Clutch brand looking for advice

D

DustBrothersRacing

Member
Hello,
I am the team captain of a relatively new racing team in Baja SAE. I know off-road applications may be a little bit out of yall's wheelhouse, but we find ourselves with some centrifugal clutch issues I believe ya'll would have experience with. We are running a Koehler CH440 14hp engine, restricted to 9.5hp, which makes peak torque of 18.5ft-lb at 2400RPM, and a rulebook enforced governor setting of 3800 RPM. We bought a cheap Chinese centrifugal clutch rated to 13hp (link below), and it works quite well on flat ground. However, when we attempt to climb a more significant obstacle, the clutch slips all they way to 3800 rpm and we only get about half the expected torque. Therefore, I am curious what clutches yall would suggest that would lock up solid at 2400RPM and would survive that much torque.
 
Petty Race Engines said:
1st question is what is the output shaft diameter?
Click to expand...
The engine shaft is 1 inch. This is going to sound odd, but I can adapt to just about anything on the output of the clutch. (I have access to a CNC machine and have to make an adapter anyway) It is a 14 tooth #40 sprocket at the moment though. The info for the clutch I'm running now was on a link, but apparently it disappeared when I posted. Ill try again.

https://www.amazon.com/dp/B09YQFBW3...pY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU&th=1
 
Why not the variable speed cv setup?
That Chinese clutch is not up too it .
There are much better 1 inch clutch's .
 
DustBrothersRacing said:
Hello,
I am the team captain of a relatively new racing team in Baja SAE. I know off-road applications may be a little bit out of yall's wheelhouse, but we find ourselves with some centrifugal clutch issues I believe ya'll would have experience with. We are running a Koehler CH440 14hp engine, restricted to 9.5hp, which makes peak torque of 18.5ft-lb at 2400RPM, and a rulebook enforced governor setting of 3800 RPM. We bought a cheap Chinese centrifugal clutch rated to 13hp (link below), and it works quite well on flat ground. However, when we attempt to climb a more significant obstacle, the clutch slips all they way to 3800 rpm and we only get about half the expected torque. Therefore, I am curious what clutches yall would suggest that would lock up solid at 2400RPM and would survive that much torque.
Click to expand...

What RPM does the clutch slip at on flat ground with just a short stab of the throttle? Anywhere near your 2400 rpm target? If so, then the weight of your Baja SAE is what's causing the clutch to dramatically overheat, and then overslip.

If the clutch goes right to 3800 any time you hit the throttle, then I'd say a dramatic increase in the weight of the clutch shoes is required.

PM
 
flattop1 said:
Why not the variable speed cv setup?
That Chinese clutch is not up too it .
There are much better 1 inch clutch's .
Click to expand...
We are not running a CVT setup because we spent 3 years melting them, or them just not shifting, sometimes both. We swapped them for a manual trans. Also, my original question is what those better clutches are? What brands do yall find to be dependable?
 
Pete_Muller said:
What RPM does the clutch slip at on flat ground with just a short stab of the throttle? Anywhere near your 2400 rpm target? If so, then the weight of your Baja SAE is what's causing the clutch to dramatically overheat, and then overslip.

If the clutch goes right to 3800 any time you hit the throttle, then I'd say a dramatic increase in the weight of the clutch shoes is required.

PM
Click to expand...
On flat ground it works great, gradual engagement around 2000RPM (probably because our first gear is 45 to 1 so almost no load). However when there is any resistance, it immediately pushes through to 3800. This includes higher gears on flat ground, hills, or a sled. (pulling a sled is one of the competition events) I would agree that the internals of this clutch are not nearly heavy enough, but they are not adjustable as far as I can tell, so I am looking for which clutches/brands yall would suggest. I know this sounds like a google it question, but all I keep finding are these same cheap chinese 8hp things. Thanks for your time!
 
Petty Race Engines said:
Bully does make a turbo 4 disk with 1” bore shaft but I think that’s too much clutch for the low rpm, Brian Carlson on here may be your go to
Click to expand...
I just saw your post after responding to the other two. Your right, that looks like one heck of a piece! It is definitely in the direction I want to go, but that 4000RPM engagement is really concerning. If I'm going to convince the school to pay $400 then I'd rather not have to rebuild it to get the engagement right. Who is Mr. Carlson, and how may I get in contact with him? Thanks for your time.
 
A Bully Turbo 4 disc would work, it can be set-up for your low engagement just fine, but if you're pulling a lot of weight and engaging/disengaging often, you'll likely burn it up....and if the school is balking about paying for a clutch, wait until a week later when you tell them that you burnt the friction discs out of it and it'll need a $200 rebuild.
If you can't get a CVT or torque converter to work (my suggestion) then consider clutching through a jackshaft to take some of that abuse away from the clutch.
The whole idea of the SAE program is to make it bullet-proof and for the students to come up with the ideas to not only make the car competitive, but handle a variety of challenges (pulling a sled, climbing hills, etc.)


-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
35 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
Can I assume you’re an engineering student? If so, go to the school library and look up the book Mechanical Engineering Design by Professor Joseph Shigley.

Chapter 14 has the information needed to design rim, cone, and disc clutches. I suggest the rim clutch since it is the easiest to fabricate.

Thomas Fehring P.E.
 
DustBrothersRacing,

Can you describe the general layout of the drivetrain? Is it simply the engine with a clutch on it going into a transmission, then to the axle? Something else?

What are the input/output shaft sizes?

PM
 
Take Tom Fehring suggestion he knows what clutches work and which ones don't, he has more clutch designs than most of us in the business. I am still in a learning stage.
 
SMC said:
Can I assume you’re an engineering student? If so, go to the school library and look up the book Mechanical Engineering Design by Professor Joseph Shigley.

Chapter 14 has the information needed to design rim, cone, and disc clutches. I suggest the rim clutch since it is the easiest to fabricate.

Thomas Fehring P.E.
Click to expand...
This is the best advice your ever going to get .
For this engineering exercise.
 
CarlsonMotorsports said:
A Bully Turbo 4 disc would work, it can be set-up for your low engagement just fine, but if you're pulling a lot of weight and engaging/disengaging often, you'll likely burn it up....and if the school is balking about paying for a clutch, wait until a week later when you tell them that you burnt the friction discs out of it and it'll need a $200 rebuild.
If you can't get a CVT or torque converter to work (my suggestion) then consider clutching through a jackshaft to take some of that abuse away from the clutch.
The whole idea of the SAE program is to make it bullet-proof and for the students to come up with the ideas to not only make the car competitive, but handle a variety of challenges (pulling a sled, climbing hills, etc.)


-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
35 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
Click to expand...
I'll Try to answer several questions at once here!
We have attempted to use CVTs in the past (going as far as buying a 3000$ gauged unit) but none of them ever worked quite right. For example, the gauged unit would never upshift past about half it's range, halving the car's top speed, and would scream like a banshee every time we stopped, and would start pouring smoke about 30 seconds later. Even after a month of tuning and five or six calls to the manufacturer, shims, weights, springs, ramps, belts, lubrication, cleaning... it did the same thing. There was also a snowmobile cvt, a comet 40, and a weird Chinese thing that isn't worth mentioning. Needless to say the stock answer of "Your car is too heavy" gets really old when you just told the person it won't upshift on a test stand, and it wont disengage at idle.

Therefore, we opted to use a Harley Davidson 6 speed this year. The engine (18.5ft-lb @2400RPM) shaft is 1 inch, the centrifugal clutch, then there is an adapter to a freewheel which is mounted on the input of the Harley trans. The freewheel allows the trans to shift smoothly when you let off the gas, and the centrifugal is still locked up. the transmission's output has a chain drive with a 3.5 to 1 reduction to front and rear differentials with a 4 to 1 reduction. 1st gear in the trans is 3.25, which gives us a 45.5 to 1 total first gear to the tires. Should give us somewhere in the neighborhood of 730lb of forward "thrust". The whole setup runs / drives perfectly except for that clutch slipping to 3800RPM. Note: yes I am planning to replace the adapter with a cnc machined part once I have my clutch choice figured, and please don't bash my welding unless you have welded oil-soaked cast iron to sheet steel. In that case you have every right to bash.
1708639478917.jpeg


As for building my own clutch in response to SMC and flattop, I would love to (and have already designed one), however time is running short before competition, and I am one of one people on my team who can run a lathe without hurting themselves, so I'd rather find something that says "will lock up at 2400RPM, rated to 20ft-lb" on the box and get back to testing as soon as possible.
 
Why not adapt a motorcycle clutch . Noram has industrial clutch's . Or an electric clutch add a micro switch that disengaged upon shifting .
Screenshot_20240222-170648.png
 
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