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Small engine breather


Jack B.'s Avatar
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07-21-05, 09:14 PM   #1  
Small engine breather

Would someone mind explaining (in detail) just how a breather operates on a lawn mower engine? What are the symptions of an engine if the breather closes up and also opens up? I have a riding lawn mower which has suddenly started blowing bluish smoke. I am trying to figure out what to look for, when I tear it apart.

 
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07-22-05, 12:16 AM   #2  
Hi Jack!

Not sure if you saw it or not, but Dave327 made a pretty good description on post #8 in this thread : http://forum.doityourself.com/showthread.php?t=220803

It's a basic reed-valve type system. Some use a fiber disk that funtions the same way. It's a check valve that lets air escape from the crankcase, but not enter. The hose coming from it directs this air into the carburetor so that it can be burned in the combustion chamber before venting to the atmosphere to reduce emissions. If the valve were to stay open, it could blow oil into the carburetor via the hose it is connected to the carb with, and it could allow a bit more oil consumption via the rings. If it were stuck closed, oil would begin leaking from seals and gaskets and the engine would probably not run very well. It would smoke pretty bad too.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

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07-22-05, 05:22 PM   #3  
Cheese,
Would you mind telling me how to test the breather. I've looked through all my B&S books but I haven't been able to find any information on it yet. The best I can remember is that you are suppose to slide a 0.015 or 0.020" feeler gauge behind the round fibre board. Anything more indicates that it is bad.

 
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07-24-05, 12:46 AM   #4  
There's no sure-fire way to check it, but the closest I've found is by cleaning the rubber hose on the outside of the valve and try blowing in it, then sucking air back through it. If you can blow through it fairly easily, then it's not working right, and if you can't suck through it, it's stuck or bad. You should be able to draw air in easily, but not blow through it.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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07-25-05, 01:18 PM   #5  
Cheese,
I went on and dissamblied the engine completely and everything "looks" good. The only thing out of the ordinary, was it had a ring-end gap on the top compression ring of 0.056", which is way beyond the factory specs of 0.035". The breather seems alright by your test but I'm going to replace it anyway. I'm going to replace the rings too. I haven't had a chance to mic the cylinder yet. I'm going to replace the seals while I'm in there and do a valve job on it. Incindentally, the top of the piston and the exhaust valve had a soft coating of on them, probably from the oil. I'll tell you one thing, this heat is getting awful. The temperture just keeps easing up day by day.

 
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07-26-05, 01:14 AM   #6  
I agree about the heat. It's almost intolerable. The humidity is so high that a 93 degree day feels like 110. I just fixed the AC on my service truck so I could get a break from the heat every now and then while doing calls.

The compression ring may have been letting a bit of excess blowby past the piston. I would replace all three rings. The breather is not a common failure item. I don't think you'll need to replace it, but you never know. Let us know how it goes!


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

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07-26-05, 10:31 AM   #7  
Cheese,
Tell me one more thing, under what circumstances should you use chrome rings?

 
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07-26-05, 12:39 PM   #8  
Azis
Had to member that one muhself
http://www.hastingsmfg.com/Service%2..._cylinders.htm

 
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07-26-05, 02:25 PM   #9  
Chrome rings should only be used in aluminum bore engines...Not even cast iron lined cylinders.

 
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07-26-05, 05:11 PM   #10  
Correct, chrome rings only in aluminum bore engines, regular steel rings in sleeved or cast iron bore engines.


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07-27-05, 05:31 AM   #11  
Thanks for all your replys.

 
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08-01-05, 02:46 PM   #12  
Cheese,
I think I've discovered the reason for blowing blue smoke (badly). I've rebuilt the engine and while I was cleaning up the final parts for re-assembly, I found a hole worn in the oil fill tube (about half-way up the tube). The loose end of the starter guard was rubbing on the oil fill tube. Underneath the manual starter shroud was still oily. Evindentally, the piston would pump the oil out the hole and the fan would catch it and throw it around to the muffler where it was smoking like crazy. I had an un-easy feeling about this engine until I found this hole. It was just as well though, for it really needed rings. Well, I guess it pays to keep your eyes open for these odd occurances.

 
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08-02-05, 12:37 AM   #13  
Glad you found the problem. I've never seen that happen before. The hole in the fill tube would also affect the crankcase pressure by basically defeating the operation of the PCV valve. (letting air be drawn into the crankcase when the piston moves toward the head).


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08-04-05, 11:21 AM   #14  
I've got another problem...after finishing the engine, it wouldn't start. The problem seems to be the lack of fire. When I get it cranked, it will fire on the first revolution, then completely stops firing. All I've got is an owners manual and it leaves a lot to be desired in the wiring schematic. Does anyone know where I might find a detailed schematic of a Snapper Model #-301016BE Year- 1997 Rear engine rider. I've already tried "public.snapper.com\Manuals" but they weren't any help. My schematic shows a "module" but doesn't say a thing about it.

 
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08-05-05, 09:19 AM   #15  
I ran into another problem, the engine isn't getting fire. I think I've found the problem but not the solution. When I disconnected the kill wire, it fired right up. I suspect the problem is in one of the interlock switchs. The owners manual that I have leaves much to be desired on the wiring schematic. There is a "module" on the schematic but there isn't a word about what is does anywhere in the text. I also went to "public.snapper.com\Manuals" and what they had, was the same thing I have. This rear engine rider is model # - 301016BE. Does anyone know of a web site I could go to - to find a better wiring schematic?

 
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08-05-05, 12:25 PM   #16  
Azis
Are all safety switches being met for starting? Blades deck park brake etc.....
If it runs with the kill wire disconnected then either a switch is faulty or a short to ground in the wiring. If you use the Illustrated parts list from snapper, you can get a look at the wiring harness and an idea of connectors wire lenths and such. The schematic should have wire colors listed. Those together with physically tracing the harnes and switches is about all you should need. Not all safety switches can be bypassed by simply unplugging, but it is a quick simple test for most.

 
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08-06-05, 12:27 AM   #17  
I don't know of a better manual, but an ohmmeter connected across the safety switches will show their condition. The module is under the seat in the area behind the shifter handle. It rarely gives problems, but if all other circuits test good, then replace it.

A common problem area on some of these is the clutch pedal safety switch. Some of them are under the frame at the back near the driven disk. It is on a metal bracket that bends easily and sometimes gets pushed back so far that it doesn't activate when the clutch is pressed. You might have to bend it back forwards a bit if this mower has that particular setup.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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