Chainsaw dynometer build.

[dynodave]

Brake VS inertia

Sorry I'll openly disagree...actually will agree inertia is simplest but IMO useless for 2 stroke air cooled.
.An air cooled engine AKA chainsaw (unless you are running new secret water cooled chainsaws) should not be tested on a flywheel inertia dyno...While I run my brake dyno for only air cooled motorcycles the principals are entirely the same for air cooled chainsaws. If you run a hot saw for competition it may not matter as much since the run times are so short. Hopefully short enough not to cook the motor, But in general a brake dyno is infinitely better to get the motor into "heat soak" and you should be tuning so the motor does not fry the pistons into melted aluminum for the period of time required to cookie a 20" log of oak.
I can tune a bike to make killer (short term) power Yet down the back straight of daytona it will spit you off with a seized engine. A heat soaked engine tune is absolutely critical.
I had and run my dyno for over 20 years on air cooled bikes.
If you think clutch slippage is a problem ....remove the springs. I would think that you would not care about measuring power sub 3000rpm. In my world I don't see having a normal clutch as any obstacle at all.:hmm3grin2orange:

 

[chadihman]

Nice to see someone agrees

Sorry Moody I think Mastermind is talking about a flywheel style load dyno. Not a saw flywheel mounted drive

 

[steve316]

I was going to make one out of a eletric motor; the outer case is your scater shield. Also you have to have some type of braking system like a front brake off a motorcycle. I have seen one made in this way; it also used a one way clutch. Looked like a simple set-up. Steve

 

[chadihman]

Would pulling a properly tuned chainsaw down to 9600 rpms and holding for 5 min fry the engine? Testing rpm would probably be between 8000-10000 rpms for a short time. Maybe 30 seconds or so. How about breaking a saw in under slight load for 3-5 min at a time?

 

[Mastermind]

Sorry I'll openly disagree...actually will agree inertia is simplest but IMO useless for 2 stroke air cooled.
.An air cooled engine AKA chainsaw (unless you are running new secret water cooled chainsaws) should not be tested on a flywheel inertia dyno...While I run my brake dyno for only air cooled motorcycles the principals are entirely the same for air cooled chainsaws. If you run a hot saw for competition it may not matter as much since the run times are so short. Hopefully short enough not to cook the motor, But in general a brake dyno is infinitely better to get the motor into "heat soak" and you should be tuning so the motor does not fry the pistons into melted aluminum for the period of time required to cookie a 20" log of oak.
I can tune a bike to make killer (short term) power Yet down the back straight of daytona it will spit you off with a seized engine. A heat soaked engine tune is absolutely critical.
I had and run my dyno for over 20 years on air cooled bikes.
If you think clutch slippage is a problem ....remove the springs. I would think that you would not care about measuring power sub 3000rpm. In my world I don't see having a normal clutch as any obstacle at all.:hmm3grin2orange:

It sounds like you have experience with this stuff......with some help I can see chadihman building this thing......then I'd want one of course.

Thanks for the input. :msp_thumbup:

 

[LegDeLimber]

I gotta come back and read this thread.

Flywheel/ Prony brake type?

I've wondered about using mockup bar mount and chain to pull hyd pump
feed pump to recurculating array of
flow gauge and variable restriction and press gauge, reservoir
etc.
got a diagram in my mind just needto sketch later and post.

sorry if already been covered, I'll prpoper readthis thread later
gotto get out side now.

qiuck edit:
think of sorta like a saw powered log splitter
but the variable restriction (load) is subed instead of the cylinder .

 

[dynodave]

dyno use

Would pulling a properly tuned chainsaw down to 9600 rpms and holding for 5 min fry the engine? Testing rpm would probably be between 8000-10000 rpms for a short time. Maybe 30 seconds or so. How about breaking a saw in under slight load for 3-5 min at a time?

A properly tuned engine should run indefinitely under full load until it's worn out and not seize. That IS the (my) criteria... for success.
The nice thing of using a brake dyno is you can also use it as a "load cell" to do partial throttle and any selected RPM you desire for any reason you choose. Break in is probably the # 1 use. So you are spot ON.
For me and the bikes, Norton or BSA twins, I load them to 8-12hp=55-70mph and synchronize the carbs for the smoothest tune up possible like BOOM-BOOM-BOOM-BOOM
NOT BOOM-boom-BOOM-boom.
You know what I mean...can't do it any other way

To do well you will need 2 thermocouples and one of them should definitely be a light mass thermocouple for the EGT...a regular one for the head temp. I run up to 8 for my dyno.

 

[chadihman]

It sounds like you have experience with this stuff......with some help I can see chadihman building this thing......then I'd want one of course.

Thanks for the input. :msp_thumbup:

I'll build you one if mine works as planned but not untill I find all the magic porting numbers and secrets:hmm3grin2orange: Really you would be the first I would build one for. You helped me out in so many cases.

 

[Mastermind]

I build you one if mine works as planned but not untill I find all the magic porting numbers and secrets:hmm3grin2orange: Really you would be the first I would build one for. You helped me out in so many cases.

This stuff is out of my area of experience.....but I'd do whatever needed of me to help.

 

[chadihman]

A properly tuned engine should run indefinitely under full load until it's worn out and not seize. That IS the (my) criteria... for success.
The nice thing of using a brake dyno is you can also use it as a "load cell" to do partial throttle and any selected RPM you desire for any reason you choose. Break in is probably the # 1 use. So you are spot ON.
For me and the bikes, Norton or BSA twins, I load them to 8-12hp=55-70mph and synchronize the carbs for the smoothest tune up possible like BOOM-BOOM-BOOM-BOOM
NOT BOOM-boom-BOOM-boom.
You know what I mean...can't do it any other way

To do well you will need 2 thermocouples and one of them should definitely be a light mass thermocouple for the EGT...a regular one for the head temp. I run up to 8 for my dyno.

Your the Man! Thanks for all your input! My wife is from Reading Mass. Her sister lives in Boston. Are you close? I don't get to excited to go see her family but I sure would if we were making a stop at your place.
My wife sometimes calls me a a##hole. I call her a Mass hole

 

[chadihman]

I gotta come back and read this thread.

Flywheel/ Prony brake type?

I've wondered about using mockup bar mount and chain to pull hyd pump
feed pump to recurculating array of
flow gauge and variable restriction and press gauge, reservoir
etc.
got a diagram in my mind just needto sketch later and post.

sorry if already been covered, I'll prpoper readthis thread later
gotto get out side now.

qiuck edit:
think of sorta like a saw powered log splitter
but the variable restriction (load) is subed instead of the cylinder .

Yup your thinking like me. A needle valve would be used to block flow from the pump back to the tank. As the needle valve is closed the hyd pressure goes up causing the pump to work harder thus the saw work harder.

 

[moody]

Sorry Moody I think Mastermind is talking about a flywheel style load dyno. Not a saw flywheel mounted drive

And the difference would be what? The load is still on the flywheel side.

 

[chadihman]

And the difference would be what? The load is still on the flywheel side.

A flywheel dyno uses a heavy flywheel that is slowly spun up to speed with the saw. You then record how much time it takes the saw to get the flywheel to a set rpm. You make the mods to the saw and time again. I really don't like this style of dyno. Moody I really hope your not taking this the wrong way. I'm just trying to help you understand this.

 

[chadihman]

This is a little sketch I drew up to explain a little better.

 

[half_full]

Ah, pictures. We all love pictures

 

[blueknobbuck]

i love that your diagram depicts an orange and white saw

 

[Mastermind]

I'm not understanding the pump to load cell arrangement.....

How to to get that measurement? By the pressure of rotational twist at 1ft away from the pump?

Very nice drawing and simple setup.

 

[chadihman]

I'm not understanding the pump to load cell arrangement.....

How to to get that measurement? By the pressure of rotational twist at 1ft away from the pump?

Very nice drawing and simple setup.

Yes. I should have explained this in the pic also. The hyd pump is being held by nothing other than the shaft that is turning it. The saw is held wide open. then I slowly turn the needle valve shut causing more pressure to be built because I'm limiting the hyd flow back to the tank. As the pressure increases so does the amount of torque to turn the pump. The harder it is to turn the pump the more the pump tries to twist. The one ft bar atached to the pump is now pushing on the load sensor. The load will show up on the display in accurate lbs. Gains to the saw should be easily found. The best part about this design is I can run the saw under load for a long time. A manual brake would get way to hot in the long testing times. Sorry for being so wordy.

 

[srcarr52]

I've had a hydraulic brake dyno at the shop for a couple of years now. I test all my kart engines on it but I haven't gotten around to make the fixture for mounting chainsaws.

 

[chadihman]

I've had a hydraulic brake dyno at the shop for a couple of years now. I test all my kart engines on it but I haven't gotten around to make the fixture for mounting chainsaws.

Am I heading in the right direction? Does my sketch look right? I ordered more parts today. I'll be starting on this in a couple days as the parts start showing up