What would cause this camshaft damage?

[SteveW]

Engine was running perfectly, I’ve only stripped the top end due to oil leaks.

Found damage to most of the lobes on the cam. There is no damage to the rest of the cam where it sits in the head and no damage to the rockers.
Also found this tiny disk of metal, about 2mm thick by 5mm diameter. Don’t think it’s part of the engine.

[McCabe-Thiele (Ted)]

I am no expert but there are a variety of causes my late father referred to that type of daage as "pick up" usually lack of lubrication associated with overheating, dirt or high mileage wear.

Google gives this cause. https://highwayandheavyparts.com/n-12843-camshaft-failure-analysis-what-causes-excessive-lobe-wear.html

[Oddjob]

The cam can be repaired by Newman cams Steve. Cost last time quoted me in 2022 was £110-120 plus VAT plus postage.They hard chrome it and grind it back to spec IIRC.

However, if you are going to do that you might as well alter the profile as it's the same cost, Hondaman suggested adding 10 degrees duration to the stock CB500/550 cam (+5 early and late on the intake side, and 5 more degrees of exhaust overlap with the intake) will really perk it up.

[SteveW]

Luckily I already have a replacement cam to go in. I’m going to stick a CB650 cam in, supposed to be a good mod for a little bit more power.

[SteveW]

Forgot to say, the bike has 16500 miles supposedly from new. The rest of the engine looks perfect, there are no ridges on the inside of the barrels.

[Seabeowner]

Is that wear or just crappy metal? Is it on the nose of the cam?

[K2-K6]

The wear (looks like lobe peak ? ) is from failure of the oil film at that site, resulting in effectively cold welding parts of the camshaft surface to it's paired rocker.
This either through fuel diluted oil or too long between changes (same end result really) that then doesn't prevent metal to metal contact.

Thats from oil quality failure.

Another contributor is to run with the tappet clearance too tight, which prevents the oil film from being established on the lobe ( many cams are simply lubricated by this "dipping" method. It leads to oil failure local to just that site, can be just on one lobe and follower pair.

If all or most are affected, then more likely just oil failure overall unless all of the tappet were too tight.  Should show some residual effects on rocker if exhamined closely.

Oil filtration plays no real part in this process, just tries to stop debris from this site spreading throughout the engine by embedding into soft locations like crank bearing or camshaft main bearing surfaces. If those camshaft bearing are ok, then it looks like the filter caught the chunky bits. After going through the oil pump 

Use Grapphogen product on installation of new camshaft to avoid initial risk.

[Oddjob]

Luckily I already have a replacement cam to go in. I’m going to stick a CB650 cam in, supposed to be a good mod for a little bit more power.

The re-profile of the old cam will match the profiles of the 650 cam but without the problems fitting the 650 will cause.

With the tacho drive gear on the 650 cam being different the tacho will read fast. Why have that?

[SteveW]

I have the 650 drive gear and a 650 tacho so hopefully all good to go.

[Oddjob]

No, you don't understand. The drive is geared differently from the 500/550 one, so it spins faster at the same revs. So the tacho reads fast, instead of it saying 2000 for instance it may say 3500.

[K2-K6]

Wouldn't change in both gearing AND tachometer give the correct instrument reading in this case ?

[SteveW]

Wouldn't change in both gearing AND tachometer give the correct instrument reading in this case ?

That’s what I thought, I’ve read several posts on mainly the US site about this and they state you only need cam, drive gear and tacho.

[Oddjob]

That is true, however iirc the 650 tacho isn’t exactly the same as the 500 or 550 one. Not to my recollection anyway, the redline was higher, the face was a different colour and the needle was different, IF you used both that may work but then it may mount differently as well