shriek in neutral & first gear

Hi all,

I brought my '73 750 back to life today after it sat a few years (building house, baby, etc.). On the last ride before I parked it the bike started making some noise while riding, but I didn't have time to look into it. Today I finally took it out of its corner, changed the oil, cleaned the carbs and started it up again. The bike runs as strong as ever but the noise is still there. When the bike is running in neutral or 1st gear, there is a shriek or horrible squeal and I'm not sure where it's coming from. The clutch doesn't feel like it's slipping. The noise almost always disappears as soon as I shift to 2nd. On the few occasions the noise showed up in 2nd gear, it disappeared when I pulled in the clutch. There's no noise in 3rd or 4th. When slowing to a stop the noise comes back as soon as I shift to 1st.

I love this bike and have done a lot of work on it after buying it in fairly rough shape, but I don't have much experience digging into the insides of clutches, transmissions or engines.

Does anyone have any idea what this might be?

Thanks for any help,
Mike

You say you changed the oil, but did you change the oil in the gearbox ? - since its completely separate.

Since it seems related to the gearbox, and only in some gears, it sure sounds gearbox related. Either the oil is low, a bush is worn or dry, or something has gone out of kilter inside - like the layshaft bearing. Look for metal out of the oil in the gearbox when you drain it (again).
Some gearbox mainshafts had a habit of bending too, although usually affects 2nd and 3rd more.

Not safe to ride like that, until you remedy it either.
A gearbox seizure or breakage can be nasty, especially in traffic.

Opethiselps ain't old bikes fun !

Ugh. Rohan, after reading your note I thought I should find out exactly what a layshaft is. I Googled "Norton Commando layshaft" & followed a link to Captain Norton's Gearbox Trouble Shooting Chart showed up at the bottom of http://home.clara.net/captain.norton/cnn3sec19.html

I see a couple interesting (is that the nice way to put it?) things:
- Grinding noise in 1st under load --> Broken layshaft. I'm getting a shriek all the time which can't be good.
- Kickstart lever travels under Load --> Layshaft broken or layshaft bearing torn-up I didn't mention it but my kickstart lever was moving backwards pretty far as I took a ride near home. Guess I'm lucky I didn't have any catastrophic problems.

So, assuming I have layshaft issues, exactly how bad is that to dig into and fix?

Thanks a lot for steering me in the right direction.
Mike

Just have a look at this bit of my rebuild thread Mike before you commit to the gearbox, "sounds" a bit like what I went through.
First noticed here:
commando-cafe-racer-rebuild-t3056-45.html#p38005
And finally diagnosed here:
commando-cafe-racer-rebuild-t3056-75.html#p38859

About all I know to screech would be clutch basket rubbing inner case, worn bushes pushing shift dog faces hard against cogs or weak variety of layshaft end bearing galling its surrounds to death. Worse case is when that troublesome bearing beats its bore too big to retain another and at times helps fracture the ridge between the bearing bores. Not safe to ride with lock up risk or disengage release low side risk. I think basic Norton motto should be, Ain't no short cuts allowed newbies.

Davamb, I am interested in your thread but can not open the links to your past posts. It could be the fact that it's 3:40 am & I'm still at work with no sleep, starting another shift in two hours but,,, ?? How's it working out?

Nope, it's not you GTSun, it was my links. Fixed them. Sorry 'bout that.
I'm afraid the movie link in the first post has gone stale and been deleted by TinyPic. I'll see if I can dig it out and repost it.
...
Found it, but can't get TinyPic to upload it. Will try UToob.
...
This is like watching paint dry.
...
Good thing I pay lots for broadband.
...
This better be worth it (to somebody), I really need my beauty sleep.
...
Here we go:
http://www.youtube.com/watch?v=jRejT0dg5O0
I've got to bail, it should be live shortly, will check in the morning. Pushing pumpkin time here.

I had a similar problem with a "screeching" gearbox on my racer. Scared the hell out of me (but for some reason never stopped me from racing...). Turns out it was the clutch pushrod spinning within the mainshaft and not getting any lubricant (you don't need a lot, but you need some). In fact, it mushroomed the end of the pushrod because it got so hot. The fix was a long story that probably doesn't pertain to your situation, but it was worth mentioning because I know the squeal well, and it's certainly disconcerting. If the squeal disappears when you pull in the clutch I would take a close look at your pushrod; easy to do, and doesn't require any teardown of the box. Check for any sign of unusual wear, heat scoring, or mushroom head.

HTH

Holmeslice said:

I had a similar problem with a "screeching" gearbox on my racer. Scared the hell out of me (but for some reason never stopped me from racing...). Turns out it was the clutch pushrod spinning within the mainshaft and not getting any lubricant (you don't need a lot, but you need some). In fact, it mushroomed the end of the pushrod because it got so hot. The fix was a long story that probably doesn't pertain to your situation, but it was worth mentioning because I know the squeal well, and it's certainly disconcerting. If the squeal disappears when you pull in the clutch I would take a close look at your pushrod; easy to do, and doesn't require any teardown of the box. Check for any sign of unusual wear, heat scoring, or mushroom head.

HTH

Click to expand...

I tried making my own push rod once. Mushroomed and everything. I barely got it out before it wow'ed out so bad that it would have required a teardown or at least removing the clutch actuator to pull it through the other way. Tool steel it the only material for this along with oil hardening of the tips an inch or so in.

Anyway, that sound like a bushing spinning on a shaft or spinning in a gear to the point of vibration. Better get into it.

pvisseriii said:

I tried making my own push rod once. Mushroomed and everything. I barely got it out before it wow'ed out so bad that it would have required a teardown or at least removing the clutch actuator to pull it through the other way. Tool steel it the only material for this along with oil hardening of the tips an inch or so in.

Anyway, that sound like a bushing spinning on a shaft or spinning in a gear to the point of vibration. Better get into it.

Click to expand...

Yep Pete - Because I run a TT box the pushrod needed to be marginally longer than stock. I made my own. My first iteration lasted one practice, and I DID have to tear the box apart to extract the pushrod due to mushrooming. I had hardened the ends, but it still mushroomed. The squeal was my 1/4" rod not getting enough oil and getting too hot. The Norton pushrod is 6mm (not 1/4"). This extra .011" allows the rod more free rotational travel. I make a new pushrod from 6mm tool steel with hardened ends and voila.

But in the OP's case, it probably is a bush or bearing spinning without getting proper lube, as you say, so yes, it should be looked into.

I got the clue off this forum this year to coat the rod in grease to tame the oil weep along its length, would that work? Never thought rod could run dry to rust and squeach. Didn't know rod could spin so learned it the easy way this time. I've got some drill bits that are longer than the clutch rod those might adapt for longer rod.
I'd heard of some cutting rod to place a ball between to drip oil off before leaked to clutch, that might work to get length right w/o a new rod.

Thanks everyone for the tips. All signs point to the gearbox so I'll start with draining the gear oil there & see what I find -- unfortunately it now looks like work is going to keep me from digging into the bike for a couple weeks, but I'll let you all know what I find after that.

Many thanks,
Mike

Mike_G said:

Thanks everyone for the tips. All signs point to the gearbox so I'll start with draining the gear oil there & see what I find -- unfortunately it now looks like work is going to keep me from digging into the bike for a couple weeks, but I'll let you all know what I find after that.

Many thanks,
Mike

Click to expand...

Mike, look for signs of bronze bushing in the oil, which will look like a sparkly bronze-colored oil slick in your drained gear oil.