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68 302 Broken piston skirts

Discussion in 'The Hokey Ass Message Board' started by 51fordor, Oct 18, 2011.

  1. 51fordor
    Joined: Sep 16, 2010
    Posts: 215


    Received a 68 302 (C8AE-8015-B) from a buddy with matching heads that was running. I started to take the motor apart to put all new gaskets and clean it up for paint and when I dropped the oil pan I found the first and second piston on the passanger side had dropped the outer skirts into the pan. There seems to be no internal damage to the block that I can see. My questions are what causes this, and where do I go from here? New engine, or do I just throw in new pistons and rings and run it to death? I am wantind to drop this in my 51 ford shoebox, but a little nervous as this is my first motor tear down and to come across this right out the gate...
    Thanks in advance guys!

    Attached Files:

  2. Piston skirt wear. Excessive wear allow the piston, to rock in the bore. Impacting skirt in to the cly wall.

    Only a matter of time before the skirt fatigue's and falls off.

    Check the bore size, at the bottom of the bore and check to see what was the skirt clearance is on the other pistons.
    Remember these little motors love to be twisted 7500 to 9000 K
    Buzzed mine to 9000k all the time fully balanced, high volume oil pump, side clearenced rods.

    If the bore is oversize, new pistons will close up the clearence. But more then likely the bore is out of round, so new pistons and rings are a band aid.

    Just might smoke real bad as the the new rings may NEVER seat in the bore. Due to a oval shaped bore

    It is best to bore the block over, since your going to put new pistons in it ..
    Last edited: Oct 18, 2011
  3. 51fordor
    Joined: Sep 16, 2010
    Posts: 215


    Thanks man for the reply. I am going to tear it down completly tonight to see what the bore was and to check the other pistons also. I am going to probally have a shop bore it and just put new pistons and rings in it so that I have no problems down the road.
  4. Kenneth S
    Joined: Dec 15, 2007
    Posts: 1,527

    Kenneth S

    Divco13 why are you talking about DZ pistons, the engine is 68 Ford 302 out of a run of the mill full size Ford car, pistons are cheap. Those damaged pistons were more likely caused by severe detonation.

  5. I have a 68 Cougar that I bought from the original owner.
    When I bought the car the motor had a slight rattle. I downed the motor and 5 of the pistons had cracked skirts.
    Probably a poor design, after all it's just 43 years old!
  6. 94hoghead
    Joined: Jun 1, 2007
    Posts: 1,290


    Those little 289/302's are tugh as nails! I'd still rebuild it though.....
  7. spot
    Joined: Jun 10, 2009
    Posts: 204

    from usa

    I had a '74 302 with the same issue. Pulled it apart found a couple more with cracked skirts. Replaced the suspect pistons. Line honed the cylinders and installed new bearings and put the shop truck back on the road. Got another 100,000 out of it before I decided the truck needed more power.
  8. 2X detonation with this wonderful fuel / gas we are stuck with using.
  9. spike427
    Joined: May 19, 2010
    Posts: 101

    from Kentucky

    They break because they are cast aluminum and not forged pistons.Cast pistons are junk and Ford knew it but didn't make these motors to be abused in any type of way other then street driving.Anytime you buzz one of these motors with any performance parts and RPM they will do this.I've been Super/Stock racing for 35 years and have seen alot of stock junk broke just like this.Check the bore and if no ridge or scuffing may be able to get by with just a hone,new rings and a GOOD set of forged pistons.
  10. finn
    Joined: Jan 25, 2006
    Posts: 764


    We had a skirt failure on my dad's 1965 Galaxie 289 when the car was still under warranty back in the day. Dealer replaced the piston and the car ran fine till we traded for a new one 80000 miles later.

    Boss 302's were notorious for cracked skirts in their TRW forged oem pistons. I got mine with the engine torn down and 6 cracked skirts.
  11. Does it not apply to all Power Plant's ?
  12. wisdonm
    Joined: Jun 20, 2011
    Posts: 444


    No stock '68 302, ran in anger, over 6000 rpm more than once. Forget 7000+. The stock rod bolts will just not take it. I limit my original '68 J code to 5800.
  13. Mitchell Rish
    Joined: Jun 10, 2007
    Posts: 1,194

    Mitchell Rish
    from Houston MS

    I ran a 83 ford truck for years - twice had to replace pistons -same problem- second time on a built engine , third time -I just kept driving . never let me down and was a great work truck - finally sold it with over 350,000 miles on one total rebuild. Conclusion - stock cast pistons on the 302 ford are junk. The short stroke puts a lot of side load in places ( cheap pistons) that others just dont see. Been there done this.
  14. terryble
    Joined: Sep 25, 2008
    Posts: 541

    from canada

    This is not about poor gas, detonation or anything else except bad design from the get go. Most 289/302 fords from that era will have cracked or broken skirts when torn down. Don't know what Ford did but later ones didn't do it, that's why there is a 351W motor in my 51 Ford.
  15. HOT40ROD
    Joined: Jun 16, 2006
    Posts: 961

    from Easton, Pa

    A lot of 68 302 blocks had the short 289 cylinder walls which made the engine prone to cracking the piston skirts. Late 68 they lengthen the bottom of the cylinder wall to keep the piston from coming to far out the bottom of the cylinder which cured the crack piston skirt problem.
  16. terryble
    Joined: Sep 25, 2008
    Posts: 541

    from canada

    Thanks for that info always wondered why they cracked/broke and what Ford did to cure it.
  17. caseyrod
    Joined: Feb 9, 2008
    Posts: 138


    what cause it is wear on the wrist pin bushing on the rod,lack off lubrication.just replace the wrist pin bushing& piston and rings off course and your good to go.
  18. Off topic, but why would a DZ piston be more expensive than a 327 piston? Are they not the same???
  19. JeffB2
    Joined: Dec 18, 2006
    Posts: 8,775

    from Phoenix,AZ

  20. tommyd
    Joined: Dec 10, 2010
    Posts: 11,328

    from South Indy

    What he said^^^^^^^JeffB2
  21. tommyd
    Joined: Dec 10, 2010
    Posts: 11,328

    from South Indy

    My last 68 302 was a fresh build 30 over and drag raced. Always shifted at 5800 and had cracked skirts when I took it apart.The pistons were cast replacements. It had the 289 style cyl walls.
  22. Ole don
    Joined: Dec 16, 2005
    Posts: 2,915

    Ole don

    Ummmmm, what is a DZ piston?
  23. Ummmmm, what is a DZ piston?

    small block chevy 302
  24. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    from Wisconsin

    Don't run cast pistons in anything that you want to push any power out of.
  25. 51fordor
    Joined: Sep 16, 2010
    Posts: 215


    Ok so my block is a 289 with 302 internals. So what is a good affordable piston that wont kill my wallet? Nothing cast...
  26. I've had very good service with Keith Black hypereutectic pistons. Cheaper than forged and stronger than cast.
  27. rallisracing
    Joined: Nov 3, 2008
    Posts: 199


    Its just the combination of short cylinder wall and rod angle loading the skirts. We raced sbf's for 15+ years. Had to run cast pistons in Stock eliminator. Turned them 6000-6500 and never broke a skirt. But we spent time on clearances & bore roundness. And there are differences in cast material. We turned our gasser 289's 9500, but with good stuff..
  28. BobbyD
    Joined: Jun 6, 2005
    Posts: 581

    from Belmont NC

    Exactly right........
  29. treb11
    Joined: Jan 21, 2006
    Posts: 3,663


    no, due to the difference in stroke between 302 & 327 (3.0 vs 3.25) the piston pin location has to be different.
  30. What breaks piston skirts is driving like a bat out of hell on a cold motor.

    And you guys that claim short/long cylinders... Has anyone actually measured? I have and there's no difference.

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