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Thread: Smashed Spark plug...

  1. #16
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    Smashed Spark plug...

    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.

  2. #17
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    Back when I had my 1995 R1100R there were many using the Autolite plug with no problem. I doubt that it is the plug.

    Sent from my SM-G950W using Tapatalk

  3. #18
    Registered User AntonLargiader's Avatar
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    Quote Originally Posted by oldcarman View Post
    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.
    Or you could just make your life simple, use the FR6DDC and spend your time doing something more interesting.
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  4. #19
    MOA #24991 Pauls1150's Avatar
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    But then, where's the fun?

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

  5. #20
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    Quote Originally Posted by Pauls1150 View Post
    But then, where's the fun?
    Agreed! Something about chasing one's tail comes to mind.

    I now refer the OP back to Post # 8.

  6. #21
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    Quote Originally Posted by Pauls1150 View Post
    But then, where's the fun?

    I really really really doubt that the plug is the root problem.
    But you have to consider that it IS possible. And it is the easiest and cheapest to test. Just change the plugs to the factory specified plugs and ride. It would be a bitch if you removed the head and didn't find anything BEFORE you eliminated the easiest possibility.

    If the stock piston to plug tip clearance is say .040" and the Autolite plug is lets say .035" longer than stock,
    the piston might not hit below maybe 5000 rpm, BUT it might hit at 7000 rpm due to rod stretch.

    I have seen many pro built racing engines (car) disassembled where there was evidence of the pistons JUST kissing the bottom of the head because the builder underestimated rod stetch. There had been what they thought would be adaquate clearance when they were assembled.







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  7. #22
    MOA #24991 Pauls1150's Avatar
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    Certainly it's possible; the photo in post 14 shows exactly that.

    But from post #1, he had already changed the plugs twice. He's not clear if he used a new "factory" (Bosch) plug each time.

    But also consider that this is an 1100GS ... Back in '98, didn't those also have a lower compression ratio as part of the difference between them and the RS and RT (along with the different intake cam) ?

    I remain unconvinced it's the plug, and I concur with Post 11. Or just possibly a stretched rod (good thing this ain't an S1000) or a worn crank or wristpin bushing.

    btw - OldCarMan, MANY of us used the Autolite AP3923 plug, including me - ZERO issues with them. For the 1150 single-plug, the 3922 (not 3923) can be used.

    Another thought just occurred to me - If a bent valve has reamed out the valve guide, he would not necessarily see a lack of cocentricity with a cursory look...
    Last edited by Pauls1150; 08-24-2019 at 03:12 PM. Reason: 'cuz i wasn't even thinking about the diff btwn the single- & twin-spark engines...

  8. #23
    CAL0987
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    Put the new plugs in... did a throttle balance and always have a terrible time balancing... something not right...maybe pull the throttle bodies and do a service
    May also pull the heads and see if anything is out of the ordinary... I trust Mr. Glaves wise opinion

    Also , need an opinion on plug tightness... i install the plugs with the tool that comes in the r1100gs toolkit, since the plug socket i have will not fit in the plug well...
    I can only get a tightness 1/4 turn past hand tight.. not enough? my reading says anywhere from 3/8 to 2/3 turns..

    Would having the plugs not tight enough be causing any problems!

  9. #24
    CAL0987
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    Have not used factory plugs...can try that...

  10. #25
    Registered User GTRider's Avatar
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    Quote Originally Posted by cal0987 View Post
    Also , need an opinion on plug tightness... i install the plugs with the tool that comes in the r1100gs toolkit, since the plug socket i have will not fit in the plug well...
    I can only get a tightness 1/4 turn past hand tight.. not enough? my reading says anywhere from 3/8 to 2/3 turns..

    Would having the plugs not tight enough be causing any problems!
    Either too loose or too tight can create problems. If you are using a tube-type plug wrench it’s not difficult to modify the wrench so you can use a regular socket and torque wrench on the plugs. See pics below...
    Best,
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  11. #26
    CAL0987
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    Tanks DeVern! Will try this!

  12. #27
    MOA #24991 Pauls1150's Avatar
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    Certainly too tight or too loose is an issue, so most plug manufacturers have a torque spec on their websites. Also note that some manufacturers, and some of us users, have differing opinions as to whether or not the threads should have a teeny bit of anti-seize on them, which will in turn cause a change of the spec and how it "feels" when installing.
    Most of us just use "one small grunt" ... 1/4 turn after hand-tightening approximates this; the ultimate goal is to compress the sealing washer but not to cause potential damage to the threads - that's a very hot area under a lot of stress 100% of the time.
    Which brings me back to the initial post: You mention that the area under the plug looks like maybe it's a little deeper than the other side... I have to think you're being faked out visually by the scarring of the metal here, as any significant "deepening" would probably have to be done by deliberate counter-boring; the threads in the light alloy head would likely strip out before the plug -with its steel threads - would cause this kind of seating damage.
    (my post 22 slightly revised)

    Unless you're not experienced with vacuum gauges, the difficulty in getting a good balance is a Big Clue. Several things can cause this, including worn throttle body body shafts, a leak in any of the smog hoses - Do you still have that awful canister? (see my earlier post 5) - a leaking intake manifold, or a valve not closing fully (burned carbon from the canister welded into the seat?) and for the correct amount of time, at the right time.

  13. #28
    Registered User dieselyoda's Avatar
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    Rod stretch is usually a myth and seems related to high speed engines, the 12K RPM kind.

    If you are going to pull the heads, I would suggest a cylinder compression test before you do, just 'cause it can provide a little useless information to give you confidence that the amount of work you have in front of you is worth it.

    As a general rule, I can't speak to our very special BMW engines that require spreadsheets to determine a bad battery or that the spark plugs must be OE as the pistons piss, the cranks crank and valves valve like any other engine, but on a gasser, the piston to valve clearance at TDCC is usually about 0.120".

    Even a skipped timing chain shouldn't cause a piston to strike a valve, which should happen first, before the plug electrode. These are non-interference fit engines.

    If the connecting rod bearing or the wrist pin bushing was the culprit, you should have a hammer in a drum sound. It should freak you out.

    I have seen piston crowns change shape and can cause interference, again though, valves first and always at overlap.

    The super easy way, not the BMW way, to check piston to head clearance is to get some 0.125" lead/tin solder. Pull both plugs. Bend the solder like an "L" with the lower part of the "L" about 3/8" and if you can, and best, 1/2". The long end of the "L" can be any length you want so you can hang on to it.

    Insert the short side of the "L" into the spark plug hole, turn over engine, by hand. Pull the solder and measure with a micrometer. Hopefully, you will catch a valve at overlap and get a real picture of the clearance. Repeat a bunch of times with the short "L" in different positions.
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  14. #29
    IBA# 5819 61996's Avatar
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    Quote Originally Posted by AntonLargiader View Post
    Or you could just make your life simple, use the FR6DDC and spend your time doing something more interesting.
    That would be the first thing I'd do.

    Joe
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  15. #30
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    Quote Originally Posted by GTRider View Post
    If you are using a tube-type plug wrench it’s not difficult to modify the wrench so you can use a regular socket and torque wrench on the plugs. See pics below...
    What a great idea!

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