Engine Break in
 

I have two engines that I am going to be breaking in. A OS 91 FX and a BGX 3500.

The question I have is which fuel should I use ?

I have Byrons fuel 15% nitro and 20% oil. I like the 20% oil for breaking in purposes, but not the 15% nitro. Would this be too much nitro for breaking in purposes ?

I also could use 10% nitro and 16% oil as an alternative. Should I up the oil % by adding Klotz castor oil to 20% ?

Thanks in advance. Cary

91 fx breakin
 

For the OS 91 FX I would use the nitro content fuel that you plan on using for flying. The only thing I would suggest in so far as oil content , is to use at least 18% and have some castor in it because the ringed engines need some for proper ring seating. Wildcat Premin Extra is what I used in mine and it is excellent fuel. One other note is to disassemble the remote needle valve assembly where it attaches to the carb and use a high temp gasket sealer arround all joints. This problem has been discussed thoroughly in RCU and I have found that mine worked great after the fix. Good Luck. :) :D

Engine Break in
 

Well considering that a ringed engine has to be run for quite some time so slobbering rich it's unflyable there's no point in wasting money on high nitro fuel. I always use a straight 80/20 all castor but a mix of castor and synthetic is fine. The 15% nitro will only hurt your pocket, not the engine :)

Engine Break in
 

Remember, Mustangman, Byron calculates their percentages by weight, not Volume like other manufacturers such as Morgan, Wildcat, Redmax, etc. Byron's 15% nitro, 20 % oil by weight fuel equates to about 11.4% nitro and 17 to 18% oil by volume. Byron's 10% nitro, 16% oil fuel has about 7.4% nitro and 13.5 % oil by volume.

Engine Break in
 

I am forced to believe that engine break in should be done at a temperature similar to running so that the expansion of all of the parts will be the same from start to finnish. It makes sense using the same nitro content for the the break in process because different nitro values create different operating temps. I think all of the manufactureres of these engines suggest this. I think it is worth the extra money in the long run.

Engine Break in
 

Mark, that reasoning is what's normally used when talking about running in an ABC engine but in fact it's quite wrong and I've never seen it in any manufacturer's instructions. If you try running in a ringed engine that way then there's a very good chance it'll be ruined. Tests have shown that varying the nitro percentage only makes a small change in running temperatures (on the order of only a few degrees) and high nitro can even make them run a little cooler.

Fuel for engine breakin
 

Thanks for the discussion of fuels-oil percentages and volumes of each. It looks like we are comparing apples to oranges when looking at percentages of oil and nitro and their volumes.

After researching the subject, I have chosen to use the Byron's
10 nitro. , 16 % oil and added 6.4 ounces of Klotz's BeNol castor oil supplement. for breaking in purposes. I will continue to use the oil supplement to provide adequate protection during normal running purposes.

One further question to all. Which is best: Synthetic oil or Castor oil.

I've been told that Castor is better for protection purposes, but is a pain to clean up off the plane afterwards.

Thanks Cary

Engine Break in
 

:D Well this one always starts an argument but in my opinion castor is by far the best. When a synthetic gets too hot it vapourises and burns. When castor gets too hot (at a much higher temp than synthetics) it has the happy knack of turning into another lubricant. Castor also "sticks" to metal better so it doesn't tend to get squeezed out of highly loaded areas like the conrod bushings. The "stickiness" is also why it stays on things like bearings and protects them from rust.

Engine Break in
 

I agree with downunder. I use cool power and add benol to it for all my engines. I like 15%.
I am breaking in a os91fx now and so far I am very happy with it. I have ran 4 tanks of fuel thru it (on the ground) but the ring hasn't set itself yet. I expect it will take a few more tanks and then it should be ready for the unloading of flight!
I try to run in the engine slow. I add some break-in time beyond what the manual says just for piece of mind and I can tell the Ring isn't set yet by the lack of compression the engine has when I roll it over by hand.
Use the 15% with the Klotz. It isn't the nitro that makes the difference on break-in, It's the luberication and the process of richening and to a point, leaning the engine. I like to use the same fuel I plan to fly on. 15%nitro- (aprox)20% oil and the oil mix should include Castor.

Engine Break in
 

more comment from down under, running in a ringed engine -- start rich--cool --then its a lot of short runs [on the bench] cool down between , gradually leaning it out till you get to a rich setting on a 2 stroke rpm[all this with carb open full] make sure you have at least 5% castor in fuel. i like to run in my engines on the bench where you can get to them[repeat, lots of short runs--3min ect] then when the engine will hold a full rpm setting [still slightly rich]same condition as nose up climb----go fly.
Ian White Yankalilla Sth Aussie