Polishing the Crank

[CHEVYTOWN13]

Does anyone do this for their saws?

I would imagine polishing the roughness would make the engine possibly rev a little faster when it all adds up(lightening piston).

Rick

 

[Meadow Beaver]

I'v'e heard of people who have messed with the crank but usually only for race purposes. You can drill holes in the crank for reduced weight= better rpms', but it seems awfully iffy to me.

 

[CHEVYTOWN13]

Thanks MMF.

Yeah, I assumed something like that would be for racing purposes only. I figured maybe if that was done along with other modifications to reduce weight/friction to the rotating assembly, that polishing the crank would make a difference for a shot at a win if the saws were evenly matched.

I'm not into saw racing, as I enjoy using the woods ported saws.

But hanging around this place, one never knows...

 

[romeo]

The best crank mod I have seen on a saw is going full circle with the bells. Polishing won't really help anything. Knife edging and polishing helps on 4 stroke motors since the crankshaft is running through the sump.

 

[Meadow Beaver]

Yeah a worksaw can get good rpm's without crank work. Doing things to the crank is tricky and risky for the rewards.

 

[CHEVYTOWN13]

Thanks for the help fellas.

I'm not sure what you mean by full circle on the bells. I'm assuming the bells are the parts of the crank that ride in the crank case.

What do full circle bells offer?

I'll take a guess and say that it takes up more volume in the crank case, thus affecting how the air mixture is scavenged?

I'm digging 2 strokes more and more

 

[Guarddog1]

I would think for a work saw you would want a little more weight on the counterweight. I believe that is what will keep speed up in the cut as it creates more rotating mass. If you lighten it with not enough hp I would think the saw would fall on its face. But rev really fast

 

[timberwolf]

No, chank weight has nothing to do with HP, all the mass of the crank does is help carry the engine over from one cycle to the next. The only things that would be improved with a heavy crank is idle and maybe a small bit of inertia from WOT no load to loaded in the cut. Throttle response would suffer though.

I'v taken a 1/4 pound or more off flywheels and not had a problem with idle though. 1/4 pound is more than could be taken off the crank without throwing balance way out. Also 1/4 pound from the outside of a 6 inch diamiter fly wheel is like 1 lb off the outside of a 3 inch diamiter crank.

Drilling holes in the crank or removing material from the crank will increase case volume and in most cases reduce how efficiently the engine pumps.

Full circle cranks work more on reducing case volume than reducing windage. Windage in a 2 stroke is not an issue like 4 strokes with a pan full off oil. the whole air mass in the case in constant motion and that is a good thing designed right it aids flow out the intake and up the transfers.

Forget all that 4 stroke mumbo jumbo, it's different for so many reasons and trying to apply 4 stroke theory to two stokes just confuses things.

 

[Guarddog1]

Ok so timberwolf teach me lets forget about 2 stroke 4 stroke stuff. I always an object in motion tends to stay in motion unless an opposing force is applied such as the friction of air or the pivot of a pendulum ( things do not spot in space until they slam into another object) So if we take a match box car at 60mph and slam it into a wall chances are the wall will not suffer much damage however if we switch the matchbox car with lets say my 1 ton pickup I have ample reason to believe the wall will suffer a tad more damage. The only difference was the mass of the object. So if I apply that concept lets say we are using an alunminum crank very little mass vs a cast one the cast one help carry the chain through the first portion of the the cut after that I would have to believe it would be mostly tourque to carry it through the rest.

:crazy1:

 

[TotalNZ]

On 2stroke dirtbikes adding flywheel weight definitely increases wot performance and HP, dyno proven

 

[kevlar]

On 2stroke dirtbikes adding flywheel weight definitely increases wot performance and HP, dyno proven

I disagree with that statement.how is adding a flywheel wieght going to change hp?

 

[gink595]

I would think it would add torque, but may casue HP to suffer up top

 

[Guarddog1]

On 2stroke dirtbikes adding flywheel weight definitely increases wot performance and HP, dyno proven

I may be uneducated here but how in the heck can adding rotating mass raise HP I can see changing the rotating mass (raising it) to maybe keep rpms up coming out of a berm at higher rpms. But I believe you would be slower out of the gate. I think you could fine tune it to the weight of the rider and bike combined. Ever take a big chipper apart what is in there but a huge flywheel with cutting edges bolted to it. what would happen if it were aluminum it would pretty much stop dead. The one we had was a Ford 2.3 engine not very much torque but once it brought that flywheel up to speed there was no stopping it. Not sure if I am correct this is just the way I view it.

 

[biggenius29]

On 2stroke dirtbikes adding flywheel weight definitely increases wot performance and HP, dyno proven

I disagree with that statement.how is adding a flywheel wieght going to change hp?

I also disagree with that. When I was racing ATV's, when we would do engine work the flywheel would always be put on a diet. A lighter flywheel will rev way quicker.

 

[TotalNZ]

I'm trying to find the magazine that had the article in it, i've got it in here somewhere.
I'm no stranger to modifying 2 stroke dirt bikes myself but i'm no physicist so i'll state it as it sort of makes sense to me, i realize alot of the time tuners will remove rotating mass because it makes the motor rev quicker which is a desirable trait especially in a quad but on a 2t MX bike which is not very tractable at the best of times you can get good results adding weight to the flywheel. I've got a CR which i've added flywheel weight too and it's much easier to ride now, might not rev as quick but gets more traction and puts it's power down smoother.
As far as the claimed HP increase, i haven't dyno'd my bike but the article i read claimed an increase and i would think the extra energy generated by the extra weight spinning at full throttle translates directly to HP.
I'm gonna have to find the article though and post it up.

 

[chowdozer]

It may be more tractable, but it won't add power. To get power out of a flywheel, you first have to put power in.

 

[TotalNZ]

It may be more tractable, but it won't add power. To get power out of a flywheel, you first have to put power in.

Yeah, that makes sense. i'm gonna have to find some figures

 

[kevlar]

I'm trying to find the magazine that had the article in it, i've got it in here somewhere.
I'm no stranger to modifying 2 stroke dirt bikes myself but i'm no physicist so i'll state it as it sort of makes sense to me, i realize alot of the time tuners will remove rotating mass because it makes the motor rev quicker which is a desirable trait especially in a quad but on a 2t MX bike which is not very tractable at the best of times you can get good results adding weight to the flywheel. I've got a CR which i've added flywheel weight too and it's much easier to ride now, might not rev as quick but gets more traction and puts it's power down smoother.
As far as the claimed HP increase, i haven't dyno'd my bike but the article i read claimed an increase and i would think the extra energy generated by the extra weight spinning at full throttle translates directly to HP.
I'm gonna have to find the article though and post it up.

BS!! I too had a cr500r that I would install the flywheel wieght for woods races. It gave the bike more traction with less wheel spin especially over trees and other obsticales. It did not give the bike more power!! it did make the power easier to control.

 

[mwood1986]

I had a whole list of things to say about counterbalance but these dam two strokes cranks are already off balanced technically not by much but by enough to keep momentum in the right direction I'm sure so if you add more weight to the crank then it'd only make sense it'd just make it more sluggish.

Therefore it'd make sense for people looking to win with similar saws would want to drill them out and modify them to make them lighter so if you bog it a little it wraps right back up right?

Yes my brain is on fire right now trying to think of the physics of it all since I don't know much about 2stroke haha

As for the flywheel thing I know on cars lighter flywheels just help the engine wrap up faster (throttle response) shaving tenth of seconds off of quarter mile times (if that) or on a dirt bike racing I'm assuming a heavier one for more control of wheel spin so it doesn't wrap up so fast and you don't fly into a hay-bail

Just my two cents I may be completely wrong on chainsaws haha
Now I'm reverting to brainless mode...

 

[TotalNZ]

BS!! I too had a cr500r that I would install the flywheel wieght for woods races. It gave the bike more traction with less wheel spin especially over trees and other obsticales. It did not give the bike more power!! it did make the power easier to control.

Did you strap it to a dyno? i doubt you'd feel a 1or2 hp difference through the seat of your pants on a CR500