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Thread: dropped valve : (

  1. #1
    Senior Member RACING JUNKIE
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    dropped valve : (

    Well its offiical I killed it I admit it, I was doing the burnout and the motor started to miss when I hit high gear pulled up to the staging lights and gassed it once to see if it would clear up and it was smoking something terrible so I cut it off, got help pushing it back and on the trailer and finished watching the races contemplating what had happened to motor.
    After removing the valve covers noticed #1 and #3 cylinders rockers were loose as hell, removed intake and head on that side and well it was a mess to say the least. It had dropped the intake valve on #1 cylinder, the valve banged around on the piston for a while till got small enough to be sucked into the intake and then into the next cylinder where it got lodged in the intake port of # 3 and bent the intake valve there. several peices of the valve and or piston made there way around in the intake wrecking havoc on 2 more pistons before it all was said and done. 2 pistons damaged and one completly gone, #1 cylinder's combustion chamber looks like hell but I think it can be fixed, the cylinder wall is screwed too so a sleeve will need to be put in there.
    My question here is how long should a set of valves be run before you would replace them to prevent this from happening again? Or do they even need to be replace periodioticly?
    As far as I know these valves have been in this motor for more than 4 plus years and I was thinking that was along time. The springs were replaced last year along with new keepers.
    I had been driving this car almost 2 seasons now for a friend and we've never had any problems till tis happened, I asked the owner he has had any previous valve train related problems before I drove it and he said never.
    The motor is a bbc 468 13 to 1, 722 lunati solid roller cam, grumpy jenkins merlin heads w/ stud guirdle. Motor has never been sprayed w/ nos and I shifted it out at 6800 via an electric shifter so its never over reved.
    Im building a 496 for my car and I'd like a heads up on if and when to replace "things" to prevent this from happening to me, or anybody else for that matter. Any info would be greatly appreciated.

  2. #2
    Senior Member EXPERT BUILDER
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    Just a thought, but were the proper keeprs installed for the retainers? Steel valves at that low of rpm should last indefinatly....
    Ed

  3. #3
    Senior Member RACING JUNKIE
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    He is a mechanic and he always uses lunati stuff just one of his routines, Ive never personally changed keepers but he said he dropped a valve in another motor years ago at the keeper and since has always changed the keepers every racing season, their cheap so why not I guess?
    Anyway the valve broke at the bottom where it tapers down near the seat not at the top where the keeper is, I was thinking fatique was a factor since it broke at that point.
    ***IN GOD WE TRUST***

  4. #4
    Senior Member DYNO OPERATOR
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    My first guess is not enough valve spring pressure on the seat.

    What I jst can not understand that I see so often now days is all of you who are beating your Big Block Chevys to death alsmost by operating them in the danger zone window. 6,600 to 6,900 rpm is the worst possible rpm to be running the Big Block Chevy. Some people do it and get away with it, and some don't. Reving to a higher rpm is actually much easier on that engine if you are using solid lift cams.

    For some reason with hydraulic cams that rpm is fine. The valvetrain harmonics when using siolid lifts of flat tappet or rollers at that rpm is horrendous and is much easier when you go up to even 7,500 rpm.

    I have never ran a BB Chevy with solid lift at less than 7.500 rpm for shifting rpm even with the old oval port heads.

    Even the bigger engines called Mountain Motors are run much higher. There was one that was big using a 5.750 stroke that did end up shifting at 7,200 to 7,400 rpm depending on the track conditions. ^32 's are being shifted on all motor engines at 8,00 to 8,400 rpm. For the life of me I do not understand all of the newer guys who keep the rpm down on those BB engines. They love rpm.

    My siggestion is to watch your valve spring pressures both seated and open and consider your spring set up as a critical part of your engine. Never set them up with more than .080 from coil bind. Off the top of my head with the cam specs you supplied I would be looking at a minimum of 260 lbs on the seat.

    Ed
    " Let all things that hath breath, praise the Lord. Praise Ye the Lord" Psalms 150 vs 6.

  5. #5
    Administrator RACING JUNKIE bjuice's Avatar
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    i have a 511 bbc chevy and i turn it close to 7,000...i now have a shorter tire and it should turn 7,200......you can feel the power difference from 6800 up thru 7200...very noticable difference.

    also for the record i have an aluminum dovanvan block 632 with Pontiac Big Chief 14 degree heads 822 roller....it made 1200hp at 7600 rpm...and i will turn that motor every bit of that.

    Just my opinion on your valve breaking and where you broke it...i think its just the attrition of parts breaking down over time..if i am correct i think you said the motor was 4 years old...thats a long time on the same parts ( in my opinion)..i do not know how much it was run but if you ran every weekend for 2 seasons you got a lot of use out of that motor. here in the South you can run year around...all 12 months on Saturday or Sunday and 9 months Thursday,Saturday,Sunday....so its possible to put FREAKY HEAP load of passes on a motor here in S.C. in a single season..if you show up each time..

    Metal WILL wear out and break...IN MY OPINION..i do not think it was your fault or your engine builders..the fact of it is run one long enough and its going to give somewhere.....


    thanks Brian
    Bjuice..

    "I'M YOUR HUCKLEBERRY ! "

  6. #6
    Junior Member APPRENTICE
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    We tell all our customers to change out the valves every year and sell them to some one else or give them away. We have found two items that affect valve longevity (other than a defect in craftmans ship). One; too loose a clearance in the valve guide. if the guide is too loose, then the valve will seat differently each time and flex it at the stem to head position. Another problem is to little seat and or pressure . As the valve slams on the seat, if there is too little pressure to keep it there it will bounce for any number of times and we all know the alterntives. We work with our cam grinders to try to set the valve down on the seat just a little bit more gently. Makes things last a lot longer.
    All this is my opinion only.
    racear

  7. #7
    Senior Member EXPERT BUILDER
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    what brand and model of valves are they?
    I seem to remember someone makeing 2 piece valves at one time.
    Ed

  8. #8
    Senior Member RACING JUNKIE
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    The valves are whatever brand came stock in the merlin heads at the time they were produced? I took the tore up head to my machine shop today to see if the head could be fixed and they said it would be cheaper to buy another casting then fix that one : ( and also I asked about the valves in the heads and they said that they've seen the merlin heads especially break allot of valves due to the fact that they use the cheapest valves they can get there hands on the time the heads are assemblied.

    Ed I tried to convince the car owner when I started driving the car to raise the shift point merely for the fact that the cam made more power higher up in the rpm range we were just starting to make power when it shifted but he insisted on leaving it at 6800 cause he said it was easier on the "motor", after what you stated earlier I guess he was dead wrong.
    Thx all for the info I will take head and shift my motor in "MY" car at 1000rpm under peak horsepower and shift into peak torque rpm, which would be right around 7500 rpm. Charles
    ***IN GOD WE TRUST***

  9. #9
    Senior Member DYNO OPERATOR
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    I will take head and shift my motor in "MY" car at 1000rpm under peak horsepower and shift into peak torque rpm, which would be right around 7500 rpm. Charles
    Charles,
    I suggest that is also not the best thing to do.

    An average ideal shift point, dpending on tranny gears, is between 500 to 600 rpm above the rpm of peak horsepower. With a nitrous engine that max hp peak rpm will be some lower.

    My 461 I had back in the early 1980's wanted more rpm than I could let it go. I had small rod bolts (Dorman HPX) and a two bolt main block, using pistons with pressed in wrist pins. Still I kept it a 8,000 rpm all the time. 8,000 rpm high gear burn-outs, 8,000 launch, and 8,000 rpm shifting with a 4 speed Chrysler box.

    My 477, before that did have good 7/16 rod bolts and floating pins. It got shifted at 8,800 rpm. Later now, I know that was too high but back then I knew no better.

    A very good friend of mine that has spent his entire life studying and developing valvetrain components, has recently joined here. If you ever see him post, ask him at what rpm ranges has his years of research proven are the most destructive to a running engine.

    I will tell you in advance it is at low speed idling. Idling is the hardest thing on a race engine. The other is at rpm between 6600 and 6900.

    I have a history of my race engins not blowing when I was racing. So far I still have that reputation s a builder. If built right and correct matching components are used and are set-up right the BB Chevy in all sizes should live.

    Ed
    " Let all things that hath breath, praise the Lord. Praise Ye the Lord" Psalms 150 vs 6.

  10. #10
    Senior Member RACING JUNKIE
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    thx Ed I'll check that out.
    ***IN GOD WE TRUST***


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