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Discussion Starter · #1 ·
I'm sure most know the signs of a bad cam. The excess valve noise from the extra clearances, engine running rough, pushrods not turning, and so on. However I pulled a cam out of my 406 last year that had only one bad lobe. It had at least .050 material worn off, however you could never tell it from the lifter. All 16 lifters looked the same and appeared to be perfect. The engine didn't miss either and I didn't hear any ticking from the valvetrain. The cam had maybe 300 miles on it, it could have been in the infancy of it's failure.
All of this is leading up to my current cam. I have a XE284 cam in my 406 now and my engine has always had a miss since installing the cam. I've checked and replaced everything but the cam. I had the intake off a few months ago and I pulled each lifter out and looked at the bottoms. They all looked great. However that doesn't mean anything since they also looked good on my other cam. All of the pushrods spin when the engine is running. I can hear a very mild ticking, but it could have always been there or could be an exhaust leak. All of the rockers move up and down when the engine is running. However there could be a couple that aren't moving as much as the rest. You can't tell by eyeballing whether a lobe is worn down a little more than the rest.
I don't have a good enough dial indicator to measure my lift on the pushrods. It looks like I may need to pull the cam and measure each lobe. I had thought about pulling the intake and then try to view the cam lobes thru the lifter bores. thats not real accurate, but it may work. I didn't need to measure the lobes on the other cam to know they were bad. They stood out like a sore thumb. I guess with the intake off I could measure how far up each lifter raises.
Any help or advice would be appreciated.
 

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4speed57 said:
I'm sure most know the signs of a bad cam. The excess valve noise from the extra clearances, engine running rough, pushrods not turning, and so on. However I pulled a cam out of my 406 last year that had only one bad lobe. It had at least .050 material worn off, however you could never tell it from the lifter. All 16 lifters looked the same and appeared to be perfect. The engine didn't miss either and I didn't hear any ticking from the valvetrain. The cam had maybe 300 miles on it, it could have been in the infancy of it's failure.
All of this is leading up to my current cam. I have a XE284 cam in my 406 now and my engine has always had a miss since installing the cam. I've checked and replaced everything but the cam. I had the intake off a few months ago and I pulled each lifter out and looked at the bottoms. They all looked great. However that doesn't mean anything since they also looked good on my other cam. All of the pushrods spin when the engine is running. I can hear a very mild ticking, but it could have always been there or could be an exhaust leak. All of the rockers move up and down when the engine is running. However there could be a couple that aren't moving as much as the rest. You can't tell by eyeballing whether a lobe is worn down a little more than the rest.
I don't have a good enough dial indicator to measure my lift on the pushrods. It looks like I may need to pull the cam and measure each lobe. I had thought about pulling the intake and then try to view the cam lobes thru the lifter bores. thats not real accurate, but it may work. I didn't need to measure the lobes on the other cam to know they were bad. They stood out like a sore thumb. I guess with the intake off I could measure how far up each lifter raises.
Any help or advice would be appreciated.
I had the same issue on a BBC with a solid FT cam. It would miss a little until I adjusted the valves and it would be fine for a couple runs (drag strip only). I finally broke a pushrod and was forced to rebuild the motor. That's when I found the cam had 1 lobe wiped but it also affected the lifter. You have covered all the tell-tale signs I know of for diagnosing without pulling the cam out. Are you running a good oil with high zinc content?
 

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I wish I had a definite answer because I've wondered the same thing myself.

However, I suspect cam lobe surfaces are case hardened, or some sort of surface treatment that isn't very thick. So once you go through that, rapid wear subsequently begins. I'd say you caught that first cam during a very tight window between intial failure and catastrophic failure. In other words, it woldn't have taken much longer before a genuine missfire situation would have occured.

Better to use a dial indicator on the lifter shell than the pushrod with hyd lifters, but as you dont' have one, do you have a good digital vernier caliper? (You can get a decent one on sale for about $20.) If so, remove the intake manifold and measure the amount of lifter above the hole in the block at max lift and again at min lift, and then compare it to some others. Use the depth guage part of th calipers for this.

As far as your miss goes, double check your valve adj and also seriously look at your ignition system. You can start with the sparkplugs, but plug wires can go bad quickly, so the midnight look-for-spark-leakage is a good idea.
 

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Discussion Starter · #5 ·
Thanks for the replies. I've been using good quality motor oil And changing it frequently. I do have some calipers and I was thinking of trying the method you suggest Argess. It should give me an indication if anything is wrong.
I haven't noticed a pop out of the exhaust or carb yet. Would the cam have to be eroded pretty bad to produce a backfire?
I'll go back over everything one more time before I start tearing into it.

Thanks so much for your help guys.
 

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Discussion Starter · #7 ·
I have an update.

I found the old lifters in my garage that went with my last cam that failed. I cleaned all the lifters really well and I found one that looked like it was sandblasted on the bottom. It didn't have the machined smooth, shiny surface. I'm sure it was the lifter that went with the bad lobe.
I also went out tonight and marked my pushrods again so I could see if they were spinning. I cranked the engine over a few times and it looks like the pushrods on cylinders 7 and 8 are barely turning. Both of them being the exhaust valves. All the other pushrods spun several times while these didn't. Last week I was pulling the plug wires off one at a time trying to pinpoint the miss. I noticed cylinders 7 and 8 didn't seem to pull the engine down when the plug wires were removed.
I'm going ahead and pulling the intake tomorrow and look at the bottom of the lifters. I'll also measure the lift of the lifters in the bores.
I've had my intake off so many times, I could do it in my sleep!

Thanks again for the replies.
 

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4speed57 said:
I have an update.

I found the old lifters in my garage that went with my last cam that failed. I cleaned all the lifters really well and I found one that looked like it was sandblasted on the bottom. It didn't have the machined smooth, shiny surface. I'm sure it was the lifter that went with the bad lobe.
I also went out tonight and marked my pushrods again so I could see if they were spinning. I cranked the engine over a few times and it looks like the pushrods on cylinders 7 and 8 are barely turning. Both of them being the exhaust valves. All the other pushrods spun several times while these didn't. Last week I was pulling the plug wires off one at a time trying to pinpoint the miss. I noticed cylinders 7 and 8 didn't seem to pull the engine down when the plug wires were removed.
I'm going ahead and pulling the intake tomorrow and look at the bottom of the lifters. I'll also measure the lift of the lifters in the bores.
I've had my intake off so many times, I could do it in my sleep!

Thanks again for the replies.
Are you running a hyd. or solid cam?
 

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i had a miss since i put my motor together finally looked at the header bolts some were about to fall out tightened them up and it was gone sounded just like a lifter, i adjusted my lifters like 5 times for nothing put more oil in and then checked my plugs and wires and distrubitor and stuff wasted lots of time
 

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Discussion Starter · #10 ·
Well I pulled my intake off tonight and I got to the lifters. It appears my cam is toast. I had several lifters that didn't look very good on the bottom. I'm going to try and measure the lift from of each lifter. I'm sure that is a waste of time since it's obvious the cam is going flat.

Thanks for your time
 
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