uni Versus CV

just a quick question for anyone who knows about cv and uni joints.i've seen uni joints used on trimable surface drives, i was just wondering if cv joints could also be used or would they not handle the thrust forces.
cheers

 

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That's what they are made to do.. to handle the thrust. Just to check what are the specs for hp and rpm for specific models..
You should more concerned about the trimming with CV bcs it has restriction with the angles. On the other hand unijoint doesn't handle thrust forces so well..

 

Both are not intended to take much axial load. If you find them in a construction where thrust is involved, it is designed for that purpose: the housing contains more than just a cv or uni joint.

 

no there not... thats why i ask the question... their both designed to transfer torque loads not thrust. also triming would be better achieved with a cv as they allow more angle drive than a uni with less vibration and more constant velocity.

CDK
so you dont think a standard cv would handle it? that seems to be what i've heard. the uni setups i have seen on surface drives have been just the uni alone taking the thrust, but mine you they are a little heavier than the usual size needed for the Hp used.

 

CDK has it right. Sorry about the inaccuracy..
Marine CV joints are normally combined with pressure bearing..

 

oh ok, is there a special marine type cv joint readily available on the market? i would prefer to use a cv joint rather than a uni as they are smaller (diameter) and are fully enclosed with a rubber boot.

 

Google Aquadrive.. There are other brands too..

 

@Jellyfish:
You can also try Python-drive:
http://www.pythondrive.com/
This is what I've been using, nice and reliable drive for shaft angles up to 8°. Simple CV's will not handle axial load, but composite drives (thrust+torque), like Acqudrive or Python-drive will. That's because they have a thrust bearing installed between the prop shaft and the CV. This thrust bearing will unload the axial force against a mounting plate fixed to the hull, so only a torsion remains for CV joint.

 

I am installing CV joints to replace old spicer 1550 series joints on my SBM surface drive. I do not require a thrust bearing as the drive has a pump lubricated thrust bearing at the transom. You can go to Aquadrive. But most all CV joints on the market are GKN (German). You can find GKN dealer who can provide the joints with the proper shaft and flanges. The shaft in my case is a heat treated 4340 Chormalloy. If you take the aftermarket route you can save over 35%. Here are some rough specs:

GKN CV Joint

Series Torque Wieght Min Length Joint Cost (w/o Flange/shaft)
21 4400 ft/lb 5kb per cv 210mm Approx $500.00 Max RPM 8000
30 6785 ft/lb 8kg per cv 295mm $1200 Max RPM 5000
32 9000 ft/lb ?? 375mm ???? Max RPM 5000

CV joints overtemp is a sign of overstress (excess angle per given RPM) and impending failure. Take a peek at Dweyer Sensors ILa10 Non-contact infrared temp sensor with the display TCS-4030. This unit is stainless, NEMA 63 and sealed. This will cost about $350 for sender and temp display. You can point it at your CV joint to monitor operating temps. The display has a alarm contact closure with adjustable setpoint. You can point these units anywhere in your driveline to monitor temperature of rotating parts. Accuracy is 2% and response time is very fast at 250ms.

Good Luck