Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: ConRod Question

  1. #1
    Hallett of a Dream
    Just to fill you in real quick, I bought my jet with a 455 in it. The motor only had 108hours on it, well it spun bearings in the #7 and 8 cylinders after 118 hours. This is the first engine I've had go that quick and upon tearing it apart, I am looking at it carefully to see what went wrong. I has forged pistons in it, which are still in great shape other that a little carbon on the tops, very little scoring on the cyl walls, rings all look good, but on the #8 piston, the wrist pin is very tight, I know, not normal. I have to take both hands to get it to pivot. Some move normal, some a little stiffer, but I noticed that on about 6 of the con rods where the wrist pin is, they are blueing. Some more than others, some with no discoloration. Is this a hardening process that is used and considered normal, or was something done wrong by the builder? Could there be other things that would cause this? Like oil starvation? Any honset input would be great. Thank you, HOD

  2. #2
    Whenever you see blue discoloration on any engine internals, you are looking at excessive heat. Your probably right about the oil starvation as being a cause, but a tight fit at assembly will also cause excessive friction(heat).

  3. #3
    Senior Member
    Join Date
    Feb 2009
    Hallett, there a number of possible answers to your question. Stock Olds con rods use a piston pin which is pressed in place. It does not move in the rod. Look at your piston and pin as you flex it. The piston should be moving on pin and pin should be stationary. Also if rod were modified for a floating pin, there would be some sort of circlips in pin boss of piston to keep them together. With pressed in pins, machinists will often heat the pin end of the rod to make pin installation easier. This MAY be what left the bluing. You would be well advised to consult a good machinist if you have any doubts at all about the rods. Now a bit of advice on Olds in general. They suffer from an oiling problem as a result of poor oil drain back from the top end. If you are going to rebuild this engine(many, myself included, will suggest replacing it with a Big Block Chevy if you plan to keep this boat)contact Joe Mondello at ( for technical advice. He can suggest what modifications you should make to add some longevity to your engine. For the record, the Olds I built for my boat back in 1985 is still going strong with the help of Joe Mondello.

  4. #4
    Hallett of a Dream
    I am keeping the olds, for some reason I am impartial to them, nothing against chevy or ford, but going back, my first jetboat ride was in a Tahiti with and Olds455 and I have had a hard-on for one since then. The pin does not move on the conrod, which is the way I always knew them to be, but also does not move freely on a few of the pistons. But the pistons do not have any heat signs or oil baking signs on them.

  5. #5
    The blue discoloration on the pin end of the con rod is due to heating the rod to allow insertion of the piston pin--"press fit" pins are not actually pressed in; instead the small end of the rod is heated which causes it to expand slightly and allow the pin to slide in.

  6. #6
    Hallett of a Dream
    Thanks for the replies, but what would cause the wrist pin to be extremely tight against the piston?? Could it be from the banging around after the bearing let loose on those rods?

  7. #7
    The Pston is tight because when they heated the rod they got it too hot causing the pin to fit tight in the piston take it to the machine shop to hone the piston boss and refit all should be ok pretty common thing to happen when installing pins

  8. #8
    Hallett of a Dream
    Good deal, thanks.

  9. #9
    I've never got a set of pressed rods back from a shop that were blue. If that's the case, it's no wonder it spun the bearings after only 118 hours.
    [This message has been edited by Heatseeker (edited September 09, 2001).]

  10. #10
    Rat Raft
    Ive removed and installed hundreds (maybe thousands) of pistons and use the heat method on all press fit pins. This is what the factory uses and many times the rods have the pin ends blued a little when they leave the factory. This doesnt hurt anything. If the pin is tight in the piston it was probably due to the hammering it took when the rod bearings spun. Often whe the bearings stack the piston hits the head. You can usually see shiny places on the top of the piston. If the pin is tight have someone press the piston off and look at the pin bore. It will probably be gaulded a little. I have scotch brited them and put them back in service if the gualding was minor but its probably best to replace the piston & pin.

Page 1 of 2 12 LastLast

Similar Threads

  1. Replies: 3
    Last Post: 04-28-2002, 07:42 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts