Camshaft / valvetrain failure... ever see this?

kaisen · 12-10-2010, 12:31 PM

I've never seen it before

This is a cam from a GM Vortec 454 (7.4L) big block. It is a hydraulic roller cam. Noticed the #6 exhaust lobe is mushroomed round.

The engine was still running fine (albeit with a small miss) when the cam was removed. The pushrod was bent very slightly, the roller lifter looked fine, the rocker, valve, retainer, and spring looked fine. The damage was concentrated at the cam. No other visible damage to the engine - no sludge, no debris, nothing.

Really odd, isn't it?

Oh Haha · 12-10-2010, 12:42 PM

Wow, I've pulled some bad cams but that is a strange one!!

There is some serious wear/pitting on the lobes. How many miles on it? Were they running 3in1 oil in it?

fastfredracing · 12-10-2010, 12:51 PM

I have never seen this on a roller cam, makes me wonder if the little roller stopped rolling on the lobe., feel the roller tip carefully see if you can feel any resistance. Either that or just another bad/soft gm cam. Back in the day I used to do one or two small block chevy camshafts per week. I held sheer mastery at the job, and my boss at the time gave me every one that came in the door. I miss the good old days where I had a motor open nearly every day. It also looks like there is some light galling two lobes over to the right. Maybe the good doctor (Dr cams) will chime in here.

kaisen · 12-10-2010, 12:51 PM

It has 89K miles

There didn't appear to be any other oil related fatigue. There are a few weird wear patterns on the lobes, but they are superficial, and they are rollers so they always look weird to me.

kaisen · 12-10-2010, 12:54 PM

Quote:

Originally Posted by fastfredracing

I have never seen this on a roller cam, makes me wonder if the little roller stopped rolling on the lobe., feel the roller tip carefully see if you can feel any resistance. Either that or just another bad/soft gm cam.

My technician did check the roller and it did 'roll' but he thought it may have taken a bit of debris that stopped it from rolling for a period of time??

Wouldn't a soft cam have failed long before 12 years and 89K miles??

The good news is that it is getting a bit of a bump, courtesy of Lunati

masraum · 12-10-2010, 01:09 PM

Looks like the lifter stopped going up-down, and essentially wore the thing round, but it is weird that instead of just wearing it flat, it seemed to pound it down. It seems more likely that the roller isn't quite as wide as the lobe so the middle of the cam was worn down by the roller, and the edges were knocked over by some other part of the lifter. The only problem that I see with that is that I would expect the mushrooming to curl rather than stick straight out to the side.

Very odd indeed.

In the late 80's, I had a HS buddy that had a '70 El Camino with a 402 (factory bored 396). We tore his motor down and found that the cam was basically missing 3 of it's lobes. Funny thing is right before that, he'd raced a mustang GT and won 1 of 2 heats (running on 6.5 cylinders).

M.D. Holloway · 12-10-2010, 01:20 PM

got some varnishing going on

DUK · 12-10-2010, 02:13 PM

How bad is the pushrod bent? Where was the pushrod bent?
If it was sticking in the guide it could cause an improper load on the lifter. I'm thinking that the roller stopped spinning and could have been caused by the pushrod.
Now my question is what bent the pushrod?

kaisen · 12-10-2010, 02:32 PM

The pushrod was barely bent, right in the middle

Yes, what bent the pushrod?

sammyg2 · 12-10-2010, 02:51 PM

Yup, I've seen something like that. Sticky lifter. The lifter bore warped and became un-round (technical term) when the engine got all the way up to temperature.

We figured the engine got way too hot once. Either that or it developed a lubrication problem with that lifter.

kaisen · 12-10-2010, 03:43 PM

Quote:

Originally Posted by sammyg2

Yup, I've seen something like that. Sticky lifter. The lifter bore warped and became un-round (technical term) when the engine got all the way up to temperature.

We figured the engine got way too hot once. Either that or it developed a lubrication problem with that lifter.

I think you're on to it. It wasn't really possible to test the hydraulic of the lifter as the pushrod was bent. So it may have been seized. The lifter bore itself mic'd round and within tolerance though, at least when cold. And it must have gotten hot around there as evidenced by the varnishing. The rest of the engine, however, had pretty normal coloration for a high-ish mile big block V8.

Jeff Higgins · 12-10-2010, 05:50 PM

The pushrod would not bend if the lifter got stuck in its bore. There would be no additional load being applied to that pushrod.

My vote is that the retainer was hitting the valve guide for some reason. Clearance was inadequate between the two for whatever reason on that one valve. Guide was too tall, something like that.

RANDY P · RANDY P's Garage

maybe somehow it got spun to the moon and bounced a valve off a piston?

Owner tried a DIY lash adjustment? It's sensitive....

rjp

kaisen · 12-10-2010, 05:58 PM

Quote:

Originally Posted by RANDY P

maybe somehow it got spun to the moon and bounced a valve off a piston?

Owner tried a DIY lash adjustment? It's sensitive....

rjp

I could see an over-rev but it took a long time to damage the lobe in that manner

Is there a significant lash adjustment with a hydraulic roller lifter. Don't you just tighten the rocker and that's that?

RANDY P · RANDY P's Garage

has to be some sort of bind up top. Does it look like it was run out of oil and overheated?

rjp

kaisen · 12-10-2010, 06:18 PM

Quote:

Originally Posted by RANDY P

has to be some sort of bind up top. Does it look like it was run out of oil and overheated?

rjp

I agree with the bind. I don't think it was run out of oil, but if it had an oiling issue it was only at the top-end. The lower end looks great. Maybe something in the LH head or oil galley that restricted oil flow for awhile?? Maybe the rocker arm stuck shut (wouldn't pivot)??

RANDY P · RANDY P's Garage

collapsed lifter causing everything to come loose? Has to be. Might've sorted itself out somehow.

yetibone · 12-11-2010, 06:01 AM

I've seen this before on a 6 litre Chebby SB-II, but without the bent pushrod. #7 exhaust lobe was flattened, the roller on the lifter galled. The symptoms were a slight skip at idle along with a tick, and some popping reversion under load. I'd determined a lack of oil was what caused it because of that lobe and lifter being the farthest from the pump, and the pump screen was partially blocked.

If the pushrod was bent, then I'd reckon the valve is sticking in it's guide at around 3/4 lift. Has any more-than-a-year-old gas been put in the tank lately?

sammyg2 · 12-11-2010, 11:10 AM

Quote:

Originally Posted by Jeff Higgins

The pushrod would not bend if the lifter got stuck in its bore. There would be no additional load being applied to that pushrod.

My vote is that the retainer was hitting the valve guide for some reason. Clearance was inadequate between the two for whatever reason on that one valve. Guide was too tall, something like that.

Iffn the lifter stuck in the up position, the piston could possibly hit the valve and bend the pushrod. that would be assuming it's an interference engine ...........

RANDY P · RANDY P's Garage

The dilemma being whether or not to rip the cylinder head off and redo it all (twacked valves n guides) ...

You are already that far into it, what's another 17 or so bolts at this point?