Heat treating connecting rod 1

[Willbriggs]

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.

 

[Tmoose]

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.

 

[Willbriggs]

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.

 

[Tmoose]

Please provide links to those pictures.

regards,

Dan T