What's on your bench?

[huskihl]

It's funny though a lot of rase cars that I know of are running ceramic bearings in the front and they take a beating that's more or less the reason why I thought they be good in saw.

A v-8 is balanced. A chainsaw is not.

 

[usmcbuckwild]

A v-8 is balanced. A chainsaw is not.

I believe he is talking about wheel bearings, not engine bearings.

 

[huskihl]

I believe he is talking about wheel bearings, not engine bearings.

That could be, also.

 

[usmcbuckwild]

And speaking of chainsaws being balanced; how far OUT of balance is a chainsaw engine. Rotating assembly VS piston weight. I wonder if there is any way to utilize a “harmonic balancer” type flywheel. Should help reduce vibrations, reduce wear on bearings, no?

 

[huskihl]

I

And speaking of chainsaws being balanced; how far OUT of balance is a chainsaw engine. Rotating assembly VS piston weight. I wonder if there is any way to utilize a “harmonic balancer” type flywheel. Should help reduce vibrations, reduce wear on bearings, no?

Can't answer that. I only know what I've read here

 

[MustangMike]

Re: Chainsaw balance … it is less expensive to "over build" the saw than to try to correctly balance it. That is partly why they all have AV. Single cylinders are tough to balance.

Easiest to balance: Straight 6 or V-12, then V-8, V-6 and 4 generally need counter weights.

 

[MG porting]

I believe he is talking about wheel bearings, not engine bearings.

Yes correct.

 

[usmcbuckwild]

Re: Chainsaw balance … it is less expensive to "over build" the saw than to try to correctly balance it. That is partly why they all have AV. Single cylinders are tough to balance.

Easiest to balance: Straight 6 or V-12, then V-8, V-6 and 4 generally need counter weights.

This I understant. But, given the opportunity, I would prefer to reduce excess vibrations and un-controlled movement.

 

[huskyboy]

This I understant. But, given the opportunity, I would prefer to reduce excess vibrations and un-controlled movement.

Reduce piston weight or a lighter piston should help ?

 

[p61 western]

Something I have thought about a little bit. What weighs more the top end or the complete crank assembly. By complete I mean bearings flywheel and complete clutch assembly. I would think the top end is lighter, but all I have is a bathroom scale here.

 

[MustangMike]

The cost of balancing a chainsaw engine makes it prohibitive, but as Mason says, usually a lighter piston will result in less felt vibrations.

 

[huskyboy]

Something I have thought about a little bit. What weighs more the top end or the complete crank assembly. By complete I mean bearings flywheel and complete clutch assembly. I would think the top end is lighter, but all I have is a bathroom scale here.

I think the counterweights of the crank are what balances the piston but I could be wrong

 

[p61 western]

I think the counterweights of the crank are what balances the piston but I could be wrong

No clue either really. It was just a thought is all.

 

[huskyboy]

I think @MustangMike said he got more vibes with a heavier bb piston in a hybrid in another thread. Makes me think the crank is designed for a certain weight piston.

 

[usmcbuckwild]

I think @MustangMike said he got more vibes with a heavier bb piston in a hybrid in another thread. Makes me think the crank is designed for a certain weight piston.

The crank HAS to be designed with a certain weight (or window of weights) in mind. Too much or too little counterbalance and the whole thing would literally vibrate apart

 

[MustangMike]

An externally balanced engine will have weights on the flywheel (the flywheel is not in balance), but an internally balanced engine has counterweights to offset the weight of the rod + piston. Not sure if chainsaw flywheels are in balance or not.

Mason is correct, a heavier AM piston produced more vibes than an OEM piston (which is lighter) on a 440/460 hybrid. However, "felt" vibes can be reduced by adjustments to the AV bushings.

 

[redline4]

I would guess a saw flywheel would be a neutral balance.
You cant achieve a perfect balance on a single cylinder crank that I am aware of.
You can get them pretty close at certain rpm ranges though.
Back when I was racing lawnmowers and building Tecumseh single cyl engines, they used a rotating balancer. Great at goverened 2650rpm, but left the block in a hurry at 6k.
So, I took them out. It vibrated like a paint shaker below 2500, but after that, smooth as can be. Never saw that low of rpm on the track anyway. Usual rpm range was 3300-7000 rpm most of the time.

 

[mdavlee]

I think that's what @TreeLife had in his. Didn't last long

I ordered some for other people. I never installed any myself. They weren’t real happy with most of them.

 

[Deets066]

Some series of saws use the same crank with 3 different size pistons. No additional vibes...

 

[usmcbuckwild]

Some series of saws use the same crank with 3 different size pistons. No additional vibes...

As I said a “window of weights”. For example all 3 of the pistons sizes are 62-72 grams in weight. This means the counter balance would be averaged for 67 grams with +/- 6 grams as an allowable limit. The counter balance effectiveness will be changed by inertia of the piston moving; slower is less effective but it smoothes out in higher RPM.