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post #1 of (permalink) Old 02-26-2002, 10:44 AM Thread Starter
 
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broken rocker arm hold down...why?

I pulled the valve covers off of the 360 I am getting ready to install in my jeep and one of the rocker arm holddown clamps(correct word?...not sure. the part that I am referring to holds the rocker arms down on the pushrods and valve springs) was broken. I replaced it with another one and turned the engine over by hand and the valves opened and closed like they were supposed to. My questions are: what would make this part break?...do they just wear out? thanks for the advice...Ben

86 CJ7 258, weber carb, rusty but trusty!!
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post #2 of (permalink) Old 02-26-2002, 12:11 PM
 
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Re: broken rocker arm hold down...why?

Do you have individual rockers or are they on a rail all attached together?

If you have singles,
By "Hold Down" do you mean the bridge that connects one to the other and keeps them from twisting, or the fulcrum (mount, tower, pivot, ect) in the center of the rocker arm?
<hr>
The most common causes for broken rocker arms (and in your case the mount) are...

1. Flaw in the material.
If there is a flaw in the base material, it's a place for a crack to get started.
If there is a flaw in the heat treating, it may have become too brittle and just snap off. (usually one quick break)
If the material is too soft, you will usually see where the crack has started, stopped, moved again, stopped ect...
There are literally billions of these things manufactured every year, and bad ones often ship to customers.

2. Lifter pressure.
Some times the valves in the lifter will malfunction.
(usually do to crap in the oil, but sometimes it's a mechanical defect)
The piston in the lifter that's supposed to pump oil up through the push rod is jammed in place and doesn't move.
This will cause the lifter, in effect, to be taller than normal, and will break rocker arms and push rods.

3. Sticking Valves.
If you had a valve stick in the guide, that will break off parts in a hurry!

4. Slop in the valve train.
Clearances that have worn and opened way up, compressed lifters (often called 'Stuck' lifters) where the internal piston is at the bottom of the lifter (Broken spring, wedged down by crap in the bore, ect.), broken valve springs, valve stem lash caps came loose, ect....

When excess clearance gets into the process, gravity pulls the push rod down, and the lifter will propel the push rod back up with quite a bit of force... But now there is slack in the system, it lets the push rod hammer on the rocker arm assembly.
This is REAL hard on things. Hydraulic valve trains are a zero lash system, and should never be allowed to hammer...



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post #3 of (permalink) Old 02-26-2002, 04:02 PM Thread Starter
 
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Re: broken rocker arm hold down...why?

thanks for the reply, Aaron. the rockers are single with the bridge connecting 2 rocker arms together, shaped like this __n__(ok, similar anyway!!). there was a bolt in each side of the bridge going thru the rocker arm and one of them was broken off at the head of the bolt. thanks again, Ben

86 CJ7 258, weber carb, rusty but trusty!!
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post #4 of (permalink) Old 02-26-2002, 04:57 PM
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Re: broken rocker arm hold down...why?

Ben ,,, I had the same thing happen to a 78 AMC 360 I dropped in a Cj-5 a couple a years ago ,,, Plus mine bent a few push rods to boot,,,, The Timing chain was shot,, You could almost touch the chain togeather in the middle... The Plastic on the cam gear was gone ,,, I got a new solid steel gear & chain & replaced everything that was bent & was good as new,,,

DEATH BEFORE 2 WHEEL DRIVE ,,,
Quando omni flunkus moritati ,,,


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post #5 of (permalink) Old 02-26-2002, 09:35 PM
 
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Re: broken rocker arm hold down...why?

I broke one once on a bad timing chain also. Bent four pushrods also. When I shut the engine down it was running fine. Went to start it up and heard a loud bang and backfire. You need to do some work on it to figure it out. To check pushrods I just lay them flat and roll them on something flat by hand. You will figure out the bent ones.

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