Has anyone really ever broken a honda balancer shaft on a GX390?

I dont think that removal is to prevent breakage but to enhance performance. I have never broke one or heard of one breaking. If and when i remove them its to get more HP and quicker revs. Just the act of spinning that big heavy chunk of steel takes HP that could be used to go faster. It is there for a purpose however. To truly get the benifits of removal, you really must balance the engine afterwards. It most always envolves adding heavy metal to the crank throws to get it right. There is a reason that in some car racing divisions there is a minimum crank weight in the rules. Not a maximum. There is a benifit to making the stuff that spins and moves lighter. The balance shaft is huge comparatively to the engine as a whole. Getting rid of it greatly reduces the weight of the stuff spinning around. JMO of course
 
I always say this when someone wants to remove a balance shaft: balancing the crank is not a bad idea, but you can't get rid of lateral vibrations in a single without using a counter balancer.

The only energy not recovered from the balance shaft's inertia is that which is lost to friction (including windage). I have heard concerns about strength, but never any reports of breakage.
 
Balancer beware

level600a said:
Balance question again, Is the removal a precaution or a necessary?
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I used to say leave it in, but I have had two oe honda blocks fail around the balancer bearing. Now the balancer comes out on all mine and of couse the bearings too. I have seen some one else snap a balancer shaft, and saw one balancer bearing smoke and disintigrate. Worst thing is to pull the shaft and not remove bearings,they WILL come out when it is running hard and hot and it aint pretty!
 
I think general consensus is if you are going to spin it above 5700-6000 it needs to come out and a billet rod used. I think those clearancing the balance shaft for the billet rod dipper are playing with fire, introducing a weak point into an off-balance high rpm spinning piece of weight. I would bet the reason the balancer shaft bearings go is because the shaft itself starts to bend in the middle wobbling the bearings in their bores.
 
I have had the ARC billet rod clear the balance shaft with no clearancing needed most of the time. Maybe 60% or so. Sometimes the shaft does need clearancing however. Get at least .060 clearance minimum. If it has to have a lot of grinding, I will usually try another balance shaft andit may clear. There seems to be a very wide variations in the balance shafts in the clone 390s and 420s. Some do need a lot of grinding. Not so much the true Honda ones but there is a little variation. Had one off one tooth when it was disassembled. If it was "properly" lined up it wouldnt even clear the stock rod. I guess it was just assembled any way it would clear to get it out the door. I cant image why the balance shaft bearings would ever let go. That baby must have really been spinning some rpms! Never had one even get a little rough. I will be checking closer now though!!
 
It's anyone's guess how well the the bearings in a clone were made. At least Honda uses quality NTN bearings. Well, NTN or NSK, I don't remember which is in my engines.
 
Thats not my point. At a certain point the centrifugal forces start to flex that balance shaft which acts like a "stir stick" in that bearing.....and they aren't self aligning. That's why the bearings come apart or the case fails.
 
First you said you thought that is what happens, now you say it is what happens. Supposition ≠ fact.

I wasn't directly addressing what you said anyway.
 
Great time for this post
actual I also have to use the balancer in my gx270 but should I run stock or c3 bearing´s?

Lars
Denmark
 
Jimbo said:
So how bad does it shake with out the balance shaft?
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Sometimes its hard to tell its not in there. Most of the time it shakes like a paint mixer at a particular rpm. Varies from engine to engine. Seems the higher the rpms the smoother it gets. Had one at about 2500 to 3000, you couldnt keep a bolt on the engine or kart from coming loose. I cant overstate the extreme nature of it. Finally destroyed the block. This engine was NOT balanced however. If removed, balancing becomes crucial.
Lars, I have never had a true Honda bearing fail. Main or balance shaft. Some of the clone ones are rough when new.
 
At the rpm that we run big blocks they are out of balance by over 100 grams. Industry standards are 2 grams. The pto counter weight is too thin, you need to add weight to it.
 
65ShelbyClone said:
First you said you thought that is what happens, now you say it is what happens. Supposition ≠ fact.

I wasn't directly addressing what you said anyway.
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Didn't mean to seem snottysorry. It's just science...if you took the side cover off and stuck the balance shaft in the one bearing and twisted it in a "stiring motion" eventually the bearing is going to give up from the "wobble" or the block will fatigue and crack around the bearing. I've seen pics of several of them like this.
 
rkcarguy said:
Didn't mean to seem snottysorry.
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Nor I. apologies if I did.

It's just science...if you took the side cover off and stuck the balance shaft in the one bearing and twisted it in a "stiring motion" eventually the bearing is going to give up from the "wobble" or the block will fatigue and crack around the bearing. I've seen pics of several of them like this.
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Yes, but the balance shaft is supported by a bearing at each end in operation. The balance masses are out near the ends where they have the most support and there is an arch in the middle opposite of them and off-center of the rotation axis that I think probably inhibits quite a bit of deflection. I wish I knew the shaft's imbalance factor because then it would be possible to estimate forces on the bearing with respect to engine RPM. My suspicion is that the block gets pulled apart by that oscillating force at higher RPM.
 
What I think happens, even if it's only .010-.020" of deflection, is the weight is slung outward bringing the ends of the shaft out of concentricity with each other and acting like an auger in those bearings. Or more simply put, the oscillation you mention is connect. No one believes me but my modified clone was exhibiting this on it's main bearings, I was deflecting the crank enough that it developed a contact patch where the crank passed thru the main bearings that was wider on the rod bearing side and narrower on the opposite side. Basically as the engine fired the rod and piston downward and it was slung 180* back up the hole, the crank deflected enough that the contact pattern was notable on the crank. I'm a fat driver on an 18 turn asphalt track and I'm hard on my engines lol.
 
Blue bandit said:
Ok so actual hear, don´t run it if possible or should try in clone block instead of cracking a Honda block ?
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Clone block is a weaker block then Honda, I ran one last year without a balancer, but it had the ARC rod and a Parson piston in it, it shook at the wrong rpm, the start rpm made my carb go nuts, so I am building a new one this year going to use balancer to help carb.
 
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