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Stripped spark plug hole...

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by kols_kebabs, May 14, 2007.

  1. My bike started running very poorly this afternoon, sounded like it was only running on 3 cylinders. So I decided to check the plugs, and sure enough, one of them had no gap and significant carbon build up.

    Cleaned it, gapped it etc... But now I can't get it back in!

    The top part of the spark plug hole is stripped, and when i try to insert it just grinds alloy off and spins in the hole. It's only the top few mm, almost all of the thread is otherwise there.

    I tried one of the plugs from another cylinder which is evidently fine, and it won't go in either, so it's not the thread on my spark plug.

    Anyone have any idea of possible repairs and cost?

    I was thinking, if I could just sand and remove the top few mm of crappy stripped thread, I might be able to get the plug to grip the remaining thread. Tricky in practice, but sort of makes sense in theory. A bit of oil down the hole probally wouldn't hurt either.

    Please tell me I won't need to have someone take the head off to put a new hole in... $
  2. Get a thread file, auto one might have them. Jam a bit of rag down the hole first to stop any shavings from going down there.
  3. Is this different to a regular file?
  4. if all else fails or it gets any worse try using a heli-coil kit but it means taking the head of to drill it..would post you a link but apparently have to have 5 posts first??

    Kit normally includes:
    - 3-4 recoil springs
    - recoil tap
    - drill bit
    - handle to use springs and tap.

    how it works....

    1. if the original thread is an M10 and its stuffed... you drill out the hole using the drill bit, which cleans off all the bad thread...

    2. using the tap provided... tap the new drilled hole...

    3. insert the spring into the new thread, which will now reduce the hole back down to the orginal M10 thread...
  5. very different :p
    If not a thread file, you can also get the right sized spark plug tap and re cut the first few mm's ? But be very carefull that your in square on to the head / spark plug hole direction, or you'll make a small problem even bigger :p

    Ps: no matter what you try, your going to have to use a rag or tissue to stop any metal getting down into the bore !! :evil:
  6. Ok, I wont tell you what you already know to be true :?
    Have to recoil or helicoil it dude. Only fix I know off. As for cost. Several hundreds at a conservative estimate :cry: Involving a few hours labour at least, head gasket, maybe rocker cover gasket, redo the timing, heli coil kit(the cheapest part by far in this little exercise :grin: )

    Trouble is when you get to this level of dismantling, seeing as its already in bits, do you give it a set of rings, valve grind- the list goes on :? Thats really all depends on the k's on the bike,was it running fine,was the power ok, etc etc
  7. It's already happened, a few alloy shavings now reside in the bore :p

    I'm optimistic about what will happen when it's next started. I apply a 'she'll be right' attitude to all my mechanical works. At 92'000k's the bore is hardly in perfect condition as it is.

    Getting the head off, retapped etc... these are things I'd defienetly rather pay someone else to look at, then pay to fix my bodge.

    Interesting, thanks. Power and running is fine, but blows smoke, definetly new rings wouldn't hurt, mabye even new pistons and a rebore, valves etc...

    Overall bike is (was!) brilliant- brakes, frame, shaft drive etc everything perfect, surprising for its age... and it is a semi-classic I enjoy. If I'm already spending, getting the full top end is something to definetly consider.

    It's so pissy, that on an old, high mileage bike, the tiniest thing has caused massive expence and problems. I would mind much less if the failure had been spectacular, that'd be a story.
  8. Helicoil is your friend, if you can get access, you can drill it while the head is on, I did it on an ED ford falcon some time back.

    Get a small piece of rag (small enough to fit in the hole and cover it with vaseline, make sure piston in cylinder you are drilling is at TDC and insert the rag leaving it just below the inner surface of the head to catch filings, worked well for the ford, and saved me removing head, cam chain exhaust/inlet manifolds etc etc
  9. Well it's head of time, even as you say its done a few k's those few metal shavings will come back and bite you hard in the hip pocket, worn bores can be easily honed out and fitted OS piston / rings, but deeply scored bores mean, throw the block out :p
  10. Ok heres da deal if some alloy shavings etc have entered the cylinder before you actualy put the offending plug back in , start the bike up and let it blow the crap out of said cylinder problem gone !!
  11. Option B is a second hand head. Bolt it on and forget all the other stuff.
    I tend to think it should be possible to get the plug back in there though with a bit of work, but I'd use an Iridium plug, so I didn't have to touch it for another 50-75 k kms!

    Regards, Andrew.
  12. I can actually probally get a second-head free, the last owner offered me a complete spare bike, I just CBF'ed at the time.

    Iridium plug sounds very smart.
  13. u know u could probaly grab a stanley knife and cut and bend the tread as required.
  14. What sort of knife are you using that can cut into an engine? Diamond tipped blade?
  15. You can get plug savers from any decent auto fix it shop

    They are a tap cut into four segments with a setting bar down the guts

    Works like this remove setting bar from saver fit it into the plug hole will make clicky sounds as the cutters slide over threads

    Then insert setting bar and unscrew from thread

    Easy peasy fixed for around 35 bucks

    Oh and when tapping holes etc in heads dip tap in grease as it makes the shavings stick to tap

    Good luck :grin:
  16. Do you end up with a smaller plug thread?
  17. Sorry mate they are a thread chaser they do not leave an insert

    Imagine a tap 4 sided with no core or inside dia say 8 mm the tap flanks would then be flexible ie collet style R8 etc

    You can then deform the tap into a undamaged section of thread and then by inserting the 8 mm bar it then becomes a rigid body

    Sorry I dont have a photo bucket so cant through up a pic
  18. I think I get it. sounds worth a try.

    I too though you could heli-coil with the head still on.
  19. Helicoils can be a problem in some applications as the face where the plug seals if it is kicked to any degree can leak

    Seen it before there are keenserts helicoils all lined up to take your money yep there not cheap but then again whats your bike worth at the end of the day ?????

    Yeah always remove the head when helicoiling spark plug holes etc its just not woth the risk of all that carbon, and alloy swarf slinging around the engine internals

    How did i learn that well one RDLC total one scrapped barrel and piston after about 40 hours of porting matching the cases shifting port heights etc all for the cost of some time and gaskets

  20. Helicoils are not meant for the extreme environment of the combustion chamber, and will always only be a temporary fix. What you need is a Timesert (http://www.timesert.com/) put in there. Similar principle, but better execution. Have had this done on the 900 when I reconditioned the head. Strong as.

    What ever you do, you really should pull the head, or you're asking for trouble.