Smashed Spark plug...

Pauls1150 said:

But then, where's the fun?

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

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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.

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...

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!

Have not used factory plugs...can try that...

cal0987 said:

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!

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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,
DeVern

Tanks DeVern! Will try this!

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.

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.

AntonLargiader said:

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

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That would be the first thing I'd do.

Joe

GTRider said:

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...

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What a great idea!

61996 said:

That would be the first thing I'd do.

Joe

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Can't hurt. Right?

Simple, cheap, just might be!

It would be interesting to hear from the OP about what the outcome was.

Another alternative is to find the correct sized deep socket, put an extension on it, and then slowly rotate it on a belt sander or similar. I was able to decrease the diameter of the socket enough to where it would fit in the spark plug hole of my R1150RS. Didn't take much time or effort at all.

beemermyke said:

Another alternative is to find the correct sized deep socket, put an extension on it, and then slowly rotate it on a belt sander or similar. I was able to decrease the diameter of the socket enough to where it would fit in the spark plug hole of my R1150RS. Didn't take much time or effort at all.

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Did you mean to reply to this thread?
Looks like a reply to the thread about getting the right socket to fit the narrow access hole for spark plugs.

Jeff488 said:

Did you mean to reply to this thread?
Looks like a reply to the thread about getting the right socket to fit the narrow access hole for spark plugs.

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Yes, I did. I admit my post was a little off subject, but I was actually replying to post #25 (GTRider) with another alternative to address the narrow spark plug hole issue.

Ok...It has been a while, but i have finally gotten around to working on my bike! Let it sit in the garage for the winter, but as spring is coming...
First thing that i did was pull the left side throttle body, and clean it. While doing this, i looked in at the valves and saw much carbon build up. I decided to pull the heads.
There was good carbon build up...what a pain to remove it..on the cylinder and the valve faces! Tried many spray cans...throttle cleaner, carb cleaner, parts cleaner., nothing worked great..what worked best was (after reading a tip on another forum).....WD40 and many scotch bright pads and a lot of elbow grease! even resorted to scraping with a spackle spreader to scrape the build up ...i was careful to not scratch metal!
Then I remembered that i needed to order new gaskets! Damn...62$ a piece! But i did find them on EME on sale for 39$ each!
So re-assembled left side and took apart right side.. same there...looked like the Spark plug may have been lightly hitting the Piston.... carbon build up and the longer autolights...I have the OEM plugs now that i ordered form EME... Bosch
There was also a great amount of carbon build up on the valves...especially the smaller ones..not sure if they are the intake or out. But the buildup was not just black , but had hardened to a rock like light grey...eventually resorted to scrapping and some 120 grit sandpaper to get it down to the actual metal. Noticed on the Piston there was contact wear from the build up valve hitting ...left a semi circle mark on the Piston.. that must have been the ticking sound i have been hearing all these years!
But have both sides cleaned as best i can and reassembled. still have to clean the left side throttle body and reset valve clearance... possibly get a TPS setting a the dealer...
But then we will see if it runs!
Will keep you posted!

Oh yes...I also made a spark plug adapter with a bolt and pin, so that i could use a torque wrench to install the spark plugs...

cal0987 said:

Ok...It has been a while, but i have finally gotten around to working on my bike! Let it sit in the garage for the winter, but as spring is coming...
First thing that i did was pull the left side throttle body, and clean it. While doing this, i looked in at the valves and saw much carbon build up. I decided to pull the heads.
There was good carbon build up...what a pain to remove it..on the cylinder and the valve faces! Tried many spray cans...throttle cleaner, carb cleaner, parts cleaner., nothing worked great..what worked best was (after reading a tip on another forum).....WD40 and many scotch bright pads and a lot of elbow grease! even resorted to scraping with a spackle spreader to scrape the build up ...i was careful to not scratch metal!
Then I remembered that i needed to order new gaskets! Damn...62$ a piece! But i did find them on EME on sale for 39$ each!
So re-assembled left side and took apart right side.. same there...looked like the Spark plug may have been lightly hitting the cylinder.... carbon build up and the longer autolights...I have the OEM plugs now that i ordered form EME... Bosch
There was also a great amount of carbon build up on the valves...especially the smaller ones..not sure if they are the intake or out. But the buildup was not just black , but had hardened to a rock like light grey...eventually resorted to scrapping and some 120 grit sandpaper to get it down to the actual metal. Noticed on the cylinder there was contact wear from the build up valve hitting ...left a semi circle mark on the cylinder.. that must have been the ticking sound i have been hearing all these years!
But have both sides cleaned as best i can and reassembled. still have to clean the left side throttle body and reset valve clearance... possibly get a TPS setting a the dealer...
But then we will see if it runs!
Will keep you posted!

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This post says "cylinder" several times when he actually means "piston". Just to clarify!

Sorry Paul!