AMC V8 Guru's....

[roosecj7]

So I have a freshly rebuilt AMC 360 (dogleg heads), standard bore, new pistons, Summit K8600 cam, hydraulic lifters, Edelbrock double-roller timing chain set, performer intake, 600 cfm carb. It fired right up on the first try, I broke it in, and it has been running great ever since. The other day I fired it up and let it idle for a few minutes then revved it slightly. When I revved it, it started making a popping/tapping noise, and has a slight backfire from the carb. I pulled the valve covers and found an exhaust valve not fully opening. As far as i can tell this is the only issue. Any thoughts on what is causing this before I go tearing it apart?

[Jeep CJ7]

There have been a few reports of the 8600/8601 wiping out lobes on the cam and that sounds like what may have happned to your engine

[roosecj7]

When you say "wiping out lobes", what exactly do you mean? The valve still opens about halfway, and does so in a smooth manner. That leads me to believe the lobe did not shear completely off, and it could not have flattened that much that fast. I'm hoping its a bent pushrod....

[247pia]

Could be lobe or push rod.

Loosen rocker and spin push rod to see if it's bent.

I would lean more towards lifter(s) that seems to happen more on freshly rebuilt engines that don't get all of the crap out.

[roosecj7]

I'll check the pushrod in the morning, I was worried it was going to be a lifter. Any way to loosen it without taking it apart if that is the case?

[247pia]

Originally Posted by roosecj7

I'll check the pushrod in the morning, I was worried it was going to be a lifter. Any way to loosen it without taking it apart if that is the case?

Pull valve cover and loosen rocker arm.

Lifter would be collapsed, take push rod and push up and down on lifter to see if it's soft.

[roosecj7]

Thanks, I'll give that a shot. If it is collapsed, is my only option taking the engine apart and replacing the lifter?

[247pia]

Just pull the intake off.

[roosecj7]

Fair enough, still a pain in the dick.

[247pia]

I have had Summit and Edelbrok both warranty the lifters for me.

[roosecj7]

Yea I've had good customer service experience with both as well.

[ELVISP]

If you don't mind me asking, what did the intitial rebuild cost you?

[roosecj7]

Originally Posted by ELVISP

If you don't mind me asking, what did the intitial rebuild cost you?

The machine work ran me around $600, which included cleaning and magna-fluxing the block and heads, cylinder hone, cam bearings, crank polishing, resizing rods, pressing new pistons, flywheel machining, cleaning valves, and assembling and pressure checking the heads. I did all the other assembly myself.

Then add parts (cam, lifters, timing chain, head bolts, rod bolts, pistons, intake manifold, oil pump gears, oil pump pickup, distributor, carb, headers, rings, pushrods, rocker arms, etc....). Probably in the neighborhood of $1500 in parts.

So, just over $2k total, and that's doing all the labor (minus the machine work) myself.

[Seabo]

Before checking lifter clearance be sure to bleed them out. Now you ran it they will be full of oil and tight. If your lifter clearance is off then you could have pushed the little clip that holds the valve in place loose. It is the biggest design flaw with AMC motors. Make sure your lifters are only collapsed about halfway through thier range when your cylinder is TDC on the fire cycle- yes each cylinder and its a pain in the ass. Been through this lots and too many guys think the lifter will take care of everything. Make sure they are not getting over compressed. There are a few ways to adjust the amount of clearnace the lifter has and none are really simple but if you get it right it will run forever. Get it wrong and you drop valves leading to rebuilding what sounds like a nice motor all over again.
Also make sure the rocker arms are not out of balance. When the engine is TDC fire for the cylinder in question does the rocker arm sit level? And then during valve open/ spring compress does the rocker arm move an equal distance on each side of the post?
Check that and adjust as needed.

[1981CJ7]

I suspect this is what you will find if you take it apart:





I also experienced the same problem, you cannot just replace the lifter it has also wiped out the corresponding camshaft lobe.

I also had the Summit 8600 and they sent me a lifter, but I needed more. Went with a Lunati VooDoo cam and love it.

[rustywagoneersdotcom]

Originally Posted by 1981CJ7

I suspect this is what you will find if you take it apart:





I also experienced the same problem, you cannot just replace the lifter it has also wiped out the corresponding camshaft lobe.

I also had the Summit 8600 and they sent me a lifter, but I needed more. Went with a Lunati VooDoo cam and love it.

I think this guy is right.

There is a CHANCE of a lifter bleeding down, bent pushrod, etc.

But my money is on a wiped out cam lobe and corresponding lifter.

It is my understanding that Lunati VooDoo cams are an offshoot of Harold Brookshire (sp?) who is the guy that started my all-time favorite cam company, UltraDyne.

[CJim7]

Originally Posted by 1981CJ7

I suspect this is what you will find if you take it apart:





I also experienced the same problem, you cannot just replace the lifter it has also wiped out the corresponding camshaft lobe.

I also had the Summit 8600 and they sent me a lifter, but I needed more. Went with a Lunati VooDoo cam and love it.

I've got one of these as a souvenir also. when it happens, it happens quick and it rounds off the cam lobe. The causes are simple: Improper break in. Trying to break in new lifters with an old cam. Lifter not rotating in the lifter journal.

[roosecj7]

Ok so I took another look this morning and this is what I found. Pushrods are straight, and the lifter in question is very squishy in comparison to the rest. I noticed another issue, though, the rocker arm bridge is bent. See the pictures below for explanation. The left would be the exhaust valve (the one with the damaged lifter).....









What would have caused this?

There is no evidence of the rocker arm contacting the bridge, but my only thought would be a stuck valve. For what it's worth the valve opens at least halfway; would it be possible for a valve to stick momentarily causing this damage?

[fifesjeep]

I had a Comp Cams 292 cam for my AMC 360 and the lobes were too soft. I brought the cam into the shop and checked it on the rockwell hardness tester... come to find out it was waaaay too soft. I took pictures and sent them to Comp Cams with the cam and they sent me a new cam and lifter set... free. Had a couple bent pushrods one looked like a crooked J... lol after that I went with one piece chromoly pushrods, harland sharp 1.7:1 roller rockers etc... lol

[1981CJ7]

For better or worse, I still think its the lifter and camshaft. That bridge is installed at a specific torque and basically just holds the rocker in place.

I'd keep digging

[roosecj7]

I agree that the lifter is trashed, and quite possibly the cam, but I'm still concerned about how the bridge got like that. Could explain whether the lifter was the cause of, or a victim, of the failure.

[rustywagoneersdotcom]

Three possibilities.

Possible Good;
Bridge got bent when lifter bled down and allowed the pushrod to drop out of its proper location. Pushrod caught the edge of the lifter, opened the valve farther than it should, twisted the rocker and pivot, thus bending the bridge. Lifter is still suspect internally, but not wiped.

Possible Better;
Rockers weren’t tight enough, allowing the bridge to turn, allowing the pushrod to jump out of its location, and resulting in a similar scenario to the above. Replace the bridge and go on with life.

Possible Worst;
Similar to the ‘good’ scenario, except caused by wiped out lifter and lobe.

[CJim7]

Originally Posted by roosecj7

but I'm still concerned about how the bridge got like that. Could explain whether the lifter was the cause of, or a victim, of the failure.

That tends to happen during the removal process. I've done it a hundred times removing the rocker bridges from the block. That's not the cause of your problem Im afraid.

[roosecj7]

Well, I'll be pulling the intake next week to see whats going on in there, hoping for the best. Thanks for all the input.

[crashnzuk]

Also, either use dedicated flat tappet oil or diesel engine oil in any flat tappet engine to help protect the lobes and lifters from wear.
Travis..