I see a few old comments about replacing conrod after break in.

looking to buy a new engine for summer racing. My last one was a Tekno OS what was oil bathed.

im tempted to break in new one myself, but not sure if this is relevant any more about replacing conrod after break in.. and if it is, is it applicable to both approaches of break in

I’ve never done it (OS and Novarossi). Supposedly the Nova engines require a con rod change after break in.

I have never seen the need to do this, I take reasonable care of my engines. I usually average between 10 an 12 gallons between rebuilds running 30% nitro. I just do a standard heat cycle breakin that was taught to me by Ron Paris (a long time ago). I also run .021” of deck clearance to prevent detonation, the old rule was .006” for every 10% nitro you are running. I run .003 extra just to make it a little easier to tune.

I just broke in a new piston sleeve combo and doing heat cycle method. The only thing I did this time compared to times in the past was I added a shim to the head button to reduce the compression for about 1/2 gallon of idle time. As I was getting closer to start to run the car I took the extra shim out and idled 2 tanks and then began the figure 8 heat cycling. This was probably the best break-in I have ever done.

If I can complete the breakin without the engine shutting down once,I don't change the con rod.

Poka-Yoke Instead

Can you please explain to me your break in process and what you mean... like stalling vs being shut off....or? I'm getting ready to do some servicing on a few engines, and possibly breaking in another one soon...

I go find a huge parking lot in an abandoned industrial park on a warm Sunday.

Heat the head with a heater for a half hour while I prep my gear. Multiple fuel bottles.

Wrap aluminum tape around the cooling head.

Dump fuel down carb, swish around. Roll flywheel untill piston is around BDC. Start car on the box forcefully. Too wimpy eats starter wheels. Keep it running with the throttle. Not idle. Maybe a tank or two. Leave glow ignitor on.

Then drive figure 8's with the head taped, and glow ignitor on. Engine may require constant throttle to stay running. Be ready for that. Do this for as much fuel as you feel necessary. Refuel on the box, while flipping throttle to keep engine running.

Lean car out a little and continue. Maybe remove ignitor. Use more speed and throttle.


Done right, engine won't need restarted throughout the run in process. Completely eliminating cold startup rod stress. Replace glowplug, it's shot. Then put a weak rich race tune. And start some practice runs at the track. Replace plug again as you put a race tune on.

The ficticious "heat cycle" can be done after the pinch had reduced to normal.

The time and fuel cost to do this, about equals the EBIS treatment from Drake. If I was completive at a higher level in nitrobuggy, I'd pony up and just get an OS from him.