Stripped GS750 Spark Plug Hole

[Guest]

Today I went out to change plugs. One was extremely difficult to remove (inside left), one is still in with some liquid wrench (inside right), and the two outside plugs (not sure cyl. #, but far left and far right) came right out as they should. I know for certain that the inside left is stripped and I'm expecting that the inside right will be too. I've done a bit of research and it seems that Heli-Coil is commonly used. Has anyone used this kit? Is there a different kit that is better? Any tips/tricks/suggestions to being successful with this repair? Thanks in advance!

[tom203]

If the plugs are difficult to remove, the threads might just be buggered up, not stripped (yet). A spark plug chaser tap might clean up the the threads enough.
bunch of guys sell these things - years ago, I got a pair of 14 and 18 mm off Snap-On. You likely need the 12mm size. Note that are different than a conventional 12mm metric tap.

[Nessism]

The first generation 750 has 14mm x 1.25 pitch threads for the plugs. Not sure about the 2nd generation.

First thing is to try to clean up the threads as tom suggests. Failing that, I'd look for a solid insert thread repair kit. Helicoils are not very good for repairing spark plug threads because they sometimes unscrew when removing the plugs.

[tom203]

The 14 mm size is real common- check with friends/relatives who work on cars and borrow one. Use thick grease on it to collect the chips that might get dislodged.

[bwringer]

A solid insert spark plug repair kit is pretty easy to find. I believe they're $35-$40 at Pep Boyz.

As noted above, a thread chaser might take care of it.

[geol]

Most bikes have the plug thread slightly tapered and if you attempt to use a regular M14 tap if will stick. If you attempt to force it to turn, it will really stick. Use a thread chaser. If you must use an insert, NAPA sells a solid M14 insert but get the right length. I like 5/8" which is short but won't extend into the combustion chamber. When using a solid insert, you will typically get some anaerobic thread locker to hold it else it will come out with the plug next time the plug is removed. You may want to use some permanent red loctite. Last point I would like to make is that when you cut the new thread for the insert, stuff WILL get into your combustion chamber and I much prefer to buy a new head gasket and take the head off. Folks will tell you to grease the tap and this will catch some of the cuttings but keep in mind they are not magnetic so once in the combustion chamber they create a bit of an issue to get out with the head on the bike. Most folks turn the engine over so that the affected cylinder is at TDC. There are marks on your mechanical timing advance (T) to set the position of the crank so turn engine to that position. With the piston all the way up it is easier to use compressed air blow out the combustion chamber and an even better solution is to adapt some sort of straw to a show vac and suck the stuff out. Again, I have done this many times and if you do take the head off, insert all four holes and be done with this problem.

[rednine12]

Thanks for the advice guys. I plan on pulling the engine this weekend to paint the frame so I'll repair the plugs then. Hopefully it goes smoother than my fork seals. Thanks again!