Run in stand/dyno build.

[RaceMechaniX]

Here is the CMB coupler.

 

[Terry Keeley]

Sure do miss the days when we made noise with this. I would hate to hazard a guess on how many pulls we made. Must be in the thousands

The nitro engine mount is in the lower center. The picture shows the over kill we used to connect the engine. We used a soft square key into Aeromarine square collets followed by a Lovejoy coupling and finally the clutch. The issues we had with this setup were:

1. Failure of the soft element in the Lovejoy coupling. Solved with the hardest available element. There were no issues after that.
2. Wear of the Aeromarine collets. We replaced the elements frequently. They still lasted for hundreds of runs.
3. Failure of the stock clutch arm. Mike made a billet version that has lasted since.
4. Twisting of the key. That occurred slowly over time but was severe when an engine seized. Replacing the key was cheap and easy.

At this point I think the Lovejoy coupling is superfluous and a one way clutch might be a good idea but is not essential. All the other parts of the drive train performed well. Mike replaced the grease lubricated bearings once after years of testing. I think we have experience with more dyno runs than most other hobbyists. I hope our experience can lead others to explore engine tuning with this great tool.

Lohring Miller

Again, can't thank you guys, Jim, Ken and all the others that have "been der dun dat", you're saving me a bunch of work!

What I'm really wondering is how all these dyno pulls translated to "real world" experience? Were you able to find stuff on the dyno that translated well to the water? If so what?

Thanks again!

 

[Terry Keeley]

Here is the CMB coupler.
View attachment 280396View attachment 280397

Thanks much, was searching everywhere for a pic of this. Looks very heavy duty, see what Jim means now about not needing a full ball but only reducing the contact area.

Here's the insert that's screwed into the clutch shoe assembly I got from Dave Marles. I'll make a one piece unit with a built in female u joint. You can see how hot the original got!

 

[Mike Bontoft]

Here are the 5mm keys and 2 of the couplers. The left coupler showing lots of wear. We considered both consumables. The system worked really well with pretty much zero failures as long as these parts were inspected regularly. One other nice feature is it could tolerate some misalignment

 

[RaceMechaniX]

Terry, that CMB universal joint is tightly piloted between the barrel section on the male end and the female engine side.
The coupler only has a few degrees of angular displacement. I believe it was intended to essentially be a straight coupler and only allow torque transfer with no thrust transfer. I'd be happy to send it to you for inspection if you want to scale it down.

 

[Brad Christy]

Terry,

I was wondering if some of these components weren't going to just be throwaway items. Sounds like they are.

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

 

[LohringMiller]

We always checked dynoed engines in real boats. Mike held the SAW record for fastest gas boat from 2004 until 2019. His wimpy 97 mph GX1 gas sport hydro record still stands. I say wimpy because the boat was capable of over 100 mph. In fact it blew off on the backup pass at over 100 mph when conditions were so rough no one else was running. We concentrated on the rigger the rest of the weekend. Mike also dominated the unlimited hydro class in District 8 with his rigger.

All this was from a serious test program that started with only an onboard tach and radar gun and ended with Eagle Tree loggers and the dyno. We spent many weekends in my and Mike's shop and at the pond trying sometimes crazy things.


Lohring Miller

 

[Terry Keeley]

Terry, that CMB universal joint is tightly piloted between the barrel section on the male end and the female engine side.
The coupler only has a few degrees of angular displacement. I believe it was intended to essentially be a straight coupler and only allow torque transfer with no thrust transfer. I'd be happy to send it to you for inspection if you want to scale it down.

Thanks, think I see now how this thing is gonna work and am making parts. Yup, fairly tight fits between all the moving parts to minimize hammering and heat.

Mine will be similar but with a pressed in pin, not sure why they went with the floating pin except maybe it being difficult to control the hole size with heat treat. I'll make a few male parts while I'm at it and leave the hole to experiment with different sizes. Hopefully it doesn't shrink (grow?) too much during hardening.

Terry,

I was wondering if some of these components weren't going to just be throwaway items. Sounds like they are.

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

May be but I'm trying to fix dat!

 

[Terry Keeley]

We always checked dynoed engines in real boats. Mike held the SAW record for fastest gas boat from 2004 until 2019. His wimpy 97 mph GX1 gas sport hydro record still stands. I say wimpy because the boat was capable of over 100 mph. In fact it blew off on the backup pass at over 100 mph when conditions were so rough no one else was running. We concentrated on the rigger the rest of the weekend. Mike also dominated the unlimited hydro class in District 8 with his rigger.

All this was from a serious test program that started with only an onboard tach and radar gun and ended with Eagle Tree loggers and the dyno. We spent many weekends in my and Mike's shop and at the pond trying sometimes crazy things.


Lohring Miller

View attachment 280444View attachment 280445View attachment 280446View attachment 280447

Very cool, I'm looking forward to learning what works (better) on the nitro side.

Curious, were you looking for certain things on the dyno that translated well to the boat? Or just torque (and therefore power) increases anywhere in the band?

Over-rev? Flat torque curve? Higher but narrow peak?

 

[Terry Keeley]

Some dirty pix for Ray...

 

[BobHorowitz]

Terry,
Regarding sizing the hole for the pin, you can use a carbide reamer on 50c S-7 without any problems. The other approach would be midget laps with lapping compound. Leave the hole a little undersize.
Bob

 

[Terry Keeley]

Terry,
Regarding sizing the hole for the pin, you can use a carbide reamer on 50c S-7 without any problems. The other approach would be midget laps with lapping compound. Leave the hole a little undersize.
Bob

Thanks Bob. Looks like these might work with a little diamond paste but I'm going to do a couple test pieces so hopefully it won't be needed.

I'll shoot for 55Rc, supposed to be a good balance between toughness and hardness for S7...

 

[LohringMiller]

In the beginning we thought peak power was the answer. However, we found that Andy Brown's 2170 props had a limit to how much pitch and cup could be increased. After that, it was rpm that mattered and we looked at over rev. In fact we actually detuned the CMB 35 with pipes that allowed more rpm. It's mechanical limit was around 25,000 rpm. At the time the difference between the G and GX record was the limit of maximum rpm on a Zenoah versus the Quickdraw. The G engine breakthrough came when Mike cut the blades on a 2170 and rebrazed them at a higher pitch. He set the G1 rigger record at 107+ mph in 2009. Mark Grim saw this and has been increasing gas records ever since.

I think nitro records have the same issues. It has taken years to get past 130 mph. Again, the records seem to be proportional to rpm. Todays props may be better as well. The solution may be gearing, but IC engines have poor torque to use for launch. I haven't seen any geared setups work well for SAW. I don't know what the limit on prop pitch is. Efficiency has to drop off somewhere at pitch to diameter ratios of over 2.5. That's the reason electrics can go so fast. They have constant power while IC engines are closer to constant torque machines with mechanically limited rpm. That gives electrics huge starting torque with very high rpm limits.

Lohring Miller

 

[Terry Keeley]

Boy does that sound familiar!

I've made 100's of runs at 100+ mph and found (for my set up) as the rpm increases above about 24K the slip goes up exponentially. I've wound these 67's up to near 30K and get over 30% slip, it might be because the tail of my boat is lifting but I don't think so. The lowest I've seen with a moderate amount of cup is about 6% at 22K.

My new props have about a 3.0 ratio and are working better in the low 20K range so far.

And around it goes...

 

[Mike Bontoft]

Hammering is definitely your enemy in any drive train especially where single cylinder engines are concerned. You will break things you would have never imagined possible. The drive key helped tremendously with this.
We should have made the key couplers from steel but never got around to it, plus the brass ones were inexpensive and readily available. The flywheel weight was 19lbs if I remember correctly. We had very few reliability issues, one of the first was the magnet flying out of it's machined recess which it had been glued into. Never to be seen again!
We always had a shield between us and the dyno and made sure never to be sideways on to it. I am in no doubt that some components have the energy to go through a person if they were to part company at high rpm.
Be Careful !!!

 

[Terry Keeley]

Hopefully this will be strong enough. Went for a 55-56Rc heat treat, good balance between toughness and hardness.

 

[RaceMechaniX]

Very nice Terry, I think you may see some high contact wear on the pin as you have a small contact area between the pin and flat on the female side coupler. You'll notice the CMB coupler's pin is flat on both ends to reduce the Hertzian contact stress and hence reduce wear. Your pin may just wear in to produce a flat after some running.

 

[Terry Keeley]

My first thought was what does a rental car company have to do with metal wear?

But I looked it up instead: Hertzian contact theory | Tribology | Tribonet

Never knew about that, figured CMB did it just to hold the pin in. Mine's made from a 5/32" HSS drill blank so should prolly be around 60Rc, maybe it'll beat the housing up?

Might need to send it back to Engineering, I'll find out tomorrow!

 

[Brad Christy]

Very nice Terry, I think you may see some high contact wear on the pin as you have a small contact area between the pin and flat on the female side coupler. You'll notice the CMB coupler's pin is flat on both ends to reduce the Hertzian contact stress and hence reduce wear. Your pin may just wear in to produce a flat after some running.

Tyler,

It might end up wearing flats on the pin, but then it'll have that much more clearance to slap around in. Not good, and exactly NOT what Terry was after....

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

 

[Brad Christy]

Terry,

I'd advise stepping up to, say, a 5mm pin, and grind flats on either end that slip fit into the slots in your coupler. This would supply .120" wide flats to engage the slots in your coupler.

You got a surface grinder yet?

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