Chainsaw dynometer build.

chadihman · Mar 2, 2013

I find it hard sometimes to find wood to cut cookies with. It's also important to have the same chains,bars, and even chain tension for getting accurate comparison. I burn firewood so most of the good hard wood is cut up for 18" splits and cookies are not the best thing for long burn times at night.

I've been thinking about this for a while. I found that google has very little info on a chainsaw dyno. Most of it came up with AS threads that didn't show up on AS search:frown:. I'm thinking about using a small hyd. pump coupled to a sprocket on a modded bar. A larger sprocket will have to be installed on the pump to keep the pump rpms down in range to avoid cavitation. I'll then plumb a needle valve onto the pumps pressure side and run the bleed off back to the hyd tank. I would then bolt a bar to the end of the pump oposite the input shaft. The bar would then be connected to a load cell for measuring torque. RPM * T) / 5252 = hp. Hold the saw wide open and adjust the needle valve too pull the saws rpms down and read the torque. I know there will be some loss in the chain and pump but this seems like it would be a really nice way to measure gains. Any thoughts on this plan? I might be crazy but this time off after surgery has me thinking a lot lately.

Walt41 · Mar 2, 2013

I have thought about this extensively and it always comes back to the clutch issue, saws would have to be tested without the clutch on to avoid variances, therefore some type of engagement assembly would have to be built into the dyno.

chadihman · Mar 2, 2013

Walt41 said:
I have thought about this extensively and it always comes back to the clutch issue, saws would have to be tested without the clutch on to avoid variances, therefore some type of engagement assembly would have to be built into the dyno.

I'm guessing your talking about clutch diameter. I really don't think the clutch would have anything to do with this. The pump would only be used to pull the engine down to its rated rpm under full throttle. A tach would measure the saws rpms and the torque sensor would read torque. If you have a stable rpm and torque then you have HP. I really just want to watch the gains on one saw at a time to find out what tweak does what.

The clutch should not have anything to do with it if the saw is pulled under load to It's rated HP rpm.

chadihman · Mar 2, 2013

I don't know of any other better way than a dyno for finding the perfect port numbers. I think my oil tank pig roaster project is gonna have to put on the back burner now. I'm feeling good about this.

rmh3481 · Mar 2, 2013

If you look around a little you should be able to find an old kart/sled dyno fairly reasonable.

Price is too high on this one but you get the idea;
Go Kart Inertia dyno, small engine

rmh3481 · Mar 2, 2013

I can appreciate building your own, but with the cost of the components you would have more than this in it; Go Kart Engine Dyno

chadihman · Mar 2, 2013

rmh3481 said:
If you look around a little you should be able to find an old kart/sled dyno fairly reasonable.

Price is too high on this one but you get the idea;
Go Kart Inertia dyno, small engine

I don't think a chainsaw would spool that thing up without toasting the clutch.

chadihman · Mar 2, 2013

rmh3481 said:
I can appreciate building your own, but with the cost of the components you would have more than this in it; Go Kart Engine Dyno

Your right I would have more than that in building my own

Walt41 · Mar 2, 2013

I was speaking of clutch slippage, it has to be eliminated for accurate numbers for comparison.

chadihman · Mar 2, 2013

Walt41 said:
I was speaking of clutch slippage, it has to be eliminated for accurate numbers for comparison.

Well that maybe could be a problem but a saw is usually run at 9000-11000 rpms in wood. At that rpm the clutch should be locked tight. If not then there's a problem with your clutch. The dyno would only pull the saw down to the rpm its usually at in wood.

CATDIESEL · Mar 2, 2013

i would think with the throttle pinned under a load you would really have to pull it down to get a good clutch to slip. most saws are going to be @ max power @ 9500+ rpms, you won't get any slippage there, as the more rpm's the tighter the clutch will grab.

Boleclimber · Mar 2, 2013

TW (username initials) built a chainsaw dynometer years ago. If I remember correctly he had it hooked up to a computer some how.

chadihman · Mar 2, 2013

The hyd pump is used as a brake. I guess a water pump could be used also. That should be cheaper than hyd components

kentuckydiesel · Mar 2, 2013

Eddy-Current and Powder Dynamometer Applications

-phillip

bplust · Mar 2, 2013

Subscribing.

kentuckydiesel · Mar 2, 2013

Also, the other day I was looking at an old scale type dynamometer that we have at our shop. Got to thinking about testing small engines with it. Basically all it would take would be an arm connected to a clutch driven by the small motor. Load up the clutch and the arm begins to rotate, thereby pulling on the dyno to give you a readout in lbs.

-Phillip

moody · Mar 2, 2013

The easiest way around the clutch is to use the fly wheel. If properly mounted it could handle a load strong enough to bring the engine down.

moody · Mar 2, 2013

Plus you could do a timing read with the starter cover off.

chadihman · Mar 2, 2013

kentuckydiesel said:
Also, the other day I was looking at an old scale type dynamometer that we have at our shop. Got to thinking about testing small engines with it. Basically all it would take would be an arm connected to a clutch driven by the small motor. Load up the clutch and the arm begins to rotate, thereby pulling on the dyno to give you a readout in lbs.

-Phillip

Yup that's exactly the method I'm going to use except I'll use a pump as a brake. The pump will have the arm attached to it. The more torque the more the pump will try to twist thus turning an arm attached to a sensor that reads pounds accurately. A clutch or a brake would overheard quickly at high rpms. A hyd pump could be put under pressure for a long time without building much heat. It could hold a saw under load until it runs out of gas.

kentuckydiesel · Mar 2, 2013

chadihman said:
Yup that's exactly the method I'm going to use except I'll use a pump as a brake. The pump will have the arm attached to it. The more torque the more the pump will try to twist thus turning an arm attached to a sensor that reads pounds accurately. A clutch or a brake would overheard quickly at high rpms. A hyd pump could be put under pressure for a long time without building much heat. It could hold a saw under load until it runs out of gas.

What about something like a small disk brake? The caliper could be mounted on the lever and the saw could turn the brake rotor.

Just trying to think cheap, yet effective.

-phillip

Chainsaw dynometer build.

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