Engine Backfire Diagnosis Led to Wiped cam Lobes

[350runner]

85swb "Fancy"

What most forget is... A hydraulic lifter at rest STILL has a spring loaded plunger which returns the top of the plunger to the top of the lifter when all lash is removed. This spring is strong enough to take up the slack in the lifter but weak enough to be over powered by the valve's valve spring. Either way, but I've seen more failed attempts while trying to set the lash with the engine running then I've seen without. Kinda reminds me of a recent thread where a guy bought a truck with a rebuilt engine that had dead cylinders and the rest had 150 psi. Any hoo to each his own brother. I can totally understand the theory behind doing the engine running method

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[Skweegle89]

85swb "Fancy"

Our shop mechanic just gave me a book on setting valve lash. If that doesn't work I'm going to pull the intake. It still just seems like a vac leak even though I can't find it. Am I not supposed to pull more vacuum at idle than I do revved up?


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[HotRodPC]

What most forget is... A hydraulic lifter at rest STILL has a spring loaded plunger which returns the top of the plunger to the top of the lifter when all lash is removed. This spring is strong enough to take up the slack in the lifter but weak enough to be over powered by the valve's valve spring. Either way, but I've seen more failed attempts while trying to set the lash with the engine running then I've seen without. Kinda reminds me of a recent thread where a guy bought a truck with a rebuilt engine that had dead cylinders and the rest had 150 psi. Any hoo to each his own brother. I can totally understand the theory behind doing the engine running method

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You are correct that the plunger SHOULD be able to hold it's own. In a perfect world, your theory is correct. I've done it the way you suggest for preliminary setting but all valves were loose. Not to the point it was making noise, but to the point I wasn't getting full lift on most valves. This being on a high performance high lift cam that we were dialing in with a degree wheel and had a dial indicator on the valves. We started with only one and when we seen how far off it was we did the rest. In short, ended up re adjusting the valves with motor running and was much more accurate.

 

[350runner]

85swb "Fancy"

Our shop mechanic just gave me a book on setting valve lash. If that doesn't work I'm going to pull the intake. It still just seems like a vac leak even though I can't find it. Am I not supposed to pull more vacuum at idle than I do revved up?


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Yes you are

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[350runner]

85swb "Fancy"

You are correct that the plunger SHOULD be able to hold it's own. In a perfect world, your theory is correct. I've done it the way you suggest for preliminary setting but all valves were loose. Not to the point it was making noise, but to the point I wasn't getting full lift on most valves. This being on a high performance high lift cam that we were dialing in with a degree wheel and had a dial indicator on the valves. We started with only one and when we seen how far off it was we did the rest. In short, ended up re adjusting the valves with motor running and was much more accurate.

If you don't mind giving him a detailed explanation of how to do it with the engine running so that if he tries it won't result in fail. What we need to help him do is get this thing back on the road.

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[HotRodPC]

If you don't mind giving him a detailed explanation of how to do it with the engine running so that if he tries it won't result in fail. What we need to help him do is get this thing back on the road.

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Very True. He may not have a choice anyway but to do it your way since he can't seem to keep it idling. That will make it hard to do with it running. I think someone already posted a chart of which valves to do first, then rotate the motor a full turn and then do the rest of them.

 

[350runner]

valve adjustment 350 chevy: http://youtu.be/z-rdCmvxGgo
Same applies to non roller rockers.

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[Skweegle89]

85swb "Fancy"

Thanks


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[350runner]

No prob.

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[Skweegle89]

85swb "Fancy"

Started it up when I got home to do one more check for vac leaks with no avail. I'm off work Wednesday so o will try to set the lash and see how that goes. It started popping out the exhaust again today. It idled on its own, but Sounds like a bag of popcorn popping at idle. Dunno where to go if adjusting valve lash doesn't work.


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[350runner]

The idle sounds like a bag of pop corn as in the lope, or inside the engine sounds like detonation.

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[Skweegle89]

85swb "Fancy"

The idle sounds like a bag of pop corn as in the lope, or inside the engine sounds like detonation.

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Idk what detonation sounds like, but the exhaust at the back of the truck just sounds like popcorn. Just pop pop pop the whole time it's idling. Not like big backfires, just popping.


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[350runner]

85swb "Fancy"

Yea that's your cam... the sound is coming from your exhaust correct?

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[Skweegle89]

85swb "Fancy"

Yea that's your cam... the sound is coming from your exhaust correct?

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Correct


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[350runner]

Nice... Kinda wish I had gotten a bigger cam.

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