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Engine basics => Engine set up tips => Topic started by: Paul Taylor on March 28, 2015, 02:31:19 PM
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I have a LA 46 that pumps raw fuel out the front bushing.
Some suggest cutting a grove around the crank to maybe slow down the fuel loss.
Can I do it with a cut off wheel? If so what direction do I cut it?
Thanks
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Great question, Paul! Unfortunately I cannot help at all........ <= S?P VD~
BIG Bear
RNMM/AMM
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I think I'd just declare that engine dead and move on.
So read the rest of this keeping in mind that I think you're beating a dead horse:
If you feel you must mess with it (or you want to declare the engine dead and play with it anyway), then you want the grove to be a normal right-hand thread -- the idea is that it'll "catch" the fuel and "screw" it backwards. Don't let the groove extend all the way out the front, and don't let it touch the intake window. I think you could do it as well with a cut-off disk as with anything. Make sure that there are no burrs sticking up from the edge of the groove -- that'll just trash whatever's left of your bushing.
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Paul, on the assumption that a groove would work (not having tried it), as Paul said it should be right-handed to pull fuel back into the case.
Using a cut-off wheel, which will lose diam as it cuts, I'd suggest starting at the rear of the shaft so that the groove becomes shallower toward the front. Fuel would also need to move past the counterweight into the case somehow.
Also, I'd want a rigid(ish) centering rig to hold the shaft stable(ish) and, if you use a Dremel-type motor, a guided, sliding "table" to move it rather than the crankshaft.
Pitch shouldn't be an issue, as I suspect cutting would be slow enough to allow turning the crankshaft by hand at a relatively constant rate as you go.
This would be a jury-rig operation, and might require rebalancing, so just my $.02.
On the other hand, someone may be able to tell you how to do it right. ;D
Terry
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I have a LA 46 that pumps raw fuel out the front bushing.
Some suggest cutting a grove around the crank to maybe slow down the fuel loss.
Don't put the groove in the shaft! If anything, put it in the bearing. You certainly won't need a cutoff tool, in the few cases I did it. I managed with a right-angle scribe and just scratched it out. it needs to start at the the front where the crank comes out, and then diagonally go back to the intake.
Brett
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Paul,
You didn't mention if there is any play in the fit of the shaft to the case (like a Fox)? I think if there is wobble you should consider a new case.
Best, DennisT
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If the engine runs great, what's the problem? ;)
Beyond that, what have you already tried? Have you checked that the existing groove in the bushing is clear? I'd pull the crank, and clean both the crank and the bushing, use the tip of an X-acto blade to chase the groove. When the groove is clear, it should pull most of the raw fuel back inside the engine, a little oil or fuel out the front is normal. Even if it's excessive, the only real issue is fuel economy will be down a little. If the crankshaft rocks back and forth in the case, it's a bit more serious problem.
While you have it apart, visually examine the crankshaft, it should be smooth, maybe a little shiny, radial grooves - especially around the intake port can be an indication that the engine has ingested sand, dirt, debris that has worn the crank, and likely the bushing.
If it really bothers you, and a bit of cleaning and polishing doesn't clear it up, I'd junk the engine and use it for parts, or give it to someone that might not mind the wet nose. A new case will cost more than a used engine. A used case will probably cost as much as a used engine. It'd be further ahead to just get another one and move on.
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in the few cases I did it. I managed with a right-angle scribe and just scratched it out.
Did it do any good? It sounds like something that might work to keep oil from weeping out, but not if there's raw fuel blurping out there.
I think I agree with Andrew -- if the engine runs, why worry?
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Did it do any good? It sounds like something that might work to keep oil from weeping out, but not if there's raw fuel blurping out there.
I think I agree with Andrew -- if the engine runs, why worry?
Because it makes a big mess. Yes, it did work, and I did it essentially exactly as described in Scott Bair's paper.
Brett
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Don't put the groove in the shaft! If anything, put it in the bearing. You certainly won't need a cutoff tool, in the few cases I did it. I managed with a right-angle scribe and just scratched it out. it needs to start at the the front where the crank comes out, and then diagonally go back to the intake.
Brett
How deep did you scribe Brett, and is a single groove sufficient?
Terry
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On Fox 35's some use a 7/16" reverse tap through the bearing. It makes a spiral groove and tightens the shaft at the same time by raising the edges of the groove a little. I seem to me you would always want the groove to be left hand or you would be screwing the oil out the front which is what you are trying to keep from.