engine knock low end

[jjz28]

I would probably use some spray on liner insulation (or paint on). That stuff is made to insulate sounds. Like what they spray on the floorboards of cars before they put the interior back in.

[Bonz]

Ahhh... GREAT idea...

Would auto parts stores have it? I assume the would?

How about spray on bed liner, or not enough sound deadening?

How much clearance between the inside of the cover and spinning rotor? Any worries there with spraying on a good coating of something?

Thoughts?

[skids]

You could install an inline restrictor in the vacuum hose to dampen the pulses. I would do that to smooth it out. I am thinking of something like an inline shutoff vlave that is bareley open. When I used to measure pressures with mine fans, I saw a trick where you could use empty jugs to dampen the pulses using a volume of air to absorbe the pulses. This would be the same concept using the hose as the air chamber and a restriction in the line like a shut-off valve...

[Bonz]

I am not sure that the pulses are an issue. The bike runs strong and smooth as my 80SG which is literally in near perfect mechanical shape and condition.

Keep in mind, I was running it on the centerstand in neutral manipulating the throttle, so there was no load on it at all. Not sure if that is anything of note, but thought I'd mention it.

Is the pulsing of the pick up coil not normal, or is that par for the course?

[tarzan]

There was a TSB on that very issue for the 80 model year. It has something to do with the timing. I used to have it saved on my computer.One of my SG's had that problem. It seems like the solution the dealers were given was to replace the advance mechanism.I will try to find the Bulletin. I don't believe it will actually hurt anything running it that way. It's just annoying.

[skids]

Is the pulsing of the pick up coil not normal, or is that par for the course?

Pulsing is usually caused by hooking the vacuum hose to the manifold instead of the No 2 carb nipple. If there is a lot of motion in the pickup assembly causing noise, and it bothers you, and you have it hooked to the carb nipple, what else can you do? This constant vibration might also cause your pickup coil wires to get brittle and break. Just thinking out loud...

[Bonz]

10-4 on that Tarzan... It runs great and is annoying as heck.

[tarzan]

I found it in another thread.

http://i304.photobucket.com/albums/n...oyat68/VA1.jpg

[Bonz]

The pickup wires were fixed/modified by a previous owner, so the pulsing could have led to that issue.

I wonder.... If the pulsing is really what does the pick up wires in, vs. normal rotation?

[Bonz]

Dang Tarzan, you are good! Thanks for the consolation that I'm not going crazy and that the bike has a legitimate noise that is simply annoying at this point in it's life.

I am going to coat the inside and try to insulate the noise away from my ears.

[BA80]

A combination of both I'm sure. I've noticed that the lower the idle the more it pulses. I'm idling at 1100 - 1200 and don't have that issue with either bike.

That top end knock at 4000 - 4500 is a non issue. Ignore it. It causes no damage at all it's just something you have to deal with. The replacement vacuum advance units are no longer available.

[Bonz]

I can't see how a "form of detonation at cruise" could sound like rod knock...

Me thinks Yamahs had noisy vacuum advance units on some bikes, period.

[BA80]

I can't see how a "form of detonation at cruise" could sound like rod knock...

It does. Worried the hell out of me when I first got my SG.

[ViperRon]

They make pads to paste on the bottom of stainless steel sinks to dampen noise one of these may help also as they are specifically designed to absorb noise.

[motoman]

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?

You COULD gorilla glue pieces of tube in there.........or you could fix the problem. If that advance dances back and forth, a pinhole in diaphram IS possible. An ignition miss on #2 can cause this too, as well as a really bad carb sync, or in need of. Could also swap out the vacuum can off that red Special and see if advance quits dancing. If it don't, I would suspect an ignition/low idle voltage issue, or carbs idle mix/sync gone array. BTW, as you've figured I'm sure, John had some scoot issues which caused us to just beat it out of Denver 4:30 in afternoon headed south for BuenaVista, rain most of way.