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Engine Knock

F

flightstick

Forum Newbie
Hi guys, firstly this is not an engine knock from pre-ignition let me explain. Did a full top-end overhaul with rebore to 1 oversize. Replaced valve stem seals and lapped all the valves. Did a leak test afterwards and everything ok. Assembled the engine and did a few heat cycles just to make sure everything beds and settles down. Last was carb adjustment and carb balancing, everything went great no issues. Had to replace the fuel tap as the unit i had was seized. Anyway a few days ago was trying to diagnose why the engine wasnt revving past 4000 rpm only to find i had a fuel delivery problem, engine would run fine when i changed over to prm on the tap so that i still need to address. Here is the issue now. Start up the engine runs real smooth with a little choke at start. Once the engine is warmed up and choke off I hear a strange knocking noise from around 1200 rpm to 2000 rpm then it goes. I cannot pinpoint where the noise is coming from sounds kinda metalic. I havent removed the tappet cover yet to check timing chain or anything else below that cover. Valve clearance was set to 0.03 to 0.05 mm on all valves during assembly. Tensioner is good and operated as it was suppose to after installation. If it was crank big-ends the noise should be there all the time correct. The frequency of this metalic knock doesnt change as rpm is increased stays the same then dissapears. Engine revs cleanly without this knock after 2000 rpm. Any other ideas what I should look for. Oil light goes out almost immediately once she fires up. Also oil in the sight glass quickly drains out on start up. Suppose I need to drain the oil as well and check for any metalic particles.
 
Is the airbox installed and fully sealed.
 
Oil in sight glass goes away when running because its all being pumped around the engine. Level drops down as normal. Engines not low or out of oil, its just that the volume filling up the oil gallies and top end consume a lot of oil.
 
If it doesn't change with RPMs, then just something vibrating...? someone recently on here had a front fender that was rattling.
 
Gents just to reply.

Noise is while the engine is running bike stationary
Im very aware why the oil goes from the sight glass, just an observation regarding oil pump etc.
 
chuck hahn said:
Oil in sight glass goes away when running because its all being pumped around the engine. Level drops down as normal. Engines not low or out of oil, its just that the volume filling up the oil gallies and top end consume a lot of oil.
Click to expand...

Yes I do understand--was just making a point.
 
dgates1 said:
Did I read that wrong??
Click to expand...

frequency.........

​​​​​​Start up the engine runs real smooth with a little choke at start. Once the engine is warmed up and choke off I hear a strange knocking noise from around 1200 rpm to 2000 rpm then it goes.
​​​​​​The frequency of this metalic knock doesnt change as rpm is increased stays the same then dissapears. Engine revs cleanly without this knock after 2000 rpm.
 
Start it and start touching everything. Side stand, center stand, mufflers, guage covers, fender.. anything you can think of that could vibrate against metal.
 
First off WELCOME, It says "frequency" of metallic knock doesn't change from 1200 to 2000 rpm., that means the knock doesn't get faster as the rpm's go up. I'm with dgates 1, something vibrating. If it were something like rod bearing, main bearing, clutch basket, cam bearing, starter clutch, the frequency would get faster as the rpms went from 1200 to 2000.. Sounds interesting, please keep us updated what you finally find is the cause.
 
rphillips said:
First off WELCOME, It says "frequency" of metallic knock doesn't change from 1200 to 2000 rpm., that means the knock doesn't get faster as the rpm's go up. I'm with dgates 1, something vibrating. If it were something like rod bearing, main bearing, clutch basket, cam bearing, starter clutch, the frequency would get faster as the rpms went from 1200 to 2000.. Sounds interesting, please keep us updated what you finally find is the cause.
Click to expand...

This is my thought as well. I have used a long screw driver to try and pinpoint this noise , with no success. I have had the bike off the main stand on the side stand still nothing . Only changes are when the rpm increase above 2000rpm. yea frequency doesnt change . Ill try and do a video tomorrow maybe you guys can hear what im hearing. . For me it seems to be coming from the top of the engine. I have even run it in gear on the main stand same result. Took the tank off and setup up fuel supply and same result.
 
As I understand it, the noise is constant on side stand, correct? What if you sat on it and slowly raised it upright?
 
flightstick said:
Damn, thats exactly how it sounds. Is this a big issue. How does one fix this?
Click to expand...

No, it's not damaging, just annoying. It can be eliminated but requires custom matching to fit a shim. I think there is a thread about how to do this. The sound is one (or both) camshafts sliding sideways as they rotate at low speed due to a little too much clearance. The sideways oscillation causes the cam to knock against a thrust surface on one of the cam pillows. Some OEM parts diagrams for early GS show a shim to take up the slack, but these were either deleted before or after production began. Never seen a shim in the flesh. When the revs build the sideways oscillation stops and they run quiet(er).
 
My understanding is that it's the cam walking horizontally and tapping the either the cover or the caps. Try shifting the bike left to right (or vice versa) to allow the cam to float around and see if the noise changes. My 550 will do this once in a while for no apparent reason when it's fully warmed up. I ignore it.
 
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