Excessive blow by on a Brodak B-40

[Andrew Borgogna]

First off I am not saying I have excessive blow by out the front, but it seems to be the only explanation for what I am seeing.  My engine requires 5oz. of fuel to complete the pattern, always has.  It runs great and I just assumed that everybody’s B-40 took 5ozs to do the pattern.  That was until Larry Renger got his running right; his engine in a smoothie uses about 3.5oz of fuel.  When we were flying on Sunday Larry pointed out what he believed was excessive blow by coming out of the front of the engine.  I guess I just never noticed it and frankly when I looked for the blow by it didn't look that bad to me.  But the comparative fuel consumption does lead me to believe Larry may be correct.

I have no intention of messing with my motor I love the way it runs and I don't mind using the extra fuel.  I have run the recommended 11x11x10 mixture and currently using 25x3x10 either way it still uses 5 oz to complete the patter.  I have enough fuel at the end of the pattern to do two additional outside loops to unwind the lines and about four extra laps.  Very consistent.
Andy

[Ralph Wenzel (d)]

When you say, "Always has", jut how much running time are you talking about? Mine required in excess of 5 oz. for a pattern when new, and wasn't truly broken in (at least, I think it now is) until it had over 2 hours of running. Performance was good during this whole time, but  fuel consumption was terrible.

[Circlejerk]

I would think that if you are getting 1.5 oz. of "blow-by" then the airplane should be saturated with raw fuel and oil. Is it?  By the way, some of the very best Fox .35's I've had, have some blow-by.

[Steve Fitton]

I have one that uses 5 ounces as well, but it runs awesome and has loads of power.  I'm not complaining!

[Andrew Borgogna]

To all the question.
1.  The engine has several hours of run time.  I believe it is completely broken in.
2.  No the plane is not completely saturated with fuel or oil.  It looks normal to me.
3.  I completely agree, the engine runs well it has plenty of power and is an all around good engine.

We just can't explain why Larry gets such good fuel milage.  Maybe my engine is normal and his is the exception.  I am glad to see that others use about 5ozs of fuel to do the pattern.  My engine trails a good blue exaust, it has a soft break to 2C when I pick the nose up and it drops back to a 4C at level flight.  I am running 5.3 lap times and using a master airscrew 11x4 prop.  I really never thought I had a problem, and maybe I don't.
Andy

[steven yampolsky]

Mine has over 200 flights on it. It still uses 3.25 for the pattern but recently I started noticing small amounts of black oily substance on the cowl. I don't think the motor lost power, it runs like clockwork. Perhaps it's just a fact of life on plain bearing motors. Just keep an extra rag with you and let it be.

Steve

P.S. I've never used more than 22.5%(50/50) oil content. I went down to 18% all synthetic the last time out and noticed less black soot deposits. This was a puerly subjective objecrvation, I know. But, is it possible that extra oil is forced out through the front bearing? The motor is built to pretty tight tolerances and extra oil has to go somewhere.

[Alan Hahn]

Andrew,
I would look at my venturi and the muffler and compare them to Larry R's to make sure they are the same. You may be running making more power. I had an La46 which was really a fuel hog---even 6 oz didn't look like enough to complete the pattern. A change to a smaller venturi and a more restrictive muffler really cut down the fuel usage to the 4oz range---but also the power too.

Steve, check to see if your muffler is loose. That is a good source of black crud--from someone who just noticed that his B40 only had a single muffler bolt still attached!Black crud is usually aluminum. Last I recall, I thought the B40 had bronze bushings---but could be wrong.

[steven yampolsky]

Steve, check to see if your muffler is loose. That is a good source of black crud--from someone who just noticed that his B40 only had a single muffler bolt still attached!Black crud is usually aluminum. Last I recall, I thought the B40 had bronze bushings---but could be wrong.

Good point! I'll check tonight.

[Willis Swindell]

I have a Brodak 40 that uses 3 1/2 oz of 10 11x11 Powermaster fuel, 11x5 Master Airscrew prop. But I am using a older smaller hole brodak muffler. It should have a .285 venturi but I haven't measured it.
Willis

I measured the venturi and muffler exhaust both were .312

[john e. holliday]

Andrew, for laughs see if you can talk Larry into swapping engines for a couple of flights and see if things change.  My Brodak 40 uses 4.25 ounces of fuel to do the pattern on the ARF Oriental.  On the kit built Olympic I could do the complete pattern on 3.75 ounces of fuel.  Have fun,  DOC Holliday

[Larry Renger]

I haven't measured the venturi, but there are a couple of other factors to consider:

I am using 59' x .012 solid lines, so I have a lot less drag than Andy does.  My lap times have been quicker, though we finally got it set to do 5.3s

I am using a bit less oil than Andy, probably just under 20%.  This improves "gas mileage"

I am running the APC 10.5x4.5 prop, Andy has a bigger (don't recall the exact size) Master Airscrew prop installed.

I have an "in" with the gods of engines.

[don Burke]

I think the last one is the answer!

[Andrew Borgogna]

Me too on the last one.  Prop is a MA 11x4.  Regarding the oil, I still required 5ozs of fuel when running the GMA blend like Larry does.  I really don't think the oil is the issue but the drag could play a big part, Larry just does not have to make as much power as I do to complete the pattern.  Less power less fuel.
Andy