Blown 468 Valve Train Problem
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Blown 468 Valve Train Problem

  1. #1
    Senior Member wagspe208's Avatar
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    Default Blown 468 Valve Train Problem

    OK, I am not the smartest guy in the world. I hav had a problem with an engine I built for a guy and am not smart enough to figure it out. I was hoping for some input.

    The engine is a lower hp $ copy of mine. It is a 468, stock type block, dart cast iron heads, ferrea valves, k1000 springs, comp stainelss rockers, and stud girdles. (my differences are 10-71 blower, jesel rockers (top end stuff) We run the same camshaft, lifters, springs, ret, keepers. So, damn near a low $ lower hp engine combo that I know works (for me I guess)

    MINE, 7800 to 8g through the traps. 10-71, never adjust (ok, 2 x a year (stupid I know)) adjust the valves. Reliable as the day is long. 8.0 sec

    HIS.. well, he says he has a 7200 rpm rev chip in in and he does not hit the chip, he says he runs 6800 to 7g though the traps. 9.0 sec

    He had a new piece (he brought it because he had a lifter failure and tore up the cam) I frehsen up the piece. He jumped 2 exhaust pushrods out of the rockers this weekend. The lfters were fine, tight, etc. Second time, hit exh. valve and bent it. I thought he was adjusting valves worng, or something. Nope, I watched him. He did the same as I do. Maybe this, maybe that, etc.
    Now, suggestions?

    I did check p to v. +.200 int and exh + lash
    New guides, no exhaust seals, proper clearances (same as I have run and do run for years)
    Pushrod lengths are right, patterns look beautiful.
    Same cam, same/ similar lifters, same pushrods, same springs, ret. keepers, valves, heads, (not rockers)
    Customer said the engine has had a history of some valve issues. Over hell, maybe 7 years I have done this engine maybe 2 or 3 times and he has had problems maybe 4 or 5 times in 7 years. So no big deal, but should not be happening.
    The ONLY THING I can think of is spring harmonics in his opeating range? I never thought of this as a drag problem, really, more of a constant rpm issue?? I run more rpm, and flash through them quicker. He runs a direct drive, so it stays in an rpm range longer. I run 7800 he runs maybe 6800?

    What do you think? I am missing something. Do harmonics set up at a certain rpm based upon spring, camshaft profile, or some of both?

    Thanks
    Wags
    Last edited by wagspe208; 09-12-2010 at 10:30 PM.

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  3. #2
    Resident Ford Nut Sleeper CP's Avatar
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    " He jumped 2 exhaust pushrods out of the rockers this weekend."

    With guide plates ? and stud girdle ?

    Harmonics are product of every part of the valve train including keepers and retainers.

    S CP

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    i'm back!! 1QuickCP's Avatar
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    i'll take a guess,being that he has the Dart cast iron heads I would look very carefully at the clearance around where the pushrod goes through the head/guideplate through its full range of motion. I have seen where the pushrod just clips the edge of the holes where it goes through the head and the guide plates need to be cut/welded/bent or the space ground on to get it not to hit.
    This is a mechanical issue, at that rpm there is nfw harmonics are causing it with k1000's on there.
    Another is that the valve is clipping the back of the pocket or the lifter bore is to tight...
    Last edited by 1QuickCP; 09-13-2010 at 05:44 AM.

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    What diameter pushrod and wall thickness? How new are the Comp rockers?
    Chris Straub
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    Senior Member wagspe208's Avatar
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    Answers to questions:
    1) Yes, he jumped 2 different exhaust pushrods out this weekend. Neither time did it bend a pushrod. With guideplates and girdles.
    2) I checked clearance around pushrod holes pretty close. It has adjustable dart guide plates on it. So, the were adusted so the tips were centered. There are zero marks on the pushrods other than at the guide plate, so no indication of rubbing, and close looking shows a min of .060 pushrod to casting (everywhere visible). Guide plates did not move during the jumping process either. Stick in a new pushrod, valve totally centered.
    3) P to V I use clay and the razor blade cut, so tons of radial clearance also.
    4) Lifters good in bores. Stock block, so not the dart tight stuff.
    5) Pushrods are CV Products 3/8 .080 stuff. Same as I use, different length, though.
    6) Rockers are brand new comp best steel pieces. (I've had pretty good luck with them for guys not wanting to buy crowers or shaft)
    7) I am very skeptical of the resonance thing also, but something is going on I do not see.

    I'm grasping at straws. I was not racing this weekend, so I got volunteered to help crew for 3 boats. LOL (total other story)

    Thank for the help guys. I do know there is tons of info here.
    Wags

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    steelcomp was here
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    I'd be looking for pushrods rubbing in the holes or maybe rocker to P/R clearance at full lift?
    Harmonics can cahnge throughout the rpm...smooth as glass at 6000, destructive at 6500, and smooth agaoin at 7000. (just an example).
    How much lift are you running?

    ETA: It doesn;t sound like harmonicss to me, but as I think...how does a P/R come out? More space between the lifter and rocker than necessary, Maybe a sticking ex valve? Do you know the stem clearances?
    Last edited by scott foxwell; 09-13-2010 at 07:12 AM.

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    Senior Member wagspe208's Avatar
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    Side info.
    They ran a 8.6? first pass, full pass.
    Round 2 they switched pulleys and put the little one on the top, so Instead of -15.7% they were +20% It ran a 8.57 lifted at less than 3/4 track, valvetrain was perfect and no lash change after that pass.
    He said it was on a mission (LOL)
    Wags

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    Senior Member wagspe208's Avatar
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    I think it is .725 lift. Small piece, I will check for sure.
    At full lift, everything I can see looks good. Absolutely no signs of contact anywhere but guide plate on pushrod.
    New guides, exhausts are .0014 to .0015 set up with my sunnen gauge. (standard stuff for me) No seals on exhuast.

    Wags

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    Senior Member wagspe208's Avatar
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    The other problem is boat drivers. I am not a fan of lugging engines. I think it just kills them. I have no idea what the prop burn rpms is, or if it runs at 3800 rpm till it kicks the tail at half track?? The driver doesn't know. LOL
    Wags

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    steelcomp was here
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    Quote Originally Posted by wagspe208 View Post
    I think it is .725 lift. Small piece, I will check for sure.
    At full lift, everything I can see looks good. Absolutely no signs of contact anywhere but guide plate on pushrod.
    New guides, exhausts are .0014 to .0015 set up with my sunnen gauge. (standard stuff for me) No seals on exhuast.

    Wags
    Well honestly, I'd never run ex clearances that tight, especially on a blown marine deal with iron heads, but if you've done it and gotten away with it, cool.
    The .080 wall p/r's might be a little "springy", too...especially ex valve opening against blower cyl. pressures.
    Just thinking out loud.

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    Senior Member wagspe208's Avatar
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    Quote Originally Posted by steelcomp View Post
    Well honestly, I'd never run ex clearances that tight, especially on a blown marine deal with iron heads, but if you've done it and gotten away with it, cool.
    The .080 wall p/r's might be a little "springy", too...especially ex valve opening against blower cyl. pressures.
    Just thinking out loud.
    This has been our standard blown gas big boat exh. clearance for years, and never a galled/stuck valve.
    You think the exh. due to extra 1" may be an issue over the intake stuff?
    I run the same pushrod. This is not saying it is not flexing by any means.
    I am just puzzled because with rocker type and rpm it is my valve train piece for piece.
    Thanks.
    Wags

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    i'm back!! 1QuickCP's Avatar
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    how many past Bg deals have you run that tight on iron heads ? do they have bronze liners of are they on the cast iron?

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    gn7
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    The fact that you smacked an exhaust valve, and are kicking exhaust PRs screams sticking valve. Are your heads iron as well. The extra 1" doesn't really cause that much change. Head material is huge. So is water flow. Not just the amount of flow, but the routing. We made a small change(we thought) to the routing of our water through the motor and the head temps shot thru the roof. All we did was allow slightly more water to exit the heads thru the rear manifold ports near the dizzy. Went from the 2 ports tied into a -6 tee and then over board. Went to 2, -6s, one from each port, over board and it changes the whole deal big time. We started getting stream from the front dumps. Went back to the old setup and the problem went away.

    But the only way I kow a PR can get kicked out is if the valve stays open when the lifter reseeds. And with .200+ piston to valve, the smacked exhaust valve is pretty much a given.



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    On my 9-1 limited late model circle track stuff,(dart iron heads
    ,390 carb) we ran .0025-.0035 because of extream heat and sticking issues

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