Register now to get rid of these ads!

Whats the general consensus on bushing wrist pins?

Discussion in 'The Hokey Ass Message Board' started by tlmartin84, Nov 13, 2012.

  1. tlmartin84
    Joined:
    Jul 28, 2011
    Posts:
    750
    Location:
    WV

    tlmartin84 Member

    Seems like this is perhaps my only option to make something "off the shelf" work.

    Is this an acceptable way to do things, is there any adverse affects on engine wear?

    My connecting rods have a diameter of .975, most of the pistons available with the correct diameter and compression height are .927.

    How is this done? bushing pressed into the connecting rod? What are they typically made of? Can you buy them somewhere or does it have to be done at a machine shop?
  2. ROADSTER1927
    Joined:
    Feb 14, 2009
    Posts:
    984
    Location:
    west bend wi

    ROADSTER1927 Member

    Bushing the rod top is fine and yes they need to be fitted after instalation. Have a great day Gary
  3. oldolds
    Joined:
    Oct 18, 2010
    Posts:
    1,109
    Location:
    strauss valley pa

    oldolds Member

    Is there enough material in the pistons to enlarge the pin hole in them?
  4. Mike VV
    Joined:
    Sep 28, 2010
    Posts:
    416
    Location:
    West side of the US

    Mike VV Member

    Any "competent" shop should be able to do this for you. Basically...done all the time to "full float" wrist pins that came from the factory as "pressed in".

    Many are bronze, pressed in and final honed (fitted !) to fit the wrist pin. The engine application and materials will dictate the oil clearance (normally in the .0007/.0009 range for a street engine).

    Mike
    Register now to get rid of these ads!

  5. tlmartin84
    Joined:
    Jul 28, 2011
    Posts:
    750
    Location:
    WV

    tlmartin84 Member

    Nope, the wrist pin is already in the oil ring on a lot of these pistons.
  6. onetrickpony
    Joined:
    Sep 21, 2010
    Posts:
    69
    Location:
    Texas

    onetrickpony Member

    Full floating pins also require some way to hold the pin in the piston. Either a nylon button between the end of the pin and the cylinder wall (drag race stuff, probably not recommended for street use) or the piston needs snap ring grooves in the wrist pin holes to keep the pin from walking out. This usually means a more expensive piston.
  7. 56sedandelivery
    Joined:
    Nov 21, 2006
    Posts:
    2,415
    Location:
    Everett, Wa.

    56sedandelivery Member

    Of course, Chevrolet did this with the original Z-28, 302 engines; only they did not bush the rod end. It was direct, slip contact between the rod end and the pin (you already have too much clearance for that to be done). As already mentioned, there has to be a way to retain the pin in the piston. You can get Speed Pro and KB pistons, both hypereutectic and forged, that work with pressed or full floated pins, fairly cheap. For the amount it will cost to rebuild your current rods, you could buy a set of after market Eagle/Scat/XYZ brand replacement rods, or even rebuilt factory rods, from that auction site we all know and love. Butch/56sedandelivery.
  8. Dan Timberlake
    Joined:
    Apr 28, 2010
    Posts:
    679
    Location:
    Massachusetts

    Dan Timberlake Member

    The back of the Sealed Power Engine catalog (and others) used to have parts listed in order of size. " Progressive size " listings. it was easy to look for pin bushings (or any other parts) that could be used for projects. I'd expect a replacement bushing already exists that can be used with minimal rework to be a press fit in the rod eye.
    0.927" sounds like SBC wrist pin.


    The best way to finish the pin bore is align boring it parallel to the finished big end bore to create a 'straight" rod. Assumptions about accuracy of the rod side faces or the original pin bore are dangerous.

    It is desirable to have 0.020" or more material in bushing bore.
    With enough material it is possible to equalize the lengths of the rods too. Just finish honing the installed bushing follows the original bushing bore with no control of rod length or straightness.

    Tobin Arp is one company that made machines for align boring rod bushings. Ours had nicely made expanding mandrels that gripped the big end bore directly.
    http://www.rhynecompetitionengines.com/assets/images/db_images/db_shop_0221.jpg

    Probably should add some oil holes to the rod eyes. There used to be plenty of theories of right and wrong ways to do that. Original 426 hemi had no holes as I recall.
  9. John Brown
    Joined:
    Feb 10, 2009
    Posts:
    594
    Location:
    South Bend, In ~ welcome to the dark side

    John Brown Member

    Just another opinion;

    Unless you plan on taking the pistons off of the rods often, there is no advantage in having full floating pistons. With each additional clearance point, you give the piston more chance to rock sideways in the bore.

    You could just have your rods honed to the correct size to fit the .927 pins and have the pins installed as a press fit.
  10. porknbeaner
    Joined:
    Sep 12, 2003
    Posts:
    25,724
    Location:
    Raytown, MO

    porknbeaner Member

    Yea for sure honeing it smaller is a damned good trick. :rolleyes:

    Bushing the rods is fine when done by a competant machinist, take them to the machine shop and have them bushed and fit. Done deal.
  11. Heo2
    Joined:
    Aug 9, 2011
    Posts:
    668
    Location:
    northern sweden

    Heo2 Member

    I realy like to se that machine that can hone down the hole
    from 975 to 927 must be some new fantastic invention
  12. tlmartin84
    Joined:
    Jul 28, 2011
    Posts:
    750
    Location:
    WV

    tlmartin84 Member

    Would solve my dilemma if there was!
  13. SimonSez
    Joined:
    Jul 1, 2001
    Posts:
    1,470
    Location:
    Auckland, New Zealand

    SimonSez Member

    Wow, you've got a magic hone that can make holes smaller? :)

    The OP has rods has a small end diameter of .975 and he wants to bush them to use pistons with a .927 pin diameter.


  14. tlmartin84
    Joined:
    Jul 28, 2011
    Posts:
    750
    Location:
    WV

    tlmartin84 Member

    I have found a rod that has a .912 diameter end, whats your thoughts on honing/boring them out to .927? 15 thousandths.
  15. porknbeaner
    Joined:
    Sep 12, 2003
    Posts:
    25,724
    Location:
    Raytown, MO

    porknbeaner Member


    maybe you could get them metal sprayed then honed to fit. ;)
  16. ROADSTER1927
    Joined:
    Feb 14, 2009
    Posts:
    984
    Location:
    west bend wi

    ROADSTER1927 Member

    That will work just fine for pressed fit or full float. Gary:)
  17. tlmartin84
    Joined:
    Jul 28, 2011
    Posts:
    750
    Location:
    WV

    tlmartin84 Member

    what do you think of the last scenario P and B??
  18. porknbeaner
    Joined:
    Sep 12, 2003
    Posts:
    25,724
    Location:
    Raytown, MO

    porknbeaner Member

    It would depend on how much meat you have to work with. If I looked at it and it was not going to be any different than a bushed rod and I had them to use I would just hone the rods and run with it.

    The thing is that what you are talking about is a floating wristpin, correct? the pistons have keepers? If that is the case it is not a press fit and you will need to give yourself some clearance for the wrist pin so it will be more like .017 and not .015.
  19. Unclee
    Joined:
    Nov 26, 2005
    Posts:
    2,093
    Location:
    somewhere south'a Houston, in Texas City

    Unclee Member

    This is the HAMB, and you know we like photos. But in the absence of that, at least fill us in on some details! What engine combo are you trying to build? Just really curious!!!
  20. John Brown
    Joined:
    Feb 10, 2009
    Posts:
    594
    Location:
    South Bend, In ~ welcome to the dark side

    John Brown Member

    Hey, I wear glasses fer a good reason, also my reading compression isn't up to snuff on all occasions either.

    That was one of my dumber reading errors. :eek:

    By the way, I used to run a Tobin Arp rod boring table back in the 70's so I know how hard it is to shrink a hole.
    Last edited: Nov 15, 2012
  21. tlmartin84
    Joined:
    Jul 28, 2011
    Posts:
    750
    Location:
    WV

    tlmartin84 Member

    LOL, I don't have any pictures.......I am trying to piece this thing together before taking the plunge and spending the money.

    I am building a Ford 300 inline 6. Rather than use the stock 300 rods, the plan is to use longer 240 rods and a shorter piston, a small block ford stroker piston (331 or 347). That will give me a nearly identical compression distance and improve the rod ratio, reduce wear, and maybe gain a little more torque while I am at it.

    The 240 rods had 2 options, .975 and .912 wrist pins depending on years. I can find .912 stroker pistons that are forged......I just don't think the extra money getting them is worth it. Hyper's are cheaper and should hold up fine for what I am wanting but most come with the more common .927 pin.
  22. Traditions Racing
    Joined:
    Sep 25, 2008
    Posts:
    3,519
    Location:
    Central East Coast Florida

    Traditions Racing Member

    Without having the rod in my hand to measure the ends, that would be foolish to speculate. However, yes possible to hone them to pin fit for a pressed pin.

    You will generally run into a issue with integrity and strength if you try and make them floating and open up the small end for the O.D. of the appropriate sized bushing.

    In the old days, some engine builders would run a non bushed full floating rod end, but this after careful placement of oiling holes and only generally for short track use.
  23. Traditions Racing
    Joined:
    Sep 25, 2008
    Posts:
    3,519
    Location:
    Central East Coast Florida

    Traditions Racing Member

    If you are concerned with strength of the .912" pin, you can have custom thick walled pins made. TR

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2013 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.