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Projects Old school cool 248 Gmc

Discussion in 'The Hokey Ass Message Board' started by Neb Hillbilly, Dec 26, 2019.

  1. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    I will have to open all my side covers and see what I think. Surfaced the rocker tips and cleaned them in preparation to assemble them. The .050 difference between the left and right rockers is killing me. If it was just intakes or exhausts I would be ok but it is both. Is a stovebolt intake worth checking? Is there any aftermarket rocker available? IMG_20200423_071001.jpeg IMG_20200423_070946.jpeg

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  2. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    I worked on the "GMC" during a conference call. This is what I came up with. Probably getting both panels cut this afternoon. IMG_20200423_103421.jpeg

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  3. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,265

    jimmy six
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    Unless you can find a set of the roller rockers made a few years ago your best bet is watching for Barkers or Thomas Magnisium on the Internet.
    Hershey or maybe the other big swaps might be beneficial. I'm sure some hoarders may have them.
    I myself would just open the cabinate above my work bench. image.jpeg
     
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  4. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    Didn't your mom tell you that you should share your toys?

    The chances of finding that stuff hear is probably the same as finding an unstyled Allis WC on steel there. All the big swap meets are DAYS away from here. Maybe someday I can go but not today. Guess I will suffer with my crappy ratio, whoa is me.

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  5. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
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    And to be clear the above the post is full of sarcasm. I wouldn't expect anyone to sell there horde especially with the way my garage looks.
     
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  6. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
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    I am going to the farm and pick up my last shaft. I doubt there is any difference but the ratio of these lefts are worse than the 1.4 that I expected.
     
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  7. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    Went to the farm and got the shaft (and sprayed all the weeds and grass growing in my grandma's farm yard). Pulled apart the last shaft not in an engine. Measured my pushrods today and the longest was 10.655 and the shortest 10.565, so I can check a few different lengths once I get all the rockers sorted out.

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  8. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,265

    jimmy six
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    Think about the lash caps if you can use them. They do help if you think about where your rocker tip is starting now with a level rocker. Your moving the valve towards the shaft as the tip moves across the valve tip. If it was really correct it moves the valve up and down directly and actually increases the lift. Did any of your rocker arm sets have the aluminum stands? Easily machined to correct the geometry...
     
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  9. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
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    I added lash caps but saw minimal difference (.002 maybe), I am leaving them on though. Nope all my stands are stamped.

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    Last edited: Apr 24, 2020
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  10. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    RichFox
    Member Emeritus

    Several years ago Bob Dalton and I ran my GMC in his Flashpoint car. At that time Bob bought all the steel parts of 12 roller rockers from Isky and a block of 6061, One Saturday in Bob's shop with Bob on the CNC and me on the vertical mill and we had roller rockers I say this because it looks like that is well within your skill set and not such a big deal if you have access to a CNC.
     
  11. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,265

    jimmy six
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    Sounds like what my guy did when mine were made Rich.. Isky tips and 6061 but no C&C. I used Torrington bearings on the shaft but looking back they probably weren’t necessary.
     
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  12. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    If I still had access to Pro-E I would design them. Funny thing is I have a recip compressor company that I work closely with. The president and I are buddies and I was explaining my frustration to him. He said they have a great CNC mill and to send him a set of rockers so he can see if they can build a set. I will send him a left, right, shaft and both styles of rocker stands. I would think with flooded oil parts should last a long time with no bearings.
     
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  13. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    RichFox
    Member Emeritus

    We did not use bearings. But it only ran a few times.
     
  14. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    GMC Side Cover.jpg So, finalized the side cover today. It will have a 1/2" diameter engine turned alum back panel and a mirror polished stainless front cover.
    I also discovered another thing, while checking the next set of lefts, I discovered that I messed up. The dial indicator was bottoming out before, so all of my whining and crying was because the stupid engineer didn't set up the dial indicator for full travel of the rocker. I reset it and rechecked all the rockers I had previously checked and found 6 above .470 lift. Close enough for now. Not that I will quit on the rocker idea but it won't be holding up forward progress.
     
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  15. dentisaurus
    Joined: Dec 11, 2006
    Posts: 395

    dentisaurus
    Member
    from Boston

    that's going to look pretty trick
     
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  16. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    Took the plugs out of the rocker shaft and when pounding one plug through I found this mess. Be sure to clean out your rocker shafts, this is about a quarter of the crap that came out. Tapped the end of the cam and used the Ford bolt recommended by the performance 6 book for gear retension. Put in my sealed power lifters. Feel a little bad to use them but they are probably better than the lifters you can buy new. Decided to reuse the tubular pushrods that came with the 248, for now. Then assembled the rocker shaft. IMG_20200425_061257.jpeg IMG_20200425_112446.jpeg IMG_20200425_112537.jpeg IMG_20200425_120222.jpeg

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  17. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,265

    jimmy six
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    Side cover looks great.
    Rich, I don’t think bearings are necessary either with full oiling to the shaft and no overflow tube.
    Good find on the dial indicator. With searching I’ve found longer adjusting screws with correct ball if the push rods are ever short. It’s also good your not trying to use the stock ones as they are pretty small diameter for the length on a performance engine of any kind.
    Removing the plugs on the shaft is something that needs to be done and sometimes missed. I get them from Dorman.
    Great watching....
     
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  18. Six Ball
    Joined: Oct 8, 2007
    Posts: 4,341

    Six Ball
    Member
    from Nevada

    When Erson left Nevada I had the chance to buy their stock of lifter material for scrap price, What looked like miles of extruded rocker aluminum bars, buckets of roller tips, adjusters, pivots etc. I didn't the skill or tools to do anything with it. I don't know where it went. They didn't take their old cam grinding machines either or the profile plates. The machines were converted crank grinders.
    I think it was in Fisher's book where he recommended used Chevy lifters, '39 I think, because they were hardened from use. I think the resurfaced them.
     
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  19. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    I should remove the overflow tube? Any other internal oil things? 2 10-24 washers under the spring? Restrictions?

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    Last edited: Apr 25, 2020
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  20. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,265

    jimmy six
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    All my stock rocker systems kept the over flow and I never had any problems with a rocker when racing. The same system has been installed on my sons engine. At the time I used 3/16” copper tubing for a feed and a small valve I put in the feed line and would dial it back a little when running the oil pump with a drill motor. I went to smaller line with the external oil pump and no over flow when installed the roller rockers. I even put restrictions into the feed line right at the head. At this time I also started spraying the distributor gear with a .060” hole in the fitting at the gear. GMC’s are not known for oiling problems.
     
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  21. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
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    Didn't you shim the pump spring? One of my over flow tubes is pinched but it appears it was done later. The fitting at the head actually has a restriction in one I have.

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  22. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
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  23. Six Ball
    Joined: Oct 8, 2007
    Posts: 4,341

    Six Ball
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    from Nevada

    Very nice. You can take pride in that!
     
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  24. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,265

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    I’ve always shimed the pump. The 2 washers aren’t much but I could control that. Guys stretching springs have no idea....
     
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  25. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    I could calculate the k of the stock spring an increase it with a McMaster Carr spri g, but the shims should be enough. What weight oil do you run.

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  26. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,265

    jimmy six
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    All my racing engines were started and broken in with 30 non detergent a parts house near me always had. After 30-40 minutes it was drained hot and 30 or 40 wt detergent was put in for a year of racing. I’ved learned that after a year Mobil 1 was good on my bearings so it’s been my norm for the last 20-25 years. I have a vacuum on that engine so it never leaks.
    On the new street engine I built for my son was started on Chevron 15-40 Delo which we run in all his dirt track engines. It will come out in 2-300 miles. We use Wix racing filters on every thing we race and normal ones on every street car.
    Since 1975 on my first racing GMC I’ve never had a bearing problem even before I added a oil filter. Head gaskets were my nemesis between the narrowest pairs. I never ran less than 12-1 and after O-ringing I have never lost one again. I use only Best gaskets now. But what ever I could get back from the 70’s up, mostly Victors.
     
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  27. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    I will likely use 10w-30 or 10w-40 Brad Penn which is Kendell oil with a different name. Lots of zinc like the delo. Great to here about the bearings, hoping 9.75 to one has no head gasket problems. Went to MLS gaskets on my BBC 427 after lifting the head in a 350hp nitrous pass.

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  28. loudbang
    Joined: Jul 23, 2013
    Posts: 39,681

    loudbang
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  29. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

  30. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 336

    Neb Hillbilly
    Member

    Soooo, can I just use a 54 chevy 235 water pump? Pretty sure they bolt up the same. I will probably see about rebuilding the GMC pump later.
     
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