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This one from a 1980 GS400E (4 valve per cylinder, "TSCC").
Greetings,
As the subject line indicates, I'm trying to discover the source of an annoying -and unsettling- rattle that my GS400 has recently developed.
The noise is very much like the sample at http://www.thegsresources.com/_forum/showthread.php?t=103896&highlight=engine+noise
though not as constant and not as loud. (Still, when it's there it can be clearly be heard over the engine as I ride even at highway speeds.) It's very similar to a noise that I've heard from the bike for as long as I can remember, though only in a very narrow power band before (only with the engine pulling, in the immediate vicinity of 4250 RPM and easily avoided), but (if it's the same source) it's gotten louder and more 'widespread' -and more random- since a recent tune up.
The level of tune up didn't involve removing the cylinder head so I doubt it has anything to do with valve clearances, cam chains, or related internal adjustments, but since the two items seem chronologically related, I'm wondering if the following information might help in the search for any educated guesses. (I took the bike back the day after the tune up, but the mechanic -whose sincerity I don't doubt- told me he didn't hear anything out of the ordinary during a test ride before I picked it up or during a second quick spin when I brought it back. So, it might be a normal noise –just one that MY bike's never made before– or due to its intermittent nature, he may simply have not heard it. In either case, I'd like to have some more information before I go back again sounding like a 2-wheeled hypochondriac.)
The work order from the tune up recorded the following procedures;
-drain carbs - usual amount of sediment
-cleaned plugs
-compression (warm) 195/200. OK
(the normal range from the GS400 service manual is Range:160-218/Minimum:130/Allowable difference:29)
-checked carb synch, OK
-set mixture/idle
-air filter OK
-changed oil and filter
-tightened drive chain
-test rode, works fine
Typical with getting the bike back after every tune up is the fact that I have to readjust my engine idle setting to get it back where I want it, as well as changing where I have to set the choke when starting up. This time it's proving much more difficult than usual to find the 'sweet spots,' and this could be completely unrelated, but I'm wondering if the noise could be engine 'knock' from an overlean mixture setting. Turning the idle setting knob (I usually set it, per the manual, at about 1300-1500 RPM) seems take things from 'stall' straight to 2000 RPM (which was where it was when I got the bike back), and starting a cold engine now requires throttle as well as choke to keep things running in the morning. (Though it fires up fine without choke if I've been riding and left it parked for a while.)
The maddening thing is that the rattle comes and goes due to what seem to be random combinations of unknown factors. (Specific engine and ground speed combinations? Ambient temperature? Left or right eye blinks?) It mostly appears (at least at a volume level that I'm aware of it) between 3 and 4 thousand RPM (which is, naturally, the typical powerband for riding around city streets), but it can appear at other speeds, under load during both accelleration and engine braking or while in neutral, or turn around and NOT be audible at an RPM where I had heard it before. Sometimes I can lose it by adjusting my engine speed with the throttle or by changing gears, sometimes it's more persistent.
Because of its unpredictablity, I haven't been able to try the trick of making a stethescope out of a screwdriver (about the only time I haven't noticed it is at idle speeds), but I can say that putting an ear against the gas tank reveals a sound like an energetic tin man trying to beat his way out from the inside. (Though I expect the tank may simply be amplifying a noise from anywhere in the engine?)
I'm reasonably confident that its not related to the clutch, because I've heard the sound while coasting along with the clutch pulled in. I've felt around the exhaust ports on the cylinder heads and don't feel any gases leaking. I've never used any fuel other than the highest octane available at the pump. No obvious problems with power at any engine speeds.
Hopefully the on again/off again factor might at least eliminate certain possibilities. Any guesses?
(And thanks for taking the time to read through all this.)
Greetings,
As the subject line indicates, I'm trying to discover the source of an annoying -and unsettling- rattle that my GS400 has recently developed.
The noise is very much like the sample at http://www.thegsresources.com/_forum/showthread.php?t=103896&highlight=engine+noise
though not as constant and not as loud. (Still, when it's there it can be clearly be heard over the engine as I ride even at highway speeds.) It's very similar to a noise that I've heard from the bike for as long as I can remember, though only in a very narrow power band before (only with the engine pulling, in the immediate vicinity of 4250 RPM and easily avoided), but (if it's the same source) it's gotten louder and more 'widespread' -and more random- since a recent tune up.
The level of tune up didn't involve removing the cylinder head so I doubt it has anything to do with valve clearances, cam chains, or related internal adjustments, but since the two items seem chronologically related, I'm wondering if the following information might help in the search for any educated guesses. (I took the bike back the day after the tune up, but the mechanic -whose sincerity I don't doubt- told me he didn't hear anything out of the ordinary during a test ride before I picked it up or during a second quick spin when I brought it back. So, it might be a normal noise –just one that MY bike's never made before– or due to its intermittent nature, he may simply have not heard it. In either case, I'd like to have some more information before I go back again sounding like a 2-wheeled hypochondriac.)
The work order from the tune up recorded the following procedures;
-drain carbs - usual amount of sediment
-cleaned plugs
-compression (warm) 195/200. OK
(the normal range from the GS400 service manual is Range:160-218/Minimum:130/Allowable difference:29)
-checked carb synch, OK
-set mixture/idle
-air filter OK
-changed oil and filter
-tightened drive chain
-test rode, works fine
Typical with getting the bike back after every tune up is the fact that I have to readjust my engine idle setting to get it back where I want it, as well as changing where I have to set the choke when starting up. This time it's proving much more difficult than usual to find the 'sweet spots,' and this could be completely unrelated, but I'm wondering if the noise could be engine 'knock' from an overlean mixture setting. Turning the idle setting knob (I usually set it, per the manual, at about 1300-1500 RPM) seems take things from 'stall' straight to 2000 RPM (which was where it was when I got the bike back), and starting a cold engine now requires throttle as well as choke to keep things running in the morning. (Though it fires up fine without choke if I've been riding and left it parked for a while.)
The maddening thing is that the rattle comes and goes due to what seem to be random combinations of unknown factors. (Specific engine and ground speed combinations? Ambient temperature? Left or right eye blinks?) It mostly appears (at least at a volume level that I'm aware of it) between 3 and 4 thousand RPM (which is, naturally, the typical powerband for riding around city streets), but it can appear at other speeds, under load during both accelleration and engine braking or while in neutral, or turn around and NOT be audible at an RPM where I had heard it before. Sometimes I can lose it by adjusting my engine speed with the throttle or by changing gears, sometimes it's more persistent.
Because of its unpredictablity, I haven't been able to try the trick of making a stethescope out of a screwdriver (about the only time I haven't noticed it is at idle speeds), but I can say that putting an ear against the gas tank reveals a sound like an energetic tin man trying to beat his way out from the inside. (Though I expect the tank may simply be amplifying a noise from anywhere in the engine?)
I'm reasonably confident that its not related to the clutch, because I've heard the sound while coasting along with the clutch pulled in. I've felt around the exhaust ports on the cylinder heads and don't feel any gases leaking. I've never used any fuel other than the highest octane available at the pump. No obvious problems with power at any engine speeds.
Hopefully the on again/off again factor might at least eliminate certain possibilities. Any guesses?
(And thanks for taking the time to read through all this.)
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