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  #41  
Old 03-10-2010, 07:44 PM
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Originally Posted by solomon View Post
HA, wow i wish i had know this, it should be added to the 5hp Guide
Actually, a fairly common mod for the 5hp flatties, is using a 5hp fly. Its smaller and lighter, but you would need a coil adapter to use one.
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Old 03-10-2010, 07:47 PM
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so are you saying that if i put my lawnmower flywheel on my 5hp it will turn more rpm?
Nope, not saying that.
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  #43  
Old 03-10-2010, 07:54 PM
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So let me get this straight, If i put a lighter flywheel on my 5hp, it will turn more rpm FASTER, but no increase in rpm? And i will need no make a coil adapting bracket for it?
  #44  
Old 03-10-2010, 08:01 PM
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Will get to it's max rpm faster. Not more rpm.
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And i will need no make a coil adapting bracket for it?
Unknown to me.
However, I did successfully transplant a 3.75hp vertical shaft flywheel to a 2hp horizontal shaft engine with no other mods.
I have a lot of "stuff" to pick and choose from.
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  #45  
Old 03-10-2010, 08:32 PM
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Yea, well sorry for hi jacking this thread lol. i will check into my mower flywheel on my next project
  #46  
Old 03-11-2010, 03:29 AM
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Quote:
Originally Posted by solomon View Post
And you going to have to get a flywheel right? Those aluminum flywheels on lawnmower engines only act as a fan really, its the blade that acts as a flywheel. BTW in your earlier post you said the engine was kinda hard to start and had a backfire, have you checked the key? it is probably partly sheared.
The key's fine, it backfires because of the advancement in timing combined with a lack of inertia due to the removed base, all mowers I've had with the base off do this. I'm not going to bother getting a new flywheel because it really doesn't need it, it's fine as it is and it will rev quicker.

Here's a post by Frederic on the effects of a lightened flywheel
on acceleration. (Thanks Frederic, you are awesome! )

Quote:
Originally Posted by frederic View Post
With less rotating mass, the engine can change it's speed quicker - up or down - from idle all the way to redline where ever that is determined to be. Kinetic energy doesn't get started at any particular RPM. Even at 1 RPM the flywheel is storing some energy. The higher the RPM the more energy can be stored. The more flywheel mass the more energy can be stored. The larger diameter the flywheel, the more energy can be stored. And the slower it will accelerate and decelerate.

How much you notice the difference depends on the power to weight ratio of the vehicle, it's gearing, and so on.

For example. Let us say a mower flywheel weighs 5 lbs, and the engine internals weigh 15 lbs, totalling 20 lbs.

If we shave off 1 lb off the flywheel, we now have 19 lbs, so 1/20, or a 5% difference.

If we're smart and remove that weight from the outside edge of the flywheel, the gain is actually higher than 5% because weight towards the hub is less useful in a flywheel role than weight at the outside diameter. About 6-1/2% increase in acceleration/deceleration capability of the engine.

That means your engine can go from 1000 RPM to 4000 RPM 6.5% faster in this example.

But your kart won't accelerate 6.5% faster.

With a 15 tooth sprocket on the engine and a 60 tooth sprocket on the axle, that's a 4:1 ratio so the live axle would have capability to accelerate and decelerate 1.625% faster than with the original flywheel on the engine, using the same made up example above.

With a tiny engine that's not much of a difference.

On a full size vehicle that produces 500 HP and has a 1:1 5th gear, that is a noticeable difference. In auto racing that noticable difference might be a factor in winning and losing. This is why road racing cars (off-road rally cars, road course track cars, etc) often have short-stroke engines with button clutches. Less rotating mass far from the crankshaft centerline allows these engines to accelerate and decelerate quickly, which gives the driver more control of the car because he/she can shift through many gears keeping the RPMs up in the engine's peak HP range no matter what the speed.
I'm currently looking for a rod dipper or some material to make one out of.

Thanks

Hayden
  #47  
Old 03-11-2010, 04:03 AM
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Have you tried using a 4 or 5hp rod bottom from a horizontal engine? Not the whole rod, just the bottom piece. you may be able to just use a rod from a horizontal engine, but the length may differ making it non workable.
  #48  
Old 03-11-2010, 05:02 AM
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Rods should never be mixed. Manufactured and marketed in matching sets only.
They are mated to each other. No two rods are identical.
Measure them with a caliper and will see differences between them.
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  #49  
Old 03-11-2010, 08:25 AM
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Quote:
Originally Posted by solomon View Post
Have you tried using a 4 or 5hp rod bottom from a horizontal engine? Not the whole rod, just the bottom piece. you may be able to just use a rod from a horizontal engine, but the length may differ making it non workable.
I'm going to use a bolt on dipper for the reasons Russ2251 mentions. The problem is, all the engines I have (that I'm happy to take apart to make this one work) have the dipper cast into the big end, I'm going to get a briggs from the tip (there is usually none there though) or get a dipper from a friend. (Or make my own)

Hayden
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Old 03-11-2010, 08:45 AM
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Quote:
Originally Posted by Russ2251 View Post
Rods should never be mixed. Manufactured and marketed in matching sets only.
They are mated to each other. No two rods are identical.
Measure them with a caliper and will see differences between them.
A verticle Engine should never be used as a horizontal one.
  #51  
Old 03-11-2010, 10:11 AM
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Quote:
A verticle Engine should never be used as a horizontal one.
Why?
I would think any problems would have reared there ugly heads after 4+ years of doing it. Nary a hiccup.
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  #52  
Old 03-11-2010, 12:49 PM
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well without mods a vertical engine would not work. Thier for vertical should not be used for horizontal.
  #53  
Old 03-11-2010, 01:06 PM
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Quote:
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well without mods a vertical engine would not work. Thier for vertical should not be used for horizontal.
You my friend are a genious!
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  #54  
Old 03-11-2010, 04:07 PM
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Un-friggin' real...
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  #55  
Old 03-11-2010, 04:23 PM
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If You just buy a new 4hp vertical and horizontal rod, you can just exchange the bottom pieces.
  #56  
Old 03-11-2010, 06:01 PM
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Quote:
you can just exchange the bottom pieces.
Very unwise. See post #48. Rod caps should never be mixed. Any engine builder worth his salt will tell you this.
Some multi cylinder engines have the rods and caps numbered so that mixing will be avoided.
I've seen examples that when mixed they will not even fit together.
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  #57  
Old 03-11-2010, 06:43 PM
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Quote:
Originally Posted by solomon View Post
If You just buy a new 4hp vertical and horizontal rod, you can just exchange the bottom pieces.
Russ is correct, i wouldn't mix rod pieces, You could probably swap out the WHOLE rod assembly though. Would be easier to use one of those bolt on dippers.
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Old 03-11-2010, 07:49 PM
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but i think the bottom of a vertical rod isn't grooved to fit the dipper. i would check to see if oyu could just use a 4hp horizontal rod.
  #59  
Old 03-11-2010, 08:17 PM
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How hard could it be to fab up a dipper? I'm picturing a piece of 16ga sheet, a little cut, bend, and drill, double check for clearance, et voila! No?
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  #60  
Old 03-11-2010, 08:46 PM
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I think it would be easier and safer to just go with a new rod lol
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