81 GL1100 - strange rapid thumping noise - valves?

[chrisbags]

Happy Tuesday,

Thanks again for all the input on the solenoid issue, I have power back and the bike is now converted to 30A blade fuses instead of the dogbone.

So here's the next mystery - when I start the bike and throttle it, I get this strange "thump thump thump thump" noise that speeds up with the application of throttle and slows down the same way. Once the bike is warm it is much less apparent and goes away totally after say half an hour. A mechanically inclined friend of mine who rides a Triumph pointed me at the valves, saying the adjustment is probably off - the bike seems to behave normally, and the sound doesn't get worse, so I'm wondering, since the motor was just put in (a rebuilt 81 motor) in May, could this just be an adjustment of some sort, like timing or valves or something like that?

I'm going to try the screwdriver stethescope method to try and see exactly where it's coming from, but I'm at a loss for why it would stop happening with the same frequency as the bike gets warm.

I'm otherwise ready to really roadtest this thing, see how she behaves on a two hour or so cruise, so if anyone has any thoughts I'm all ears.

Ride safe!

 

[Trak]

I don't think it's valve's,, i could hear one bank on mine,,, checked them,, they were pretty much right on,,, .. anyway's valve's would be ticking.. mine kknocks on low rpm takeoff.. think its sumthn w/carbueration.

 

[AApple]

Metal expands when it gets hot. It's possible the valves are a little loose, and when the engine gets to operating temp, and the valve stems "grow", they could get quieter. Could also be an oiling problem that when hot, the thinner hot oil is able to fully circulate around much mo betta.
Noises are hard to determine over da innernet....sometimes they's hard to determine in person, too. See if you can narrow down the location of the noise, and we can go from there.

 

[mcgovern61]

mine kknocks on low rpm takeoff.. think its sumthn w/carbueration.

Low RPM knocking like that sounds like your carbs are not synced. One carb out will make a funny knocking sound at idle and can also make the primary chain slap around a bit.

 

[chrisbags]

Thanks guys, I'm going to put the screwdriver stethoscope method to work and see if I can localize it.

 

[mcgovern61]

Thanks guys, I'm going to put the screwdriver stethoscope method to work and see if I can localize it.

If you could make a video and post it, we could help pretty quick!

 

[chrisbags]

I will do that- I only get to work on it on weekends thanks to work travel, but as soon as I'm back in Maryland I'll do just that. Thanks for the idea!

 

[danf]

Chris, Mac called it, Carbs are out of sync..That noise will go away like magic.. Once you sync. the carbs..

 

[chrisbags]

the more I look into these issues the clearer it's becoming this is the place to get all the answers...now if I only had the mechanical ability to match the good advice. Seriously, is it like brain surgery to sync carbs? I know about the tools you need but assuming you have a vaccum gauge set can you really do this yourself? I'm concerned about messing it up more, but I want to learn how to do this stuff myself. Is it a safer bet to adjust the idle up to a higher RPM and then sync the carbs? I would guess that might reduce the chances of getting any valves stuck closed - and readjusting the idle back to spec afterwards, or is that an altogether bad idea?

Thanks guys.

 

[mcgovern61]

the more I look into these issues the clearer it's becoming this is the place to get all the answers...now if I only had the mechanical ability to match the good advice. Seriously, is it like brain surgery to sync carbs? I know about the tools you need but assuming you have a vaccum gauge set can you really do this yourself? I'm concerned about messing it up more, but I want to learn how to do this stuff myself. Is it a safer bet to adjust the idle up to a higher RPM and then sync the carbs? I would guess that might reduce the chances of getting any valves stuck closed - and readjusting the idle back to spec afterwards, or is that an altogether bad idea?

Thanks guys.

It might just be easier for me to take a ride down to your place with my tools and sync gauges and show you once! (Love to do that....any reason for a ride!!) BUT, I am still recovering from knee surgery and cannot hold my bike up yet. However.....if you are looking for a reason to go for a ride, come on up and we could sync them here! (Plus I could go over all of the main key issues with your bike real quick!) :wave:

 

[chrisbags]

Hey Gerry thanks for the offer! Sorry to hear about the knee man, I just got out of an ankle boot myself, got clipped by a dude in a camry who didn't even look, just ran the stop sign. Took the front wheel and hub right off the front fork of my nighthawk and planted me in the road. It was awesome. Is it ok to ride the thing while it's making that noise? if it is, Mantua is an easy but pretty ride from where I am.

 

[dan filipi]

Syncing can be a bit tricky the first time doing it but I'm sure after Gerry shows you once you can do it and once they're synced they hold it pretty well.