Tappet cover stud - how to install after rebuild

[Mark Tierney]

Maybe this is obvious, but I am a little confused. I completely restored a 1980 650SG this winter and it runs great. However, one tappet cover stud pulled out of the engine. What I don't quite understand is how these are originally installed. They are threaded on both ends, but the engine block has no threads, just a very cleanly bored hole. I can't imagine that internal threads could shear off this cleanly. Any insights? Are they epoxied in place? Do I thread the hole and use an insert? Any suggestions appreciated. The issue is I can't snug the acorn nut down enough to stay in place.

Thanks

 

[DogBunny]

The threads are so completely stripped that you can't tell that there ever were threads, but there were.
Buy a Helicoil or some other thread repair kit. Hopefully it's a hole that's easy to get to, but can still be done even if not.

 

[rebel542]

The threads will pull out that easy if over tightened. The easiest and neatest fix is Time-sert.

 

[5twins]

I just fixed one of these for a ham fisted local guy. Yes, the threads can pull out so cleanly, it will look like there never were any in there to start with. When he showed it to me, I removed the stud and the threads came out with it like a little coil spring. The hole in the head was mostly clean with just a couple threads left at the bottom. I repaired it with a Helicoil. This was the first blind hole I ever fixed but it worked out quite nicely. What you need is the special Helicoil bottoming tap to get threads deep enough into the blind hole. Luckily I just bought some off eBay.

 

[Mark Tierney]

Thanks for the feedback, I never would have guessed that threads could break out this cleanly. Now that I think of it, I do recall some small amount of material in the threads on the stud that looked like a spring. I'll get a helical and clean this up. Thanks for the information.

Mark

 

[5twins]

If this was one of the small studs on the 3 hole covers (and it probably was), the size is the a standard M6 x 1. This small size bolt abounds on most motorcycles and is one of the most commonly stripped. It's the size of all your side cover screws and the pinch bolts for your lever perches. Anyone into old bikes should have at least this size Helicoil kit (I have M4, 5, and 8 as well). Here's the special bottoming taps you'll need to do a blind hole .....

http://www.ebay.com/itm/130705967851?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Use the normal regular tap included in the kit to get the threads started, then switch to the bottoming tap to finish.

 

[fredintoon]

- - - What you need is the special Helicoil bottoming tap to get threads deep enough into the blind hole. Luckily I just bought some off eBay.

Hi 5twins,
ALL helicoil taps are special, they have the same pitch as the hole they are salvaging but they are fatter in diameter.
Got a link for those E-Bay taps?

 

[Mark Tierney]

Thanks. You are correct, it was one of the 3 hole covers. I'll look to order tonight.

 

[5twins]

I realize all Helicoil taps are special as far as size and pitch goes. I was referring to the the style or type of tap. Normal taps for through holes are either the taper or plug type. They have 7 to 10 (taper) or 3 to 5 (plug) chamfered threads at the tip to ease starting of the thread cutting process. The bottoming tap only has 1 or 2 chamfered threads so will cut full threads deeper into a blind hole. If the blind hole is deep enough, you may not need the bottoming tap. In the case of these valve cover stud holes, they aren't deep enough so the bottoming tap is needed.

 

[fredintoon]

- - - In the case of these valve cover stud holes, they aren't deep enough so the bottoming tap is needed.

Hi 5twins,
normal Helicoil tap will bottom out before the full stud depth is re-tapped but will it tap deep enough to get the Helicoil all the way in?
Seems to me the thread on the stud is a fair bit longer than the Helicoil?
But yes, I opened the link to those Helicoil bottoming taps.
Not shy about the price, are they? Plus as much again for shipping to Canada.
It'd pay me to buy another Helicoil kit, grind off the end of one of the 2 taps I'd then have and be in profit by all the extra inserts in the new kit.

 

[gggGary]

Another way to skin this cat.

http://www.xs650.com/forum/showthread.php?t=28729&highlight=valve+cover+stud+repair