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  • April 23, 2024, 03:57:09 PM

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Author Topic: Brodak .40  (Read 16781 times)

Offline Perry Rose

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Brodak .40
« on: March 28, 2024, 04:16:49 PM »
I won the engine in a raffle. I broke it in as required in the instructions.  It starts easily but at the end of a flight the prop stops as if the engine is seizing. When hot the prop is dragging as if it's cold and castor left over. When it is cold the engine is much looser. I didn't want to but I took it apart, removed the crankshaft and polished it with 2500 and 3000 grit paper. I think that will end the tightness when hot. One run on the bench shows some promise.
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Offline Robert Zambelli

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Re: Brodak .40
« Reply #1 on: March 28, 2024, 08:25:02 PM »
What fuel are you using?
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Offline Dave Hull

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Re: Brodak .40
« Reply #2 on: March 28, 2024, 10:23:39 PM »
I have related this before in perhaps more detail, but the short version is that the symptoms you cite also match a known issue (at least with the Brodak .25):

If the case and/or muffler interface has not been machined or lapped it will distort the piston/liner fit. It may feel nice when cold, but once run, it starts to bind up. Check your case and muffler. We lapped the muffler on my friend's engine and the problem went away, and the engine did not appear to be damaged. It probably had less than a dozen runs on it before he stopped to figure out what was going wrong.

Dave
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Offline C.T. Schaefer

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Re: Brodak .40
« Reply #3 on: March 29, 2024, 06:09:29 AM »
Pluis one on that Dave.  Also, crank end float?
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Offline Dave Hull

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Re: Brodak .40
« Reply #4 on: March 30, 2024, 04:28:58 PM »
C.T.--What specific issue with end float? Rubbing the crank pin on the backplate?
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Online Lauri Malila

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Re: Brodak .40
« Reply #5 on: March 30, 2024, 04:48:32 PM »
Quote from: Dave Hull on March 30, 2024, 04:28:58 PM
C.T.--What specific issue with end float? Rubbing the crank pin on the backplate?

If the axisl play is too small, it may jam in running temperature as the case casting expands more than the steel shaft. L
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Offline C.T. Schaefer

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Re: Brodak .40
« Reply #6 on: March 31, 2024, 05:38:16 AM »
Yes, that's what I was talking about. One of our guys had that issue and I had one with the muffler interface.
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Offline Dennis Toth

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Re: Brodak .40
« Reply #7 on: March 31, 2024, 09:04:38 AM »
If there is crank end float you can use an OS 36 - 40 drive washer shim. I have also add this to my Fox 35's to reduce the end play.

On the muffler distorting the case, could run a one size larger drill through the muffler mount holes in the case to give a little wiggle room. Also, add a gasket.

Best,   DennisT
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Offline Dave Hull

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Re: Brodak .40
« Reply #8 on: April 01, 2024, 10:32:07 PM »
Dennis--The issue I noted of the muffler warping the case (and liner) wasn't from misalignment of the bolts. Rather, the muffler interface surface was sandblasted, not machined, and it wasn't flat. Pulling a non-flat muffler up against a machined-flat engine case warped the case and caused binding as the engine warmed up.

C.T. and Lauri--Ok, I understand your comment on axial clearance over operating temps. I haven't seen one that tight before. If I already had the engine apart, I'd lap the nose of the case so that messing with washers wouldn't be needed.
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Offline Steve Glass

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Re: Brodak .40
« Reply #9 on: April 06, 2024, 12:49:50 AM »
Sorry no link, google ‘mike nelson machine concepts’ and look for his article on the Brodak 40.

Mike used a ring to insulate the head to keep the heat in. Excessive cooling means that the ABC pinch stays too tight to run.

Steve
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Offline Steve Glass

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Re: Brodak .40
« Reply #10 on: April 07, 2024, 02:01:10 PM »
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Online Motorman

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Re: Brodak .40
« Reply #11 on: April 07, 2024, 10:21:38 PM »
If it's too tight when hot and loose when cool then you don't want to do things to keep the heat in.

As far as axial end play, you want about .010" between the front of the case and the back of the thrust washer.

Hard to say what's wrong without seeing it but I will say this: The B40 piston is not made from the best (high Si) metal. The piston expands quite allot when the engine's running. That's why you think it has enough run time because it's loose when cold but when it heats up the piston gets tight.

After the official break in, you need to put about 80 flights on it before it starts acting right.

Hope that helps,
MM 8)   
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Offline john e. holliday

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Re: Brodak .40
« Reply #12 on: April 08, 2024, 10:36:53 AM »
I still have my B-40 from when they first came out.  Raed instructions and ran it on the ground about ten runs on 5 minute runs.  Mounted in plane and started flying it on a slightly rich setting doing loops and inverted flight.  Had to J-B Weld muffler on as one of the ears broke when wind caught the plane coming out of clover leaf.   Still runs great. Just needs an airplane. D>K
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John E. "DOC" Holliday
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