Gearbox oil looks like metallic brass. How much is normal?

I received my dream bike 1974 Commando on May 28, 2015. The odometer shows 19,400 miles. I have the receipt from P.O. that the gearbox was rebuilt by Fair Spares in 2001, though it's not listed on the receipt what the bike's mileage was at the time. Today I was checking the gearbox oil level by looking through the top plate area. The level was fine, right at the level screw. But the dark brown oil was full of suspended brass-coloured tiny specks giving off a metallic shine. I immediately changed the oil. The fresh oil is transparent and I can now see to the bottom of the gear case. Is this normally what one would see in a Commando gearbox when it's time to change the oil? Is my gearbox "breaking in" or is it "breaking? It shifts perfectly.

~ Kim Z.

Re: Gearbox oil looks like metallic brass. How much is norma

Commando gearboxs have a party trick where the layshaft ball bearing type installed originally weren't quite up to the task,
and can begin to self destruct after a fair mileage.
layshaft-bearing-upgrade-t8879.html

Its just possible the brass cage is starting to go, and that is the metal you see.

If it wasn't for this gearbox foible, we'd just recommend you ride it and see if more metal appears in the oil.
But if this hasn't been upgraded, and fails, the results can be nasty.
So it is STRONGLY recommended that this be checked and upgraded if necessary, to the heavier roller bearing type.

Some (older) gearbox oils also don't like yellow metal bearings, and can dissolve them.
Which is what your description sounds uncomfortably like.
But this was sorted out many years ago. As long as your gearbox oil wasn't added many years ago ?

Sorry to be the bearer of not so happy news.
Ain't old bikes fun !
Cheers.

P.S. A lot of metal in the gearbox oil really should always be investigated.
Catching things before they fail is far better than letting it all self destruct.
Not to mention not risking the rider or bike ....

Re: Gearbox oil looks like metallic brass. How much is norma

there is quite a few bronze bushings in the tranny so they probably have been wearing themselves away for what ever reason over time.

Re: Gearbox oil looks like metallic brass. How much is norma

Sleeve gear bush moved sideways and chewed up by the spline or gear, not uncommon to strike gold

Re: Gearbox oil looks like metallic brass. How much is norma

The sleeve gear bush and the layshaft 1st gear bush are made of phosphor bronze which is very brittle. When they move small pieces break off and sink to the bottom of the gearbox case.
Dismantling the gearbox is not difficult if you have the right tools. If the sleeve gear bush is still OK you don't have to remove the mainshaft so the primary side can remain untouched.

Re: Gearbox oil looks like metallic brass. How much is norma

Hi kim Z.
The way you describe the oil it sounds more like metallic bronze paint than gearbox oil. With that much metal in suspension, you can't not investigate further. Off with the outer and inner covers for a looksee at least.
Ta.

Re: Gearbox oil looks like metallic brass. How much is norma

I have had both the sleeve gear bushing come out and be ground up by the main shaft splines and also I have had the first gear bushing work itself out and grind itself into the layshaft bushing. Recently I had to dismantle the gearbox because the sleeve gear bushing worked itself loose and was broken up by the main shaft again. So I was just getting ready to order a new Mark III type sleeve gear which has a circlip that prevents the bearings from coming out. However my original gear looked just to good to throw away. It was an 850 Mark II sleeve gear so it already had one circlip on the clutch side of the gear. So I thought why not try to make it more like a Mark III with the circlip on both ends of the sleeve gear. So I tie wrapped a Dremel motor to the tool holder on my lathe and then slowly and carefully ground a new circlip groove on the inboard side of the other sleeve gear. Surprisingly it worked out pretty well!

Here is a picture of my Dremel tool setup:


Here is a picture of the end result with the circlip installed:


Seeing how you have an 850 Mark II and if this bearing is indeed coming out of your sleeve gear it may be possible to take the gear to a machinist and have him grind a circlip groove to match the other circlip groove on the other side.

Peter Joe

Re: Gearbox oil looks like metallic brass. How much is norma

Nice job well done, and well thought out...another plus for the forum.