the original threads. If I had buggered the threads up, I would take a flat tipped bottoming metric tap (or take a Tap the right thread size and carefully grind off the tip of it to make my own bottoming tap) and re-chase the threads in the hole all the way to bottom.. I then would use the new metric screw to replace the one I had lost, I would also put a smear of Blue Loctite on the new screw placed into a freshly cleaned set of internal threads so I knew this repair was the best it could be..

IMHO,, I personally dont care much for Heli-Coil's.. I have used them and,, they dont always fail but I have seen them go south on more than one occasion - you know,, unscrew the screw and the heli coil comes out too.. That, and the fact that you still gotta chase new threads to use the heli coil so your oversizing the hole anyway.. I have found that by going SAE in place in Metric that you can usually just tap in the next size up SAE threads if the entire hole to bottom is ruined (usually this is not the case). Then you just replace the screw with an SAE threaded screw.. I know,, sounds back yard mechanicism to the max to lots of folks but,, fact is,, IMHO,, so is using a heli coil because the fully correct way of repairing such a mistake is replacing the case = lots of work = lots of ..