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  • 2 Post By techinspector1
  • 1 Post By pat mccarthy
  • 1 Post By rspears

Thread: another BBC valve adjustment question with picture
          
   
   

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  1. #1
    TOW'D is offline CHR Member/Contributor Visit my Photo Gallery
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    another BBC valve adjustment question with picture

     



    Fresh valve grind on marine 7.4L Mercruiser.
    On #1 cylinder crank timing mark both lifters are even and slightly above their holes - push rods centered and sitting in rocker pocket.
    There are Hi Performance guides under the rocker bolts guiding the push rods.
    I pushed up and twisted the push rod and tightened the rocker arm bolt till the push rod stop moving then cranked 1/2 turn more.

    On #1 intake the push rod stopped turning so I cranked the bolt another 1/2 turn.


    then I noticed that the Hi Performance guide was still loose on the bolts and that the bolts were not seated flush, yet the push rods would not turn by my fingers.
    any help would be appreciated on what I'm missing
    cheers
    Hank

  2. #2
    techinspector1's Avatar
    techinspector1 is offline CHR Member Visit my Photo Gallery
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    It has been my experience that twisting the pushrod to take the slack out of the system will end up with valves off their seats from excessive preload.
    Also, you don't want the intake and exhaust tappets to be even with each other necessarily. You want each tappet to be on the heel of the cam lobe when doing the adjusting. Both the intake and exhaust tappets cannot be on the heel of the cam lobe at the same time. Please read through this tutorial....
    http://www.crankshaftcoalition.com/w...stment_SBC/BBC
    While there are at least 3 different methods to lash valves on a motor, this procedure is bulletproof if you just follow the instructions given. Many fellows have come back later and thanked me for writing this.

    .
    Last edited by techinspector1; 10-29-2015 at 04:33 PM.
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  3. #3
    tdkkart is offline CHR Member Visit my Photo Gallery
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    Quote Originally Posted by TOW'D View Post
    Fresh valve grind on marine 7.4L Mercruiser.


    Something is odd here, as it doesn't appear that you have traditional rocker studs holding the guide plates "Hi Performance guide", down to the head.
    It also appears that you have bolts holding everything down instead of nuts, which suggests to me that the valvetrain is intended to be non-adjustable, ie: simply tighten the bolts down tight and go, no normal adjustment needed.
    It's been a long time since I've been inside a BB Chevy, can't say for sure if or when they switched to this system.
    I would talk with whomever did the valve work and see what they say.

    Typically you should have something like this, stude with threads on both ends holding the guide plates, rockers slip down over the threaded studs and then a nut adjusts the rocker.

  4. #4
    pat mccarthy's Avatar
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    it going to be very hard to set the lash on rockers thats a gen 5 or 6 and that is a tower bolt and NO lash adjustment can be made . you would need to change it over for a rocker stud done many . you use the 7/16 /3/8 Arp 135-7102 or on race engine i drill and tap head for a 7/16 top and 7/16 bottm stud then rocker arm stud setup you will need and older mark 4 rockers and guild plates less you buy new balls for your old rockers to fit the 7/16 stud as the tower is about 1/2 and the rocker ball is bigger as well comp sells a kit and others but i just use the older mark 4 hard ware
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  5. #5
    rspears's Avatar
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    Post deleted. Pat was typing before me, and his comment made mine irrelevant.
    Roger
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  6. #6
    TOW'D is offline CHR Member/Contributor Visit my Photo Gallery
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    Gee Wiz guys,
    what does that mean Pat?
    No adjustment? How does that work.
    all push rods are the same size on each head- I put them back in the same order
    dayum I'm corn fused now
    thanks
    Hank

  7. #7
    rspears's Avatar
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    Chevrolet Big Block Engine Generations - Chevy High Performance

    Scroll down to Picture 9/17 to see and read the differences.
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    Roger
    Enjoy the little things in life, and you may look back one day and realize that they were really the BIG things.

  8. #8
    TOW'D is offline CHR Member/Contributor Visit my Photo Gallery
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    Thanks Roger,
    a lot clearer now
    Do I have to make the conversion to adjustable or how to torque the tower bolts
    I love this site
    cheers
    Hank

  9. #9
    rspears's Avatar
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    Quote Originally Posted by TOW'D View Post
    Thanks Roger,
    a lot clearer now
    Do I have to make the conversion to adjustable or how to torque the tower bolts
    I love this site
    cheers
    Hank
    My understanding of BBC is only what I've read through the years. The scuttlebutt seems to be that unless you're going to a lot bigger cam the OEM studs are OK, no need to change but it looks to me like your tower studs are not installed right to hold the guide plates. That said, Pat is your best bet for what's right, and what's not on the BBC. Maybe he'll jump back in and give you the answers.
    Roger
    Enjoy the little things in life, and you may look back one day and realize that they were really the BIG things.

  10. #10
    pat mccarthy's Avatar
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    gen 5 and 6 was the first years of the pre set lash so less you remove the tower bolts and use the kit from comp or buy a set of older mark 4 big block rockers arms or roller rocker arms then the ARP stud are needed or the older GM 7/16 studs as they have a 7/16 part of rocker stud that screws in to the head then you would need to drill and tap the head to take older rocker stud . for a engine that had much valve work or been deck or longer valve bigger cams and valve spring with more lbs then many like the bigger stud . BUT if your engine is OEM stock then you preload should be the same as stock and will be ok . less machine work as been done bigger cam sunk valve milled heads all valve height needs to be the same as Then your best bet is the adjustable valve train then you need to buy the parts to make it so .this is much like many engines made have pre load set . there 8 push rods shorter are intake... 8Ex longer .. over the years they are not the same over all length.i hope this is clears up some things
    Irish Diplomacy ..the ability to tell someone to go to Hell ,,So that they will look forward to to the trip

  11. #11
    TOW'D is offline CHR Member/Contributor Visit my Photo Gallery
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    when I pulled the head apart I pulled the push rods out and stuck them in order in a plastic oil container that I cut 8 holes- but I think I'll pull the push rods and check them for heights differences
    The engine is stock but has had one head replaced before I started working on it.
    I'll see if I can get the torque specs on those rocker bolts
    yes it is getting a lot clearer
    cheers guys
    Hank

  12. #12
    TOW'D is offline CHR Member/Contributor Visit my Photo Gallery
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    thanks for the help guys
    I found that the torque is 40 to 50 ft lbs
    Hank

  13. #13
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    Hi guys I know this is an old post hope someone can help me here so I put back a gen v block with vortec heads on non adjustable rockers. And there seems to be a 100 though gap and if I bottom out the rocker bolt it keeps the valve open. What could of happened and it came form an running engine just the crank was bad. So replaced that and it started now it doesn’t and I see all the valves are open and 100 psi compression but once the valves closed got 150.

  14. #14
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    Yes, several years old.... and in that time - all those experts have left. RSpears is still here so maybe he can help and there are a couple of others ( Glenn comes to mind) who know a lot of cheby stuff so maybe they can help?? Give'em a chance to sign on and we'll see what happens... I'm a blue oval type... sorry

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