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Engine basics => Engine set up tips => Topic started by: Robert Zambelli on May 08, 2021, 02:18:58 PM
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When there is a problem with a Brodak engine, it is usually sent to me to evaluate and determine appropriate action.
After having done around 50 different engines, here's one that really has me baffled.
A fellow sent me a Brodak 049 MK II, claiming it would not run for more than a minute or so.
I checked it out, saw no signs of abuse or tinkering, checked the plug, tightened all six bolts and set to work.
It started right up, ran for around a minute and quit!!
Let it cool, tried it again, same thing - always ran a minute or so.
Then the usual: I tried two different fuels, 10 and 25% nitro, 50/50 synthetic/castor.
Then a number of different props - from 5 1/2 -3 up to 6-4.
Six different plugs.
Removed the one head shim.
No matter what I did, same results. Running anywhere between rich and screaming lean, it always ran for around one to one and a half minutes.
The compression is fine and the engine turns over silky smooth and starts easily.
Tiny bit of TDC pinch which is typical for the MK II.
So, any suggestions??????????????
Bob Z.
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An engine won't run unless it has fuel. The problem could be in your tank set up. That looks like the only thing you didn't change, and it looks like it is doing it consistently. I would check the tank, fuel line and such. Might not be anything wrong with the engine. Id the problem persists, something in the needle valve assembly.
Good luck!
Dan McEntee
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Bob, if it were mine, i would do as Dan says first. Maybe try a 1/2a combat type pressure bladder or a non pressure balloon since they work so well without any venting just for giggles. Next i would polish the crank good, i have had a few Norvels that turned over smooth but would die after a while and polishing the crank good fixed the problem, not my idea someone on here told me a while back! Good luck
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If you have a laser thermometer, run the engine then quickly check the temp of the front part of the case, and the front drive part of the crank/drive washer
Randy
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Hello, All, and thanks for the advice.
Dan - I thought about the tank and decided to try another (same) engine. It ran perfectly through the whole tank.
OK, Randy - I'll try that.
Motorman: the very instant it stopped, I tried to turn it over and it turned perfectly - no sign of seizing.
Yes, I checked the clearance between the front of the case and the drive washer - around .015. It also moved freely axially as soon as it stopped.
Very puzzling - it just stops. Doesn't lean out, go rich, doesn't misfire - NOTHING. It JUST STOPS.
I let it cool a bit and it starts right up and then again, it STOPS!
Bob Z.
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If it was seizing up on the shaft, I would think you would see fuel boiling out the venturi right as it stops. Shooting the temp while it's running would show something for sure. I bought one of these from a forum member late last year that was having similar problems. When I got it, I just ran a prime through it to check the basics. I pulled the needle valve to eyeball through the spray bar while holding it up to a lights, then ran a thin wire through it but don't remember seeing anything come out. Put it all back together and put it on a test stand and it fired right up once I got the needle set to the proper setting, and ran several tanks f fuel through it. I would have to look up the thread to really remember the details, but I'm thinking he either had a bad batch or fuel, or I was able to clear something from the spray bar that may have been interfering with fuel flow. Don't take much on these little things. I have seen swail in NVAs before andn my wild a$$ guess it was something hanging on from when the feed hole was drilled.
Keep us posted,
Dan McEntee
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Hey. I'm not an engine expert, but symptom of just stopping, without sag, or warning, really sounds like glo plug. But you have tried different glo plugs. All the same type or brand? Will it stay running if you left the battery on the glo plug?
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More interesting replies!!
Yes, Dan, I did clean out the spray bar and checked the hole orientation.
While it was out, I blew through it with compressed air.
Floyd: I tried more than six different plugs - Fireball hot and standard, Merlin, Fox, OK Cub, Veco and a few with no name.
Didn't matter if the glow driver was attached or not - still stopped.
I'm really starting to believe that it's somehow heat related.
I'll try Randy's suggestion with the infrared thermometer.
Bob Z.
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Just for S's and G's, here is the thread on the Brodak .049that I got from Wayne Collier;
https://stunthanger.com/smf/engine-set-up-tips/brodak-mkii-049-cl-need-help/msg609261/#msg609261
My post #34 is where I got it running. I didn't get a chance to mess with it until a few months after I got it from him.
Type at you later,
Dan McEntee
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Grasping at straws here but maybe there could be a spiral crack emminating from the inlet hole in the shaft.
A slight amount of heat added and it acts like an expanding bolt.
You don't detect it because you are driving the prop and not the big end, in other words when you drive the front of the crank the crack closes and has no drag but when it's driven from the other end of the shaft, the big end the crack opens up.
Chris.
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Hello
When I get a real dud engine that suddenly stops you can normally feel some binding or distortion of the piston/liner or it runs real bad because the liner is in backwards or it has a reverse rotation crank. Without any of these signs I would pull it down examine every part carefully and then start substituting parts from a good running engine. Some engines run fine with poor compression and others seem to run poorly with reasonable compression and small engines are more sensitive to everything!
Regards Gerald
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What happens if you try to start it right after it quits?
My thoughts as well. This has to be heat related or it is really an OK Cub disguised as a .049 in which case I would want to know how you got it to run that long.
Ken
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Problem solved!!
Details to follow.
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It will be interesting to hear the answer.
My guess - some sort of tank issue, like a broken clunk line.
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It will be interesting to hear the answer.
My guess - some sort of tank issue, like a broken clunk line.
Scroll down to rely #6 and he said that he tried another engine on the same test stand set up and it ran the tank out fine. I'm still betting on a needle valve issue. Something suddenly blocking off fuel flow. I have had that happen to me twice with engines.
Type at you later,
Dan McEntee