Topic: CB500 Transmission Noise

[jaytee-nz]

Just took my recently finished 1972 CB500 for a test ride and there is a problem.
There is a constant "whine" coming from the transmission (or at least in that area) in all five gears. However, it only occurs under load. As soon as I back the throttle off, the noise / whine goes away. I don't believe its chain related as the chain is new and the sprockets are in good condition.
When I assembled, the engine I checked the gearbox bearings and they spun nicely without any growling noises. The gears looked in nice condition with no excessive wear (that I could see anyhow).
Before I remove and strip the engine, does anyone have any suggestions as to what the cause of the noise is?
Also, the clutch works fine but the gear changes are a little sticky (up and down). Don't think this is the issue, but thought I would add this just in case.

[dave500]

is it loud and obviously not normal,they all will whine somewhat,if its bad it may just be a bearing?

[bryanj]

Primary shaft bearing? Never seen bad ones but anything is possible

[jaytee-nz]

Yeah, it is quite loud Dave - definitely more than normal. I'm picking a bearing too.

[jaytee-nz]

Thanks Bryan. That bearing did go through my mind, especially as it's only making a noise under load. As soon as you button off, it stops.

[HondaMan]

I'd guess the primary gear's bearing, too.
Was there a big "burr" on the "C" transmission shifting fork, and did you grind it away? I've seen those make a high-pitched noise when pulling a load (but on very high-mileage engines, like 40k+ miles' untouched inside).

[BenelliSEI]

Before tearing into anything have you checked drive chain/sprockets alignment? If the rear axle has shifted you can get some real chain whine….

[jaytee-nz]

I'd guess the primary gear's bearing, too.
Was there a big "burr" on the "C" transmission shifting fork, and did you grind it away? I've seen those make a high-pitched noise when pulling a load (but on very high-mileage engines, like 40k+ miles' untouched inside).

It definitely sounds a like a bearing issue. A friend of a friend who knows these engines very well said that shaft bearing behind the clutch basket is a known "whiner" if worn.
I'm about to remove the engine and perform surgery so I'll come back with the results.

[jaytee-nz]

Before tearing into anything have you checked drive chain/sprockets alignment? If the rear axle has shifted you can get some real chain whine….

Yep, did that Benelli when I fitted the new chain (I hoped it was a chain issue but it wasn't).

[jaytee-nz]

So it looks like Bryan gets the prize. Both primary shaft bearings are in bad shape with one worse than the other.
I vaguely recall looking at the worst one during reassembly thinking it was maybe suspect, but stupidly thought "she'll be right" as we say in NZ !
The worst one is just a common 6205 bearing but the other larger one has some oddball numbers on it. I'll visit my local bearing supplier on Monday and see what they can do.
I've checked and double checked all the transmission bearings and they are fine.
Thanks to everyone for helping out.

[M 750K6]

Well done for letting us know the outcome. How many miles on the bike?

[bryanj]

Thats the first set of those bearings going bad i have heard of, was the bike stood for a long time doing nothing?

[HondaMan]

I have seen a CB550 (similar arrangement) with those bearings bad when the owner ran some very-high detergent motor oil in it and rode mostly interstates and freeways to his work. He mentioned how he "...noticed foam on the dipstick..." when he checked the oil when he got to work several days, because he had also noticed a "...small power drop..." after hitting freeway speeds with a cold engine, then it would slow down a little as it warmed up (lost some power). He blamed the carbs: I suggested he stop using that oil, but he didn't. This is an important thing, especially with today's oils that are low (or void) of zinc and contain high amounts of detergents. Make sure your oil is low-detergent and add some ZDDP for long, happy results.

[jonda500]

I had to replace a bearing in my 400-4 - I suspect I actually caused it to go bad by accidentally leaving a paint brush bristle caught inside it...  my mechanics teacher used to say "cleanliness is next to godliness" when working inside engines.
John

[HondaMan]

I had to replace a bearing in my 400-4 - I suspect I actually caused it to go bad by accidentally leaving a paint brush bristle caught inside it...  my mechanics teacher used to say "cleanliness is next to godliness" when working inside engines.
John

A string from a frayed set of coveralls can do the same thing.

I won't tell how I know this...

[jaytee-nz]

Thats the first set of those bearings going bad i have heard of, was the bike stood for a long time doing nothing?

Unknown I'm afraid as it came with no speedo.
Generally, the engine was very clean inside and doesn't look like it's done high miles.

[jaytee-nz]

I have seen a CB550 (similar arrangement) with those bearings bad when the owner ran some very-high detergent motor oil in it and rode mostly interstates and freeways to his work. He mentioned how he "...noticed foam on the dipstick..." when he checked the oil when he got to work several days, because he had also noticed a "...small power drop..." after hitting freeway speeds with a cold engine, then it would slow down a little as it warmed up (lost some power). He blamed the carbs: I suggested he stop using that oil, but he didn't. This is an important thing, especially with today's oils that are low (or void) of zinc and contain high amounts of detergents. Make sure your oil is low-detergent and add some ZDDP for long, happy results.

I don't know what oil has been run it previously, but I used genuine dinosaur 20w50 oil. Having said that it's only done about 5 miles with this oil, due to the problem.

[jaytee-nz]

Well done for letting us know the outcome. How many miles on the bike?

Unknown as it came with no speedo.

[bryanj]

If its clean i would def suspect standing for a while empty and corrosion in the bearing races