What caused this? Camshaft

Gday from Australia.

Purchased a 81 XJ550 as my first project bike which was unmolested for the most part and somewhat unloved. Still rides beautifully despite having leaking front forks which leaked on the brakes, meaning she went, but didn’t like to stop.

Thanks to this forum I’ve since rebuilt the front forks, rebuilt both calipers, the master cylinder, new discs and replaced brake lines with stainless steel. She now stops!

I also replaced the leaking tacho seal and she is due for an oil change,

After reading the forum and a strong recommendation to check valve clearances, I tackled that yesterday.
7 out of the 8 gaps were out of spec being just slightly under the required gap. New shims ordered and will move on to the oil change and carb clean once installed.

My main concern is the exhaust camshaft, It has a hell of a gouge out of one of the side lobes and can’t work out what would have caused this and if there would be other issues I may have to look at. As I said, it runs beautifully and has good compression across all cylinders?
Any ideas??

 

looks like someone rotated the motor without a shim there.
If there are no burrs sticking proud of the cam surface I wouldn't worry about it.
If there are you'll have to remove them with a file

 

Hard to tell from your pic what exactly you are referring too. Here is a pic of a cam after rotating without a shim (yup that was me). Minor damage on the edge of the lobe where it ground on the bucket edge that cleaned up well. If you had an issue with the cam the shim would be chewed up. Did you get a look at it?

 

Cheers,

No burrs and no evidence of any other damage or shavings.

The shim underneath was unmarked.

Not a great photo, the damage was to the side of the left side of the lobe not the face

Play on

 

Unlikely to be a mistake without shim. I suspect fuel in the oil and lubrication breakdown. A file won't touch it, but if you want to dress it back a stone is the only answer - not easy to do with engine in the frame, bearing in mind you have to isolate the are to prevent any carborundum getting into the works. You could pull the cam and measure how much has dissappeared? Then easy to rub down.

 

Look like someone was in there playing with something to do the shims? That and the amount of left over form a gasket in the pic. I see nothing that would cause any running issues.

 

Methinks you are looking at the wrong pic....

 

That is just a machining mark from the factory, nothing to worry about.

https://global.yamaha-motor.com/business/cf/example/casting/ex005/

 

Interesting. Thanks for the link.

So a machining mark from cleaning up a cast cam?

Makes sense if there is no other damage and I suspect the valve clearances have never been checked before

 

So your issue is the grinding marks on the side of the lobes? If so @Dave in Ireland is correct. I thought you were pointing to scuff marks on the cam peak itself?
Fwiw I don't like them, they shouldn't be there, but hard to say from the pic.

 

Yes the side lobe was my concern. Bad photo sorry.

Machine marks makes sense. Was concerned it had a previous major problems, as I’ve only just bought the bike!!

Appreciate all your help. Can continue the rebuild without worry.

Cheers

 

The camshafts are forged, and then ground to the proper specifications. All machining leaves telltales. Even grinding leaves telltales if you know what to look for.

 

Forged? Most cams are chill cast, but maybe Yamaha forged them? Explains how someone I know used to make 4 cylinder “Big Bang” engines.

 

I’m pretty sure they were forged, but I may be remembering another machine.