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metallic tapping noise

  • Thread starter Thread starter Dave_17954
  • Start date Start date
Dave_17954 said:
this noise dont start happening until at least 3,000 rpm. anything less and its quiet.
Click to expand...

Can you reproduce the 3000+ rpm tapping noise when the bike is neutral? If so get a friend to maintain the throttle in "noise zone" while you find the noise using the long screwdriver method. Place the screwdriver tip next to the #4 sparkplug to identify a wrist pin knock. Then move to the top of the valve cover. You will hear a lot of background cam chain racket but if its tapping in neutral you will isolate it. Place a fan in front too.

I am sure you have checked already but have you thrown a timing light on it to see if your GS timing is advancing correctly? Next is the #4 cr the same as the rest?
 
yes i also have checked the cam tensioner has good action to and moves freely. i'll be digging into the carbs this winter. like you say it never hurts to clean them and put in some kits. i've been riding since 1976 and i've never had a cycle make this kind of noise and i have ridden suzukis before to cant remember if they were gs's or not tho. i do recall haveing a suzuki 550 and it being black cant recall the model tho. i do know it never had engine noise tho. ive been a small engine mechanic for a number of years have been around engines most of my life so when i hear a noise coming from a motor i know somethings amiss. eventually i'll find it. i dont throw in the towell so easily :) thanks for all the imput
 
yes you can hear the noise in nuetral when you rev the motor. i took my cycle down to the cafekidd who lives nearby and he could hear the noise also we did the revving and listened with the screw driver. noise just seems to come from the upper end of number 4. You can hear it much easier when you ride it which the kidd did. ive rechecked shim clearances (twice) and everything else mentioned in my posts and posted some pix to. I have more pix of this area if anyone wants to see. going to check the timing when i get the chance. for now my vaca's over and its back to work. so i can only work on it on the weekends now. and as ive mentioned the #4 plug is running hot compared to the other 3. i can pull them and take a pic of the ends if that would help show how they are burning. let me know.......
 
I still think carbon knock is a possibilty here. For instance... lets say the #4 valve seal (or even bad rings) leaks oil into the combustion chamber, yes a good amount gets burned off but it leaves a residue. In time the residue builds, raises the compression ratio and carbon knock shows it self.
The facts are, has a noise in just one cylinder above 3000, that same cylinder has a plug that shows signs of overheat. Maybe a super lean condition on the #4 carb but that typically shows itself in the exhaust popping when you let off the throttle.
I totally agree that it is hard to diagnose a noise that we cant hear, but there are only so many things it can be on the #4 cylinder.
If it were me, I would run some top engine clean(or B&G) thru the intake vacumm port on the #4 carb. Just be carful not to hydrolock the motor.

Just an thought.

Good luck with it Dave
 
I couldnt find any b&g around town so I went with the seafoam. followed instructions on can. I put around 5oz down in the #4 cylinder actually through the intake of carb. and about 1 1/2 oz into the tank left it sit the appropriate amount of time started it up and there was lots of smoke for sure. after letting it clear itself i took it for a ride (20 miles) and yes the noise is still there same as always. maybe check the timing this weekend.........
 
Hey Dave, sorry to hear that did not do it for ya. Good luck in finding the problem. I hope it turns out to be something easy like carb adjustment or rebuild verses wrist pin or a broken piston skirt:eek:.

Bri
 
Still havent located the source huh? It certainly is puzzling. I wish I could have been more help, but you'd already suspected MY usual suspects. I kinda wonder about the wristpin thing. But then i still wonder about a possible head gasket leak, or an exhaust leak as well...
 
I took the exhaust off last weekend and checked everything. my new exhaust gaskets still looking in excellent shape and checked for any exhaust rubbing or touching the frame aka clamps etc. but could find nothing out of place. I'm borrowing a friends timing light tomorrow and will check my timing here in the next couple of days. When i do find the source of this noise i'm having one hell of a party for sure.
 
We obviously have discovered that 4 is buring hot which would be lean.

Have you checked the float level--fuel level in the bowls?

This 3G knocking.... if you are at 3g steady cruising down the road in 3rd and you do 1/4 throttle does the noise get audibly louder or does it just increase its frequency?

3g crusing going to WOT... does it still knock?

A. you could try a 3 step colder plug to see if the knock goes away as a diagnositic measurement.

B. You need to determine why it is running lean on one carb? Have you double checked for vac leaks with soapy water in a spray bottle? Air box rubbers tight?
 
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Dave_17954 said:
I took the exhaust off last weekend and checked everything. my new exhaust gaskets still looking in excellent shape and checked for any exhaust rubbing or touching the frame aka clamps etc. but could find nothing out of place. I'm borrowing a friends timing light tomorrow and will check my timing here in the next couple of days. When i do find the source of this noise i'm having one hell of a party for sure.
Click to expand...

Did you peak in to inspect the color of the deposits on the valves? Was # 4 a lighter gray compared to a brown or black on the other 3 cyls?

Oil (carbon) could be built up on the back of the #4 intake valve as well soaking up the atomized fuel causing the CC to run lean. I would further explore what's going on with the #4 fuel delivery circuit.


I also didn't notice if you have installed a robert Barr o-ring kit yet along with intake boot o-rings; have you?
 
I put new carb boot o-rings in the last time i had my carbs off. never made any difference. I'm going to post pic of spark plugs and i'm going to try and do a video while riding down the road hopefully this will turn out. if it does i'll post a link to the video probably on you tube. that way people can hear the noise to get a better understanding of what its sounding like. havent really gotten into any carb work been concentrating on valve area. like i said earlier maybe do a carb/top end overhaul this winter if i dont locate source of the noise before then.
 
engine noise

engine noise

finally tore down my 1981 gs650gl in search of my mysterious engine noise and quite possibly have it located. tore down the top end today and this is what i found in the #4 cylinder. the area from which the noise was coming from. no broken rings but looks like they were stuck at one time. the other 3 cylinders showed the usual normal wear and tear. gonna measure it and hoping to just hone them out and put in a new set of rings in all 4. and the usual maintenence while i'm in this deep. gaskets looked good but will replace of course. will take the cylinder head and block down to my local machine shop and let them work it over in the meantime time to round up gaskets and get my seat redone and clean up wiring harness connectors. lots of things to do to my suzi girl lol.
041.jpg



045.jpg
 
WOW, good find. :eek:

That would definitely be making the noise.

Now I wonder ... why didn't I see these posts while it was happening? I live not too far from TCK, but was out of town at the time, so could not have stopped by to lend an ear, but this is the first time I have seen anything about your problem.

Good luck with the rebuild, hope just a honing and re-ring job will take care of it. :-k

.
 
The number #4 conrod seems to have excessive side to side play compaired to the other 3. Is this normal given its next to clutch? push/pull on the conrod and its snug. Can see no signs of any abnormal wear and tear on the crank just the side to side play. Measured the piston,valves, springs and all well within spec according to suzuki service manual. Should I split the case and change the bearing in #4 (actually I'd change them all if i split the case)? There was no noise coming from the lower end when I had it together and running. Had numerous people listening to it as well as a very qualified motorcycle service mechanic and even he said didnt sound like lower end noise. I will pick up head tomorrow from machine shop and he said it could be honed out with just a bottle brush and it would clean up fine. Don't really want to split case if i dont need to. Thoughts?? And is the porosity between the #3&4 and right above the #1 valve area normal? I'm a machinist by trade and if I ran something like that I'd question it. The gaskets were good when i tok them off.
004.jpg

010.jpg
015-1.jpg

035.jpg
 
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Do the marks on the #4 cylinder have ridges? Does your nail catch on it?
I'd measure the back and forth play and ask a techy.
 
yes. thats what there honeing out. they're not deep but you can feel them. machinist there said a bottle brush hone job should clean them up.
 
016.jpg

heres my # 4 crapped up bearing. number 3 looks very similar while numbers 1 & 2 shows wear but not nearly this bad. will replace all 4 sets. should i replace the crankshaft bearings as well? none of them look really to bad. I have pix and also whats the best / easiest way to remove and reinstall valve guide seals. the guides themselves are in excellent shape. what kind of tool could i use..........
 
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Check the crank journals. Get some plasti-gauge and use it to establish what the bearing torque should be. You may need a crank in the end. Look out for journals that are not square any longer. A crank can be turned, sometimes oversized bearings can be found.

Also torque the rod up and measure the diameter in several directions on the big end and make sure it is round within specs.

In this situation you need to measure everything and pay attention to the details. I would also check the rods to make sure they are not twisted or bent. These things do happen.

As a final suggestion I would examine that #4 piston for ring to groove clearance and check the piston wrist pin as well. The violence that took out the bearing plays hell with the piston and wrist pin.

There is around 15 tons of force on the rod at highway speeds. It is a fast tug but still a lot. Things have to lubricated and at the proper clearances for it all to work right.
 
Dave_17954 said:
I have pix and also whats the best / easiest way to remove and reinstall valve guide seals. the guides themselves are in excellent shape. what kind of tool could i use..........
Click to expand...

Use a needle nose to get the old ones off and your finger to put new ones on. It's that simple
 
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