I haven't broken-in an engine since two years ago. I actually took care of my engines using good fuel and good tuning judgment and maintenance. But lately I have been plagued with bad luck.

I started using Maxxy 30% late last year and shimmed my enignes accordingly. However this year, one of my engine's rear bearing broke without even finishing a gallon of fuel, then my back up engine, the conrod expanded but no damage to engine was caused. Am I using the wrong precentage now? I see everyone at the track now uses 20% or even 16%.

So now that I got me a brand new engine, what's the deal... forget my 30% and go down to 20%? and if so what are your recommendations? Brand and such.

Maxy is good fuel. I run Byrons Gen II.

What motors are you having problems with and what is your new motor?

30 is fine though many people prefer 20 in .12 motors.

First engine to break was OS 12TZ EB MOD. Conrod expaded and broke crankcase
Second engine that broke: stock mugen ninja .12 it was like sand blasted inside. Piston and sleeve still can be salvaged.needs bearings.
Back up engine: salvaged OS 12TZ EB MOD Conrod is lose, will replace.

New engine: OS TZ SPEED TUNED II

This all started after using the 30%

The Ninja does not surprise me. They had real reliability issues.

Tho OS's were probably just old. Nitro does bad things to metals over time even if you run them dry and put after run in.

I think it was Ron Paris that used to recommend completely filling the motor with oil for long term storage.

The recommended fuel by most manufacturers for .12 engines is 16% and for .21 engines is 25%. I try to stick to it if possible.

Locally, 16% is hard to come by so most of us uses 25% for .12 and .21

I think the altitude also affects the tuning or the type of fuel used. Correct me if i am wrong.

Break in the motor with what ever percent nitro you're planning on using. Sometimes $#it happens.....

does it matter how much oil iam using 10% in my max power 21 onroad 721 08 with 25% nitro

RCMAd:

This is fine. Most fuels start at 10% and go up/down maybe one percent or two depending on nitro content.

e.g. Byron Race fuel II gen 20% nitro contains 11% Oil
Byron Race fuel II gen 25% nitro contains 10% Oil

Maxxy's 30% nitro contains 8% oil and lastly Tornado fule 16% nitro contains 12% oil.

The problem then becomes the quality of the oil.

I know I am going to get an argument on this one, but the problem is your engines.

The ninja engines had some growing pains. The OS TZ engines are notorious for rod problems. Especially if they are modified. You don't hear about these problems with Novarossi engines. I have never broken a rod on my Sirio .12 engines either. There is a reason why some engines cost more than others. This has been my observations over the past 3 years.

OS TZ's do have rod problem... I remember that I broke a TZ's conrod even before the first gallon of fuel. And like Scott Fisher said, engines suffer even more if they are modified. Honestly, even with Novarossi, or any other engine, I always change my conrod each gallon. As well as the conrod pin. Its better to pay $35 each gallon, than $500 after 3-4....