bad camshafts ??

[Mathh]

Has anyone of you seen this before?
On my quest for the still existing vibration on the Special I decided to recheck valve clearances, which were still good.
But then I noticed this on both the intake and exhaust cam lobes from the #1 cylinder.









I don't have a clue how that gets there, the chamber under the cam is filled with oil, the cams were oily, I had to wipe them clean to have a good look. When we did the valve clearances the last time I had noted some light pitting but not as bad as this. A layer on top of both the intake AND exhaust lobe has disappeared and you can feel the difference when scratching with your fingernail (the lobe that is :grin

So three questions:
1) how is this possible?
2) can this be the cause of the 4000+rpm vibration when warmed up after approx 15-20 minutes , 10-15 miles riding?
3) which other cams can I use in this '79 3H3 engine?

[ossjughead]

LMAO i have the same thing well from 4000 to 4300 ish the vibration on my 82 1100 and the motor is perfect so i just run through it quick and dont let it bother me anymore.

Jim

[XSPastor]

Hmmmm...

I wouldn't be too concerned. That's the only part of the cam that touches the shim, so it's going to look different. If your clearances are within spec, I would look elsewhere for your vibration. I really doubt that it's the valves. Have you synch'ed the carbs lately? How are your motor mount rubbers?

[DiverRay]

The cams can be repaired, or replaced with either the 2H7 78 cams, or the '79 cams. As far as the cause, #1 is on the "downhill" side when you park with the side stand. The dirt may have migrated down, and caused this at start up. This is a WAG, but then you knew that!
I am looking at reground cams for my '78 engine. There are two or three companies in the US that do that type of work. You should have one someplace in the EU.

[wingnut]

My 81 has a vibe at about the same RPM and my cams are perfect. So don't think that's the cause. Most of the 4 cyl in line Yamaha's I've ridden have this narrow band of vibration to some degree. My XJ 650 has it at 4900. Right at 60 mph, PITA. I've tried tuning around it, re-torqued the mount bolts, ect ect. Its a resident frequency thing and I'm just use to driving thru it or cruising just to either side of it. If anyone dose know what the cause is and how to correct it I'd love to hear it. Those cams do look worn. I've heard stories of guys changing out valve shims and removing them with a magnet. There by magnetizing the shim. The shim becomes a particle magnet and collects ferrous shavings floating around in the oil and there by becoming a lapping surface for the cam lobes. Just a theory

[Mathh]

Thanks for the replies guys. going to swap the cams just to make sure.

[b.walker5]

I might be wrong but it looks to me like you are losing the hardening off the cam lobe. As i understand it, when cams are made they are heat hardened a few microns deep on the lobe surface and once you wear through the hardening they wear very quickly. It's usually caused by a temporary lack of lube to the surface which overheats very quickly.

My daughter had a car a few months back that did this...



This is an extreme case, but thats what they can turn into if left untreated. Oddly enough this engine was still running fine, It was just hard to start.

As for the vibe, it seems to be common around the 4k to 4.5k mark. Short of blueprinting and balancing your engine I don't think you'll get rid of it.

[trbig]

I don't know right off hand what the 78-79 cams' specs are, but you measure that from the back of the cam to the top of the lobe with a micrometer and there's a max wear measurement for the lobes.

Tid