How bad is this? Cam lobe pitting

I've been doing a valve adjustment on my X engine this weekend, and to my horror I see some serious pitting on the end of some of the cam lobes.
For those of you who haven't had the pleasure of seeing the cams from an X, the intake cam has 3 lobes per cylinder (one for each valve, obviously) and the exhaust cam has 2 lobes per cylinder. All 3 of the intake lobes for cylinder 1 are pitted, and there are wear marks on the bearing surfaces between those valves. All of the other lobes on the other 3 cylinders are fine, as are the exhaust lobes. The engine has about 50,000km (30,000 miles) on it.

Obviously this cam needs replacing, but I have a couple questions:

1. Can I get another season out of it (maybe 5000 km) and replace it in the fall?
2. What would cause this on only 1 cylinder? An oiling problem seems most likely, but there is no obvious cause of that. Or maybe the cap was overtorqued at the last valve adjustment?

 

Personally I would replace that cam sooner than later. Keeping it in there is inviting trouble.

MN

 

That is not good. I have to agree with MN, it won't be long before that get's worse in a bad way. One place with high contact and it's specifically designed to be a smooth transition-which yours no longer has.

It could be oil starvation but I don't think so. Considering it's only on #1 I would suspect there was foreign materials or debris that got in there or something is up with #1 I-valves with respect to opening freely. Could also be a faulty cam from the beginning-contamination in the pour. I have frequently seen pitting on the back side of cams when the motor sits for a long time, but that is usually just surface rust.

 

Possible the camshaft had a manufacturing defect. It almost looks as if the pits were there before the lobes were ground. There doesn't seem to be any surface galling, just pits. What do the followers look like?

If the head or engine has been apart before maybe a fault in the rebuild - spring bind or valve-to-piston clearance.

Overtorqued bearing cap doesn't seem too likely. Oiling yes if there is evidence of galling.

 

What caused it? Could very well have been OLD OIL.

When a four-cylinder motor is stopped, ONE of the cylinders is going to have its valves (intake or exhaust) held open; there is no instance in the crank rotation where all 4 cylinders will have all valves closed. One cylinder had to have had its cam lobes in firm contact with the buckets.

I'm betting that #1 was the cylinder whose intake valves were held open when the motor did its "sitting." (An '85 with that few KMs on it had to have sat for a time at some period in its life.)

If that was the "lucky cylinder" and the bike was parked with old oil in it, the acids formed by a combination of old oil and moisture can do that kind of damage. I've seen plain bearings that look like worms tunneled through them, from the acids formed from sitting in old oil. Your damage is similar in appearance.

Regardless of cause, I would NOT trust that cam shaft. At all.

 

I think you should take a close look at your lifter buckets (correct term??) for scoring.

Watch E-Bay for parts.

 

It's an "X" motor; the "aspirin-shims" don't get touched by the cams...

 

You beat me Fitz !!

 

that was bad from the factory, no doubt about it.
another 5000K ? it went 50,000 already, probably be OK but if you use it, it's your fault if it ruins the engine

 

I used too send-out Cam to:

ed iskendarian racing cams
16020 s. broadway
gardena ca 90248
phone: 323.770.0930
fax: 310.515.5730

Isky might not be repairing Cam, any more.

Here's another outfit to check with:

Oregon Cam Grinding, Inc.
5913 NE 127th Avenue #200
Vancouver, WA 98682
Phone: 360-256-7985
Fax: 360-256-7465

http://www.oregoncamshaft.com/regrinding.html

 

Thanks for the feedback everyone. For the sake of my ego, I prefer to believe that it was a manufacturing fault. Although I can't totally discount the idea that I did something stupid (it happens) like leave some debris in there in the last valve adjustment.
But bigfitz's explanation of 'old oil' could be it. This engine hasn't sat for years at a time, but in years gone by I believed that it was best to change oil in the spring rather than have fresh oil sitting in the crankcase over winter gathering moisture. So I would leave the dirty oil in for the winter and change it in the spring. I have since learned the error of my ways and now I know to store it only with fresh oil, but maybe the damage was already done.

 

Does anyone know if the Canadian-spec 750X shares the same camshafts with the US-spec 700X? CBnutt has one from his 700X that he is parting out. Both are 85's.

 

It didn't come from the factory like that, nor did it last as long as it did like that. Yamaha had better QC than that, especially with 20-valve race motors.

Believe me, I've seen damage exactly like that before. At some point, that bike sat, possibly outside, for a while with old oil in it, and that was the cam that had its valves pushed open. The lobes were sitting in puddles of nasty nasty stuff; the nastiest of which crept into the tiniest of clearances.

Unfortunately, it's been run for a while since the damage occurred, as you can see signs of discoloration as a result of overheating in the damaged areas.

Although those particular vendors may or may not still be doing it, repairing camshafts isn't a lost art; I'll bet somebody up there in Canuckistan actually knows how to do it too.

I would recommend repair over replacement, since that cam matches the head. Tell the machine shop not to mess with the journals.

In the name of mechanical empathy, please don't put it back in like that.

 

Not to worry, I have been convinced not to put it back in. It will either be repaired properly or replaced before the motor runs again.

 

I'm with fritz on that acid / oil damage. Makes sense from every thing I know about cam wear (which is a bit; friends dad was a metalurgist for GM, I ate dinner with them a lot).

Should be a fairly cut 'n dry procedure for a good engine shop to weld on some new metal, heat treat the rod, and re-grind. Its the same process they use to do custom cam profiles.

 

Keep in mind that with that many miles, you're best off if you can find a place that's qualified to repair it, and don't let them mess with the journals.

That's the one long-term Achilles' Heel with any OHC motor that runs the (iron) cams directly in the (aluminum) head (no bearing shells.)

Those cams have spent their whole LONG life in those bearing shells, and vice-versa. If it were an under 10,000 mile motor, I'd say go ahead and find a decent cam, Plastigauge it, and run it if it passes.

At that mileage, however, those cams have developed a real relationship with the head. One I wouldn't want to mess with if at all possible. It would probably be worth a slightly higher cost to repair rather than eBay or scrounge a cam, in terms of the long-term prognosis.

 

your going to have to explain to me why other lobes and buckets were unaffected, some of them were touching too. wouldn't the tiny clearances that the nasty oil crept into be called a crack? that would be kind of like a defect wouldn't it ? could the crank have tiny clearances too, and all the plain bearings have larger clearances that seem to be alright. i wonder why