metallic tapping noise

[Dave_17954]

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 :-k

 

[Guest]

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

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 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.....

 

[Dave_17954]

tapping solved maybe!!

tapping solved maybe!!

while reshimming the #4 exhaust which seem to be where this noise is coming from I happened to take an upclose pic of the shim bucket without the shim in it. it looks to me if you look real close that the end of the valve is protruding ever so slightly through the bucket casuing a bulge in the center. this it would seem to me cause the shim to actually rock back and forth similar to a teeter totter as the cam lobe passes over it. is this this mysterious valve noise ive been looking for? does anyone out there have a good used shim bucket for a 1980 gs650gl? I want to replace this one and reshim to spec and cross my fingers .

 

[Dave_17954]

well it looks like a false alarm on my shim bucket. removed the exhaust cam and took out the bucket in question yesterday and everything looks fine. looked over the entire area there and couldn't see anything out of the ordinary. guess its time to learn to live with it

 

[waterman]

What does your cam chain look like? I am probably way off base but I had a cam chain rattle around from a suspect tensioner that made a horrible racket around 2500 rpms. Bike ran perfect but sounded horrible. Eventually have rebuilt and replaced chain, tensioners and guides. This bike currently has a slight rythmic knock at idle that I think is clutch related. I may check it out this fall.

Just to clarify, the 650 shaft models were plain bearing lower ends not the roller bearings like the many other gs. The 650e has roller bearings.

Keep digging, something will show up eventually.

 

[Dave_17954]

hi

hi

actually i have a pic of the cam chain. it looks like new. just sounds like that noise is coming from the #4 valve shim area. the bike runs perfect, idles great no other problems. I ride it everyday and this noise has been there ever since i got it. it has 31,000 miles on it and i change oil religously (20w-50 castrol) run 87 octane and correct heat range on the plugs. the plug color looks excellent. i can find no lose nuts or bolts or anything out of place. the rest of the motor is quiet. only this one area and i can only hear it at speed not at idle. the noise is intermittant at highway speed. i did the bearing check with pushing down on the pistons (all 4) and they are all tight. i've cleaned and rechecked the tensioner no difference. ive disconnected the tach cable no difference.

 

[bwisted]

I don't think there is a problem in the valve train here. Taking the spark plug wire off doesn't change a thing in the valve train. I would be looking towards detonation. With no more combustion pressure or temperatures, it sounds like detonation. Detonation can be caused by many things. Lean mixture, carbon build up, poor fuel, oxygenated fuels, spark plug heat range, etc. With 30K miles, I may not lean towards bearings, unless you have specific reasons to go that route.