metallic tapping noise

[Guest]

Hello all....I own a 1981 gs650l with approx. 30,000 miles on it. I've adjusted the valve clearances and numerous other small repairs. It runs great and has a smooth idle.The problem I'm having is a tapping noise coming from the right side of the engine. I took it to my local shop and the mechanic (40+) yrs experience listened to it and ruled out rod, cam chain, valve noise. What he done was unplug the number 4 plug wire and low and behold this noise went away. he suggested new boots all 4. i swapped the boots around and the noise is still coming from number 4. when i ride for a short distance with the wire disconnected theres no noise what so ever and as soon as you hook it back up and rev motor or ride the noise is there. at idle there is no noise. could this be a coil going bad or maybe plug wire? any thoughts? the other 3 cylinders all sound good and strong. bike runs great except for this noise which is driving my batty. i'm taking a long bike trip next month and want to get this resolved. any ideas / suggestions

[chef1366]

Sync the carbs.

[Nessism]

Sounds like a bad rod bearing. How is it that your mechanic ruled that out? Pulling the plug and eliminating the noise is a classic way to find out which rod is worn.

[Dave_17954]

hi

I was wondering if it was a rod bearing bearing wouldnt it make noise even with the plug out? we actually just disconnected the plug wire and didnt remove the plug itself tho. (#4). could it be that this plug is not getting a full spark? faulty plug wire/coil kinda like a spark knock or something. the other 3 cylinders are all quiet even before pulling the wires off. it idles quiet and smooth and does have good acceleration and top end power. going down the road at a steady rpm or speed it will make this noise. i thought rod bearings only sounded bad under load like acceleration. when i pulled the plug wire and rode it the bike was very quiet. I was thinking of trimming back the plug wire and getting some fresh wire into the boot to see if that would make a difference. going to trim the plug wire and look at the spark plug itself to see how its burning today. for now its bedtime lol. i thought of synching the carbs to but it just runs to smooth and does have good idle and pick up. ive tried different octanes in it also and i use 87 unleaded if i use the 93 i get a little misfire out of it . how does pulling a plug wire eliminate a rod bearing noise?

[Nessism]

If the cylinder is not firing, such as when you pulled off the plug wire, the rod will not be loaded thus no noise. I'm not aware of any type of noise that will occur as a result of a poor spark.

Not sure if the problem is a rod but from what you describe, it could be. Does the noise increase with engine load?

[flyingace]

Dave,
Somewhere in the forum archives is a test for rod bearing failure. In short, remove the plugs and spin the #4 piston just past TDC. Stick a 1/4" dowel in the plug hole and push down. If there is any noticable movement, you probably have a bad rod bearing. I would also do the test on #1 to compare to #4.

[Dave_17954]

Good idea on that rod test. gonna redo the plug wire end today and check plug. maybe compare to other cylinders. next few days try that rod test. the noise doesnt get louder under load its a constant noise sometimes i notice tho when im cruiseing down the road the noise goes away. i've never ridden a full day without hearing it tho. ive noticed to that if i go a certain rpm the noise will go away it seems. also under acceleration the noise will start around 2,00 rpm then when i get to say around 4200 -4500 sometimes it disappears but not always...Ive been a small engine mechanic for bout 12-15 yrs and i'm used to engine noises but this ones baffling as to its origin. i'm sure now ive got it isolated to the #4 cylinder. If it is a rod bearing is there an additive like lucas oil i can use to quiet it some or maybe a different heat range in plugs?

[flyingace]

Maybe others can chime in, but I don't think an additive is going to do a lot of good. You are dealing with roller bearings, not plain.

From what I have read, a big-end bearing failure is characterized by a steady knocking sound that increases with engine speed - this doesn't sound like yours. However, the failure may be in the early stages and not yet a full 'knocker'. Nessism is right about pulling the plug wire as a test for bearing failure - it points towards the possibility.

It's funny, but your story sounds similar to mine. I have a noise I tried to get rid of - a sort of clacking sound which I too thought was bearings. Finally, I gave up and decided that if it was anything serious, the source of the noise would eventually become obvious. That was 12,000 miles ago.

Good luck.

[jonshep]

Man that's hard to diagnose without hearing up close and personal. Could be many things, even carbon buildup in the combustion chamber. Had an old dealer, with way more than 40 years experience, tell me one time (31 years ago) that I just had "rider-itis" when I asked about some engine noise. He said ride it...and if it breaks...I will come and get you. So do you tear it down and inspect, or...

[Dave_17954]

checked plugs all the way across and they are all a nice light brown with no carbon buildup. set the gaps at .65mm which they were all very close. also trimmed back the plug wires on all cylinders. will ride to work tonight and hope for the best. if its the rod is it worth a tear down this winter. I live close to the cafe kid (dayton) hopefully we can hook up when our schedules allow and i can let him take a listen to......

[Dave_17954]

well the noise is still there....am i just stuck listening to it while i'm riding?

[catbed]

earplugs???

[1980GS1000E]

Try holding it at a little above redline for 5 mins and see if it goes away.

[TheCafeKid]

How loud is this noise? My 1100G at times sounds like a threshing machine to me, but some people say it sounds perfect. You could have a really loose valve shim, but again, i think that noise would increase with RPM. You should bring it down here and let us give a listen. We can attempt the rod bearing test, but I personally am not entirely sure its that.

As a note, I ran out of gas today sitting in a parking spot. The bike started to make all KINDS of wracket, and I was instantly worried. It didnt act as if it was running out of gas, but it wasnt moving either. I put it on prime, and got it to fire back up, and all the noises were gone. Its possible one cylinder is starving. Could be a bunch of different things, and as said, it could be one of those things you live with till it breaks. Then, you'll know what it was :P Bring it down sometime, and we'll check it out. Im not an expert by any means, but I generally have a good ear for stuff like this. I drive people crazy picking out noises in my motor....

[Dave_17954]

I shot you an email cafe kid.....