Author Topic: Connecting rod material  (Read 803 times)

Offline jclouden

  • Full Member
  • ****
  • Posts: 17
  • Front Royal, VA USA
Connecting rod material
« on: October 17, 2017, 03:49:41 PM »
I am working on Philip Duclos's Odds 'n Ends Hit 'n Miss engine and I have a question on the connecting rod material.  The material called out in his book is "tempered aluminum" and I have no idea what that is.  I have 6061 and 2024 aluminum on hand so one of those would work well for me but I don't know what the best choice would be.  The related issue that I have with this is the aluminum to steel bearing surface between the connecting rod and the crankshaft.  It seems to me that any type of aluminum would wear quickly at the bearing surface.  Making the connecting rod with brass bearing inserts would solve this problem (if it is a problem?) but I am not sure how to go about that.  Any thoughts on this would be much appreciated.

Thanks,
Jon

Online b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 10870
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Connecting rod material
« Reply #1 on: October 17, 2017, 04:29:21 PM »
Jon, if you have both I would opt for the 2024, though either should work in your case. I made the con rod for the Briggs& Stratton engine 5+years ago now from 6061 and it is still working perfectly and running directly on the cast iron crank pin and the steel wrist pin. There is splash oiling on both connections which helps with wear no doubt. More important that the relative materials though is the alignment. So long as the con rod is perpendicular to both the crank pin and wrist pin, with no angular forces from mis-alignment, reasonable lubrication should prevent premature wear given how little these engines run. Bronze sleeve bearings would add extra insurance but may need to be split for the crank end at least. Just my 2 cents.

Bill

Offline jclouden

  • Full Member
  • ****
  • Posts: 17
  • Front Royal, VA USA
Re: Connecting rod material
« Reply #2 on: October 17, 2017, 08:50:55 PM »
Thanks Bill.  I'll go ahead with the 2024 with an oil cup at the wrist pin and no brass bearing.  The splitting of the brass bearing at the crank end was where I was having trouble thinking that through.
Thanks again,
Jon

Offline 90LX_Notch

  • Full Member
  • ****
  • Posts: 1231
  • North Eastern Pennsylvania USA
    • YouTube Channel
Re: Connecting rod material
« Reply #3 on: October 17, 2017, 10:13:48 PM »
Jon-

To make a split bearing:

Turn the bearing material od to fit the connecting rod id at least 3 times the required bearing width.

Bore the bearing id to fit the crank pin. 

Mill the bearing to .002 over half the od forming a "C".

Cut two "C"s free.

Carefully sand one bearing "C" to fit the bearing cap or connecting rod.

Assemble the cap, bearing and connecting rod.

Sand the second bearing half untill it slips into the assembly.


There are some pictures on page 18 of my "Tiny" build.

http://www.modelenginemaker.com/index.php/topic,6968.msg153255.html#msg153255


When I made mine, I was very careful with my setups and fits.  When I milled the bearing I indicated it to make sure it was parallel to the table.

-Bob

Edit: Fixed link
« Last Edit: October 17, 2017, 11:06:55 PM by 90LX_Notch »
Proud Member of MEM

My Engine Videos on YouTube-
http://www.youtube.com/user/Notch90usa/videos

Offline jclouden

  • Full Member
  • ****
  • Posts: 17
  • Front Royal, VA USA
Re: Connecting rod material
« Reply #4 on: October 18, 2017, 03:49:56 PM »
Bob,
Thanks for the reply.  I am going ahead with the aluminum rod without a brass bearing.  I'll see how that works out but will keep your split bearing process as backup.
Jon

Offline awJCKDup

  • Full Member
  • ****
  • Posts: 39
  • Central Indiana
Re: Connecting rod material
« Reply #5 on: December 20, 2017, 08:40:35 PM »
I've been working on the "Demon" engine for a while now, and I'm close to making the rods. The print says aluminum rod with brass insert, (brass not bronze?). Aluminum and brass I have on hand.

It took me 3 tries to get the main inserts correct. So I was thinking about making them like George does, entire rod out of bronze, needs no insert, but I would have to buy the bronze.

Another option would be to make them out of aluminum, with no insert like Doc did. I have used this method on slower running engines and it has worked well, not sure about the longevity in a higher rpm engine, and yes I know Briggs engines ran like that for years. I have material on hand.

So If you guys could give your opinions, especially if you have first hand experience either good or bad, it would be appreciated. I should also comment that from past history I don't put much run time on my engines.

Thanks John
Ps. Steve if you read this, I have the plans for the blower and I was wondering if the G-code for the housing was available, I don't have a lot of experience with writing code or drawing in 3d

Offline Brian Rupnow

  • Full Member
  • *****
  • Posts: 3623
  • Barrie, Ontario Canada
Re: Connecting rod material
« Reply #6 on: December 20, 2017, 08:54:55 PM »
Just go ahead and use the 6061 aluminum without a brass or bronze bushing. Unless you plan on working this engine really hard over long periods of time, the aluminum rod will work fine.---Brian

Offline awJCKDup

  • Full Member
  • ****
  • Posts: 39
  • Central Indiana
Re: Connecting rod material
« Reply #7 on: December 22, 2017, 07:39:05 PM »
Thanks Brian, that is the way I was leaning. Wow everyone must be busy this holiday season, your the only one who replied

John