engine knock low end

[briguy66]

My 1980 1100 special that has 27K miles has developed a lower engine knock. Sounds like lower case on #1 or #2 and is not upper valve noise. Sounds worse below 1500rpm but there at all times to some degree. Tried adding oil in all cylinders and also "riding" it out but still there after 20 mile gentle ride.This began after first cold start this year. Bike was winterized, carbs drained, engine oil changed, etc etc. end of last season. Nothing metallic in oil. Runs great except for noise. Anyone have a theory as to what the sound is?

[Rasputin]

Any chance of a video of it making the noise? That can help immensely in hearing what you are saying.

[jjz28]

Could it be the primary chain? I know the xs750 does this a lot if the chain has slack in it. One of these gurus will help you out soon.

[motoman]

Might try pullin' off the vacuum hose on #2 carb itself. If it stops, may have a bad diaphram in the vacuum advance, which is under the left side ignition cover.

[jjz28]

good one motorman, or maybe the hose is disconnected.

[bikerphil]

Out of balance carbs can cause a knocking too, make sure they are in sync. Thin oil like 10W40 can cause knocking or fuel in oil, low oil level.

[natemoen]

Make sure your vacuum advance is connected to the #2 carb BODY and not to the carbs intake boots.

[ViperRon]

Pull wires off plug one at a time you should here a change. Check exaust bolts, rattling exaust can create all types of noise expecially if it bumps engine or frame.

[WMarshy]

My 1980 1100 special that has 27K miles has developed a lower engine knock. Sounds like lower case on #1 or #2 and is not upper valve noise. Sounds worse below 1500rpm but there at all times to some degree. Tried adding oil in all cylinders and also "riding" it out but still there after 20 mile gentle ride.This began after first cold start this year. Bike was winterized, carbs drained, engine oil changed, etc etc. end of last season. Nothing metallic in oil. Runs great except for noise. Anyone have a theory as to what the sound is?

Did you leave your tank full of gas during storage?

[briguy66]

Problem solved!

I indeed reversed the octy and vacuum advance lines upon reassembly of carbs. Guessing I'm not the first one to do this. The knock is gone- I cannot express my true appreciation for all of your help. Thought I was in for a partial motor rebuild. "Oh The Joy" You guys are the best!

[Rasputin]

Congrats on getting it done. Have fun and ride safe!

[Bonz]

I've been chasing a noise in my refurb'd 80G that I am now fairly certain is something going on under the timing cover with the vacuum advance.

-Been trying to justify it as a cam chain noise, but I just can't call it that after more and more miles of riding and listening.

Anyway, the vacuum line is hooked to the #2 carb body. I can unhook the vac line and the engine idle speed drops. I then apply vacuum (suck on it) to the line and idle speed picks back up, and the noise continues, it does not stop when I unhook the line or put vacuum to it.

When I take off the timing cover, everything "appears" to be in good repair and condition (previous owner did the pickup wire fix), but the knocking noise I'm getting is for sure coming from the vac advance area.

What could be going on with the vac advance? Fixes, remedies?

[Bonz]

Vacuum advance NOISE, ideas?

More to add... read above post to get the jist of where I'm at...

With the timing cover off, the noise is less noticeable, the timing cover "contains" the noise and makes it amplified.

What I hear is a metallic "tinging" while the motor is running and the noise is being generated by the timing wheel. That is to say, the timing wheel makes a distinct metallic noise when touched/tapped and that same type metallic noise is what I hear when the engine is running. I cannot find anything that is loose or rattling, yet that harmonic tinging is present. There is also a sporadic and random "knock" with the timing cover on, but cannot hear it with the cover off.

The pickup coil rocks back and forth in the same direction it "rotates" as the engine idles. As rpm rises initially under light throttle, the coil begins to rotate (still rocks back and forth as it rotates) and as rpm rises more the back and forth rocking gets smaller and smaller relative to higher engine rpm, then is steady as it approaches the travel limit and at max advance.

The noise drives me nuts, and with what I have found/not found, not sure where to look?

[bikerphil]

I've run across a few ignition covers that have a rubber noise damper attached to the inner wall to quiet this down, must have been a common issue. I am very familiar with that noise you are describing, it seems to do it with certain motors and others not at all. Does your ignition cover have that damper?

[Bonz]

No damper. Hmmm.... I have an 80SG that is quiet and no damper. Weird that an 80G would be noisy, but noisy it is. That's the first I've heard of a damper on the inside of the timing cover.

Got me thinking... How could a guy put some strips of old bike inner tube in there, to make a damper of sorts, and keep them from coming loose and winding up in the works?