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I recently did some engine work and when I took it out for a test drive I floated a valve. It is a 396 with stock lower end and a Lunati cam 235/525. I just had a valve job done on the stock 2.06/1.72 heads. I also put in new springs, hyd lifters, roller tip rockers, and put a Performer RPM manifold on it. This was the first time I tried to adjust valves and I'm hoping I just had one to loose. I was at about 5200 rpms when it went. Is this what happened or is there some other problem? The springs are correct for the cam and the shop set the spring pressure.

Also, since I have the manifold off (had to find a lifter) what is the correct way to adjust the valves. My understanding (after doing it wrong the first time) is to set a valve on the back side of the cam lobe. Tighten it just until there is pressure on the lifter and then turn 1/2 turn. How much pressure do you initially put on the lifter? Should I see it start to depress? thanks for any help...
 

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not sure why you floated a valve if everything is as you say..valve only floats if the spring pressure is not enough to overcome the inertia of the valve...if you have the right springs and they are at the correct installed height and pressure you should of been able to go to 6500. I adjust the valves as you say, and to know when the slack is gone I tap the rocker arm up and down on the valve tip while I tighten the lock nut..as soon as the tapping noise stopps I give it the 1/2 turn...also if you really did float the valves I would replace the springs now, each time you float em the springs get weaker and will float even earlier, and possibly break.

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70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
 

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Rob,

I have had one spring out of a brand new set that was weak. Had the same symptom as you at about 5800 RPM in a 427. Chased that miss for several months and finally replaced the springs. Voila, problem solved.

Dan

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69 Cortez silver SS 427
69 azure turquois Malibu 250
ACES #02351
Team Chevelle Gold #35
 

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Rob,

I have had one spring out of a brand new set that was weak. Had the same symptom as you at about 5800 RPM in a 427. Chased that miss for several months and finally replaced the springs. Voila, problem solved.

Dan

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69 Cortez silver SS 427
69 azure turquois Malibu 250
ACES #02351
Team Chevelle Gold #35
 

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Bummer. The valves bounce off the seat their own harmonic pattern, which has little to do with the cam timing. They "float".If the shop checked them they would;ve found one not in spec. You need to replace them with heavier springs before you bounce one off a slug.
 

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Rob

What is the physical damage you have that yor're referring to as "floated a valve"? Did you break a pushrod or rocker arm? It's really not likely that you floated one valve on a fresh engine unless there's a really defective valve spring, which should have been found during assembly when the machinist ran all the springs through the tester to see what installed height they needed.

Might want to have that spring tested again, being sure it's tested at it's actual installed height.

One easy way to get burnt on a valve adjustment is to accidently adjust one of the valves without the pushrod being seated properly in the rocker arm, this is easy to do and hard to see, it'll pop in later and you'll have a lot of clearance.

Sounds to me like you need to have a heart-to-heart talk with this machinist, maybe he was in a hurry and checked a couple installed heights/pressures and figured the rest would "be OK." Ain't necessarily so....

Tom
 
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