Smashed Spark plug...

Smashed Spark plug... 1998 R1100GS

Own 1998 R1100GS..
Problem is right side spark plug electrode is getting bent/crushed by the piston.
About 2 years ago, on a cross country trip, the right side plug electrode totally was destroyed. Got the bike home and redid both side cylinder heads/seals. Saw nothing out of the ordinary(to me at least).Figured it might have been due to valves not being adjusted in a long time. replaced the plugs and ridden ever since.
Everything was fine until i just replaced both side plugs last week (Autolite 3923). Ran fine for 2 weeks and yesterday suddenly lost compression, and i limped to work. Pulled both side spark plugs and the right side Ground electrode was bent to the side. bent it back and bike was better , but not quite right(probably gap)...but again half way home started again. Pulled off and pulled the plug..bent again. Managed to get home with bike getting progressively worse, with bike stalling in driveway.
Have read a lot about the possibility of the piston bearings failing... causing the piston to be coming farther out, and hitting the plug?
Have always noticed a "ticking" coming from one of the cylinders while riding. Plug hitting Piston?
Another thought occured to me. I looked in the plug well and it seemed to be well worn, probably from having plug put in and taken out for 20 years. Maybe it has worn enough to let the plug get seated further into the well and cause it to hit the piston? This combined with overtightened plug? Could i add an indexing washer to move the plug back?
Was wondering if this might be a fix, rather than disassembling the whole cylinder to examine the piston setup, and finding all was well ...just to find my problems were caused by a worn plug well.

Any thoughts?

Chris

Chris,
Are you sure you're using the correct plugs? It sounds like they have too long of reach. I can't imagine the plug hole would have changed depth over time.

Carbon buildup on the piston?

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RadioFlyer said:

Carbon buildup on the piston?

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That would be my first suspicion.

If spark plug depth was wrong, the electrode should smash right away. Same if the con rod bearing or piston wrist pin came loose but the noise would be horrendous.

Keep in mind, these bikes use a cam ground piston which changes shape when they get hot.

All true (though that would be a LOT of carbon), but alternatively: Chris, you say that it lost compression... How did you determine this?
I'm wondering about a bent valve; or maybe your smog canister puked? Those little bits can be sucked in via the vacuum hose.

"Ordinary" and normal ticking may be a slightly loose valve (like the way I set 'em) or sideplay on the rocker shaft.

6322 said:

Chris,
Are you sure you're using the correct plugs? It sounds like they have too long of reach. I can't imagine the plug hole would have changed depth over time.

Click to expand...

1998 r1100gs..
Autolite app 3923

Pauls1150 said:

All true (though that would be a LOT of carbon), but alternatively: Chris, you say that it lost compression... How did you determine this?
I'm wondering about a bent valve; or maybe your smog canister puked? Those little bits can be sucked in via the vacuum hose.

"Ordinary" and normal ticking may be a slightly loose valve (like the way I set 'em) or sideplay on the rocker shaft.

Click to expand...

By compression, i mean, I was riding along in 4th...40mph...then suddenly , no power...slowly slowing down thru the gear range... same thing happened last time the spark plug lost its head...riding on one plug instead of two...

That plug and that piston have clearance. Carbon bits, or a carbon buildup can cause a collision. I would stop riding until I had pulled the heads and determined what was colliding with the spark plug.

PGlaves said:

That plug and that piston have clearance. Carbon bits, or a carbon buildup can cause a collision. I would stop riding until I had pulled the heads and determined what was colliding with the spark plug.

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Did that once before and found nothing... was trying to avoid pulling the heads again!

Are you stuck on Autolite plugs? I think I would try a set of NGK's or some other brand to see if the problem repoccures. If not you're all good, if it does re-occure I don't see an alternative to pulling the heads.
Dumb question, you are installing the plug with the sealing washer in place, correct? (Sorry, just covering bases).

If the issue was/is the length of the plug reach the collision would happen the first time the piston came to top dead center. Since this seems to be erratic something is in the combustion chaamber that is not supposed to be there.

CNRed said:

Are you stuck on Autolite plugs? I think I would try a set of NGK's or some other brand to see if the problem repoccures. If not you're all good, if it does re-occure I don't see an alternative to pulling the heads.
Dumb question, you are installing the plug with the sealing washer in place, correct? (Sorry, just covering bases).

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Yup, sealing washer does not come off...wonder if the plug dimensions differ between plugs...

cal0987 said:

Yup, sealing washer does not come off...wonder if the plug dimensions differ between plugs...

Click to expand...

See Post #11.

In my 1996 R1100RT I am also using the Autolite XP 3923. I pulled one of mine out and compared it to the Bosch FR6DDC that I removed from it a while back. See pic. The Auotlie measures about 0.090 in longer than the lBosch when measured from the sealing washer to the tip. That longer of a plug may bring it very close to the top piston.

PGlaves said:

If the issue was/is the length of the plug reach the collision would happen the first time the piston came to top dead center. Since this seems to be erratic something is in the combustion chaamber that is not supposed to be there.

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This makes the most sense.

For my 1996 R1100RT my Haynes manual calls out NGK BCPR7ET. Clymer calls out NGK BKR7EKC-N. Also saw the same numbers on some Auto Parts cross reference, when I put in the Bosch FR6DDC number. When I look at various models of the R1100 and R1150 in my Haynes and Clymer, I didn't see the Autolite 3923 called out. I think I will check some of these other plugs out and measure the ( Thread Reach + Electrode ) dimension, to make sure they are no longer than the BMW original Bosch FR6DDC.

Back when I had my 1995 R1100R there were many using the Autolite plug with no problem. I doubt that it is the plug.

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oldcarman said:

I think I will check some of these other plugs out and measure the ( Thread Reach + Electrode ) dimension, to make sure they are no longer than the BMW original Bosch FR6DDC.

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Or you could just make your life simple, use the FR6DDC and spend your time doing something more interesting.

But then, where's the fun?

I really really really doubt that the plug is the root problem.

Pauls1150 said:

But then, where's the fun?

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Agreed! Something about chasing one's tail comes to mind.

I now refer the OP back to Post # 8.