Run in stand/dyno build.

[Mike Bontoft]

Especially he scratch built it from plans. I chromed the iron liners and ground them when I was messing with that 20 years ago, still have all the stuff and plan to try it again some day.

Flames? Never! I take any and all the help I can get. IIRC I put a pretty good press on it, maybe 1/2 thou or so. Rudy texted me saying they make bearings with a keyed outer race and that's what I think I got there, you might even see it in the pic. I'm gonna mount a pully on the end of the wheel and try to spin it up to maybe 8K with the starter before I fire the motor, hopefully it'll be easier on the clutch.





The inner bore is keyed, outer race pressed in but I might add a key there too.

https://www.vxb.com/CSK15PP-One-way-p/kit10968.htm

Yes come to think of it I have seen keys on the outside of the bearings used on multi speed RC car transmissions. It looks like on those (taking into account the gear ratio) get overdriven at about 10 TO 12k.

 

[Marty Davis]

Looking at it again I think what happened in that first run was the one-way clutch bearing let go. I hope it's gonna be up to the task.

Clutch locked the wheel up at about 10.5, steady climb to 13, one way let go (rpm sensor is on the housing, not the wheel). Brought the power back, bearing hooked back up at about 13K, motor dragged the wheel down to about 10.5 where the collet unscrewed and clutch let go, wheel coasted down.

CHT seems OK, EGT is wonky but I'm just using an Eagle Tree thermocouple for now.

I looked up the rating for the CSK15 clutch bearing, 13.5 nm which is about 10 ft.lb...

We went through a dozen one way bearings before we gave up on them. Only a problem on the 67 and 90+ engines.

 

[Terry Keeley]

We went through a dozen one way bearings before we gave up on them. Only a problem on the 67 and 90+ engines.

What happened to them?

 

[Terry Keeley]

 

[Mike Bontoft]

The pre speeding of the inertia wheel could be made into an automatic feature that always keeps the wheel above a preset RPM. This being a fix for the particular problem of matching inertia wheel mass for on and off pipe situations. The reason we were burning pistons in my opinion is the engine was spending way too much time in a pre ignition area. The inertia wheel was too large, yes! , but way too large for an engine in an off pipe transitioning situation. Would use another one way clutch though!. I like it!

 

[Charles Perdue]

Mike, I built a dyno for the Briggs flat head engines when we were racing them. For a one way clutch I used one made for a Ford tractor PTO. This is a VERY strong unit. It was the wrong rotation so I cut it off and turned it around, re-welded it back together then mounted it on the main flywheel shaft. Bullet-proof, never had a problem. When we stopped racing, I sold it to a guy in Idaho. Still being used the last I heard.

On another dyno similar to the one that you are using for your toy engines, I used a homemade ratchet jaw type one way clutch. Made it using a drill press, hacksaw and files. Google One Way Clutch 3 jaw by thang 010146 and you will find a 3 D rendering of what this one looks like. It is old school but it works great also.

Charles

 

[Marty Davis]

What happened to them?

They just started slipping and wouldn't hook up at all.

 

[Marty Davis]

The pre speeding of the inertia wheel could be made into an automatic feature that always keeps the wheel above a preset RPM. This being a fix for the particular problem of matching inertia wheel mass for on and off pipe situations. The reason we were burning pistons in my opinion is the engine was spending way too much time in a pre ignition area. The inertia wheel was too large, yes! , but way too large for an engine in an off pipe transitioning situation. Would use another one way clutch though!. I like it!

Terry:

I suggest that you design the inertia wheel so that it spools up to your rpm in the time it takes you to go up one of the SAW's. That is how we designed our wheels. It only makes sense. If you are doing just record trial SAW's then have a second wheel.

 

[Brad Christy]

Terry,

Question....

Aren't we just interested in the duration of acceleration given a specific mass of the flywheel? Does it really matter the size/mass of the wheel if these are knowns? Can't we just plug and chug the numbers and arrive at a HP number regardless? Sure, a lighter/smaller wheel will spool up faster, but if it's against a know resistance, isn't that all that matters?

OK.... Multiple questions......

Idiots always ask the best questions, don't they?

Thanks. Brad.
Titan Racing Components
BlackJack Hydros
Model Machine and Precision LLC

 

[Terry Keeley]

The pre speeding of the inertia wheel could be made into an automatic feature that always keeps the wheel above a preset RPM. This being a fix for the particular problem of matching inertia wheel mass for on and off pipe situations. The reason we were burning pistons in my opinion is the engine was spending way too much time in a pre ignition area. The inertia wheel was too large, yes! , but way too large for an engine in an off pipe transitioning situation. Would use another one way clutch though!. I like it!

You mean you burnt pistons because the motor spent too much time off the pipe and that it was pre-igniting (detonating?) there?

From my Eagle Tree stuff I usually see the pipe come in between about 15-17K and go from there.

Mike, I built a dyno for the Briggs flat head engines when we were racing them. For a one way clutch I used one made for a Ford tractor PTO. This is a VERY strong unit. It was the wrong rotation so I cut it off and turned it around, re-welded it back together then mounted it on the main flywheel shaft. Bullet-proof, never had a problem. When we stopped racing, I sold it to a guy in Idaho. Still being used the last I heard.
On another dyno similar to the one that you are using for your toy engines, I used a homemade ratchet jaw type one way clutch. Made it using a drill press, hacksaw and files. Google One Way Clutch 3 jaw by thang 010146 and you will find a 3 D rendering of what this one looks like. It is old school but it works great also.

Charles

Looks like the TDK guys used the same type of tractor PTO one way clutch on their kart dyno:

Terry:

I suggest that you design the inertia wheel so that it spools up to your rpm in the time it takes you to go up one of the SAW's. That is how we designed our wheels. It only makes sense. If you are doing just record trial SAW's then have a second wheel.

That'd be only a few seconds then? Wouldn't I possibly "miss" parts of the power curve if I did that? It might better simulate a SAW run tho for sure.

Terry,

Question....

Aren't we just interested in the duration of acceleration given a specific mass of the flywheel? Does it really matter the size/mass of the wheel if these are knowns? Can't we just plug and chug the numbers and arrive at a HP number regardless? Sure, a lighter/smaller wheel will spool up faster, but if it's against a know resistance, isn't that all that matters?

OK.... Multiple questions......

Idiots always ask the best questions, don't they?

Thanks. Brad.
Titan Racing Components
BlackJack Hydros
Model Machine and Precision LLC

Lol, another idiot here then!

All the info I've read says to spin the wheel up in 5-10 sec.,10-15 etc., etc. Then I found a comment on Performance Trends what you really want is 3-500 rpm/sec and a light went off.

Most dynos built are for cars, bikes, karts where the rpm range is only maybe 5 - 10K so 5- 15 secs works. Our range is more like 15-20K (say 12 - 28K on a .67) so we want more like 30-45 sec (32 to 53 in this case). I've seen a lot of noise spikes in data from other model engine dynos and felt if the acceleration was slower it might help to smooth them out. Plus you have a better chance of getting more accurate data to find that tenth of a HP somewhere in the curve. Brian Spitzer told me "professional" dynos took rpm data at 200 Hz in the 90's, now they're up to 400 Hz and more. These "backyard basher" units are only at 50 Hz, more reason to spread out the run.

My first little attempt there told me a lot. The wheel took 13 sec. to go from 10.5K to 13K which is only about 200 rpm/sec. So I've cut the wheel down (so far) from 6" to 5.5" diameter, doesn't sound like much but it reduces the inertia by about 30%.

I'm gonna take my Consigliere's advice and key the outer race in the housing with a dog point set screw so it can't spin again.

I'll "pre-spin" the wheel with the starter so the motor/clutch isn't wore out before lock up at about 10.5K.

And my new thermocouples shud be here tomorrow!

 

[Charles Perdue]

Yes Mike, same type of one way clutch as TDK on Kart dyno....Yep. If it works then use it.

 

[Terry Keeley]

I'll bend them as needed, thanks Mike!

 

[Terry Keeley]

Mystery solved, it even had 5-6 tenths press fit. Added a dog point set screw per my Consigliere.

 

[Terry Keeley]

Well, after a year or so on this project I think I'm finally getting somewhere.

I got the wheel sized about right. The eddy brake works, gets up to about 100*F so not too bad. EGT and CHT working well and pre-spinning the wheel helps a bunch.

The "Mule" is a bone stock CMB 67 with a well run piston/sleeve and bearings. Needle is definitely on the rich side but not slobbering, I'll figure out how to zero in on that next time (EGT prolly).

It has a weird sounding jump in rpm around 21K, first time it happened I thought I broke something, power drops right off after. Any ideas?

Gotta figure out how to put EGT and CHT on the power curve better.

Once I figure out how to get a good needle setting without burning pistons the testing will begin.

 

[Steve White]

Sounds like a 747 spooling up in Dr. Frankenstein's lab.

What you described reminds me of something from the karting days. They call it the "Rotax Bog" - the engines run smoothly through it, but the engines come on at 7K and drop out around 10K, then pick back up for another 1500 RPM and drop off at the top end.

Your setup almost sounds like some kind of harmonic vibration - strange.

 

[Ray Sametz]

Oh yea,

 

[Mark Bullard]

Bad, bad, bad, harmonic vibrations. Don't know what is causing it. But something is not happy.

 

[LohringMiller]

We often saw hollows in the power curve. Pipe design is partly responsible. Also, our Walbro carbs didn't meter equally over the whole rpm range. We set up everything for peak to over rev performance. Lower rpm s didn't matter as much.

Lohring Miller

 

[Terry Keeley]

Here's a clip of three runs where it "bogs" just after 21K. At first I thought I might be closing the throttle too soon but on the last run you can see I stayed in it a second or two after I clicked off the data recording. The curves above are from that last run.

I don't think it's a harmonic/vibration whatever, I didn't feel anything weird. The first time it happened I figured I blew the plug but it's perfect.

Pipe? Carb? Maybe it's just the sound of the motor giving up? You can see from the curves the power drops off sharply at that point...

 

[dwilfong]

Terry look at the correlation of the EGT and the power drop.
800 deg
Richen it up and see what it dose.
Then lean it a little.
See if it dose it at the same EGT.
Looks like it just went lean.
You may not have enough load now.
Can you add some load with the mag break?