# What is Dual Shaft



## jsup (Nov 19, 2017)

I'm fairly mechanically savvy, I can do a whole lot. Built a few cars, working on these snowblowers, etc.. 

What I do not understand, but have heard reference to, is dual shaft machine. I'm not sure what's meant by that. 

I'm sure it's a simple thing, but drives me nuts when I don't understand a term.


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## classiccat (Mar 1, 2014)

Engines where the cam also has an output shaft for driving the traction assembly; convenient since it runs 1/2 of the crankshaft RPM.


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## vmax29 (Oct 19, 2017)

:grin: It means it has two shafts. 

Sorry I have no idea what it really means, just couldn’t resist.


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## jsup (Nov 19, 2017)

classiccat said:


> Engines where the cam also has an output shaft for driving the traction assembly; convenient since it runs 1/2 of the crankshaft RPM.


The replacement engines I'm familiar with, and my knowledge of these things is limited as compared to the enthusiasts here. 

I get the 2:1 ratio. It's too early but I have to wonder how that effects torque at the wheels. I have to think with the cam going around 1/2 as much, you'd use a bigger pulley, resulting in more torque? I have to draw that one out. 

Does the cam "shaft" come out of the front or back of the engine? Same side as the engine crank? If you do a repower, and only have a single shaft, can you adapt either the machine, or the engine? 

Just wonderin.


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## jsup (Nov 19, 2017)

vmax29 said:


> :grin: It means it has two shafts.
> 
> Sorry I have no idea what it really means, just couldn’t resist.


And I thought this was going to be complicated.


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## Dauntae (Nov 10, 2016)

vmax29 said:


> :grin: It means it has two shafts.
> 
> Sorry I have no idea what it really means, just couldn’t resist.


But that’s EXACTLY what it means


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## deezlfan (Nov 8, 2017)

The second shaft runs 'backwards' so repowering a machine with a single shaft will require a bit more work. Without modifying the drive or linkage you get 3 or 4 reverse and 1 or 2 forward speeds. It can be done, it just requires a bit of forethought. The dual shaft motors are common on rototillers too. This is a Briggs but Tecumseh engines are very similar.


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## vmax29 (Oct 19, 2017)

I honestly didn’t get it either. There was a picture in a post referring to it a while back and I was wondering how that worked. 
Interesting.


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## jsup (Nov 19, 2017)

deezlfan said:


> The second shaft runs 'backwards' so repowering a machine with a single shaft will require a bit more work.


Ah ok. Are there conversions for re-powers on replacement engines or are you just relegated to rebuilding the dual shaft?

Is this new technology or new technology? Is it still used? I also note on my internet search, that they're also used in tillers and other equipment, and it seems like it's old tech, not new. Am I wrong?


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## stromr (Jul 20, 2016)

It may be considered old tech but not because it didn't work. I imagine it is no longer used because it was more expensive to make and other ways were found to do the same job with out the added complication. I still see plenty of twin shaft engines for sale used so there's no need to convert your equipment.


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## deezlfan (Nov 8, 2017)

The technology is as old as small OPE engines from what I have seen. The new machines don't use it very much anymore. I would assume because it increases complexity and therefore cost. 

From what I have seen, most people that are repowering using a single shaft engine are using a combination of two pulleys on the output shaft and flipping some of the drive wheel components inside the blower trans. Another mod I read about featured cutting off the shift arm, flipping it over and rewelding.


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## jsup (Nov 19, 2017)

stromr said:


> It may be considered old tech but not because it didn't work. I imagine it is no longer used because it was more expensive to make and other ways were found to do the same job with out the added complication. I still see plenty of twin shaft engines for sale used so there's no need to convert your equipment.


I don't have an immediate need, I was just curious.


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## YSHSfan (Jun 25, 2014)

As others replied before a dual shaft engine has 2 PTO shafts. The one from the crank runs CCW and typically at 3600rpm, the cam runs at 1800rpm (half the speed) but also it turns CW. I have no idea what difference it makes in torque, but I do know one thing... the older Yamaha engines have a single shaft PTO but it is cam driven, and I’ve heard and read a few occasions that this engines have a lot of torque and power some times comparing an 8Hp Yamaha to an 11hp or 13hp Honda, would it be related to the cam PTO instead of crank PTO? Or is it just an impression from the Yamaha snowblower owners. I just don’t know.....


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## Toro-8-2-4 (Dec 28, 2013)

RE the single PTO driven off of the cam shaft.........Torque is a function of HP and RPM.....so if you cut the RPM in half you really need a relatively powerful engine to have a decent functioning machine. Interesting that Yamaha has done that. Also.....Throwing distance and speed of snow removal is a function of impeller velocity and size. So they must use a relatively large impeller and or use a very small pulley on the impeller shaft. I don't think anyone makes a dual shaft machine any longer. The Snow king Techumseh engines from the 90's were dual shafted. As deezlfan said they are probably more cost to put out and so they dropped the design. It does make for easier belt changes. There were some benefits. You can change the tractor belt with out touching the auger belt. Plus the belts wore better with it going at a slower speed.

There are plenty of threads on repowering these machine with a single PTO shaft engine. For those with interest check them out so you don't waste time reinventing the wheel.


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## RedOctobyr (Mar 2, 2014)

YSHSfan said:


> the older Yamaha engines have a single shaft PTO but it is cam driven, and I’ve heard and read a few occasions that this engines have a lot of torque and power some times comparing an 8Hp Yamaha to an 11hp or 13hp Honda, would it be related to the cam PTO instead of crank PTO? Or is it just an impression from the Yamaha snowblower owners. I just don’t know.....


No, the useful output from the engine has nothing to do with which shaft you use to drive the machine. It has to do with the design of the engine's internals, and how much power/torque they can get from the engine's guts. 

But using an output from the camshaft, vs the crankshaft, doesn't change anything. The camshaft output *would* have twice the torque of the crankshaft output, since it turns at half the RPM. 

But since horsepower = RPM * torque, it all comes out in the wash. Twice the torque, but half the RPM, yields the same horsepower. Once you use a larger pulley on the camshaft output to drive the rest of the machine at the proper speed, you're back where you started, using a crankshaft output. 

The performance of the Honda/Yamaha/etc engine derives from the other hard work put into the engine design & build, not where you grab the output. 

I don't think there are many new engines with dual shaft outputs (I'm tempted to say none, but there's gotta be something). So if you're repowering a machine that was built for a dual-shaft engine, like people said, you'll either have to do some rework to get the machine operating normally with a single-shaft engine, or you can buy a used dual-shaft. Or, if it's a Tecumseh, for instance, you can buy a similar, functioning, single-shaft Tecumseh variant, and swap some of the parts from the dual-shaft version to the good engine, thereby converting it into a dual-shaft.

Edit: Toro-8-2-4 beat me to it


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## jtclays (Sep 24, 2010)

I had


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## GoBlowSnow (Sep 4, 2015)

Ive got a 8HP Techumseh twin shaft on one of the John Deere TRS27s I work on for my church. The engine was a replacement for what was originally on there. The extra shaft axle was cut flush with the block (somewhat) as it was not needed. not sure why a twin shaft was put on there as a replacement but that extra shaft vibrates enough that it shakes the unit. I'm going to have to take the engine apart someday to see if I can remove the shaft completely.


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## jtclays (Sep 24, 2010)

9654


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## RedOctobyr (Mar 2, 2014)

Agreed. Even if the extra-long camshaft is cut off poorly, it really shouldn't cause much of an imbalance. If you cut it off very gradually (like the cut was close to parallel to the shaft, vs perpendicular to the shaft), then you could cause the shaft itself to be somewhat imbalanced. 

But if it's cut off fairly-square (perpendicular to the shaft), then it's not something that I would expect to cause any vibration. In addition, the shaft's diameter will be fairly small, so any imbalance will still be located close the center of the shaft, reducing the shaking it could cause.


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## Waterlooboy2hp (Nov 29, 2011)

jtclays said:


> I had saved Waterlooboy2hp modification he did to convert a Predator to dual shaft, but sadly all the pics were lost to photoscam (bucket). He basically added an extended camshaft and machined a new sump cover. It was obviously more complicated than most would do ----
> ==================================================================
> 
> 
> ...


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## jtclays (Sep 24, 2010)

:icon-clapping-smile


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## Clutch Cargo (Dec 27, 2015)

> But since horsepower = RPM * torque, it all comes out in the wash.


Just so we're all on the same page:

Hp = (T*N)/5252

Where:
T = Torque (lbft)
N = RPM


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## jsup (Nov 19, 2017)

Waterlooboy2hp said:


> jtclays said:
> 
> 
> > I had saved Waterlooboy2hp modification he did to convert a Predator to dual shaft, but sadly all the pics were lost to photoscam (bucket). He basically added an extended camshaft and machined a new sump cover. It was obviously more complicated than most would do ----
> ...


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## Spectrum (Jan 6, 2013)

For what it's worth Gilson used the dual shaft engines extensively in the late model designs. It replaced a stage in the traction drive speed reduction simplifying the build. It also provided a direction that was adaptable to the design. As a stock engine option I'm pretty sure it was to their advantage cost wise.

In all of my correspondence I don't recall any engine issues related to the cam shaft loading. Unless you do something off the wall the traction system can only generate so much loading.


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