Yet another learning experience

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m-l_johnny
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Yet another learning experience

Post by m-l_johnny » Sat Apr 03, 2010 7:51 pm

Last July I did the 4.0 head swap on my 4.2. I followed the advice/ steps from all of the writeups that are out there. Got the Jeep all back together and was very happy with the performance. The one thing that was a bit annoying was that it sounded like a sewing machine. Didn't think too much of it, kinda sounded like that before.
So fast forward to about a month ago and 7000 mile later.... I was tooling down the interstate and noticed the engine started running a bit rough and a loss of power. First thought was a bad plug or wire. Plugs weren't that old but the wires had about 40,000 on them. Changed out plugs, rotor, cap and wires. No difference. It was about that time I noticed I didn't have the tap anymore. I was a bit concerned that one of my lifters wasn't lifting anymore. Did a compression check and only one cylinder (#3) was lower; about 20 lbs. That plug was also badly fouled. Discussions with one of the guys I work with that has done a lot of auto repair was leading me in the direction of thinking I had a burned valve or bad valve seal/guide.
When I finally got a chance to start tearing into things, this is what I found.

Image

It's hard to make it out in the pic, but the bolt in rocker 5 is about halfway out. Notice the end of the keeper at the base of the spring for 6
Being an engine mechanic novice/ idiot and not knowing if there was more to the story, I pulled the head. The condition of the top of the chamber didn't surprise me. The top of the piston did.

Image

Image

I then started discussing/ asking questions of a local guy that builds race engines. He was going to do any necessary machining. He didn't think there was anything wrong with the valves. The piston was clean from the crankcase oil being sucked past the rings. With the intake valve not opening, something had to come from somewhere and the oil was it.
He asked me what the preload was on the lifters. My response was "The what?" After a brief tutorial and explanation about how reworked blocks, heads, etc. change the total valve train height, he suggested I research "rocker arm geometry"
What an education! Of all the write-ups I read regarding the head swap, every single one said to reuse the old pushrods and rockers.
Here's what not checking for proper preload can do. Notice the circular mark from the valve stem.

Image

There is only one way with non-adjustable rockers to get the proper .020"-.060" preload. Best way is to change to a different length pushrod. Shim can be added between the pedestal and the rocker if the arms are too long.

So after doing all the measuring, I ended up using stock length for the 4.0; 9.650" lng, a whopping .050" shorter than the stock length for the 4.2 that was in there. While I was in there I also replaced the lifters. Kinda like having the transmission out and not doing the clutch.
Another thing I did this time when torquing down the rockers was to cycle the engine around so each valve being torqued was completely closed. Before I just threw the rockers on and torqued 'em where they sat.
Now the engine sounds great! I think it's the quietest it's ever been, even when I first got it off the crate. It's nice to have the performance back. :biggrin:
Hi. I'm Johnny.... And I'm a Jeep addict....

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Brent Borgaard
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Re: Yet another learning experience

Post by Brent Borgaard » Sat Apr 03, 2010 7:57 pm

Nice save. Was that a smashed valve spring retainer?
How did i spend four grand on parts in one month?

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Re: Yet another learning experience

Post by ReneDave » Sun Apr 04, 2010 8:40 am

Glad to see you got it sorted Johnny! I'm guessing you replaced the pushrods after I saw you last week, what'd it take to get it started that night?
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Re: Yet another learning experience

Post by john3676 » Sun Apr 04, 2010 8:46 am

Jonny great story, it had it's ups, it's downs, I laugh, I cried, and man can't beleave what it must have been like to live it! A rollercoster ride of emosion. Glad it had a happy ending. :D

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Re: Yet another learning experience

Post by RkyMtnH » Sun Apr 04, 2010 8:50 am

john3676 wrote:Jonny great story, it had it's ups, it's downs, I laugh, I cried, and man can't beleave what it must have been like to live it! A rollercoster ride of emosion. Glad it had a happy ending. :D
What an ass . :lol:
X2 on happy ending
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Re: Yet another learning experience

Post by slvrjp00 » Sun Apr 04, 2010 8:53 am

Glad to hear you got the old CJ running again Johnny. I hope that means we will see this on the club ride May 15th!
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Re: Yet another learning experience

Post by m-l_johnny » Sun Apr 04, 2010 4:48 pm

Brent Borgaard wrote:Nice save. Was that a smashed valve spring retainer?
No. That was the end of the bridge/ retainer.

Image
Hi. I'm Johnny.... And I'm a Jeep addict....

'76 CJ7 money pit of fun.
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Re: Yet another learning experience

Post by Toaddragon » Sun Apr 04, 2010 9:38 pm

Nice save could have been worse and you learned allot. Thanks for passing the info and experience along.
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Re: Yet another learning experience

Post by rj91jeep » Sun Apr 04, 2010 10:39 pm

guess i should pull the valve cover on my cj some time and check it all out again. i am running a 4.2L block with a 4.0L head and 4.2L push rods right now. i didnt do the mod where you fill in some of the coolant ports either. i have about 2000 miles on it so far with no blown headgaskets yet but im waiting to see how long it last.
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Re: Yet another learning experience

Post by Slewis » Mon Apr 05, 2010 7:25 am

John3736 wrote:Jonny great story, it had it's ups, it's downs, I laugh, I cried, and man can't beleave what it must have been like to live it! A rollercoster ride of emosion. Glad it had a happy ending
:lol:

Good stuff Johnny! I guess you caught it at the right time.
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Re: Yet another learning experience

Post by m-l_johnny » Mon Apr 05, 2010 7:28 am

rj91jeep wrote:guess i should pull the valve cover on my cj some time and check it all out again. i am running a 4.2L block with a 4.0L head and 4.2L push rods right now. i didnt do the mod where you fill in some of the coolant ports either. i have about 2000 miles on it so far with no blown headgaskets yet but im waiting to see how long it last.
If the block and head were never decked, you might be OK. Does it make more noise than the typical I6? That's one of the signs of preload being wrong; too much or too little.
I've wondered about the necessity of closing up the water jacket holes that don't match up. From what I've read there can be situations where there is some overlap of voids on the block. Didn't see that in my application. :smt102
Hi. I'm Johnny.... And I'm a Jeep addict....

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Re: Yet another learning experience

Post by m-l_johnny » Mon Apr 05, 2010 7:30 am

john3676 wrote:Jonny great story, it had it's ups, it's downs, I laugh, I cried, and man can't beleave what it must have been like to live it! A rollercoster ride of emosion. Glad it had a happy ending. :D
I LOL'ed.
Thanks, Ebert! :lol:
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'76 CJ7 money pit of fun.
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Re: Yet another learning experience

Post by john3676 » Mon Apr 05, 2010 9:15 am

2 :smt023s up!

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