Definitely a cam lobe that went flat. I had an interesting conversation with an engineer at a cam company I deal with for circle track engines. He said that in the last few years cam failures have increased approximately 30% on non-roller camshafts. When I asked him why, he said that it was because many of the oils we buy for our vehicles no longer have sufficient zinc in them, which is critical to camshaft life. This was something I did not know, and I haven't researched the oils yet to determine which ones, if any, still have zinc in them. There is probably an additive available too.
When you install a new cam, make sure that you use the proper assembly lube on the lifter faces and the cam lobes. The first 20 minutes of a camshaft's life are the most critical. There are proper break-in procedures available all over the net and from any cam manufacturer. The standard rule of thumb is to run the engine for 20 minutes at a minimum of 2000 RPM. I have also read that it is a good idea to vary the RPM between 2000 and 3000 by slowly revving the engine. I also run an extra quart of oil to promote more splash lubrication for the cam, but make sure you correct the oil level before driving, or you could have other problems. I was also told not to use synthetic oil for cam break-in, but I think you'll get mixed reviews on that.
Chris
Copy of:
What a drag....
On a remanned engine, that just screams faulty cleaning work. That strongly implies dirt or metal shavings have plugged up one or more oil passages which caused the cam to burn off. If it was just dirt in the lifter, the pushrod would still be moving with a loud clacking noise at it hit the rocker.
The only fix I know is a complete tear down with each oil channel's flow verified before reassemble. Just putting another cam in it will end up with the same result likely.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT'sMikeG wrote:
Collapsed lifter would be my first guess. As I went to look for the lifter hiding in the bottom of a very deep hole, I might find the real problem, but I think the lifter is where you need to start. I am not sure why you would swap a rocker or the push rod, but checking for a bent push rod makes sense. If the pushrod was straight, I would have kept looking for the lifter, and not bother swapping the rod and rocker.
Thanks for the very informative replys. As much as I can tell, and my limited logic on this, the majority of answers I have received is pointing to a rounded camshaft. I grounded out the coil, so that the engine would not start and 'jiggled' the rocker arm while cranking. It never got tight. I was able to look down the small push rod hole and observe the lifter. It was not doing a thing. I changed the rocker and push rod just incase one was bent etc. that I could not detect with my eye. The push rods were of equal length, and straight when rolled across the floor. The major concern now is that: if by chance the oil passage to that lifter or all lifters for that matter are clogged with crud of unknown substance, I don't feel safe unless I somhow clean them all out. Perhaps not ideal with the engine installed, and 2nd...what has happened to all the metal that was ground off of the cam? I know most of it is suspended in the oil, the filter probably has taken out some, but I am sure it circulated throught all the bearings. Last oil change was about 1000 miles ago, and I am guessing that this grind down has taken several thousand miles. Never noticed anything unusual in the oil. So.....my strategy will be to first pull the head, then the lifter and look at the cam. Priced a cam yesterday = $200.00 Yipes. Stay tuned!!!! TX Mike
I discounted the possibility of the rounded cam shaft because I like to think the problem will always be the cheapest thing to fix. In this case, even if the cheapest thing isn't the broken part du jour, it rests right on top of it. If the cam is rounded off, odds are good that the lifter will be seriously worn too.
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