454 Backfires - Problem Identified

Hello All - Newbie Here - wanting to share a recent find.

Recently I started experiencing backfires on my 454, so the first thing I did is read all the related threads posted on this board, and began checking the recommended items (carb, distributor, vacumn leaks, valve springs, etc).

After all the checks and still not finding the issue, a friend of mine recommended a method in which I have never heard of before (raised my eyebrow) and that was to pull the rocker arm covers, and push gently on each rocker arm while the motor was running. In theory, it should slap your hand if the valve is working correctly, and if there is a weak or damaged spring or retainer, it will show up.

Now I dont know (being new here) if this is a recommended test, but it worked! When my friend pushed the intake rocker for piston 1, the engine almost died. We compression tested the cylinder, and it was showing good compression. At this point we pulled the rocker arm off, and the two piece locking retainer was broken severely, but had one side still holding on.

The symptoms I experienced were as follows:

--Runs great at an idle
--Runs fine bringing up RPM's in driveway
--Starts backfiring under a load at mid-high rpm's (while driving)

Anyways - looking to replace this retainer tonight, but I am sure this is the cause of my issue as all other components checked out. Thanks for all the great info on this board, as I made it a long way diagnosing the other componets to find this issue.

Tabers,


Sounds likeyou got the handle on the problem. Just wondering, when you found that on Cyliinder NO. 1 did you check the rest? Could be more of them, especially if a high rpm run did in NO. 1. Just thinking. ;) ;)

Going to check it hopefully (knock on wood) tonight, and see if this is it. Since all others looked good, I am hoping it is a fluke, and not just a sign of more to come. I dont have a tremendous amount of experience on valve issues, so it will be some trial and error. I will post a reply once its back together and see if that was the final issue.

Thanks!

Now how ya gonna change the retainer without dropping the valve into the cylinder ?????? One method is an air hose screwed into the spark plug holewith the rocker arms off for that cylinder air preasure will hold the valves closed for ya....
another method if'n ya don't have a compressor or the air hold tool is get some clothes line rope fill the cylinder with it thru the spark plug hole and gently turn the motor over ( by hand) untill the rope compresses and holds the valves closed...... Be sure and leave some rope hangin out so you can remove it

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Originally posted by Streets
My mom always did the clothspin thang in the backyard on the clothesline.. :LOL:

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Were they the one pc. wood kind or the spring loaded 2 pc. wood kind??? I found all kinds of uses for the spring loaded ones .... when i didn't get caught taken 'em that iz' He HE:LOL: :LOL: :LOL: **)

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Originally posted by pro70z28
Were they the one pc. wood kind or the spring loaded 2 pc. wood kind??? I found all kinds of uses for the spring loaded ones .... when i didn't get caught taken 'em that iz' He HE:LOL: :LOL: :LOL: **)

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When Streets was a kid they were chipped out of stone, or carved out of dinosaur bones!!:eek: :p :LOL: :p :LOL:

All righty then.... For ya young uns, clothes line rope is a white rope about the diameter of a pencil ya can get it at Wally World........

Geeeeeez, I hopes they still know what a pencil is...... My youngest's school specifies mechanical pencils......

Oh yeah Pro. had ta get the spring loaded ones ta hold the baseball card in your bike spokes for that Harley sound (LOL)

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Originally posted by Bob Parmenter
When Streets was a kid they were chipped out of stone, or carved out of dinosaur bones!!:eek: :p :LOL: :p :LOL:

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Spoz' they had to be extra H.D. to hold up the buffalo skins on da' tree branches. He He he:LOL: :LOL: :LOL: **)

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Originally posted by HWORRELL
Oh yeah Pro. had ta get the spring loaded ones ta hold the baseball card in your bike spokes for that Harley sound (LOL)

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Duals....... front & back. :) :) :)

Thanks guys for the great idea's. I was considering the airhose option @ 70-100 psi of pressure, but since streets mentioned it failed right before he was finished, this has me a little worried.

I think I will try the clothes line idea, as once this is compressed, I can take my time with the spring off, and make sure I find the best retainers available. If the machine shop indicates their a cheap retainer (based on what I have left of the one), I may replace all of them to ensure I dont have this happen again a month from now.

Do any of you guys know the best spring compression tool for heads that are mounted on the block still? All my buddies do not have one, and I may need to purchase or rent one for this project. I see one in Jegs (black handled -looks like nail puller), but I want the best tool for the job, since I will most likely only want to do this once.

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Originally posted by Tabers71


Do any of you guys know the best spring compression tool for heads that are mounted on the block still? All my buddies do not have one, and I may need to purchase or rent one for this project. I see one in Jegs (black handled -looks like nail puller), but I want the best tool for the job, since I will most likely only want to do this once.

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I have an old one from my auto repair shop days. It's the nail puller type you are talking about. Pulls off a nut on the rocker stud. Works good.

Guys -

The clothes line did the trick. I was able to hold the valve up (firmly) long enough to replace the faulty keepers with some new ones. Car is back up and running. I do have some valve train tick that wont seem to go away after adjusting the number 1 rockers (previous problem area). I either suspect there is an exhaust leak, or something a little more deep than I diagnosed previously.

Motor runs good, backfire resolved, but seems to be loading up a bit under quick acceleration. So a question to you all, what do you think could be occuring if its not an exhaust leak, and seems to be loading up a bit. I am wondering what caused the keepers to give in the first place, and wondering if I am overlooking a flat cam or ???

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Originally posted by Tabers71
Guys -
I am wondering what caused the keepers to give in the first place, and wondering if I am overlooking a flat cam or ???

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Hi I have a little story for you... :

Back when I still had my 396 in my camaro I had a world of problems witch could have been avoided if I had just pulled the engine the first time and checked it.

It all stared with a pushrod going thru the rocker arm (made a nice little hole). Well no big deal I just replaced the rocker arm, and of I went..... When I went to readjust the rockers after a while I noticed that the valve with the new rockerarm, wasn't opening as much as the others...... Okay then I got a new cam (the lobe had been worn down) new lifters gaskets etc. and replaced the lot. Changed the oil and filter. I then Flushed the engine with new oil and changed again.
After breaking in the cam for 30 min. I went for a small drive and erevything seem fine. The next day I was gonna go to a carmeet and have fun..... I got the car and I was of, after about 10 miles the engine started going clonk clonk.... :( .... And I had just spun a rod bearing, and cracked a piston.... So I didn't get to the meet... :( When I had the heads redone the machinist told me that he had replaced a bend valve, and guess what it was the same valve that I had replaced a rockerarm on......


So now I have a new 454 ... I hope it dosen't break a rocker arm... :)

I'm not saying that this will happen to you, I did this to myself by not checking everything properly.

By the way I have used the compressed air trick lots of times ... the trick is to block the engine so it can't spin and then squite a little engine oil into the cylender thru the sparkplug hole, you are working on.

That trick ... Pushing down on the rockerarm with the engine running, couldn't you accidently bend the valve by pushing the valve down into the piston... Or am I just not getting it???

Sune Larsen

Sune - Thanks for sharing your experience. It helps to rethink this a little more (seeing the big picture). I took the car for a nice long ride yesterday, getting on it a little bit here and there. It seems to be running good, but I notice at the top of the RPM range (about 4 grand), it starts a little hesitation until I shift into the. It almost feels like a misfire or cutting out. I did replace the plugs when I repaired the valve keepers, and gapped them at 45 like the guy at the autoparts place recommended. Maybe I need to revisit this?

I have been very frustrated with this 454, as it was sold to me as "just freshened up" with less than a 1000 miles on it. What I am seeing now is that it is possibly an old tired motor, and needs a rebuild. Reason I say that is the oil pressure is fairly low, compression is not as tight as to be expected, and it has far too many leaks to have everything "freshed up". The plan is to try and make it through summer (I think I just cursed myself), but I want to have a ride to go to meets and an occasional skip work and play day..hehe.

As far as the pushing down of the rockers to identify the problem, it was not very hard. It is more of a gentle place the palm of your hand on the rocker, and if it pushes back against your hand (due to spring tention, etc), then its fine. In my case, when we lightly pushed on the intake of cylinder 1, it almost killed the motor immediately. The idle dove quickly. I see your point about pushing it down a valve onto a cylinder head, but we didnt push that hard. The rods and springs keep it pretty much intact, unless of course you have a broken spring or keeper.

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Originally posted by Tabers71
but I notice at the top of the RPM range (about 4 grand), it starts a little hesitation until I shift into the. It almost feels like a misfire or cutting out. I did replace the plugs when I repaired the valve keepers, and gapped them at 45 like the guy at the autoparts place recommended. Maybe I need to revisit this?

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I don't know what that might be??? About the gap... I can't really remember, but it is either 30 or 45 or both depending or what type of heads... anybody??

I'm looking forward to hear what you find out hesitation..


Sune Larsen