Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Heat treating connecting rod

Heat treating connecting rod

Heat treating connecting rod

Hi, I'm new on this forum. Im currently working on a project trying to increase the horsepower on a old mini bike engine without using any aftermarket parts. I did a lot of work to get more power and rpm. Now I want to increase to tolerances of the internals.

The stock connecting rod is die casted aluminum alloy 380. On other forums I've researched that the stock rod usually breaks at RPMs above 4,500. Is there a way to increase the strength of the rod to keep it from breaking at higher RPMs. I thought about heat treating the rod, but I don't know the proper procedure for die cast aluminum. Also it is possible to weaken the metal If it were to be heat treated twice, because it may have been heat treated during the manufacturing processes. If you know of a good way to strengthen cast aluminum, or have any good ideas that may help me please let me know thanks.

RE: Heat treating connecting rod

Can you find out if broken rods are found in conjunction with seized rod bearings? If so, improvements in the lube system may be required.

Can you find out more about WHERE the OEM rods break?
If the break starts at a machined in corner, then improving the geometry can reduce the stress concentration by 50% or so.

After the geometry is optimized, Shot peening with clean coarse glass shot can provide a nice increase in fatigue strength, but not overcome basic material limitations.

A lighter piston will make life easier on the con rod, bearings, and crank.

RE: Heat treating connecting rod

Thanks for the help. The model engine I have is a Briggs 3hp (60102). I found a few pics online of other flathead Briggs from around the same year that have thrown rods. Most of them look like they broke towards the bottom near the crankshaft.

The crankshaft is bearingless, but there is a small hole in the end cap to maintain a thin film of oil in between the rod and the crank. I made the inlet of the hole a tiny bit larger so that it can pick up a little bit more oil on each stroke. I as well lighten up the piston already. If anyone else has anymore ideas please send them through. Anything is appreciated.

RE: Heat treating connecting rod

Please provide links to those pictures.


Dan T

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close